Geologic Map of the Area Around the Nebo Annex, Marine Corps Logistics Base, Barstow, California

This map and report present the results of a new geologic field survey of the area surrounding the Nebo Annex of the Marine Corps Logistics Base, near Barstow, California. The map provides a detailed geologic framework that will assist geotechnical and hydrologic operations at the base. The report describes the geologic materials and structures that are shown on the map and explains their significance in terms of regional geologic history.

Certain results of the geologic survey have special practical significance for the Nebo Annex. In particular, we found that the Marine base is traversed by several northwest-trending faults of the Camp Rock-Harper Lake system (faults A-E on the map). Fault C is especially noteworthy because it obstructs the flow of shallow ground water; moreover, it probably has moved during Holocene time and should be considered a potential source of earthquake hazards. The major characteristics of this important group of faults are described more fully near the end of this summary.