undifferentiated rock units

Paleontology and geology

Subduction of the Farallon Plate continued beneath the western margin of the North American Plate. The ancestral Sierra Nevada rose and was eroded, and the Coast Ranges began to rise. The eroded sediments from the ancestral Sierra Nevada (sand, gravel, and volcanic material) were deposited east of the rising Coast Ranges. These sediments became the rock layers of the Central Valley (i.e., the Great Valley Sequence) and record the position of the Cretaceous shoreline in California. Exposed throughout the Central Valley, the marine rocks have yielded abundant fossil remains of ammonites, marine reptiles, bivalves, and even plants.