LOS ANGELES COUNTY.

By W. H. Storms, Assistant in the Field.

The mining industry in this county is not as extensive as that of some of the neighboring counties, but there are mines in Los Angeles County of unquestioned value, and others which have a prospective value, dependent to a great extent upon the success achieved in working certain base ores, which occur in comparative abundance.

THE KELSEY MINE.

One of the most interesting mines in the county is located in the rugged mountains about 8 miles from the town of Azusa, in the San Gabriel Cañon. It is commonly known as the Kelsey Mine, and has become famous as a producer of silver ore of fabulous richness.

The country is made up almost entirely of metamorphic rocks, having schistose, gneissoid, and massive structure. Both hornblende and mica occur in these rocks abundantly, the former being frequently altered to chlorite, or by further change to epidote. Dikes of porphyritic rock have been intruded into the crystalline schists. In the immediate vicinity of the Kelsey vein are intrusions of a dark green, much decomposed, and shattered rock, probably diorite. Faults, great and small, are numerous throughout the region. Within a few hundred feet of the mine is a great fault, which may be plainly seen cutting the mountain. The displacement must reach many hundreds of feet. It has resulted in bringing in contact on a horizontal plane rocks of entirely different character. On the south side of the fault the rocks are made up of quite regularly bedded micaceous sandstones, more or less schistose, and having a prevailing buff or light gray color. These rocks dip east at an angle of 20° to 30°. On the north side of the fault the rocks are harder, of a dark gray color, and containing considerable hornblende. These rocks are more gneissoid and massive than schistose. The dip is much less regular than on the south side of the displacement. Large, lenticular masses of quartzose and feldspathic rock are of frequent occurrence in the hornblende gneiss, evidently the result of the segregation of the contained minerals. On the whole there is much more evidence of the disturbance on the north side of the fault than on the south side. It is in this area of greatly disturbed strata that the Kelsey vein has formed.

The vein is of the fissure type and occupies the line of a fault plane, that at first, perhaps, was a mere crack, but which has become enlarged by the movement upon themselves of the rock masses forming the walls, resulting in a grinding and crushing of the rocks by the attrition and pressure incident to this movement. Into this crevice mineral waters found their way, carrying in solution the minerals now constituting the vein.

The Ore.—The silver occurs as native and as glance (argentite), possibly partly as chloride and in combinations with sulphur, cobalt, and arsenic. The associated minerals are cobalt bloom (erythrite), a hydrous cobalt arsenate, nickel arsenate (annabergite), carbonate and silicate of copper (chrysocolla), iron oxide, and black oxide of manganese in a gangue of baryta (heavy spar), with calcite (lime spar) and some quartz. A clay selvage usually separates the vein material from the wall, this feature being well developed in places on the foot wall side, as though open crevices had occurred and the finely divided material which was carried by the percolating waters had found a resting place when an open space was reached, the absence of any current permitting the material to settle.

The clay may have been derived in part from the decomposition of the overhanging wall, the fine silt settling by gravity on the foot wall side of the vein. In places a soft, clayey gouge constitutes the entire vein filling, suggesting that the clay selvage and gouge are also partly due to the attrition of the walls. Galena occurs sparingly in small disseminated crystals, but the occurrence is so infrequent as to be scarcely worth mentioning. In width the crevice varies from a thin seam to over 4 feet. A banded structure is not uncommon in the vein.

The rocks inclosing the vein differ in various parts of the mine. A much decomposed rock, containing iron in the form of carbonate, occurs frequently, while a chloritic, more or less schistose, sometimes massive, rock, also plays an important part in this connection. The dike of dark basic rock, resembling diorite, previously referred to, is exposed at numerous places throughout the workings, often in contact with the vein, or close to it. Since its formation the Kelsey vein has been subjected to severe torsion, which has resulted in abrupt fracture and displacement. To me it seemed very probable that the vein was the result of chemical precipitation, and no doubt, to some extent, the replacement of country rock along the line of a fissure or fault plane; that subsequent to the filling in of the vein the region was subjected to further violent disturbances, which fractured the rocks along an east and west course, and causing the turning of a large mass of rock formation lying south of this fault to the west. The vein being included in the general movement, was deflected from its natural course north and south. I came to these conclusions from close observations taken along the surface of the ground on the course of the vein, and in all accessible underground workings.

Most of the ore extracted from these workings has been high grade, usually running over $200 per ton, small lots often assaying several thousand ounces. The property, at the time of my visit last spring, was under the management of Dr. Endlich, E.M. This gentleman was making every effort to systematically open and recover a vein that had been as systematically and outrageously gouged. The workings were in bad condition and at some points were positively dangerous. The mine was gradually assuming an improved appearance and promised to yield better returns than ever before. A good mill has been erected at the foot of the mountain, in the San Gabriel Cañon, where a large stream of water flows during the entire year. An office, boarding house, stables, corrals, etc., had been built for the accommodation of men and animals. In addition to this I found a complete assay office and chemical laboratory, and here Dr. Endlich was experimenting with the rich cobalt and nickel ores. As a result of his labors in this direction he exhibited several bars of cobalt speiss containing a very high value in silver. The assorted ore contains from 7 to 15 per cent in cobalt, 2 to 3 per cent nickel, and from 1,000 to 1,400 ounces silver per ton.

Dr. Endlich thus describes his methods: “The ore is crushed through a twenty-mesh sieve, mixed with sufficient litharge to produce an 8 per cent charge, and enough borax is added to take up the gangue (quartz, heavy spar, carbonate of lime, magnesia, and iron). Carbonate of soda and flour are mixed with the charge. If the percentage of arsenic in the ore is sufficiently high to produce speiss none is added; otherwise some metallic arsenic is mixed in. Some sulphides in the ore and reduced sulphur from the heavy spar are utilized to produce mattes. The mixture is melted in large Dixon crucibles; the slag poured off, and the metallic product allowed to cool. The bars obtained are composed of lead, silver, cobalt, nickel, arsenic, and sulphur, principally; the lead being in the form of sulphide, the cobalt and nickel in the form of arsenides. The bars contained from 4,500 to 7,000 ounces silver per ton. The slag contained a trace of silver, and averaged about 0.75 per cent cobalt, which can be worked over by arsenizing, if desired, and the cobalt obtained in the resulting speiss.”

At this writing about 560 pounds of ore has been treated in this way and the product shipped to Balbach’s works in Newark, N. J., for refining.

THE VICTORIA MINES.

This property is situated but a short distance from the Kelsey Mine. The Victoria Mine was operated under English management for an English syndicate two or three years ago. Lately all operations have been suspended. The property, whatever it may be worth, is a monument to mismanagement of the worst sort.

THE LORDSBURG STAMPEDE.

In the month of March, 1892, the report went abroad that rich silver and gold-bearing rock had been found in the mountains north of Lordsburg, 28 miles east of the city of Los Angeles. So glowing were these stories that a general stampede for the new mining field ensued. Farmers left their homes, merchants and clerks in some instances temporarily closed their stores to join in the rush to Lordsburg. Unfortunately the stories proved to be unfounded, and, after three weeks of excitement, all had left the mines excepting a very few, who still had hopes of making a find.

CEDAR MINING DISTRICT.

Fifty-five miles by rail northeast from Los Angeles, on the line of the S. P. R. R., is the Cedar Mining District, the principal village being about the railway station called Acton. In the low hills about Acton, which rise out of the valley that skirts the northern base of the San Gabriel range of mountains, are located the gold mines which have been worked for many years by Mexicans and Americans.

THE RED ROVER.

This is the name of the principal mine in the district. It was located and worked many years since by Mexicans, but has during the past eight or ten years been in the hands of Americans. The vein strikes northwest and southeast, dipping to the southwest at an angle of 50° from the horizon. The rock is a white, fine-grained, saccharoidal quartz, showing in places bluish bands. It contains free gold in variable amount, with some iron sulphuret. A very large amount of quartz has been stoped from the vein and crushed in various mills.

The Red Rover is quite extensively developed, the new vertical shaft being down over 400 feet. The old inclined shaft, which is sunk on the vein, is down 220 feet. Several levels are run out from both these shafts, which are 200 feet apart. The new shaft was sunk between the main vein and a spur which branches from it. A crosscut was run out toward the spur, which is opened on the surface, but it was found it did not go down. A crosscut was then run toward the main vein, which was found intact, and a drift was carried in 60 feet on the vein.

The country rock is mostly massive metamorphic, very much broken and faulted. Nearly every mine in the district has been displaced more or less by these faults. For some reason the Red Rover has been shut down for some months past. It is understood that operations are to be resumed.

THE NEW YORK MINE

Is situated within half a mile of the Red Rover, and is similar in character. The quartz is said to mill $10 to $25 per ton. The owner has a five-stamp mill, which is complete and does good work. The vein is from 1 to 3 feet in width. It has produced considerable bullion.

Other mines of the vicinity are the Topeka, Union, Escondido, King of the West, and Santa Clara, each of which has seen better days. The first three mentioned have been large producers, but are worked down to the water line, and a base ore proposition now faces the owners in the form of iron pyrites.

IN THE MAIN RANGE.

Up in the main range of the San Gabriel Mountains, on the north slopes of this rugged chain, are located a number of veins, on which considerable work has been done. The veins are well defined, ranging from 1 to 4 feet in width, striking northwest and southeast, and dipping uniformly to the northeast at a high angle. All of these veins contain gold, but all quickly run into sulphurets. All the mines are idle at present, but something brighter is hoped for. The sulphurets are said to contain sufficient gold to make chlorination profitable. If this is actually the case there is an abundance of material to work upon.

LIPARITES AND TUFAS

In the region about Acton are many hills of liparite (quartz-bearing trachyte) and tufa, which are identical with the rhyolites of the Calico region—the same violet-brown, porphyritic liparite; the same pea-green and buff-colored tufas; the same conglomerate; in fact, an exact facsimile of the Calico range. There are no great beds of sedimentary rock, however, and these liparite hills are comparatively small, isolated masses. As far as my knowledge goes ores of silver have never been found in these rocks in the Acton district. Careful prospecting may possibly discover such ores.

PROSPECTS OF THE CAMP.

Owing to the fact that the gold mines of this district have been worked to the water line, almost without exception, what now remains to be done to perpetuate the prosperity of the district, is to concentrate the sulphurets, working them by chlorination in works built in the district. Wood and water are both obtainable at moderate cost, and the sulphuretted ores of this district that contain but a very few dollars per ton should pay. The cost of mining, transportation, crushing, and concentrating should not exceed, ordinarily, $5 per ton of quartz, and the expense of treating the concentrates should be under $10 per ton. Base ores containing $10 per ton as it comes from the vein should realize a profit in this district, and I am told that many of the mines produce rock of a much better grade than that mentioned.

SAN DIEGO COUNTY; ALSO ORANGE AND SAN BERNARDINO COUNTIES.

By Harold W. Fairbanks, F.G.S.A.

The topography of this region has been quite thoroughly described by W. A. Goodyear, in former reports of the State Mining Bureau. The structure of San Diego County is comparatively simple. Three main divisions might be made: the desert on the east, the Peninsula range of crystalline rocks in the middle, and the nearly level mesa on the west. The Peninsula range is supposed to represent the southern continuation of the Sierra Nevadas, but in just what relation it stands to the Sierras has been a matter of dispute. The Peninsula range in San Diego County forms one main mountain chain. It maintains this simplicity of structure southward, forming the backbone of the peninsula of Lower California. Northward it becomes broader and more complex, rising in the lofty San Jacinto and San Bernardino ranges on the east, and the Santa Ana range on the west, while the region between is filled with mountains and valleys irregularly disposed.

Complex as is the topography of this region, the geological problems, though often difficult to solve, are quite simple. The higher mountains are formed wholly of ancient crystalline schists and massive rocks, respecting the age of which a great diversity of opinion has existed; while the region bordering the coast consists of unaltered Cretaceous, Tertiary, and Quaternary deposits.

Owing to the very limited time given me to prepare my field notes for the press, they will be given substantially as they were taken in the field, without any attempt at systematic arrangement.

