Salt Spring Slate
Salt Spring Slate
Late Jurassic, Oxfordian to Kimmeridgian
Chiefly black sericite slate with lesser widespread graywacke and tuff along with local thin conglomerate layers. Small lenses of dark-gray limestone are found locally in the slate. Unit also contains local amphibolite and chlorite schist derived from mafic to siliceous metavolcanic rock. Chiefly marine sedimentary rocks containing dominantly epiclastic rocks that overlie and intertongue with Gopher Ridge Volcanics (unit CWGR). Includes rocks previously mapped as Merced Falls Slate. In southernmost part of belt close to the batholith and in the Adobe Hill roof pendant, the unit consists chiefly of biotite-quartzite schist, metadacite and metarhyolite schist, chlorite schist, andalusite schist, and amphibolite derived from basalt or mafic tuff. Imlay (1961) reports late Oxfordian to early Kimmeridgian Buchia from this unit along the Cosumnes River.