GEOMORPHOLOGY OF CIMA DOME, MOJAVE DESERT, CALIFORNIA

Abstract

Cima Dome, a remarkably smooth symmetrical alluvium-fringed rock dome in the desert of southeastern California, is the prototype of Davis' granitic desert dome, supposedly convex and presumably developed by backwearing of a granitic fault block. Transit-stadia profiles across Cima Dome show concave or essentially straight slopes and demonstrate that it is not convex except to a slight degree in the uppermost 25 feet. Geophysical explorations by resistivity, gravity, and seismic methods on the southeastern flank reveal no boundary fault or any form unequivocably identifiable as the convex suballuvial bench deduced by Lawson. At its deepest point the granitic rock floor is buried by 1300 feet of overburden composed of 550 feet of alluvium, or geophysically comparable material, and 650 feet of more coherent rock, presumably welded rhyolitic tuff. Cima Dome is primarily a regraded part of an extensive late Pliocene-early Pleistocene erosion surface, Hewett's Ivanpah upland, now buried by Pleistocene volcanic rocks immediately to the west. The dome may be an erosion residual on that surface or it may have been created largely by subsequent deformation, primarily warping. Evidence cited favors the warping hypothesis. The present profile of Cima Dome is due to erosion and regrading in the current cycle, and in most places the smoothness of slope and the symmetry are due to uniform debris yielded by granular disintegration of homogeneous quartz monzonite composing the dome. The relations at Cima Dome and elsewhere suggest that the role of recent warping merits consideration with regard to the origin of closed basins, broad divides, disintegrated drainages, areas of dissection and related landscape features in the desert of southeastern California.