The complex geology of Henry W. Coe State Park can be better understood by looking at the park's major rock types, terranes, special features such as faults and volcanoes, and mineral deposits. Much of the material in this section is based on personal observations made by Judy Rood, a series of field trips led by Clark Blake of the U.S. Geological Survey, and reference to the limited literature on the geology of the northern Diablo Range. Because geological theories on the evolution of the Franciscan Complex are changing as more is learned about these complicated rocks, some of the information in this chapter may change over time.