The crystalline rocks of San Diego County are varied in character, and of much interest. No opportunity has been given me to study the large collection made, and the determinations given are simply the result of superficial examination, and are subject to correction.

The bay of San Diego is bordered on the east by gently sloping mesas of modern Tertiary and Quaternary age. These unaltered strata are characteristic of the western slope of the Peninsula range through its whole extent. They sometimes rise as high as 3,000 feet; though in San Diego County they do not exceed 1,500 feet. The upper portion of these beds consists to a great extent of coarse, loosely cemented conglomerates. The rivers issue from the higher mountains through narrow valleys or cañons, and have cut valleys, often quite broad and with very steep sides, through the mesas to the ocean.

The Otay mesa has a height of about 500 feet, the western portion being somewhat higher than the eastern, indicating a recent elevation near the coast. The soil of the mesa is adobe, due to the decay of porphyry mountains to the east. Under the adobe there is a calcareous marl, often many feet thick.

The first exposure of the older rock seen as one goes up the Otay River, is in a hill rising through the mesa about in the center of the grant. It is a part of the extensive porphyry intrusives, which, in southern San Diego County, form a number of high mountains between the granite and the mesa. To this formation belong the San Miguel and Otay peaks. This exposure on the Otay River is a felsitic breccia. It contains a felsite base (intimate mixture of quartz and feldspar), in which are imbedded fragments of felsite and chlorite. No more rocks appear for about 2 miles up the river. Then we reach the base of the long ridges which lead up to the Otay Peak. Some interesting rocks are exposed where the stream issues from the cañon. The greater portion are fine dark to greenish aphanitic rocks, with green chloritic or epidotic nodules. Bunches and dikes of coarse to fine grained porphyritic rocks occasionally appear. They probably belong to the diorite porphyrites. The rock continues very much the same for several miles farther east; at times it is almost wholly feldspar. In the cañon above El Nido Post Office it changes to a light green feldspar porphyry. Near the western edge of the Jamul grant a dark-colored porphyry takes its place, and a little farther east it becomes jet black, with small white feldspar crystals, producing a very pretty effect.

The mesa conglomerates extend along the top of the low hills bordering the valley nearly to the eastern edge of the Jamul grant. A great variety of rocks appear along the Campo road between the Jamul grant and Sheckler’s, on the Cottonwood. Near the eastern end of the grant the porphyry is followed by fine-grained granitic rock, frequently becoming schistose. Numerous dikes and bunches of dark diorite cut through this rock. As Dulzura Post Office is approached, these rocks change to mica and hornblende schists, and are filled with intruded dikes of diorite porphyrites. Bodies of massive syenite and coarse granite were also seen. About Dulzura many of the dikes have the appearance of diabase. Between Dulzura and Sheckler’s the country rock is largely micaceous and chloritic schists. Massive granite forms the high, rugged mountains east, extending in an arm westerly across the road. The schists have a northwest strike, vertical dip, and are evidently of metamorphic origin. They form a strip of country extending in the line of strike from near Sheckler’s to the Sweetwater River, and are situated between the wide belt of porphyry on the west and the coarse intrusive granites on the east, which rise to form Lyon’s Peak and other rugged mountains.

The first rock met east of Sheckler’s, on the Campo road, is coarse hornblendic granite, so decomposed that a fresh specimen could not be obtained. Dikes of fine-grained granite intersect it in every direction. Three miles west of Potrero, mountains of olivinitic diabase rise on the north side of the road. This rock is very similar to many large bodies of intrusives through the mountains between Julian and the Tia Juana River. It has evidently been intruded into the granite, for dikes extend out, intersecting the latter rock.

Potrero is located in a valley of several hundred acres in extent, and surrounded by granite mountains. It has an elevation of 2,400 feet. South of Potrero, along the boundary line, the mountains show large areas of the dark dioritic and diabasic rocks. The hills immediately south of the valley consist of hornblendic gneiss; strike east and west. Eastward, toward Campo, the rock is chiefly a coarse white granite, very easily decomposed. It shows a slightly gneissoid structure for a number of miles. It does not seem to represent the bedding of a sedimentary rock, but of parallelism of the constituents, induced in the magma by movement or pressure. Long, drawn out, lenticular inclusions are often present, and are arranged parallel to the schistose structure. These consist largely of hornblende, with little feldspar.

In the vicinity of Campo the topography of the country changes from that of high mountains and deep, narrow valleys, to an elevated mountain plateau with meadows and rounded granite ridges. The mountains are covered with brush, while live oaks are numerous in the valleys. The country maintains these features while gradually rising to the divide 8 miles east of Campo. The granite is so deeply decomposed along the summit region that no good samples could be obtained. Campo has an elevation of 2,600 feet. The bare, rounded ridges closely resemble those left by glacial action, but their slope is produced simply by the cleaving off successively of the more angular portions in great slabs. Many fine examples of this manner of decay appear about Campo. The corners are decomposed faster than the smooth surfaces, and thus finally a shelly concentric structure results. The fresh massive central portion weathers out like water-worn bowlders. The presence of rugged angular ridges results either from a less inherent tendency to decay, or to a comparative freedom from crushing. Four miles northeast of Campo is an outcrop of coarse hornblendic granite, with large six-sided mica scales and numerous yellow crystals of titanite. The height of the divide is 3,800 feet. Near the summit the rocky ridges all disappear and the country becomes covered with granitic sand. Erosion here is evidently very slight. The country descends gradually on the east to Jacumba Valley, being sandy for some distance. This finally gives place to bare, rocky ridges and cañons. Veins of fine granite, and others of feldspar and quartz, are abundant on the eastern slope.

Before reaching Jacumba Valley a body of mica and hornblende schist is encountered. The schists do not form a regularly defined belt, but often appear as inclusions in the granite. These inclusions have a very variable strike, and from their relation to the granite it is evident that the latter is intrusive.

Jacumba Valley empties northward into the desert through a narrow gorge. It has an elevation of 2,600 feet, the same as that of Campo. It is several square miles in extent, the greater part of which is in Lower California. The warm springs here are considered quite medicinal. The schists just described occupy a large area west and north of the cañon through which the valley empties. They are cut in every direction by dikes of granite and others, consisting of a very coarse aggregate of quartz and feldspar with a little muscovite mica. A high mountain several miles north of the valley is distinctly ribbed all over by them. The schists extend northward toward those which outcrop on the eastern slope of the Laguna Mountains and at Julian, but are cut off by a body of intrusive granite. They undoubtedly belong to the same series. Gold-bearing veins have been found in them a little north of Jacumba Valley.

