Hi Chris. This is what I meant by westward movement. Take Care…Don in creepy town

In Pliocene time, about seven million years ago, a zone of separation developed on the East Pacific Rise. The future Baja California peninsula and a piece of future California were sheared from mainland Mexico along a lateral fault, possibly the ancestral San Andreas fault which was then, as now, oriented northwest-southeast. During this early period of development, movement was right lateral, with the sheared-off slab moving northwest, but always in close contact with the mainland.[1]

The northwest movement seems to have been repeated slippage along the principal members of the San Andreas fault system -- the Elsinore fault, the San Jacinto fault, and the main San Andreas strand itself.

About four million years ago, the San Andreas fault proceeded to play a key role in the next phase, the opening of the mouth of the Gulf of California. While the Baja California peninsula continued to move to the northwest as a whole, its southern end began to rotate westward, opening a seaway between the new peninsula and the mainland.

This movement is thought to have been caused by torsional stress. That is, while the primary movement continued to be northwest, the northern end of the Baja California peninsula became locked against the mainland, causing the southern end to rotate westward, creating the seaway that was to become the Gulf of California.

As the Gulf continued to open, Baja California moved out to sea while the Peninsular Ranges of California remained attached to the mainland block. Movement along the San Andreas fault system was vigorous, and the San Jacinto fault became the most active member. At this time, the San Jacinto Mountains and the Santa Rosa Mountains were sharply compressed and uplifted.

• Baja