The range extends about 40 mi (64 km) east–west from the Hollywood Hills in Los Angeles to Point Mugu in Ventura County. The mountains form a line between the San Fernando Valley and the Los Angeles Basin, separating "the Valley" on the north and west-central Los Angeles on the south. The Santa Monica Mountains are parallel to Santa Susana Mountains, on the north side the San Fernando Valley. Beginning at the eastern end of the San Fernando Valley, the mountains are bordered to the north by the Los Angeles River. The river flows south after Elysian Park, defining the easternmost edge of the mountains. Mt. Washington, on the other side of the river, has almost the same native plants and weather.