Greenschist member
Greenschist member
Jurassic
Chiefly greenschist and lesser metamorphosed pyroclastic rocks in the southern part of the western metamorphic belt. This unit forms part of the Don Pedro terrane of Schweickert (2015). It forms a discontinuous elongate band east of the Melones fault between Placerville and Mariposa with a disconnected continuation in the Coarsegold and nearby roof pendants. Greenschist derived from basalt and andesite breccia, pillow lava, and mafic tuff. Unit locally contains hypabyssal intrusive rocks and lenses of metagabbro. Pyroclastic rocks chiefly consist of metamorphosed tuff containing mostly saussuritized feldspar and actinolite with some epidote, chlorite and sericite. Pyroclastic rocks similar in mineralogy to greenschist, but more commonly bedded, with small-scale folding and boudinage structures. Primary structures in unit in most areas obliterated by intense deformation. Metamorphosed at lower greenschist facies. Metavolcanic rocks in the southern roof pendants are higher grade, largely amphibolite.
Metavolcanic units near the Merced River yielded a ~187 Ma Rb/Sr whole-rock age (Bateman and others, 1985), and a small pluton in this unit near Mariposa yielded an Ar-Ar age of ~169 Ma (Herzig and Sharp, 1992). Farther southeast, near Hwy 41 in the Coarsegold roof pendant, this unit has yielded a detrital zircon MDA of ~187 Ma, and an MDA of ~165 Ma in an unnamed pendant about 10 km south of that. The unit is locally intruded by the ~162-177 Ma Don Pedro intrusive suite (unit Gdp), so much of the unit is probably that age or older. However, a greenstone body northwest of Mariposa and one northeast of Lake Don Pedro have yielded Late Jurassic ammonites (Imlay, 1961; Clark, 1964), and elsewhere a metavolcanic body includes an ~167 Ma clast (Sharp, 1988; Schweickert, 2015), so those parts of the greenstone are Late Jurassic, postdating the plutonic intrusion. The unit in this area is also called the volcanic member of the Sullivan Creek terrane or the greenstone of Bullion Mountain. 
The Early and Middle Jurassic part of this unit is magmatically linked to the coeval Don Pedro intrusive suite (unit Gdp) forming Don Pedro Island arc deposited on and intruded into the western margin of the Calaveras Complex.
West of Millerton Lake, also includes: