Statement of Problem: The northern Mojave Desert is the least studied and least understood part of the Eastern California Shear Zone, a broad swath of strike-slip faults that departs from the San Andreas fault near the Transverse Ranges in southern California and passes east of  the Sierra Nevada.  This zone accommodates about 20% of interplate motion on poorly defined faults, and represents a significant seismic hazard for cities through the Mojave Desert and north to Reno, NV, as well as for military bases and national parks, utility corridors to major coastal population sources, and transportation routes. Modeling of the zone is crucial for San Andreas fault models, and the northern Mojave Desert represents a critical, but poorly understood, link in such models.  This northern Mojave Desert part of the zone transitions from several strike-slip faults spaced across a broad area of the southern Mojave Desert to just three major strike-slip faults in the southern Basin and Range province.  The nature of this transition, including which faults are active and changing patterns of active faults through time, remain to be identified.  Recently completed 1:100,000-scale USGS mapping of surficial geology across the northern Mojave Desert has identified many new faults, trends in ages of last slip on faults, and active faults that previously were not considered to have slipped during the Holocene.  These provocative findings represent a major step forward in understanding and yet are only partly studied due to the scale and time constraints for the previous mapping.  Detailed 1:24,000 scale maps of selected faults and their intersections will significantly reduce uncertainties in the new findings, as well as nicely utilize the regionally consistent intermediate-scale mapping.  In addition to providing better understanding of the neotectonics of a critical part of the Eastern California Shear Zone, detailed mapping in the northern Mojave Desert will take advantage of the superb desert exposures to examine minor tectonic features that are difficult to study in more vegetated areas. The results will provide lessons for interpreting fault features in urbanized or vegetated areas.  Complete delineation of subtle “off-fault” deformation by minor faults, folds, and warps also has the potential to provide generalizable lessons for other areas.  Tectonic clues may be determined from geomorphology and extrapolated to other areas.

Objectives:  We will describe selected faults and related deformational features such as folds in both time and space in order to understand the neotectonic evolution of the northern Mojave Desert, which has received little study since many active faults were outlined by Dibblee (1961) and Jennings (1973).  This improved understanding of the fault systems through time will then be provided for models of the Eastern California Shear Zone and the San Andreas fault system. We also seek to develop better understandings of geomorphic records of neotectonics in terms of the geomorphology associated with different styles of faults and the decay of this geomorphic signature with time.  Such an understanding can lead to rapid evaluations of fault history from a knowledge of geomorphology, a topic of interest since Bull and Wallace (1984) and Bull (2007) developed the basic concepts.

Information from an earlier project description (below):

USGS conducts several studies of importance for understanding the Desert Southwest, many of which focus on understanding a particular area or topic. Starting in 2001, the mission of this desert landscape study has been to characterize surface materials of the entire desert southwest. Research efforts focus on surficial mapping and evaluation of earth materials by:

• What process deposited them
• How old they are
• Their physical properties

This information will be condensed onto landscape maps, allowing land managers to better manage lands by, for example:

• Making predictions about behavior of surface materialsUnderstanding changing landscape processes over timeIdentifying areas susceptible to impacts
• Identifying areas likely to harbor archeological artifacts.

The landscape maps will integrate the diverse desert studies, allowing more consistent and effective management of these beautiful lands. Principal tasks in the project

1. National Map DatabaseSurficial Geologic MappingSurface Process InvestigationsRemote Sensing ResearchEcological Processes
2. Earthquake