Title: The Geologic Story of Yellowstone National Park
Author: William R. Keefer
Illustrator: John R. Stacy
Release date: October 25, 2019 [eBook #60574]
Most recently updated: October 17, 2024
Language: English
Credits: Produced by Stephen Hutcheson and the Online Distributed
Proofreading Team at http://www.pgdp.net
A review of the geologic processes and events responsible for the spectacular natural wonders of the Yellowstone country, commemorating the 100th anniversary of the oldest and largest of our national parks.
For sale by the Superintendent of Documents, U.S. Government Printing Office
Washington, DC. 20402—Price $1.25
Stock Number 2401-1209
“* * * and behold! The whole country beyond was smoking with vapor from boiling springs, and burning with gases issuing from small craters, each of which was emitting a sharp, whistling sound. * * * The general face of the country was smooth and rolling, being a level plain, dotted with cone-shaped mounds. On the summit of these mounds were small craters from four to six feet in diameter. Interspersed among these on the level plain were larger craters, some of them four to six miles across. Out of these craters, issued blue flames and molten brimstone.”
Description credited to Joseph Meek, 1829; quotation from page 40 of the book “The Yellowstone National Park” by Hiram Martin Chittenden (as edited and published by Richard A. Bartlett, University of Oklahoma Press, Norman, Oklahoma, 1964). Photograph is of Midway Geyser Basin.
“Be it enacted by the Senate and House of Representatives of the United States of America in Congress assembled, that the tract of land in the territories of Montana and Wyoming lying near the headwaters of the Yellowstone River is hereby reserved and withdrawn from settlement, occupancy, or sale under the laws of the United States, and dedicated and set apart as a public park or pleasuring ground for the benefit and enjoyment of the people * * *”
Approved March 1, 1872—signed by:
James G. Blaine, Speaker of the House
Schuyler Colfax, Vice-President of the United States and President of the Senate
Ulysses S. Grant, President of the United States
By William R. Keefer
Illustrated by John R. Stacy
Based on a planned series of technical reports resulting from comprehensive geologic studies in Yellowstone National Park by the author and his colleagues, H. R. Blank, Jr., R. L. Christiansen, R. O. Fournier, J. D. Love, L. J. P. Muffler, J. D. Obradovich, K. L. Pierce, H. J. Prostka, G. M. Richmond, Meyer Rubin, E. T. Ruppel, H. W. Smedes, A. H. Truesdell, H. A. Waldrop, and D. E. White.
GEOLOGICAL SURVEY BULLETIN 1347
UNITED STATES DEPARTMENT OF THE INTERIOR
ROGERS C. B. MORTON, Secretary
GEOLOGICAL SURVEY
V. E. McKelvey, Director
Library of Congress catalog-card No. 79-169200
First printing 1971 (1972)
Second printing 1972
In the aftermath of the Civil War, the United States expanded the exploration of her western frontiers to gain a measure of the vast lands and natural resources in the region now occupied by our Rocky Mountain States. As part of this effort, the Geological and Geographical Survey of the Territories was organized within the Department of the Interior, and staffed by a group of hardy, pioneering scientists under the leadership of geologist F. V. Hayden. During the summer of 1871, these men, accompanied by photographer William H. Jackson and artist Thomas Moran, made a reconnaissance geological study of the legendary and mysterious “Yellowstone Wonderland” in remote northwestern Wyoming Territory. The scientific reports and illustrations prepared by Hayden and his colleagues, supplementing the startling accounts that had been published by members of the famous Washburn-Doane Expedition a year earlier, erased all doubts that this unique land was eminently worthy of being set aside “for the benefit and enjoyment of the people.” By Act of Congress on March 1, 1872, our first National Park was established.
During the past century, 50 million people have toured Yellowstone National Park, marveling at its never-ending display of natural wonders. No doubt many have paused to wonder about the origin of these unusual and complex geological features—a question, needless to say, that has intrigued and challenged scientists from the very first days of the Hayden Survey. During the past decade a group of U. S. Geological Survey scientists, in cooperation with the National Park Service and aided by the interest of the National Aeronautics and Space Administration in remote sensing of the geologic phenomena, has been probing the depths and farthest corners of the Park seeking more of the answers. Some of the results of this work, and those of earlier studies, are described in this book to provide a better understanding and enjoyment of this great National Park.
V. E. McKelvey, Director
U. S. Geological Survey
The vivid descriptions brought back from the Yellowstone country by the early explorers and trappers (see frontispiece), whose reputations for telling tall tales were widely accepted if not altogether deserved, fell upon the disbelieving ears of the nation for more than half a century. Yet the intriguing rumors persisted, and during the years 1869-71 several expeditions staffed partly by scientists and engineers rediscovered this unique region atop the backbone of our nation. We now know that the earliest visitors, even if prone to exaggerate, could not do justice to the long-hidden secrets of Yellowstone, for none of them saw all of the fascinating features that occur within this great National Park.
