Page [Frontispiece Midway Geyser Basin] II [Plate 1. Geologic map of Yellowstone National Park] 36 [Figure 1. Geographic map of Yellowstone National Park] 2 [2. Index map showing photograph localities] 3 [3. Skyline of the Gallatin Range in northwestern Yellowstone National Park] 6 [4. View north along the Yellowstone River and Hayden Valley toward the Washburn Range] 6 [5. The rocks of Yellowstone National Park] 8 [6. The geologic time scale] 10 [7. View downstream along the Lamar River and closeup view of Precambrian gneiss] 12 [8. Positions of seaways and landmasses during the middle part of Permian time] 14 [9. Crowfoot Ridge in the southern Gallatin Range] 15 [10. Mount Everts] 16 [11. The faunal succession in sedimentary rocks] 17 [12. Beds of limestone along Pebble Creek and closeup views of outcrop and fossils] 18 [13. Common kinds of geologic structures produced by deformation of the earth’s crust] 20 [14. Geologic structures in Yellowstone National Park] 22 [15. Intrusive and extrusive igneous rock bodies] 24 [16. The Absaroka volcanoes and their rocks] 25 [17. Massive beds of volcanic breccia of the Absaroka volcanic rocks and closeup view of outcrop] 26 [18. Massive layered breccias of the Absaroka volcanic rocks at Barronette Peak] 28 [19. Giant petrified tree trunks in Yellowstone’s fossil forest] 29 [20. Closeup view of a specimen of intrusive igneous rock] 30 [21. Bunsen Peak, a body of intrusive igneous rock] 31 [22. Outline of the Yellowstone caldera] 35 [23. Various stages in the development of the Yellowstone caldera] 40 [24. Extent of the rhyolite welded tuffs that once covered Yellowstone National Park] 42 [25. The Yellowstone Tuff at Golden Gate and closeup views of tuff specimens] 43 [26. Cross section through the Mount Washburn-Canyon area, showing relationships along north edge of the Yellowstone caldera] 44 [27. View southeast across Yellowstone Lake toward the Absaroka Range] 45 [28. Radar image of lava flows in southwestern Yellowstone National Park] 46 [29. Obsidian Cliff] 47 [30. Thick rhyolite lava flow along Firehole River and closeup view of specimen] 48 [31. Brecciated lava flows] 49 [32. Outcrop and closeup view of glassy rhyolite lava] 50 [33. Basalt flows at Tower and closeup views of outcrop and specimen] 52 [34. Giant glacial boulder of Precambrian gneiss at Inspiration Point] 54 [35. Glacial terrain along the Northeast Entrance Road] 56 [36. Typical profiles of canyons cut by stream erosion and glaciation] 57 [37. Aerial oblique view of Electric Peak] 58 [38. Extent of ice in Yellowstone National Park during the maximum spreading of the Pinedale glaciers] 60 [39. Beds of sand, silt, and clay deposited in a glacially dammed lake in Hayden Valley] 61 [40. Waterfalls in Yellowstone National Park] 62 [41. Grand Canyon and Lower Falls of the Yellowstone River] 65 [42. Various stages in the development of the Grand Canyon of the Yellowstone] 66 [43. Common kinds of thermal features in Yellowstone National Park] 70 [44. Norris Geyser Basin, showing solid floor of hot spring deposits] 72 [45. Diagram of a thermal system] 72 [46. Infrared image of a portion of Upper Geyser Basin] 73 [47. Mound of geyserite (sinter) at Castle Geyser] 75 [48. Terraces of travertine at Opal Springs and closeup of specimen] 76 [49. Algal-colored terraces lining the west bank of the Firehole River] 78 [50. A geyser in action] 80 [51. Rock rubble surrounding Seismic Geyser in Upper Geyser Basin] 83 [52. Old Faithful in full eruption] 84 [53. Mud volcano near Pocket Basin in Lower Geyser Basin] 86 [54. Reactivation of a fault during the Hebgen Lake earthquake of August 17, 1959] 88
Yellowstone Country
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.