The San Bernardinos run for approximately from Cajon Pass in the northwest - which separates them from the San Gabriel Mountains - to San Gorgonio Pass, across which lie the San Jacinto Mountains, in the southeast. The Morongo Valley in the southeast divides the range from the Little San Bernardino Mountains. Encompassing roughly , the mountains lie mostly in San Bernardino County, with a small southern portion reaching into Riverside County. The range divides three major physiographic regions: the highly urbanized Inland Empire to the southwest, the Coachella Valley in the southeast, and the Mojave Desert to the north. Most of the range lies within the boundaries of the San Bernardino National Forest.