Los Angeles County Department of Regional Planning

Significant Ecological Areas

Facts about LA County Biota

Natural Regions of Los Angeles County

Los Angeles County has a variety of natural regions within its 4,083 square mile area, and is one of only two counties in the nation that possess such geographical and biological diversity. The County contains miles of beaches, offshore islands, a coastal mountain range, inland valleys surrounded by hills and mountains that reach 10,000 feet above sea level on Mount Baldy, and the western-most part of the Mojave Desert. The County has identified Significant Ecological Areas in each of these natural regions, identifying the unique character of the landscape and the variety of nature features to be found in the County.


The climate along the coast is very mild. Temperatures do not fluctuate greatly, and the marine air crossing the region is quite moist. These factors create an environment that supports a variety of vegetation, including many submerged rocky shorelines, kelp beds, and saltwater marshes. These areas provide habitats for many shoreline birds, including the endangered California brown pelican and least tern.

Coastal Mountains

The Santa Monica Mountains are relatively low mountains, which skirt the Malibu Coastline. A variety of natural habitats are found in this region, such as freshwater aquatic communities, riparian oak woodlands and savannahs, coastal sage scrub and many sensitive plant and animal species, such as Lyon’s pentachaeta. This area is of such significance that the National Park Service designated 150,000 acres as the Santa Monica Mountain National Recreation Area.

San Gabriel Mountain Range

Much of the San Gabriel mountain range is located in the Angeles National Forest. The Verdugo and Santa Susana mountains, although not as large, have similar topography and biological attributes and are located close to the San Gabriel range. These mountains are further inland than the coastal mountain range and subject to extreme temperature changes, especially in the higher elevations. Snow is common in this mountain range over 4,000 feet, especially on Mount Baldy, which rises 10,000 feet above sea level. Specific to the higher elevations are mountain meadows, freshwater lakes and streams, as well as coniferous forests such as yellow and big-cone pine.

Peninsular mountain ranges

The Puente Hills and Chino Hills comprise the northern tip of the Peninsular Mountain Range, which runs through Orange County and San Diego counties. The climate is relatively dry in these lower elevations, and provides an ideal environment for walnut and oak woodlands, inland sage scrub, and those animal species that thrive in these native communities.

Coastal Plain

The coastal plain and adjacent valleys are comprised of the Los Angeles basin, San Fernando Valley and San Gabriel Valley. This entire region is intensely developed, but certain areas still retain biological significance. In particular, lowland riparian areas along several soft-bottomed reaches of the Los Angeles River, San Gabriel River and Ballona Creek support freshwater aquatic communities and a variety of plant and animal species.

Inland Valleys

The Santa Clarita Valley is surrounded by the Angeles National Forest and the Santa Susana mountain range. The valley is on average, ten degrees warmer in the summer and colder in the winter than the coastal region. Native to the Santa Clarita Valley are several species of oak trees: Blue oak, Interior Live oak and Coast Live oak.


The Antelope Valley, located in the south-western edge of the Mojave Desert, vastly differs from the mountain ranges found immediately to the south. This desert region experiences minimal rainfall and extreme seasonal changes in temperature. Summers are extremely hot, and winters can be very cold, particularly when the valley experiences a light snowfall. This area is known for its Joshua tree woodlands, yucca trees, grasslands, wildflowers and a variety of desert scrubs and cacti.

Offshore Islands

Catalina is the only island with significant human habitation near the California coast. Located 22 miles south of the Palos Verdes Peninsula, the island has a land area of 75 square miles and is characterized by rugged hillside topography and steep cliffs along much of its shoreline. Level terrain is limited to the floors of a few large coastal canyons. A number of vegetation communities occur on the Island, including coastal sage scrub, Island chaparral and several unique plant associations. Similarly, it has known endemic populations of at least six different species of plants and no less than sixteen different species of animals, most notably the Catalina Island Fox. The Catalina Island Conservancy manages 42,135 acres on Catalina Island, providing the highest level of conservation protection to 88 percent of the island. The County exercises no regulatory control over the San Clemente Island, which is an uninhabited military reservation.

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Los Angeles, CA 90012
T: (213) 974-6411 . F: (213) 626-0434
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