Preliminary geologic section from Pahute Mesa, Nevada Test Site, to Enterprise, Utah

The 154-mile long geologic cross section trends nearly perpendicular to the structural grain of the Basin-Range province in Nevada, and in Utah extends eastward into the transition zone between the Basin-Range and Colorado Plateau provinces. The structure is characterized by complex thrust: faults, involving uppermost Precambrian to lower Mesozoic sedimentary rocks, and normal faults which cut: the thick sequence of Tertiary volcanic rocks as well as older rocks. Some of the normal faults are the result of caldera collapse. The principal normal faults trend northerly west: of Delamar, Nev., and form north-trending basins and ranges. Farther east the principal faults trend northwesterly, and form a moderately rugged highland rather than distinct basins and ranges.

The uppermost Precambrian-Paleozoic strata thin markedly eastward across the region. The pre-Pennsylvanian sedimentary rocks vary from 32,500 feet: in thickness at the Nevada Test: Site (Harley Barnes, E. N. Hinrichs, F. A. McKeown and P. P. Orkild, written commun., 1963) to 4,500 feet: in the Beaver Dam Mountains in western Utah (Cook, 1960). Thick Mesozoic deposits, similar to those of the Colorado Plateau, are present in western Utah, but are represented in eastern Nevada by only thin patches of Triassic rock.