干旱区生态环境知识资源中心

Digital elevation data were used to evaluate the topographic implications of the late Neogene Eastern California Shear Zone (ECSZ). Analysis shows that the ECSZ has directly affected >18% of the surface of the Mojave Desert block (MDB); uncertainties regarding the distribution of strain in basins suggest that the area of effect may be larger by perhaps a factor of 2. Remaining areas are likely due to Quaternary erosion or are inherited from pre-ECSZ times. Major drainages and basins of the MDB are developed along transtensional depressions within the ECSZ. These depressions established the regional and local base levels that have governed erosion by running water. Local topography is closely tied to the style of strain. Highlands of the MDB; are spatially associated with (1) areas that have or are currently undergoing contractional strain associated with transpression within the ECSZ and (2) areas that lie adjacent to uplifted transpressional belts that bound the Mojave Desert (San Bernardino and San Gabriel Mountains). In contrast, lowland areas are spatially associated only with transtensional areas within the ECSZ. Examination of the topography in the transtensional areas also reveals two, distinct populations of elevation. Spatial analysis indicates that areas that have undergone the greatest local transtension associated with dextral shear are also the lowest topographically. These areas formed during the earliest phase of movement of the ECSZ (late Miocene to early Pleistocene). The second population is coextensive with recently formed transtensional basins that continue to be active.