At the north end of Jacumba Valley, and on the west side of the outlet, is an area of volcanic rock, probably basalt. It forms a table-land, gently sloping toward the valley, and rising 600 or 700 feet at its northern end. It is underlaid by gravels and conglomerates. Just east of this is a black butte, rising perfectly symmetrical to the same height. It consists of bedded lavas, with tufa at the bottom. In spite of the fact that it is shaped like a crater, its structure is different, and it is probably a remnant of the flow which once covered the outlet to the valley.

The high range of mountains between Jacumba Valley and the desert has an altitude of something over 4,000 feet, but where the road crosses it, it is only 3,100 feet. Basalt outcrops also on the eastern side of the valley. North of the road to Mountain Springs it forms a series of plateaus, the highest of which reaches a height of 3,900 feet. It forms the summit of the range, being 800 feet above the granite forming the pass. South of the pass several miles the granite rises much higher and the lava lies along its western slope, extending an unknown distance below the line.

Large deposits of water-worn bowlders and gravels lie along the eastern slope of Jacumba Valley. Among them are pebbles of porphyries, black quartz, and others not seen in place in this part of the county. A short distance west of the summit they are found in beds with gravel and sandstone, dipping southwest. These late Tertiary deposits are overlaid by the volcanic beds. The volcanic plateau which rises so high north of the pass has a thickness of 500 to 600 feet. Massive and bedded lavas form the upper half of this thickness, the lower portion consisting of a volcanic breccia. The beds lie nearly horizontal. On the west are two lower terraces, also capped with lava and abutting against the higher. The whole is underlaid by sand rock of granitic origin. It is nearly level in places, in others it dips to the southwest. It is very strange that these lava beds, with nearly level flowage lines, should be found at such greatly varying elevations about Jacumba Valley, and be underlaid everywhere by such similar tuffs and sandstones. My investigations disclosed no volcanic vent, and it is possible that the lava issued from fissures, as was noticed elsewhere in the county. Another interesting question is the origin of the sandstones and conglomerates. The sandstone underneath the high plateau is higher than the divide at that spot, and the only granite within miles that exceeds it in height, is the narrow ridge which rises on the southeast. The erosion must have been very great along the ridges since the sandstones were deposited, but the valley cannot have changed much. There may have been great elevation along the crest of the range bordering the desert since the deposition of sandstone, tilting up the sandstone and lava on the eastern slope, but elevating without great disturbance those near the summit. Southeast of Mountain Springs is a body of bedded tufas reaching an elevation of 2,300 feet, and dipping to the east away from the range at a considerable angle.

The presence of these modern sandstones at so great an elevation nearly on the crest of the Peninsula range is a very interesting fact. Either Jacumba Valley was a lake, or a great elevation has taken place in comparatively recent times, raising the valley from the sea-level. Appearances indicate that during late Tertiary times this range was almost submerged beneath the sea.

The rocks between the summit and Mountain Springs are chiefly gneissoid, at times granitic. They contain bodies of fine dark mica schist, and many dikes of very coarse muscovite granite. The descent to the desert is very abrupt over bare granite ridges. Mountain Springs, an old stage station, is located on the side of the mountain at an elevation of 2,300 feet. From the springs the road descends along the dry bed of an arroyo to the desert. The most of the distance is through a rocky cañon, where there is an excellent opportunity to study the relations of the gneiss and granite. For some distance down from the springs the rocks continue to be gneissoid, but through the lower end of the cañon they become more massive and coarse, and all the veins characteristic of the gneisses of the higher mountain region disappear. At the upper end of the cañon is a dike of very coarse granite, with large biotite crystals instead of muscovite. This is the only instance in which biotite was seen in one of these coarse dikes. Banded gneiss, varying from very thin to very thick bedded, alternate with other rocks, to all appearances massive granites, but in surface decay the latter break up into slabs of varying thickness, parallel to the schistose structure of the gneisses. The banding is caused by an excess of mica or hornblende, chiefly the latter, arranged in parallel layers. These strata are often very thin, varying from one fourth to one half inch and upwards in thickness. They are very regular, but often discontinuous; stop, and in course of a few feet begin again. These features are generally supposed to indicate metamorphic origin, but at one spot a body of dark mica schist is cut by a dike a foot wide or more of this dark banded gneissose rock. This dike cuts across the stratification of the mica schist, showing conclusively the intrusive nature of at least a part of these gneisses; and it is quite possible that the inclusions of mica schist are the only really sedimentary rocks present. In places the rocks which show this banding have the constituents arranged in the bands independent of any direction. At one spot a distinct, well-defined mass of mica schist, 15 feet across, is imbedded in a granitic rock. At one side this gneissoid structure extends through the inclosing rock and abuts sharply against the mica schist. The banding shows no constant direction; in the cañon it is northeast. The bands sometimes become wavy.

As the cañon opens out to the desert, hills appear on either side formed of volcanic tuffs. They dip northeast 30°. Underneath is a sandstone wholly unconsolidated and dipping in the same direction 40°. This contains no lava pebbles. The fragments of the tuff are quite varied in character and generally quite angular. They are imbedded in a volcanic mud, free from granitic detritus. In some of the strata appear thin beds of lava, seeming to represent a flow. These tufa hills extend northwesterly along the base of the granite mountains for 10 miles or more. It is not known how far they go in a southerly direction. In places they form mountains of considerable size high up on the side of the range. The range of mountains between this point and Carrizo Creek appears also to have some volcanic beds on its southern slope. The open desert at the foot of the mountains has an elevation of 1,200 feet. It slopes gently for miles in an easterly direction and consists largely of loose sand.

