Plants
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.
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Wildlife
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.
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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.
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