Yucca Mountain, in the south-central part of the Basin and Range Province, is characterized by structures typical of the Cenozoic extended terranes and oroclinal bending of the Walker Lane belt. The mountain consists of a series of ridges that bifurcate southward from a plateau-like remnant of a middle Miocene volcanic apron. The ridges are underlain by eastward tilted structural blocks and separated from one another by west-dipping, steep normal faults. Toward the south, the dips of normal faults decrease, but the number of normal faults, the amount of offset on individual faults, the amount of eastward tilt of the strata, and the degree of internal deformation within structural blocks all increase. Dips of major normal faults decrease southward. The northern end of the mountain has been extended about 10 percent, whereas the southern end has been extended about 60 percent. Progressive clockwise rotation about a vertical axis has produced a 30° oroclinal bend over a 25-km distance from north to south at Yucca Mountain.
Shallow exposure into the middle Miocene volcanic rocks beneath Yucca Mountain precludes observation of structural accommodation below the high-angle faults at the mountain. However, indirect evidence suggests the presence of an accommodation structure under the mountain, probably a low-angle normal fault at depths between 1 and 4 km. This evidence includes domino-style tilting of the blocks, probable listric faults, internal block deformation, closely spaced major normal faults, a probable decoupled stress field between Paleozoic and Tertiary rocks, and low-angle normal faults exposed in areas adjacent to Yucca Mountain. The presence of low-angle normal faults at several levels above a basal detachment fault to the east and west of Yucca Mountain suggests that an interconnected stack or tier of low-angle normal faults may exist under the mountain.
Rates of extensional deformation at Yucca Mountain reached an apparent maximum with geologic strain rates of nearly 10-14/sec between 13 and 11.5 Ma and decreased to about 10-16/sec afterward.
Clockwise oroclinal bending of rocks both at Yucca Mountain and at ranges affected by the Las Vegas Valley shear zone suggests that deformation is related. Except for small dextral strike-slip faults at the northern end of the mountain, the bending does not seem to be accommodated by the geometries of strike-slip faults. Oroclinal bending of rocks at the surface may reflect movement on deeper strike-slip zones or flexures that are partially decoupled along preexisting low-angle faults.