The Calaveritas quadrangle is in the western foothills of the Sierra Nevada, east of the Mother Lode gold belt. Most of the quadrangle is underlain by a strongly de• formed bedrock complex that is locally covered by small deposits of undeformed stream gravels and rhyolite tuff.
The bedrock complex consists of metasedimentary rocks of Paleozoic age-known as the Calaveras forma• tion and the green schist sequence-and intrusive and meta-intrusive rocks of Mesozoic age. More than three• fourths of the quadrangle is underlain by rocks of the Calaveras formation, which consists largely of inter• bedded graphitic schist and quartzite but includes scat• tered lenses of limestone. A sequence of green schists, designated '' amphibolite schist'' on earlier maps, is present in the southwest corner of the quadrangle and probably underlies the Calaveras formation. Intrusive and meta-intrusive ro~ks include. irregular masses of granodiorite and ultramafic rocks, and small diorite dikes; they cannot be dated more closely than post• llariposa and pre-Chico. Metasedimentary rocks of the bedrock complex have undergone two periods of defor• mation: the first and most intense formed the folds and schistosity, and the second formed slip cleavage in both the metasedimentary• and the intrusive rocks. The slip cleavage is parallel to the Mother Lode vein system and cuts- across structures formed during the earlier period of deformation.

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