Abstract

Four separate, parallel, lithologic and structural belts containing Jurassic rocks can be recognized in northern and central California. These are the: eastern Sierran belt, western Foothills belt, Great Valley or “Knoxville” belt, and Franciscan belt. These belts record lithospheric plate movements and periods of continental accretion during the Jurassic and Cretaceous Periods.

Rocks representing these four belts are also present in southern California, the borderland, and Baja California. The continuity of the belts has been disrupted, however, and the trend of some rotated. Analysis of the present distribution and lithologic character of these belts provides important clues to the structural evolution of the borderland. The late Mesozoic history was dominated by convergence of plates, creation of andesitic arcs, and subduction of trench deposits to form the four belts. Later strikeslip faulting has disrupted their original simple pattern.