These mountains are no longer the massive giants they once were. The eruptive forces and volcanoes that produced the Santa Monica Mountains are no longer active, but the modest structures they left behind, such as the iron-rich red and orange rock we see. You can learn more about volcanoes all over the world by visiting the United States Geological Survey's Volcano Hazards Program. By clicking here you can see real-time monitoring of many of the Earth's most active volcanoes.