MI-100 Summary Report on the McQueary Gulch Trench, Williams Fork Mountains Fault, Grand County, Colorado


This publication is based on a CGS paleoseismic trenching project executed in 2005, part of a wider CGS research effort on Quaternary faults across the state. The trench was excavated across a secondary scarp associated with Williams Fork Mountains fault, a late Cenozoic structure in north-central Colorado. The fault lies at the western edge of the Williams Fork Valley and eastern base of the Williams Fork Mountains in Grand County. It trends northwest-southeast and juxtaposes Proterozoic rocks in the footwall against Miocene and late Oligocene Troublesome Formation in the hanging wall. Digital PDF download. MI-100D

From the Abstract:

In 2005, the CGS conducted a paleoseismic investigation of a scarp in Quaternary deposits at the northern end of the Williams Fork Mountains fault in north-central Colorado. The scarp is located in McQueary Gulch in the northwest part of the Williams Fork Valley. Although this location, at the far end of the fault, was not ideal for a paleoseismic investigation, it was the only feasible location for our study at that time due to budgetary, access, and scheduling limitations. The trenched scarp, herein called the “lower scarp,” is located in the hanging wall of the main fault trace at the range front. The lower scarp, 4.8 m high, is 50 to 80 m north-northeast of and downslope from the range front, and has a maximum scarp angle of 22.0º.