How was the San Gabriel Mountains formed?

The San Gabriel Mountains were primarily formed through tectonic processes, specifically the interaction of the Pacific and North American tectonic plates. Over millions of years, the collision and movement of these plates caused the Earth's crust to uplift and fold, creating the mountainous terrain. Additionally, volcanic activity and erosion have shaped the landscape, contributing to its current topography. The mountains are part of the larger Transverse Ranges, which are characterized by their east-west orientation due to the unique geological forces at play.