Conglomerates such as the Pinyon are not the only clue to the time of mountain building. Another type of evidence—faults—is demonstrated in figure 16. The youngest rocks cut by a fault are always older than the fault. Many faults and the rocks on each side are covered by still younger unbroken sediments. These must, therefore, have been deposited after fault movement ceased. By dating both the faulted and the overlying unbroken sediments, the time of fault movement can be bracketed. Observations of this type in western Wyoming indicate that the Laramide Revolution reached a climax during earliest Eocene time, 50 to 55 million years ago. Mountain-producing upwarps formed during this episode were commonly bounded on one side by either reverse or thrust faults (fig. 16B and 16C) and intervening blocks were downfolded into large, very deep basins. The amount of movement of the mountain blocks over the basins ranged from tens of miles in the Snake River, Salt River, Wyoming, and Hoback Ranges directly south of the Tetons to less than 5 miles on the east margin of Jackson Hole (the west flank of the Washakie Range shown in figure 1). The ancestral Teton-Gros Ventre uplift continued to rise but remained one of the less conspicuous mountain ranges in the region (fig. 47). The Buck Mountain fault, the great reverse fault which lies just west of the highest Teton peaks (see geologic map and cross section), was formed either at this time or during a later episode of movement that also involved the southwest margin of the Gros Ventre Mountains. The Buck Mountain fault is of special importance because it raised a segment of Precambrian rocks several thousand feet. Later, when the entire range as we now know it was uplifted by movement along the Teton fault, the hard basement rocks in this previously upfaulted segment continued to stand much higher than those in adjacent parts of the range. All of the major peaks in the Tetons are carved from this doubly uplifted block. The brightly colored sandstone, mudstone, and claystone in the Indian Meadows and Wind River Formations (lower Eocene) in the eastern part of Jackson Hole were derived from variegated Triassic, Jurassic, and Lower Cretaceous rocks exposed on the adjacent mountain flanks. Fossils in these Eocene Formations show that it took less than 10 million years for the uplifts to be deeply eroded and partially buried in their own debris.