White Ridge Quartzite

The unit was first defined by Stark and Dapples in 1946, during their mapping of the Los Pinos Mountains, and named for White Ridge, a prominent ridge in the northeastern part of the mountains.^[1]

The unit is a thick sequence of massive quartzite beds, white to reddish or tan in color, 2 to 7 feet (0.6 to 2 m) thick. There are also scattered beds of sericite schist that become more numerous in the uppermost part of the formation, where the quartzite beds thin to 1 to 2 feet (0.3 to 0.6 m) in thickness and the beds are reddened by hematite. The quartzite often contains significant sericite, biotite, and hematite. The total thickness of the formation is up to 3,700 feet (1,100 m). The beds dip steeply to the west, at a dip angle of 32 to 70 degrees.^[1] The formation overlies the Abajo Formation and in turn is overlain by the Estadio Schist.^[2]

Detrital zircon grains in the formation are almost identical in age and isotope composition to the underlying Sevilleta metarhyolite, suggesting that the sediments of the quartzite were weathered almost exclusively from local sources. The minimum zircon age is about 1650 Ma,^[2] and radiometric dating of underlying and overlying formations place the age of the White Ridge Quarzite between 1650 and 1588 Ma.^[3]