Faults were mapped using stereoscopic pairs of low-sun-angle aerial photographs (approximate scale 1:12,000) and concentrated on interpreting geomorphic features and surfaces. Maps were compiled at scale 1:24,000, then recompiled for publication at a scale of 1:62,500. The low-sun-angle aerial photographs are most useful for interpreting scarp morphology in alluvial terrain where surfaces are of low relief. Consequently, faults in high-relief bedrock areas were not studied extensively. Fault scarps and other fault-related features subsequently were identified and studied in the field.
Fault scarps were studied for evidence of recurrent displacement by means of fault-scarp morphologic techniques. The methods utilized for this fault-scarp study were developed and described by many workers (for example, Slemmons, 1977; Wallace, 1977, 1978; Bucknam and Anderson, 1979; and Pease, 1979). The geomorphic and structural nomenclature used herein also follows these sources, as well as some previous studies of a similar nature in other regions (for example, Clark, 1973; Brown and Wolfe, 1972; Ross, 1969; Vedder and Wallace, 1970; and Brown, 1970). Faults and fault-related features were classified according to a scheme originally compiled by Slemmons (1977) (table 1). Clark (1973) also described some of the features useful in identifying recent faulting.
Table 1. Geomorphic features associated with active faults, ranked
approximately by frequency of occurrence
Two methods were used to estimate the ages of faulting along the Death ValleyFurnace Creek fault system. One method involves the interpretation of fault-scarp morphology using the techniques of Slemmons (1977) and refined by Wallace (1977), who showed that slopes along fault scarps in alluvium are controlled successively by gravity-, debris-, and wash-related processes. The original surface of the fault scarp is replaced by an erosion surface and a debris slope; the slope of the erosion surface and debris slope gradually decline through time (fig. 3). The rate of slope decline depends on the process that controls the steepest slope on the scarp. By estimating the duration that each process controls the maximum slope angle, Wallace (1978, fig. 12) estimated the age of faulting that produced scarps (fig. 4). The estimated age appears to depend on climate, character and consolidation of the faulted material, orientation of the fault, and the height and slope of the original fault scarp (Wallace, 1978; Pease, 1979; and Pierce and Coleman, 1987). Low scarps decline in slope more rapidly than high scarps; thus, the original type and amount of dip slip are also important (Bucknam and Anderson, 1979).
The second method used to estimate the age of faulting events in the Death Valley area is based on interpreting the relative ages of fault-related features and successive geomorphic features. For example, at some localities a fault cuts an older alluvial surface or surfaces, whereas a younger surface remains undisturbed across the fault trace. At many localities, scarps in progressively older stratigraphic units and (or) geomorphic surfaces have progressively larger offsets, indicating that recurrent faulting occurred along the same trace.
We employed a four-fold classification for geomorphic surfaces along the Death ValleyFurnace Creek fault system (table 2), incorporating sparse age control from the Death Valley area; this classification is derived from similar classifications developed by Denny (1965), Hunt and Mabey (1966), Hooke (1972), and W.B. Bull (written commun., 1974). We consider the general chronology shown on table 2 to be a reasonable geomorphic tool useful for estimating the relative ages of surfaces in a small area; however, correlations from one area to another may not be accurate, and correlations between distant areas may be misleading. The correlation problem is paramount between Fish Lake Valley and Death Valley where the climates of the valleys and adjacent mountains differ widely. Consequently, the estimated ages for geomorphic surfaces cited in table 2 should be viewed as approximations requiring much refinement. Some refinement has occurred in Fish Lake Valley (Reheis, 1988; Sawyer and Slemmons, 1988).
Table 2. General characteristics of geomorphic surfaces, Death ValleyFurnace Creek Fault system, California and Nevada [in, meter; >, more than; , not applicable]
Last Updated: 24-Jul-2009