slightly more than 80 million years ago, the region's landscape was flat and monotonous; a condition that persisted during most of the Late Cretaceous. Rocky Mountains rise The period of uplift that resulted in the formation of the ancestral Rocky Mountains is called the Laramide orogeny. Mountains already existed west and southwest of Wyoming, with progressively older mountains (up to Jurassic age) trending west into Nevada. Latest Cretaceous time saw the formation of a low broad northwest-trending arch along the approximate area of the present Teton Range and Gros Ventre Mountains. Part of the evidence for the first Laramide mountain building west of the Teton region is the several hundred cubic miles of quartzite boulders derived from the Targhee uplift, which was located north and west of the northern end of the present-day Teton Range. Streams carried boulders, sand, and clay from the uplift eastward and southeastward across what would become Jackson Hole. Flakes of gold and some mercury are in the resulting Harebell Formation. Two huge depositional troughs were formed in central and southern Wyoming from fine-grained debris carried farther east and southeast. Many of the larger boulders were derived from Precambrian and possibly lower Paleozoic quartzites, meaning that at least of Paleozoic and Mesozoic rock must have been stripped from the Targhee uplift before the quartzites were exposed to erosion. Tertiary uplift and deposition The tectonic setting of western North America changed drastically as the Farallon Plate under the Pacific Ocean to the west was shallowly subducted below North American Plate. Called the Laramide orogeny, the compressive forces generated from this collision erased the Cretaceous Seaway, fused the Sierran Arc to the rest of North America and created the Rocky Mountains. This mountain-building event started in the Mesozoic 80 million years ago and lasted well into the first half of the Cenozoic era 30 million years ago. Some 60 million years ago, these forces uplifted the low-lying coastal plain in the Teton region and created the north-south-trending thrust faults of the nearby Wyoming Overthrust Belt. Uplift intensified and climaxed a few million years later early in the Eocene epoch when large thrust and reverse faults created small mountain ranges separated by subsiding sedimentary basins. One of the reverse faults, the north-south trending 10 mile (16 km) long Buck Mountain Fault, elevated what is today the central part of the Teton Range. By about 34 million years ago, these