About 200 million years ago the Pacific Plateau slided under the North American Plateau. Because of the enormous preasure at the earth's crust the sea-bottom was pushed upwards. The land which appeared out of the ocean is California as we know it today. Especially the Sierra Nevada mountains carries the signs of this enormous disruption.
This fase was followed by centuries which scaled off the surface. The outside layers of the granite monolites broke and seperated itselfs. This created bare and round tops which are so characteristic for the Sierra Nevada.
The last important geological fase was about 30,000 years ago. The temperature at the earth is rising and this caused melting glacier-water. This water worn off the softer parts of the rocks and formed some mountain-peaks and mountain lakes.