Named for a prominent ridge on eastern side of pre-Cambrian section of Los Pinos Mountains in northeastern Socorro Co, NM in Southwestern Basin-and-Range region. No type locality designated. Forms high eastern ridge crests in northern half of Los Pinos Range. Occurs north of Hwy 60 extending south of Hwy for about 10 mi. Width of outcrop ranges from 500 ft on north end, widens to 1 mi in central part, then narrows to less than 0.5 mi in northern part. Basal part consists of massive quartzite beds 2-7 ft thick which vary in color from white to light pink, tan, and red. Impure shaly beds occur throughout unit, becoming prominent near top. Near top, thin beds of gray quartzite 1-2 ft thick alternate with schistose zones of gray and white sericitic schist. Hematite stains beds light pink to red near top. Thickness ranges from 900 ft near Sierra Montosa to 3,700 ft in central part of belt. Conformably overlies pre-Cambrian Blue Springs schist (new); disconformably underlies pre-Cambrian Sevilleta rhyolite (new). Geologic map. Measured stratigraphic cross sections. Pre-Cambrian age presumably based on regional geology and stratigraphic position.

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