The Newhall Pass separates the Santa Susana Mountains from the San Gabriel Mountains to the east. Newhall Pass is the major north-south connection between the San Fernando and Santa Clarita valleys, and Interstate 5 and a railroad line share Newhall Pass. The Santa Susana Pass (containing SR 118) connects the Simi and San Fernando valleys, and separates the Santa Susana Mountains from the Simi Hills to the south. Santa Susana Pass State Historic Park is located in the Simi Hills, just south of the Santa Susana Pass, at the northwestern edge of the San Fernando Valley. The Santa Susana Mountains are not as steep or high as the San Gabriel Mountains.
The western half of the range lies in Ventura County, and the eastern half lies in Los Angeles County. The southeastern slopes of the Santa Susana Mountains are part of the City of Los Angeles, and housing subdivisions, including Porter Ranch, have been built on the lower slopes of the range. The city of Simi Valley lies to the southwest. North of the range is the fast-growing city of Santa Clarita, and several large subdivisions in unincorporated Los Angeles County, including Lyons Ranch and Newhall Ranch, have been approved for development. The Sunshine Canyon Landfill is at the mountains' eastern end, and several canyons in the northwest corner of the range have been proposed for more landfills.
The mountains have a mild climate, with warm, dry summers and cool, wet winters (Mediterranean climate type). Snow falls in winter in some higher areas, such as Oat Mountain, but melts quickly. Annual precipitation totals vary between 18 and 25 inches, depending on exposure to the rain-bearing winds. Most of the rain falls between November and March. Because of the summer drought, wildfires sometimes occur in summer and fall before the rains start, especially during hot, dry "Santa Ana" wind events (mostly between late September to mid November).
Peaks
The highest peaks in the range are Oat Mountain (1,142 m; 3,747 feet), Mission Point (845 m; 2,771 feet), Rocky Peak (827 m; 2,714 feet), and Sand Rock Peak (765 m; 2,511 feet). The summit of Rocky Peak lies directly atop the line separating Ventura and Los Angeles counties and is indicated by a battered marker embedded into the sandstone boulder summit.
The first discovery of oil in California was in Pico Canyon, on the north side of the mountains, The California Star Oil Works, later Chevron, succeeded with Pico Well No. 4. It became famous not only as the first well in California, but also as the longest-producing well in the world, having been capped in September, 1990 after 114 years. Well No. 4 has the distinction of being the first site in Los Angeles County to be listed on the National Register of Historic Places, in 1966. The surrounding town, Mentryville, is maintained as the oil "ghost town" Mentryville Historical Park, within Pico Canyon Park. Many active oil and gas fields remain in the area, with some of the larger operators including Vintage Production, Freeport McMoRan, and the Southern California Gas Company. The largest of SoCalGas's four underground storage natural gas facilities is within the Aliso Canyon Oil Field north of Porter Ranch.
Note: the Santa Susana Field Laboratory, once operated by and still owned by Rocketdyne until toxics are cleaned up, is actually in the Simi Hills, which are adjacent to the south of the Santa Susana Mountains.
A handful of fascinating amphibians live in the area. Streams and creeks support populations of Pacific tree frog, the small amphibian whose signature chorus adds an aura of mystery and inexplicable beauty to the surrounding land. Western toads often make their appearance at nightfall, emerging from burrows in search of water and insects, while California slender salamanders are often found under the cool leaf litter and canopy of oak woodlands. Many reptiles thrive in the Santa Susana range. Lizards that are likely to be observed on any given day include the common western fence lizard and the equally abundant side-blotched lizard. Somewhat less frequently observed but still present are the southern alligator lizard, western skink, whiptail, and the seemingly rare coast horned lizard. Southern Pacific rattlesnakes and gopher snakes are perhaps the most commonly observed snakes, but a lucky hiker might also encounter other species including the striped racer, California kingsnake, and ring-necked snake.
The mountains are part of the Southern California coastal wildlife corridor the connects Los Padres National Forest with the Santa Monica Mountains.[5][4]
The Rim of the Valley Trail is a plan in progress for connecting the parkland and recreational areas of the San Fernando, Simi, and La Crescenta Valleys via the Santa Susana Mountains. Rocky Peak Park and O'Melveny Park have trail sections already.[6][7][8][9]