Between Mountain Springs and the summit is another illustration of the fact that lamination in a crystalline rock is no proof of its sedimentary origin. A small dike less than 2 inches thick cuts across a coarse biotite gneiss at an angle of 30°. It is separated from the gneiss by a thin layer of quartz and feldspar. It is made up of the same constituents as the gneiss, arranged so as to show a well-pronounced gneissoid structure. This is very similar to the large dikes seen in the cañon.

The road was followed back to Campo, and from there the Laguna Mountains were climbed. The road ascends a long, narrow cañon on the southern slope. At the entrance to the cañon, 4 miles southeast of Buckman’s Springs, the mountains are high and rocky, being formed of thin-bedded gneisses, which, in many places, blend into mica schists. They strike parallel to the mountain axis, a little west of north; dip 70° northeast. Three miles up the cañon the gneiss becomes thick-bedded and is finally replaced by mica diorite, which forms the hills on both sides. Granitic dikes outcrop near the junction and sometimes apparently in the diorite. There is often a blending between the two, as if the intrusion of both took place nearly at the same time. The region east of the southern end of the mountains is formed of coarse granite, decomposed to a considerable depth. The mica diorite extends northward, forming the whole central and western part of the mountains. On the east it is bordered by a slightly higher ridge, forming the crest of the mountains. This rock does not decompose as easily as the granite and gneisses on the west, and there consequently remains a mountain plateau having an elevation of about 5,500 feet. There is a considerable amount of pine timber and open meadows. The dark diorite forms one of the highest peaks of the Laguna Mountains, rising 6,250 feet. The highest portion of the mountains lies to the northeast, and is formed chiefly of a quartzose mica schist. From the eastern crest of the range a most magnificent view of the desert is obtained. The strata on the crest strike north 15° west, dip 70° northeast. The descent of 4,000 feet to Vallecitos is very abrupt. Near the crest it is almost as steep as the dip of the rocks. The mica schists in places approach gneiss in composition, but all of this series of rocks forming the crest and eastern slope very probably belong to the Metamorphic Series. South of this point the Laguna Mountains do not terminate so abruptly, but extend out in long, gradually descending ridges for many miles. The mica diorite extends north of the Laguna about a mile, when the schists on both east and west sides unite and extend north toward Banner. They are intruded by granite and diorite in many places. The body of diorite forming the Laguna plateau is about 8 miles long and 1½ to 2 miles wide. The highest peak is not over 200 feet lower than the Cuyamaca, rising 6,300 feet. The diorite seems to have been intruded in the middle of a considerable area of mica schists, for this rock outcrops on all sides. On the west, toward Pine Valley, they carry the gold veins of the Pine Valley district. The descent is very abrupt to Pine Valley and Buckman’s Springs. The schists and gneisses extend about 3 miles south of the main portion of the mountains, when they are replaced by coarse hornblendic granite.

Buckman’s Springs has an elevation of 3,400 feet. Here are some very excellent soda springs, the only ones I know of in this section of the State. A coarse, dark diabase outcrops in the edge of the mountains just north of Buckman’s and also a little farther south, on the west side of the valley.

A narrow cañon leads up to the divide which separates the valley of the upper Cottonwood from Pine Valley. The western prolongation of the diorite of the Laguna Mountains appears near the road on the divide. The prevailing rock is, however, of a granitoid nature and filled with many large bunches of massive white quartz. Pine Valley has an elevation of 3,800 feet. Gneisses and hornblendic and micaceous schists outcrop between the valley and the divide east of Descanso. The strike is north and south. One mile southeast of Descanso there is another outcrop of the coarse diabase or gabbro which forms so much of the Cuyamaca peaks. Descanso has an elevation of 3,400 feet. The rock which outcrops for a number of miles along the road to Stonewall is a coarse, easily decomposed granite, rising in rounded knobs over a rolling, brush-covered country.

The Pine Valley district lies in a belt of gneissose, mica schist, and quartzose rocks, which extend in a direction a little west of north. They begin about 2 miles south of Pine Creek and extend, probably unbroken, through to Banner and Julian. It is 4 miles north to the Deer Park district. The metamorphic schists widen as this district is approached. They extend from the desert slope to Deer Park, where a body of diorite has been intruded, and from there westward 2 miles to the Cuyamaca grant. A half mile west of the camp the slaty mica schists and quartzites are well defined. A vein of gold-bearing quartz has been traced for several miles in these rocks, and a number of locations have been made on it. The strike is north and south, dip 80° to the east. A body of white crystalline limestone lies in this formation, about 1½ miles southwest of Deer Park. The body of micaceous diorite which extends through this camp is about a mile long, and is quite gneissoid in places. Near its southern end it incloses narrow bands of hornblendic and feldspathic rock, containing garnets. The veins are numerous in this diorite, and extend in every conceivable direction. The diorite has been greatly crushed at some time, with fissures in every direction; hence, the irregularity of the quartz veins. The veins are generally bunchy, and not often very large. They seem simply to follow the exceedingly irregular fracturing of the diorite, which is decomposed to a considerable depth. The work thus far in this district has been confined to the surface, so that nothing can be said in regard to the permanency of the veins. The elevation of the camp is 4,600 feet.

Two miles northward an outcrop of coarse biotite muscovite granite was met. It is about 2 miles long and 1 mile wide, having schists on all sides of it. This is the only example of typical granite (according to Rosenbusch) that was seen in Southern California. A broad valley, occupied by Mr. Harper’s ranch, has been eroded in the center of this granitic mass.

Northward, along the crest of the range overlooking the desert, mica slates appear. They are so little metamorphosed as to closely resemble argillaceous slate. They strike a little west of north, dip 70° to 80° east, and maintain the same character north to Banner and Julian.

The road from Julian to Stonewall crosses mica schist and gneisses for about half the distance. Then we met outcrops of a dark basic rock, ranging from fine to very coarse texture. It extends southward and covers a large extent of country. The three Cuyamaca peaks, the highest in the southern part of the county, are formed of this rock. This rock was again met about half a mile west of the Stonewall Mine. It extends westward across the mountains for at least 2 miles, and some miles south of the main peak. In places it has a schistose structure. Near the outlet of the Cuyamaca reservoirs it is filled with vein-like aggregates of coarse hornblende crystals, which are probably the result of secondary crystallization in fissures or cracks of the almost consolidated magma.

