EFFECTS OF THE EASTERN CALIFORNIA SHEAR ZONE ON THE TOPOGRAPHY OF THE MOJAVE DESERT

The topographic implications of late Neogene tectonism were evaluated using digital elevation data and other constraints within a GIS environment. Our study shows that the Eastern California shear zone (ECSZ) is strongly expressed in the topography of the MDB and suggests that the ECSZ has been a major factor in the evolution of the landscape since its inception in late Miocene time. Major drainages and basins are developed along transtensional depressions. Tectonism, through the creation of relief, has focussed erosion along the boundaries of strained areas of the ECSZ. Soda Lake, created by transtension, is the lowest point in the MDB and is thus the regional base level that governs erosion regionally by running water. Highland areas within the Mojave are highly correlated with areas of transpressional strain. These general tectonic-topographic relationships are consonant with predictions of the geometric-kinematic model of Dokka et al. (1998). Topography and the strain domains are spatially associated within the ECSZ. Areas of high elevation in the Mojave Desert block are spatially associated with: a) areas that have or are currently undergoing transpression within the broad, distributed zone of right shear of the ECSZ; and b) areas that lie adjacent to uplifted transpressional belts that bound the Mojave Desert (San Bernardino Mountains). In contrast, transtension within the ECSZ is predicted to have produced the lowland areas. Areas that have undergone the greatest local transtension associated with dextral shear within the ECSZ are also the lowest topographically. These areas are associated with the earliest phase of movements (bracketed between ~13 and 1 Ma) of the ECSZ. The second population is coextensive with transtensional basins that are currently active. Remaining areas of the MDB owe their origin to Quaternary erosion and landscape inheritance. We propose that the accordant summits and deeply weathered bedrock plateaus within the ECSZ are all that remains of a Mojave-wide erosion surface(s). This surface may be correlative with previously documented pre-late Miocene surfaces in the western MDB and eastern Mojave Desert.