Named for Robbers Mountain, prominent peak in Pilot Knob 15' quad, approximately 8 km southwest of type section, San Bernardino Co, CA. Type section designated in (unsurveyed area SE/4 SW/4, Wingate Pass 15' quad) beginning at 35 deg 32'14"N, 117 deg 09'04"W, following bearing of 280 deg. Reference section (T29S R39E, Garlock 7.5' quad) designated in El Paso Mountains, beginning 1.7 km east of Gerbracht Camp, 35 deg 26'53"N, 117 deg 49'05"W, initially following bearing of 260 deg. Consists of informal lower metaconglomerate member and upper meta-argillite member. Metaconglomerate member (about 80 m thick) consists mainly of pebble-sized pale-pink to pale-red-purple, flattened, angular meta-argillite, silty meta-argillite, and chert clasts. Lower member is conformably overlain by meta-argillite member (about 30 m thick), which is predominantly platy laminated meta-argillite and silty meta-argillite; weathered outcrop ranges between pale red to pinkish gray and pale yellow brown to light gray color. Robbers Mountain overlies with slight unconformity or disconformably different units of Devonian age. Upper part is faulted or removed by erosion. Age may range from latest Devonian through Early Mississippian; however age is tentatively set at Early Mississippian (Kinderhookian) based on conodonts which occur in lower part of meta-argillite member in type section.

Source: GNU records (USGS DDS-6; Menlo GNULEX).