Flooding that filled the Central Valley region of California to the point of becoming an inland sea, with water lapping from the Coast Ranges to the Sierra Nevada foothills, was part of Native American oral traditions. And that is exactly what happened in the Great Flood of 1862. If a similar major flood occurs, there will be catastrophic consequences.
California encompasses tremendous diversity, and this includes rocks of virtually every age, reflecting a long and dynamic geologic history. I'm fond of all types of rock, but my favorites are shales, sandstones and limestones that preserve evidence of ancient plant and animal life. The older the fossils, the more interesting.