This website of the United States Geological Survey (USGS) and the National Park Service (NPS) discusses the geology of Yosemite Valley in California, beginning 100 million years ago with the formation of the granite rocks found in this park and continuing with jointing, exfoliation, and erosion through ice and water. Bedrock Geology includes details about the formation, classification, and descriptions of the plutonic bedrock. It also discusses the relationship of landforms to rock composition and structure and their role in shaping the Yosemite valley.