The narrative follows three teenage friends who join a pack-burro camping expedition into remote Sierra country, accompanied by a young geologist and an elderly prospector. Their journey mixes outdoor adventure—wildlife encounters, trout fishing, rodeo scenes, firefighting with an air patrol, cave exploration, avalanches and earthquakes—with hands-on geological investigation: tracing glaciated canyons, giant sequoias, sulphur springs, fossils and the region's volcanic features. Action centers on pursuing forest incendiaries through a labyrinthine limestone cave and a fossil discovery that prompts discussion of earth formation and ancient life. The book interleaves episodic thrills and practical survival skills with accessible explanations of geologic processes and terminology.