By the time the modern-day visitor enters Yellowstone National Park through any of its five entrances, he probably will have traveled through many parts of the Rocky Mountains and grown somewhat accustomed to the “lay of the land.” But this will in no way lessen the exciting impact of viewing the natural wonders of Yellowstone for the first time. Immediate attention, of course, is still drawn to the remarkable array of geysers, hot springs, and other thermal phenomena which in sheer numbers and variety are unsurpassed throughout the world. But, as if these were not enough of an attraction, nature has also provided an incredible setting of sparkling rivers and lakes, thundering waterfalls and cataracts, awesome canyons and gorges, and lofty glaciated mountain peaks and extinct volcanoes. Truly this is a land apart, a spectacular masterpiece of nature that fully deserves the accolade of “wonderland” bestowed long ago by early explorers and trappers. (See figs. 1 and 2.)
YELLOWSTONE NATIONAL PARK AREA, showing rivers, lakes, landforms, roads, towns, settlements, and major geyser basins (stippled). The Park embraces 3,472 square miles (2,221,770 acres), and its boundaries traverse a distance of nearly 300 miles. Yellowstone Lake, with an irregular shoreline of 110 miles and a surface area of 137 square miles, is one of the largest natural mountain lakes in the United States. (Fig. 1)
INDEX MAP showing localities where photographs (and one sketch, fig. 35) were taken to illustrate this bulletin. For photographs of distant views, arrows point in direction of view. Numbers refer to figure numbers in text. (Fig. 2)
Beyond the first stirring impressions derived from the grandeur of the vast Yellowstone wilderness and its myriad wildlife, assuredly shared by people of all ages and from all walks of life, the various aspects of the Park take on a very different meaning for different individuals. The artist sees grand vistas to be painted, the naturalist delights in the flower-laden meadows and the native habitats of many kinds of birds and animals, the engineer visualizes the amount of energy stored in the waterfalls and steaming geysers, and so on. To the geologist, in particular, who studies rocks and fossils and all of the natural processes involved in shaping the surface of the land, and to all those who would share such interests, Yellowstone takes on a very special meaning. For the Park is foremost a geological Park, created by an extraordinary sequence of natural processes and events that have combined to produce an immense outdoor laboratory for studies that have contributed to a fuller knowledge and a better understanding of the earth itself. The geological aspect of the Yellowstone country is reflected by its very name, given long ago to the river that issues from the great canyon of the “yellow rocks.”[1] This report, borrowing from a century of scientific study within and around the Park area, describes the geological “how, why, and when” of this unique and fascinating region.
Some 600,000 years ago the rumblings of an impending volcanic eruption sounded ominously across the Yellowstone country. Suddenly, in a mighty crescendo of deafening explosions, tremendous quantities of hot volcanic ash and pumice spewed from giant cracks at the earth’s surface. Towering dust clouds blackened the sky, and vast sheets of volcanic debris spread out rapidly across the countryside in all directions, covering thousands of square miles in a matter of minutes with a blanket of utter devastation. Abruptly, a great smoldering pit—a caldera 30 miles across, 45 miles long, and several thousand feet deep—appeared in the central Yellowstone region, the ground having fallen into the huge underground cavern that was left by the earth-shaking eruptions. Lava then began oozing from the cracks to fill the still-smoking caldera.
Thus, in one brief “moment” of geologic time there was launched that incredible chain of events which led to the creation of many of the natural wonders of Yellowstone National Park. Heat from the enormous reservoir of molten rock which produced the massive eruption still remains deep within the earth beneath Yellowstone, sustaining the spectacular hot-water and steam phenomena for which the Park is so justly famous. The formation of the caldera and the eruption of lavas profoundly influenced the shape of the present-day landscape. Once a land covered almost entirely by mountains, the part that collapsed—nearly one-third of the total Park area—is now characterized by low rolling plateaus formed from the thick lava flows that filled the caldera (figs. 1 and 2; see fig. 22 for the outline of the Yellowstone caldera). Moreover, the carving of the spectacular Grand Canyon of the Yellowstone (fig. 41) and the fashioning of the large interior basin now occupied by beautiful Yellowstone Lake (fig. 27) were closely related to this mighty volcanic event.
North, east, and south of the central plateaus are extensive mountain ranges and other highlands which provide much of the Park’s scenic beauty (figs. 3 and 4). Formed by many episodes of intense mountain building and ancient volcanism, these uplands bear the lasting imprints of a wide variety of geological activities that date back approximately 2.7 billion years. Indeed, as we study all the features of the Yellowstone landscape, we find in them a most impressive and fascinating story of that ageless conflict between the internal forces of nature that raise the land through the upheaval of mountains and the eruption of volcanoes, and the external forces of erosion that wear the land down. It is this vast relentless interplay of giant forces that determines the appearance of any given place upon the earth’s surface. And, in few other places around the globe can the processes of both building up and tearing down the landscape be illustrated more dramatically than in Yellowstone National Park.
