Plants & Wildlife
Vegetation types within the Santa Monica Mountains Conservancy zone range from moist coastal canyon bottoms in the Santa Monica Mountains, to desert transitional areas at the headwaters of the Santa Clara River. With the exception of the areas that border the Mojave Desert, all of the vegetation within the zone is influenced by the effects of the Pacific Ocean. The resulting cool, wet winters and hot, dry summers create a Mediterranean-type ecosystem. By far, the dominant vegetation sub-type in the zone is chaparral. Chaparral is composed of drought and fire tolerant evergreen shrubs that range in height from four to ten feet. Unless recently subjected to fire, or some other type of disturbance, this plant community is generally too dense to penetrate. Another unique shrub community to Southern California is sage scrub, which varies between coastal and inland types. Sage scrub vegetation contains fewer stout, woody shrubs, and more openings with fine, delicate plants.
The expansive valley floors between the mountain ranges in the Conservancy zone were plowed and farmed long ago. They are now entirely developed. The precise former native plant cover of the San Fernando, Simi and Santa Clarita Valleys was never adequately recorded. It is suspected that native perennial bunch grasses were dominant elements. Throughout the zone, over ninety-five percent of the native grasslands have been displaced by foreign invasive plants.
The most common riparian (stream-related) woodland species in the Conservancy zone are various willows, coast live oak, California sycamore, and Fremont’s cottonwood. Less common species that are relics of the last Ice Age include white alder, bigleaf maple, and black cottonwood.
On slopes, and in valleys where rainfall concentrates, groves of evergreen coast live oaks are common throughout the Conservancy zone. These evergreen oaks provide food and shelter for numerous species of wildlife. Deeper soiled areas in the Santa Susana Mountains, the Simi Hills and the Santa Monica Mountains support the deciduous valley oak. A widely dispersed tree in the Santa Monica Mountains, and to a lesser extent in other ranges, is the California black walnut. Other interesting trees found in the Santa Susana and San Gabriel Mountains are the bigconed Douglas-fir and California bay laurel.
All parts of the Conservancy zone are rich in wildlife. This richness is supported by a tenuous network of cross-freeway habitat linkages and wildlife corridors that keep the various ranges biologically inter-connected. Population analyses show that without these movement corridors, all of the mountain ranges, except the San Gabriel Mountains, contain insufficient habitat area to support larger mammals. The most common medium and large-sized mammals in the Conservancy zone are coyotes, mule deer, bobcats, raccoons, and skunks. Just away from the urban edge, other predators, such as grey fox, mountain lion, American badger, long-tailed weasel, and ringtailed cat, occupy various niches. The ecosystem’s top predator, the mountain lion, is present everywhere except the fragmented eastern end of the Santa Monica Mountains that bisects the Los Angeles metropolitan area. Because they fear humans, however, they are rarely seen. The Santa Susana and San Gabriel Mountains support populations of black bears. The abundance of seed produced by the Mediterranean plant communities supports numerous prey species—such as rabbits, squirrels, rats, mice, and other rodent species. Seven species of hawks, eight species of owls, peregrine falcons, golden eagles, northern harriers, American kestrels, and white-tailed kite share in this bounty of prey. The Conservancy zone is also part of the Pacific Flyway. As a result, the resident Southern California bird species often share company with neo-tropical migrants and other unique species, such as Canadian geese.
There are over eighteen species of snakes and eight species of lizards in the zone. The most common snakes are pacific rattlesnake, gopher snake, California king snake, and California striped racer. The rattlesnake is the only venomous snake in California. They seek shade during the hottest summer afternoons and hibernate during the winter. The zone supports five species of frogs, three species of toads, and five species of newts and salamanders. As in most parts of the world, frog populations have declined, probably due to climate change and pollution.
The widely scattered perennial streams in the zone still support unique populations of native fish. Topanga and Malibu Creeks contain tidewater gobies, arroyo chub, and the federally-listed endangered, southern steelhead trout. The Santa Clara River supports these species as well as the federally-listed endangered, unarmored three spine stickleback. Some of the upper reaches of the Los Angeles River at the foot of the San Gabriel Mountains harbor populations of the Santa Ana sucker and speckled dace.
Geography and Geology
The Santa Monica Mountains Conservancy zone covers an area from the edge of the Mojave Desert to the Pacific Ocean. The zone encompasses the whole of the Santa Monica Mountains, the Simi Hills, the Verdugo Mountains, and significant portions of the Santa Susana and San Gabriel Mountains. In addition, the Mountains Recreation and Conservation Authority (MRCA) also owns or manages thousands of acres in the Sierra Pelona Mountains and in the Whittier/Puente Hills. From north to south, these areas drain into the Santa Clara River, Calleguas Creek, numerous smaller coastal watersheds in the Santa Monica Mountains, and the Los Angeles River and the Rio Hondo.
The Santa Monica and Santa Susana Mountains each contain at least one 3,000-foot high peak. The portion of the San Gabriel Mountains in the zone contains several 5,000-foot peaks. Average annual rainfall totals can be as low as ten inches in the desert. Adjacent areas can receive over twenty five inches on the northern sides of the Santa Susana and San Gabriel Mountains and coastal canyons of the Santa Monica Mountains.
The area’s geologic diversity rivals any region in the world. Sedimentary, volcanic (igneous), and metamorphic substrates are well distributed in the zone. The rocks range in age from two billion years to one hundred thousand years old. The geologic and topographic diversity of the area is attributable to plate tectonics, past glacial climates, and numerous faults.