The Baja California peninsula is of tectonic origin and separated from the mainland millions of years ago as a result of a colossal earthquake. It has been walled in by two seas, the Pacific and the Sea of Cortez ever since.
A tremendously volcanic active period broke off part of the continental plate and lifted the earth crust, forming the infamous San Andreas Fault. Slippage between the two plates, which began two and a half million years ago, continues to this day, pushing the peninsula northwestward 33 feet every century.
Mountain chains plunged into the sea, where their peaks formed strings of islands large and small along the Pacific coast.
View Baja California Sur Islands in a larger map