THE WARM SPRINGS VALLEY FAULT SYSTEM, A MAJOR RIGHT-LATERAL FAULT OF THE NORTHERN WALKER LANE, WESTERN NEVADA

The Warm Springs Valley fault system (WSVFS) is one of three major right-lateral faults in the northern Walker Lane. The system has well-developed, late Quaternary tectonic geomorphology over 35 km, but may be up to 95 km long with potential extensions in Warm Springs and Honey Lake Valleys. The system is typically made up of two or more fault traces in parallel and anastomosing patterns. The WSVFS is a quintessential transtensional fault with a strong tendency to step to the right at large and small scales, creating extensional areas. The WSVFS traverses several sedimentary environments, and has different geomorphic expression in each. In the basin sediment of Warm Springs Valley, fault scarps, vegetation lineaments, and small push-up features created by the last few events along the fault are visible (short-term geomorphic expression), and there are large areas where alluvial processes are young or active, and there is no convincing tectonic expression. Long-term geomorphology (mid to late Quaternary) is buried or not sustained. In the alluvial fan environment, long-term geomorphic expression, such as linear ridges, is nearly continuous, whereas expression of the last few events is subtle and sparse, and commonly is buried, eroded away, or indistinct. In the bedrock environment, long-term gemorphic expression is abundant and continuous, including linear ridges, valleys, and drainages, sidehill benches and swales, fault scarps, oversteepened hillslope bases, and fault facets. Similar to the alluvial fan environment, short-term geomorphic expression is sparse.

Four trenches excavated along the southern portion of the WSVFS expose at least three, and potentially more, latest Pleistocene paleoearthquakes. Evidence includes offset deposits, fault-fissure deposits, colluvial-wedge deposits, liquefied and laterally spread deposits, and a sandblow. One of these paleoevents appears to have occurred while Warm Springs Valley was inundated with water, possibly the high stand of Lake Lahontan, a latest Pleistocene pluvial lake.