Sierra Madre Occidental Sierra Madre Occidental The Sierra Madre Occidental is a major mountain range system of the North American Cordillera, that runs northwest–southeast through Northwestern and Western Mexico, and along the Gulf of California. The Sierra Madre is part of the American Cordillera, a chain of mountain ranges (cordillera) that consists of an almost continuous sequence of mountain ranges that form the western "backbone" of North America, Central America, South America and Antarctica. The Spanish name "sierra madre" means "mother mountains" and "occidental" means "western" in English, with these being the "Western Mother Mountains". To the east, from the Spanish "oriental" meaning
Peninsular Ranges Francisco, Sierra de la Giganta, and Sierra de la Laguna in Baja California. Palomar Mountain, home to Palomar Observatory, is in the Peninsular Ranges in San Diego County, as is Viejas Mountain and the San Ysidro Mountains. The Peninsular ranges run predominantly north-south, unlike the Transverse Ranges to their north, which mostly run east-west. Rocks in the ranges are dominated by Mesozoic granitic rocks, derived from the same massive batholith which forms the core of the Sierra Nevada Mountains in California. They are part of a geologic province known as the Salinian Block which broke off the North American Plate