 Parts of California and western Mexico form the partial edge of the Pacific Plate; the two plates meet along the San Andreas Fault.The southern portion of the Caribbean and parts of Central America compose the much smaller Caribbean Plate.The western mountains have split in the middle, into the main range of the Rockies and the Coast Ranges in California, Oregon, Washington, and British Columbia with the Great Basin (a lower area containing smaller ranges and low-lying deserts) in between.