Checking billy barr’s snow log…
The mountains northwest of Aspen, Colorado, are composed of Pennsylvanian through Triassic evaporites and molasse of the Eagle Valley, Belden, Minturn, Maroon, and State Bridge formations. Southwest of the Roaring Fork River and its tributary, Woody Creek, are Jurassic through Cretaceous sediments that unconformably overlie these older rocks. This entire sequence is located in the Elk Range thrust sheet. Along Woody Creek and the Roaring Fork River, Bryant and Freeman have mapped the continuation of the Castle Creek fault zone. These writers interpreted the fault zone as a southeast-dipping normal fault with a horst of Eagle Valley formation continuously present between the Pennsylvanian-Triassic and Cretaceous beds within the fault zone. Southwestward thrusting on a decollement within the Eagle Valley evaporite sequence would explain (1) its presence in the fault zone, (2) the 17,000 + ft of stratigraphic throw, and (3) the structural discordance across the fault zone. The author interprets the fault zone to be a northeast-dipping gravity slide that has been thrust off and possibly pushed by the Laramide Sawatch uplift. Cross sections through the area have similar geometry to those for the Elk Range and Hunters Hill thrusts to the south-southwest. The upturned heel is exposed along themore » Sawatch structural front between Hunter Creek (north of Aspen) and Lenado. These relationships suggest that another thrust paralleling the Fryingpan River is possible to the north. The author proposes the name Roaring fork thrust for the fault zone in the Woody Creek and Roaring Fork River valleys. The Castle Creek fault zone should be reserved for the fault zone in the drainage south of Aspen and the southwest projection of the Homestake shear zone, against which is appears to terminate.« less
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