The Chumash native Americans leave evidence of their habitation from the pictograph rock paintings in remote areas. A modern population live on the Santa Ynex Reservation.

Chumash petroglyphs can be seen at Chumash Painted Cave State Historic Park, Santa Barbara, California. (34.504167, -119.786944)

This area of the ecoregion includes coastal and alluvial plains and some low hills along the coast of Southern California, and it extends over 200 miles south into Baja California of Mexico. Coastal sage scrub and chaparral vegetation communities with many endemic species were once widespread before overgrazing, clearance for agriculture, and massive urbanization occurred.

Coastal sage scrub includes chamise, white sage, black sage, California buckwheat, golden yarrow, and coastal cholla. The chaparral-covered hills include ceanothus, buckeye, manzanita, scrub oak, and mountain-mahogany. Coast live oak, canyon live oak, poison oak, and California black walnut also occur. A small area of Torrey pine occurs near San Diego.

Like other areas of central and southern California, the Southern California Mountains have a Mediterranean climate of hot dry summers and moist cool winters. Although Mediterranean types of vegetation such as chaparral and oak woodlands predominate in this region, the elevations are considerably higher, the summers are slightly cooler, and precipitation amounts are greater than in adjacent ecoregions, resulting in denser vegetation and some large areas of coniferous woodlands.

In parts of the Transverse Range, a general slope effect causes distinct ecological differences. The south-facing slopes typically have higher precipitation of about 30-40 inches, as compared to many of the north slopes of the range with about 15-20 inches. However, the high evaporation rates on the south contribute to a cover of chaparral.

On the north side in some areas of the ecoregion, lower evaporation, lower annual temperatures, and slower snow melt allows for a coniferous forest that blends into desert montane habitats as it approaches the Mojave Desert ecoregion boundary.

Woodland species such as Jeffrey, Coulter, and Ponderosa pines occur, along with sugar pine, white fir, bigcone Douglas-fir, and, at highest elevations, some lodgepole and limber pines. Severe erosion problems are common where the vegetation cover has been destroyed by fire or overgrazing. Large portions of the region are National Forest public land.

Pacific Crest Trail

Inland Desert Route

West Coast Scenic Route

The Transverse Ranges are a group of mountain ranges of southern California, in the Pacific Coast Ranges geographical region of North America but north of the Peninsular Ranges.

The Transverse Ranges begin at the southern end of the California Coast Ranges and lie within Santa Barbara, Ventura, Los Angeles, San Bernardino, Riverside and Kern counties. The name Transverse Ranges is due to their east–west orientation, making them transverse to the general northwest–southeast orientation of most of the coastal mountains in California.

The Transverse Ranges begin west of the California coast Point Conception headlands and extend eastward about 310 miles to the Mojave and Sonoran deserts.

The name Transverse is due to the east-west orientation, making them transverse to the general northwest-southeast orientation of most all of the coastal mountains in California.

The above photo was taken showing the coastal marine layer in West Los Angeles, California from Griffith Park Observatory, taken afternoon of 11 December 2010 (34.120189, -118.286501).

A marine layer is an air mass that develops over the surface of a large body of water, such as an ocean or large lake, in the presence of a temperature inversion. The inversion itself is usually initiated by the cooling effect caused when cold water on the surface of the ocean interacts with a comparatively warm air mass.

A marine layer can come in a number of different forms depending on the current atmospheric conditions. It may manifest itself as merely a cool, humid air mass without any cloud cover, or it may be accompanied by clouds. In many cases, marine layers can consist of dense fog. Often associated with marine layers are stratus clouds, which are lumpy, often uniform clouds that form at low elevations of less than 3000 feet.

Since marine layers are pushed ashore by westward winds (a wind traveling from the west to the east), there will almost always be a wind present in a marine layer. Technically, the marine layer is a medium within which clouds may form under the right conditions; it is not the layers of clouds themselves.

There are several areas of the western coast of North America where the offshore marine layer is enabled by the relative cold sea surface temperature of the Pacific Ocean. The unusually cold water that traverses the coasts of southern British Columbia, Washington, Oregon and California, and which arrive through a process called the California Current, a cold water North Pacific Ocean current, which transports polar water from the Gulf of Alaska southward to as far south as the southern Baja California Sur coast near to the Punta Eugenia.

This process creates anomalously cool water temperatures not normally found at the latitudes of California, and which results in a strong temperature inversion.

Occasionally, the marine layer becomes particularly deep, and the clouds on land can persit throughout the day. This can happen at any time of the year and has inspired colloquialisms such as May Gray and/or June Gloom.