Pg. 31, pls. 1-11. Name given to isolated mass of volcanic and hypabyssal rocks, at western edge of exposed bedrock south of La Grange. Base of formation, lying on Merced Falls slate (new) is exposed immediately south of Tuolumne River but top is not preserved. Thickness as exposed uncertain, but probably more than 3,000 feet. Volcanics not exposed in Tuolumne River section and relatively poor exposures about 1 mile south of La Grange were examined to complete Tuolumne River section. Here, bedded pyroclastic rocks form northeastern and lower part of unit. Southwestern higher part of unit consists of massive rocks without amygdules but with small feldspar phenocrysts and hardly with quartz phenocrysts. Stratigraphic relations to Merced Falls slate indicate Late Jurassic.
Type area: about 2 mi south of La Grange, Stanislaus Co., central CA.
[Author does not capitalize rank terms; however, units are considered formal.]

Source: US geologic names lexicon (USGS Bull. 1350, p. 562-563).