Hill (1933) visited the site and the following geologic description is a summary of his observations. Extensive exposures of mineralized quartz diorite and schist occur in a hydraulic cut on the Zimmerman property. Near the southwest or lower end of the cut, a fault zone strikes east and dips 85 N. The fault zone consists of 11 feet of blue clay gouge that contains a large amount of fragmental quartz and silicified schist. Some of the fragments contain arsenopyrite and have a peculiar greenish-yellow stain. A few samples from a 3-foot zone of silicified mineralized schist contained as much as 0.08 ounces of gold per ton.

Northeast of the gouge, the rock is quartz diorite. For seven feet above the fault, the diorite is badly crushed, but farther to the northeast, it is less altered, breaks in blocky forms, and is cut by several minor fault fractures that strike from west to N 60 W. Southwest of the main fault, the rock is highly silicified schist with many quartz veinlets and everywhere contains a small amount of finely disseminated arsenopyrite. The rock is bluish gray, hard, and heavier than the normal quartz-mica schist. For at least 70 feet south of the main fault, this rock is broken and crushed, and there are several well-defined slip planes that vary in strike from N 70 W to west and dip north, all roughly parallel to the main fault.