This page describes briefly the layout of the peninsula and the major geological features. We point the reader to other websites that provide much more detail than given here about the geology. Here we distill some of the most interesting aspects of the physical geography and geology of the peninsula for the naturalist traveler.
Baja California separated from mainland Mexico approximately 6 million years ago and a rift zone and transform faults underly the Gulf of California. This transition zone separates the Pacific and North American plates. Earthquakes show the location of the faults making up this zone. There are some areas of recent volcanism in Baja California; in fact much of the exposed surface rocks in the peninsula are volcanic. However, there are two large areas of plutonic igneous rocks (granite) that solidified far beneath the Earth’s surface. These granitic areas (batholiths) are in the Cape Region and in northern Baja California – a continuation of the Southern California batholith. But between these two batholiths the surface rocks are primarily volcanic of various ages.
The geological substrate is important for the appearance of the landscape. Granitic rocks weather differently from fine-grained volcanic rocks and the stereotypical central Baja California landscapes and their vegetation are seen on granitic rocks. The soils that result from weathering of the two basic types of rocks are also different, resulting in different vegetation patterns on the different substrates.
Historically recorded volcanic activity is rare in Baja California (most recent probably 1746), but volcanoes and volcanic landforms are widespread – though the most obvious cinder cones and other flows are usually off the main highway and so are not immediately obvious. Probably the most obvious are the Tres Virgines Volcanic complex just northwest of Santa Rosalia. Cinder cones west of San Quintin are visible from the main highway, but in the distance.
For more information on Baja California volcanism see this website.