SKYLINE OF THE GALLATIN RANGE in northwestern Yellowstone National Park, as viewed from a point on the road between Canyon Village and Norris Junction. The range consists chiefly of Paleozoic and Mesozoic sedimentary rocks and Precambrian metamorphic rocks that were uplifted by folding and faulting of the earth’s crust. The dark-gray rocks along the roadcut in the left foreground are rhyolite lava flows of the Solfatara Plateau. (Fig. 3)
HAYDEN VALLEY. View north along the Yellowstone River and Hayden Valley toward the Washburn Range. Mount Washburn, part of an ancient Absaroka volcano, is the highest prominence (elevation, 10,293 feet) on the skyline to the right, and Dunraven Pass is in the notch in the center of the skyline. The foot of the range marks the north edge of the Yellowstone caldera. Hayden Valley is cut in glacial lake sediments that overlie thick lava flows covering the caldera floor. (Fig. 4)
Geologists believe that “the present is the key to the past.” After observing lava erupting from a present-day volcano or limestone forming in marine waters, we infer that similar types of ancient lavas or ancient limestones formed in virtually the same ways. This kind of reasoning is used to interpret the origins of all types of ancient rocks, for all the known geological processes that form rocks seem to have been operating since the earth’s beginning.
Figure 5 shows the many different rock units that have been recognized in Yellowstone National Park. Arranged in a vertical column according to the geologic time intervals in which they formed, these rocks represent a large part of total earth history (fig. 6). A generalized geologic map (plate 1) shows the distribution of the various units (or groups of closely related units) exposed at the surface throughout the Park area. This map and figure 5 summarize much of the information that is necessary to interpret the Park’s geologic history—in essence, to provide answers to these two important questions: What were the geologic events that formed the rocks? When did these events occur?
If we were to walk backward in time at the rate of one century per step, the first step would return us to 1872, the year that Yellowstone National Park was established. But to return to the oldest recorded event in its geologic history, we would have to walk (at 3 feet per step) some 15,000 miles, or three-fifths of the way around the world! Occurring far back in the antiquity of the Precambrian Era—approximately 2.7 billion years ago according to radiometric dating (fig. 6)—the oldest event resulted in rocks so crumpled and changed by heat and pressure that their original character is obscure. These rocks, having been transformed from still older ones, are called metamorphic rocks. Considered to form part of the very foundation of the continent itself, they are also commonly referred to as basement rocks.
THE ROCKS of Yellowstone National Park, separated into individual units or formations and arranged according to their geologic ages (see fig. 6). A formation is a body of rock that contains certain identifying features (such as composition, color, and fossils) which set it apart from all other rock units. The identifying features of each formation provide valuable clues bearing on its origin. Most formations are given formal names, and usually each formation is thick and widespread enough to be recognized over broad areas. Some, however, change character from place to place, and different names may be used in different areas even though the rocks represent the same geologic time interval. (Fig. 5)
| AGE, IN THOUSANDS OF YEARS | ROCK FORMATION OR UNIT |
|---|---|
| 40± to present | Stream sand and gravel |
| Hot-spring deposits | |
| 9 to 250± | Glacial deposits |
| 60 to 600 | Plateau Rhyolite |
| 600 | Upper Unit, Yellowstone Tuff |
| 600 to 2,000 | Rhyolite and basalt lava flows |
| 2,000 | Lower Unit, Yellowstone Tuff |
| 2,000+ | Rhyolite and basalt lava flows |
KINDS OF ROCKS SHOWN IN COLUMNS
Sandstone or stream sand
Conglomerate, glacial moraines, or stream gravels
Volcanic breccia
Shale
Limestone
Dolomite
Lava flows
Welded tuff
Travertine or geyserite
| ROCK FORMATIONS | AGE, IN MILLIONS OF YEARS | PERIOD | ERA | |
|---|---|---|---|---|
| Northern part of park | Southern part of park | |||
| Thick lava flows, welded tuffs, glacial deposits, and hot-spring deposits | QUATERNARY | CENOZOIC | ||
| 2-3 | ||||
| Pliocene, Miocene, and Oligocene rocks not known to be present | ||||
| 37-38 | ||||
| Absaroka volcanic rocks | Absaroka volcanic rocks (Eocene) | TERTIARY | ||
| 53-54 | ||||
| Volcanic and sedimentary rocks (largely eroded away before Absaroka volcanic rocks were deposited) | Pinyon Conglomerate (Paleocene and Cretaceous) | |||
