Granodiorite Formations and Bear Gultch Resevoir
Warm afternoon light bathes Bear Gulch Reservoir, Pinnacles National Park, California, USA. The granitic basement is the Santa Lucia Granite and Granodiorite. These granites formed when masses of molten lava slowly cooled as they rose through the earth’s crust to a point where they completely solidified. A slow cooling process allows individual crystals to grow fairly large. Subsequent uplift from faulting and erosion of overlying material exposed these rocks at the earth’s surface. These are the oldest rocks in the park, 78-100 million years old. They form the basement upon which the rest of the rocks at the Monument lie.