There are many great ways to learn about the geological history of California, including reading some of the works by noted writer John McPhee. Additionally, the state of California's Department of Conservation has created these very fine online geologic field trip guides. It might be more accurate to say that the site is an interactive index of web pages that contain geologic field guides containing photographs, maps, texts, and directions for local natural features from Humboldt County down to the Inland Empire. The index is organized into geographic regions collectively referred to as the "Geomorphic Provinces of California". Additionally, these geological areas are subdivided into groups like Owens Valley, Lassen Park, and Point Reyes. Overall, it's a great resource, and one that will be appreciated by just about anyone with a penchant for geology or the Golden State.