| 65 | ||||
| Landslide Creek Fm | Harebell Formation | CRETACEOUS | MESOZOIC | |
| Everts Formation | (Eroded away before Harebell was deposited) | |||
| Eagle Sandstone | Bacon Ridge Sandstone | |||
| Telegraph Creek Fm | ″ | |||
| Cody Shale | Cody Shale | |||
| Frontier Formation | Frontier Formation | |||
| Mowry Shale | Mowry Shale | |||
| Thermopolis Shale | Thermopolis Shale | |||
| Kootenai Formation | Cloverly Formation | |||
| 136 | ||||
| Morrison Formation | Morrison(?) Fm | JURASSIC | ||
| Swift Formation | Sundance Formation | |||
| Rierdon Formation | ″ | |||
| Sawtooth Formation | Gypsum Spring Fm | |||
| 190-195 | ||||
| Woodside & Thaynes(?) Formations | Chugwater Formation | TRIASSIC | ||
| Dinwoody Formation | Dinwoody Formation | |||
| 225 | ||||
| Shedhorn Sandstone | Phosphoria Fm and related rocks | PERMIAN | PALEOZOIC | |
| 280 | ||||
| Quadrant Sandstone | Tensleep Formation | PENNSYLVANIAN | ||
| Amsden Formation | Amsden Formation | |||
| Mission Canyon Limestone | Madison Limestone | MISSISSIPIAN | ||
| Lodgepole Limestone | ″ | |||
| 345 | ||||
| Three Forks Fm | Darby Formation | DEVONIAN | ||
| Jefferson Formation | ″ | |||
| Bighorn Dolomite | (Not exposed, except for isolated outcrops of some formations in Falls River area, in southwestern part of park) | ORDOVICIAN | ||
| 500 | ||||
| Snowy Range Fm | ″ | CAMBRIAN | ||
| Pilgrim Limestone | ||||
| Park Shale | ||||
| Meagher Limestone | ||||
| Wolsey Shale | ||||
| Flathead Sandstone | ||||
| 570 | ||||
| Gneiss and Schist | (Not exposed) | PRECAMBRIAN | ||
| 2,700 | ||||
THE GEOLOGIC TIME SCALE—the “calendar” used by geologists in interpreting earth history. Column A, graduated in billions of years (B.Y.) and subdivided into the four major geologic eras (Precambrian, for example), represents the time elapsed since the beginning of the earth, which is believed to have been about 4.5 billion years ago. Column B is an expansion of part of the time scale in millions of years (M.Y.), to show the subdivisions (periods—Cambrian, for example) of the Paleozoic, Mesozoic, and Cenozoic Eras; column C is a further expansion to show particularly the subdivisions (epochs—Paleocene, for example) of the Tertiary and Quaternary Periods. The principal events in the geologic history of Yellowstone National Park are listed to the right of column C, opposite the time intervals in which they occurred. The ages, in years, are based on radiometric dating. Many rocks contain radioactive elements which begin to decay at a very slow but measurable rate as soon as the parent rock is formed. The most common radioactive elements are uranium, rubidium, and potassium, and their decay (“daughter”) products are lead, strontium, and argon, respectively. By measuring both the amount of a given daughter product and the amount of the original radioactive element still remaining in the parent rock, and then relating these measurements to their known rate of radioactive decay, the age of the rock in actual numbers of years can be calculated. The decay of radioactive carbon (carbon-14) to nitrogen is especially useful for dating rocks less than 40,000 years old. (Fig. 6)
Gneiss, a coarsely banded rock (fig. 7), and schist, a finely banded rock, are the most common kinds of metamorphic rocks in Yellowstone. Originally, the gneiss probably was granite, and the schist was a shale or sandstone. Outcrops of the gneisses and schists occur only in the northern part of the Park (pl. 1), where they form the central cores of some mountain ranges such as the Gallatin Range (fig. 3). They also lie buried beneath younger rocks in many other areas of the Park.
From the time of the metamorphic event, when the gneisses and schists were formed, until the deposition of sediments of the Cambrian Period (figs. 5 and 6), there is virtually no record. It is reasonably certain, however, that several times during this 2.1-billion-year interval the region was intensely squeezed and uplifted into high mountains and then deeply eroded. By the end of Precambrian time, approximately 570 million years ago, the ancient Yellowstone landscape had been reduced by erosion to a flat, stark, almost featureless plain, which was soon to be flooded by a shallow sea encroaching from the west. This very old surface is now partly exposed in some places across the Buffalo Plateau, at the north edge of the Park (fig. 1).
LAMAR RIVER. View downstream (west) along the Lamar River in Lamar Canyon. The rocks along the river banks are coarsely banded Precambrian gneisses more than 2.5 billion years old, some of the oldest rocks in Yellowstone National Park. (Fig. 7)