The formation in the vicinity of the Stonewall Mine is biotite gneiss. Toward the east it is not sharply defined from the mica schists. On the west it is generally more granitoid, though at one spot near the lake there are finely laminated schists, dipping 70° southwest. Southward, also, the gneisses become more massive and coarse. At the northeastern base of the main peak a body of coarse granite is partly inclosed in the norite. This norite assumes a dioritic habitus near the granite, with the development of biotite mica.

The valley of the Cottonwood was followed down several miles, when it was left and the Morena Valley traversed to its head. The mountains south of the valley are formed of a dark syenite. North and northwest the higher mountains consist of granite, with a great development of mica and hornblende schists along the slope facing the valley. Many granite dikes have been intruded into the schists. North of Mr. Candler’s there is a great dike of pegmatite, carrying small garnets, tourmaline, mica, and large masses of quartz. This pegmatite dike cuts across the cañon, forming a precipice on its lower side. On the upper side the soil has been retained, forming a small but fertile valley. The strike of the mica schists on the north is quite unusual, being north 75° west, dip nearly vertical. Dark syenite lies on the west of this little valley. Morena Valley has an elevation of 3,400 feet. A rough road leads over the mountains west to McClain’s ranch, a distance of 10 miles; the highest point reached having an elevation of 4,000 feet. Near the summit there outcrops a body of coarse eruptive rock, probably a diorite. It consists of coarse hornblendic aggregates in a light-colored feldspathic matrix. This is followed by syenite, and that by coarse white granite as far as McClain’s. The granite about the valley is coarse, with dark, fine crystalline inclusions. It has every character of a truly eruptive rock, even to the minute spaces between the components, left at the time of crystallization. The road now descends to a branch of the Cottonwood, and from the creek there is a long, gradual ascent to the pass north of Lyon’s Peak. The north side of the pass is formed of another high and rugged granite range. This section is one of the wildest to be found in San Diego County. The mountains are bare granite, often precipitous; the valleys small and covered with brush. Crystalline limestone is reported to have been found in the granite 5 or 6 miles northeast of Renney’s Pass. A very interesting eruptive rock outcrops east of the pass, on the north side of the road. In places it resembles the norite from Cuyamaca peaks. The rock consists largely of large, dark, cleavable crystals filled with small granular crystals of a green color, probably olivine. A large portion of the dark crystals are undoubtedly pyroxene, though there are some showing hornblende cleavage. This is one of the most peculiar and interesting rocks seen in the county, but, from lack of any opportunity to make a microscopic examination, no more definite definition can be given.

Coarse granite extends some distance west of the pass. It is decomposed to such a depth that no specimens could be obtained. A mile west of the pass a fine granite, apparently metamorphic, replaces the other. It contains much quartz, little mica, and yellowish feldspar. Some distance down the new grade a large body of diorite outcrops. It is one of the southern arms of a great mass of coarse, dark rock which forms the high mountains about Dehesa Post Office, on the Sweetwater. A large portion of this rock very closely resembles that forming the Cuyamaca, and is probably a gabbro.

Near the foot of the grade, 2 miles east of Jamul Post Office, this rock is very coarse, with large hornblende crystals. It extends out in the form of arms or dikes into the adjoining granitic rocks. This rock is very tough and heavy. Gneiss outcrops for 2 miles westward. It varies between thin-bedded micaceous strata and thick-bedded, almost granitic forms. It strikes north 15° east, dips 70° to 80° east. Farther down, toward the Oakdale House, this is replaced by coarse eruptive granites. Just below the Oakdale House there is a very interesting contact between granite, quartz porphyry, and diabase. The first rock exposed below the house is a rather dark micaceous syenite. Beyond this the rock becomes coarser, containing large grains of quartz and glassy feldspar, with inclusions of a very dark diabasic rock. In a little cañon which comes down to the road from the east, this rock comes into contact with one which varies from a feldspathic mica schist, through a gneiss, to a quartz porphyry. The junction is very irregular and the two rocks are slightly mixed; sometimes branches of the syenite are partly inclosed in the porphyry. Some portions of the syenite show gas pores, or spaces left at the time of consolidation, one fourth to one half an inch in diameter. They are partly filled with secondary quartz. The next rock exposed up the cañon is a mica schist; strike 15° west, dip vertical. Quartz porphyry follows this, then an irregular dike of granite, in which are imbedded nodules of quartz porphyry, some nearly a foot in diameter. Above the granite there appears a granitoid gneiss, with many cavities, arranged with their longer axes parallel to the schistose structure. This changes into a coarse, knotty granite, containing large nodules of dark petrosilex. A slight blending is noticeable. Farther up this is succeeded by a micaceous quartz feldspar porphyry, showing a somewhat gneissoid structure. It is out at right angles to this structure by jointing planes lying thickly together. It has a milky, vitreous luster, and contains inclusions of very coarse granite. The next rock exposed is a diabase 200 feet across. It is coarse in the middle and aphanitic on the edges. Adjoining it are bunches of granite and a fine, dark, compact mica schist, showing traces of little pebbles in places. The schist changes to a petrosilex, which comes in contact with a dike of very coarse granite. At the upper edge of this granite outcrop, and inclosed in it, is a stratum of fine, dark mica schist and a dike of quartz porphyry. At one end these inclusions are hidden, but at the other they have been bent, fractured, and the pieces separated some distance in the granite. (Fig. 9). This is a most interesting example of the intrusive nature of the granite.

The granite dike is bounded on its upper side by one of aphanitic diabase 2 feet wide, followed by granite again. Nodules of the diabase appear in the edge of the granite. A stratum of wavy quartzose gneiss 10 feet wide follows the last dike of granite. It changes across the strike into a coarser gneiss, and that into irregular and partially blended masses of coarse granite, filled with long fragments of porphyry similar to a dike on the east. (Fig. 10.) The quartz porphyry is very compact and brittle, and has a conchoidal fracture. The porphyry dike has a width of 8 feet. About it is still another dike of granite 12 feet across, and containing many long fragments of a diabasic rock, which appears next in the succession.

