Abstract 0 Road log begins at the Keystone Lodge in Keystone, Colorado. North of the hotel, Proterozoic granite and felsic gneiss are exposed on the upper elevations of the un-named mountain. The lower slopes of the mountain consist of Pleistocene till that overlies the Precambrian rocks. Drive west on U. S. Highway 6 to the intersection with Interstate 70 (exit 205). 0.6 North of the highway, the Williams Range thrust fault that placed Proterozoic rocks over Cretaceous shale and sandstone is exposed just north of the borrow pit (situated above the shale cliff). The trace of the fault south is covered by Quaternary rocks in the Snake River area, is then exposed along the lower slopes of Keystone Mountain ( Widmann et al., 2003 ). Shale and sandstone of Cretaceous age crop out adjacent the highway to Dillon and form the northern slope of Swan Mountain (south of the Snake River Arm of the reservoir) and the peninsula to the west ( Kellogg et al., 2008 ). 1.4 Highway crosses the Snake River. 2.4 Snake River. Pierre Shale (Cretaceous) forms the dark gray outcrops just north of the highway. 4.0 Dillon Reservoir. The west portal of the 21-mile long Harold Roberts Tunnel is located on the end of the peninsula west of here. The tunnel transfers water beneath the continental divide into the South Platte River which flows through Denver. Eastward, the Williams Range thrust is concealed beneath Quaternary units near the power transmission line on the bottom slopes of Tenderfoot Mountain (11,441 feet).