The Horseshoe Gulch area includes 16 square miles in the
Eastern Paleozoic Belt of the Klamath Mountains geologic province
north of Callahan, California. Fossiliferous Late Ordovician and
Silurian limestones and unfossiliferous greywackes, arkoses, shales,
mudstones, schists, and phyllites, and other terrigenous clastic
rocks are exposed in a broad fault zone...