Abstract

The Mojave Desert region is crossed by young northwest-striking right-slip faults. Restoration of their displacement indicates that the over-all shape of this region has been considerably distorted. The assumption that the region was always in contact with the Sierra Nevada forms the basis for the following conclusions: (1) The slices between the faults, and the faults themselves, were rotated counterclockwise, possibly by as much as 30°; the precise magnitude and timing of the rotation can be checked by paleomagnetic studies. (2) Because of this deformation, the part of the San Andreas fault adjacent to the Mojave Desert was bent; originally the fault was much straighter. (3) The major deformation of the Mojave Desert was a west-trending left shear that was supplemented by the left slip on the Garlock fault. A similar deformation, without rotation of blocks, was accomplished in the eastern Transverse Ranges by left slip on approximately west-striking faults.

This crustal shearing resulted from the position of the Mojave Desert between the regions of crustal spreading in the Great Basin and those in the continental borderland and the Salton Trough. The shearing of the Mojave Desert accommodated lateral variations of crustal spreading.

These deformations distorted the shape of the margin of the North American plate during Neogene and Quaternary time. They mainly reflect movement normal to the plate boundary, whereas much larger movement occurred contemporaneously parallel to the plate boundary.

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