Name applied to a 300 m thick feldspathic schist that is exposed in cliffs (its type locality) near Pilar, northern Picuris Mountains, Taos Co, NM in the Southern Rocky Mountain region. Named for an old mining camp located at base of the cliffs. The schist contains quartz and feldspar megacrysts. A high Mn-rich horizon present near top. Base is nowhere exposed. Is one of four formations [not in a sequence] assigned to the Vadito Group (revised) exposed in the cliffs below Ortega Formation (redescribed) of Hondo Group (new). Its stratigraphic position relative to Marquenas Formation (redescribed, revised) of Vadito not stated, though both formations occur only in the Picuris--Glenwoody in the north part in one area and Marquenas in the south part in two areas. Was referred to as felsic schist at Pilar in earlier reports. Geologic map. Nomenclature chart. Is associated with rocks about 1,700 Ma or Early Proterozoic age.

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