The diabase is cut by small, interlacing granite seams for 6 or 8 feet, and also contains some large, irregular, lenticular masses of the same rock. Still farther is another dark dike cut squarely across by granite. Fine granite and quartz porphyry dikes occur still farther east. The porphyry dikes all run about north 35° west, average dip 70° southwest. They extend along the summit of a ridge for more than half a mile, when the coarse granite becomes the country rock. On the summit of the hill at the head of the cañon are strata of metamorphic rock, and also some veins of pegmatite, cutting across the porphyry. This wonderfully varied succession of rocks does not cover a width of more than a quarter of a mile. The relations exhibited here prove that the porphyry and diabase, as well as the schists, are older than the granite. The strip of country between the ancient porphyries of San Miguel and the coarse granite of Lyon’s Peak and the ranges north is remarkably rich in its variety of intrusive rocks.

On the north bank of the Sweetwater, just above where the Spring Valley road crosses, is a large exposure of coarse granite, containing so many inclosures of a dark dioritic rock as to present the appearance of a conglomerate. It is cut by bunches and ramifying dikes of fine granite and diorite.

At Dehesa the granite is replaced by norite, which forms a high mountain on the north side of the river, and extends southeasterly 3 or 4 miles, forming two high peaks. In this are veins of hornblende aggregates, and in general appearance the rock bears the closest resemblance to that on the Cuyamaca.

The crystalline rocks exposed between the Sweetwater and El Cajon Valley generally show more of a dioritic composition than granitic. They have a glassy feldspar, much hornblende, and little quartz. There are two varieties: one is light colored, and forms most of the country; the other is darker, occurring in bunches and dikes. Southwest of the valley the rocks are more granitic. On the road to Spring Valley they give place to a hard, light—colored felsitic rock, containing specks of chloritic matter. Masses of granite appear in places, intruded into the rock. As it decays it becomes jointed, and seems to be reduced mostly to kaolin. Near the railroad, northwest of Spring Valley, rocks outcrop which belong to the series of dark intrusives, tuffs, and porphyries so extensively developed west of the granite. The rock here has a fragmental appearance in weathered specimens. It has a dark green color, and is of uncertain composition. The most western exposure of this rock, before it becomes covered by the mesa, has much the same character. It is without doubt an ancient intrusive, very greatly altered. It contains bunchy dikes of white feldspathic composition, which easily reduce to kaolin. The whole exposed width of these rocks west of the granite at this point is over a mile, about half of which is tufaceous. By tufaceous is not necessarily meant a fragmental intrusive deposited in water, but for lack of any other term it is used to designate those fragmental intrusives of plutonic origin which are so abundant in California.

Between the Oakdale House and the Sweetwater River, on the road to the dam, dark quartz mica diorites outcrop. They have been intruded by coarse granite in veins and bunches. A body of dark aphanitic rock, of uncertain origin, is inclosed in the diorite near the river. It may be a portion of the aphanitic rocks associated with the porphyries farther west. A little distance down the river the diorite is succeeded by conglomerate rocks, containing small garnets. The fragments are feldspathic in composition. Dark feldspathic porphyry then forms the prevailing rock for some distance. It shows great variations. Much of it contains no distinct crystals of feldspar, but is mottled by light green felsitic bodies of irregular outline. These contain chloritic substances, which decay out, leaving holes. There is a great variety of these ancient intrusives exposed along the sides of the river north of San Miguel Peak. None of the other crystalline rocks in San Diego County appear so old or show so much alteration.

Farther down the cañon the rock assumes a fragmental appearance, having masses of feldspar in a dark matrix. It finally becomes a pronounced breccia, being formed largely of angular, felsitic fragments. The base in which these fragments lie decays away and leaves them standing out on the surface. This may be a tuff formed in water, but the matrix has undergone such alterations that nothing certain can be said about it. This breccia continues to the lower end of the cañon. An interesting, light-colored dike was observed here. It is so filled with minute spherical amygdules as to resemble in structure an oolitic limestone. The breccia continues as far as the Sweetwater Dam, where it is replaced by feldspar porphyry. The porphyry shows much variation; in places no feldspar crystals are present, chlorite taking their place. These rocks disappear a quarter of a mile west of the dam, and mesa-like hills extend down to Chula Vista. These consist of soft sandstones and some calcareous deposits. Dark rocks, belonging to the series just described, outcrop near the mesa road from San Diego to El Cajon. It forms a long ridge south of La Mesa. The rocks are in part tufaceous, and in part dark green and massive, with felsitic inclusions. Near the Eleven-Mile House the granite is filled with dark, bowlder-like inclusions. Hornblende is an important constituent of the granite. It is more than likely that many of these so-called granites are really diorites. The mesa formation terminates in an abrupt escarpment on the west of Cajon Valley. The valley comprises many thousand acres of very fertile land. Granitic knobs rise in many parts of the valley, showing that the alluvium deposit is underlaid by it at no great depth. North of the valley, for a number of miles, the crystalline rocks are covered by the mesa conglomerates. Granitic rocks are the only ones exposed for many miles east of Lakeside. Just above Forster’s there is a small outcrop of gneiss and mica schist; strike north 35° west, dip 70° northeast. The rock exposed along the grade is a coarse biotite granite, with much quartz and glassy feldspar. A dike of quartz porphyry varying to granite porphyry outcrops by the road at the top of the grade. This does not seem to be sharply defined from the adjoining granite. A dark hornblende granite or diorite begins here and outcrops along the road for several miles toward Ramona. Three miles from the town there appears a dark rock with a somewhat resinous luster. It is probably a diabase. The Santa Maria is a large, plateau-like valley, with low granite hills surrounding it. Light-colored granite, becoming somewhat hornblendic, extends some distance east of Ramona, when it is replaced by a dark diorite. The latter extends along the road for 2 miles. It has glassy feldspar, and in places much mica. Four miles west of Ballena the granite is filled with pegmatitic veins, running in a northwesterly direction. They carry brittle crystals of black tourmaline, garnet, and muscovite mica. East of Ballena the rock becomes coarser and somewhat gneissose, with an abundance of mica. There are no bedding planes, simply a parallelism of constituents. This schistose structure has a northwest direction. The gneiss changes to mica schist on the grade above Santa Ysabel. The schist alternates with occasional strata of quartzite; strike north 25° west. The quartzite is a white, fine, granular variety, containing a little mica. Coarse gneiss outcrops again farther up the grade; at the top it becomes finer, carrying some hornblende, and alternating with strata of fine mica schist; dip northeast. The gneiss often becomes granitoid. The lamination has no constant direction, and resembles a flowage structure. This granitoid gneiss extends to within a mile of Julian, when there is quite a sharp transition to a gneissoid mica schist. That gives place to a fine schist, and a quarter of a mile west of Julian to a pearly hydro-mica schist. The schists strike north 20° to 30° west, dip 70° northeast. At Julian the rock is a dark, thin-bedded mica schist, usually termed a slate. There are also dark felsitic rocks and some gneisses. The belt of dark slaty mica schists is about half a mile wide. Toward the Balkan Mountain the rocks become more gneissoid. This mountain seems to be formed wholly of gneiss and mica schist. In some places the rock is nearly massive, and contains a large amount of quartz.

