Abstract Excellent exposures of both an early Proterozoic uncon formity and the Precambrian-Cambrian unconformity occur in the Nemo area along the eastern side of the Precambrian core of the Black Hills approximately 18 mi (30 km) northwest of Rapid City (Fig. 1). Although the two unconformities are exposed relatively near one another, there is approximately 1.5 Ga difference in their ages. The lithologies and structure of these localities permit significant inferences about tectonic events and geologic history of the Black Hills.

Abstract The schedule for today will include a visit the Richmond Hill deposit, north of Terry Peak, and if time permits, the Carbonate district. The trip will then return to Lead, and travel to Rapid City via Nemo Road and the quartz-pebble conglomerate occurrences. The route is shown on Figure 1.