Bishop Tuff formed from eruption that created the Long Valley Caldera

This outcrop is exposed in a rock quarry in Chalfant Valley about 25 km (15 mi) southwest of Long Valley Caldera. The two main units of the Bishop Tuff deposit are visible here: (1) the lower 5 m (16 f) of the section consists of the pumice that fell to the ground (airfall pumice) downwind from the eruption; and (2) the upper 5-6 m (16-20 f) of the section consists of the basal part of the pyroclastic flows that swept at hurricane speed away from the eruption. The thin dark "layers" just below the contact between the units are stains from an ancient groundwater table (manganese oxide stains).