The rocks forming the mountains near the road from San Felipe to Vallecito are nearly all gneissoid. The real desert begins on leaving San Felipe Valley. The road extends southeast for 5 miles and then turns southwest, descending a narrow, rocky gorge to the head of Vallecito Creek. Near where the road turns to the southwest, the gneisses are cut by innumerable dikes of coarse granitic composition. Many of these run parallel, cutting across the strike of the gneisses, and give the appearance of a bedded formation. In the cañon, before reaching Vallecito Creek, mica schist appears. It is bent and twisted into every conceivable direction, and varies exceedingly in structure and composition in the course of a few feet. The dip is northeast, and often at a small angle. The granite dikes often carry garnets, being quite similar to those between Julian and Banner. They were probably intruded after the eruption of the granite, and the related metamorphism.

At Mason’s granite and gneiss both appear as intrusives in the schists, and are themselves cut by coarse dikes similar to those described. Between this point and Banner, in a direct line, gneiss is the prevailing rock. The high mountain east of Banner is more granitoid.

There is a sandy valley of considerable extent about Mason’s; eastward a low ridge is crossed, and the road descends to Vallecito Valley between barren granite mountains, gradually descending until the open desert is reached. When the granite is hard these mountains are very rugged, but in places they are covered so deeply with soft, decomposed material as to closely resemble the Tertiary deposits farther east. The mountains often show pale purple to brown tints. On examination they appear to consist of a white granite, which has been so shattered as to break up into pieces, averaging not over 2 inches in diameter. This rock presents a very similar appearance for miles, particularly on the north side of the creek.

At Palm Springs the soft clay beds of late Tertiary age begin to appear. They dip in all directions, though that to the south and southwest is the most common. Toward Carrizo Station these are often covered by granitic detritus. The Tertiary beds widen out where the road strikes Carrizo Creek, and at Carrizo Station they have a width of nearly 10 miles. They rest against a granite range north of the creek and south along a long ridge which terminates in Carrizo Mountain. They also extend a long distance up Carrizo Creek. Four miles below the station harder sandstones and strata of shells cap the clay hills. This shell layer near the creek is 10 feet thick and contains pectens and oyster shells, belonging to the Miocene-Tertiary. The clay hills which surround Carrizo Station form a veritable Bad-Land. They show many different colors, and are perfectly devoid of any vegetation. They have been eroded into a most confused network of hills and cañons, and are so soft that it is difficult to travel over them. Six miles below this station and a mile north of the creek there rises a rugged granite range, facing the open desert. It rises from the desert quite precipitously nearly 2,000 feet, but blends westward into the ridges which run east from San Felipe. The granite is coarse and deeply decomposed. Sharp, angular grains of quartz stand out so prominently as to tear anything with which they come in contact. The thin-bedded shell strata rest against the slopes of the mountain, and near the southern end rise against the eastern slope at a very high angle in sharp, jagged points. These strata rise above the granite ridges at the point where they occur, and dip fully 70° to the east. (Fig. 11.) Resting on the summit of this granite ridge, and immediately west of the steeply inclined and jagged points of the Tertiary strata, is the southern outcrop of a bed of coarse, hard sandstone, which rises along the summit of the ridges to the north and dips west, extending down the western side of the range for a thousand feet or more, dipping at an angle of about 30°. This sandstone outcrops along the crest of the ridge for nearly a mile. It is, however, not absolutely continuous, the granite rising through it in places. Near the southern end it is so highly metamorphosed as to be with difficulty distinguished from the granite at the contact. In fact, the two formations have become so intimately united, that a fracture of the granite made near the sandstone, instead of stopping at the contact, extends into the sandstone, so that the two rocks break off together. The contact is so exceedingly irregular that it seemed at first sight as if the sandstone had been intruded by the granite. Deep, narrow crevices extend into the granite, and are filled with sandstone. Some granite bunches are almost inclosed in the sandstone. The most interesting feature of this sandstone is the presence in it of an abundance of well-preserved corals of a type fully as old as the Cretaceous. Fragments of two species of a large oyster and poorly preserved specimens of univalve and bivalve shells are also abundant. There are at least two species of coral, many specimens being at least a foot in diameter. The sandstone is literally filled with them toward the southern portion of the outcrop. They also extend down into the crevices and cavities in the granite. The sandstone shows somewhat less metamorphism toward the north, where it contains some strata of pebbly conglomerate. The granite is intersected by many veins of coarsely crystallized feldspar and quartz. From these veins many of the pebbles in the conglomerate have been derived. At the highest point of the ridge the sandstone has the greatest thickness. Here it is broken up into great blocks 15 feet square, piled in the greatest confusion, as if by an earthquake. One great mass overhangs the almost precipitous granite escarpment at an elevation of 1,000 feet above the desert. Many fractures extend from the sandstones through into the granite. The sandstones, as well as the granite mountains north, have been baked a dull red color by the intense heat of the sun. To account for the peculiar position of this sandstone, as well as the steep inclination of the Tertiary beds at the southern end of the mountain, we must suppose that an extensive fault has taken place along the edge of the range facing the desert. The general inclination of the Tertiary beds to the west and southwest is also evidence of an uplift along this line.