Los Angeles County

Geological Influences

The vineyards of Los Angeles County are widely spread out into two main production zones: The Santa Monica Mountains and the high mountainous region between Sierra Pelona Mountains and the Mojave Desert. Several small vineyard sites are located within the city of Los Angeles itself. The Santa Monica Mountains were created by the confluence between the Pacific Plate and the North American Plate. The soils are primarily sedimentary and volcanic on elevated slopes that are prone to erosion. In some cases, vineyard parcel sizes are limited for fear of erosion and to prevent ecosystem disturbance. 

The second production zone, bordered by the Sierra Pelona mountains and the Mojave Desert, is located in the northeastern quadrant of the county. Here sandstone, basalts, volcanic rock and Precambrian Pelona Schist make up the complex geology. Due to the bisecting Santa Clara river, cooling influences from the Pacific Coast are felt in vineyards to the west, while those on the eastern side of the mountains are hot and continental. The Tehachapi Mountains, the Sierra Pelona Mountains and the San Gabriel Mountains wedge the more continental viticultural areas into the western outskirts of the open Mojave Desert. In this area, valley fill, alluvial soils, several fault lines and younger rock characterize the geological landscape, with crystalline, granite and quartz found in the mountainous areas.

Mountains/Rivers/Other Key Influences

Sierra Pelona Mountains: constitute the most important geological barriers separating the Los Angeles County viticultural zones. This range runs from west to east, separating Los Angeles from the Mojave Desert. Peak elevation is 5,905 feet (1,800 m) and is significant enough to form a barrier between the Pacific-cooled Los Angeles Basin and the arid, hot climate of the High Desert. 

San Andreas Fault: cuts the northeastern quadrant of Los Angeles County, atop of which is located the Leona Valley. The fault marks the intersection of the Pacific Plate and the North American Plate responsible for the creation of the Transverse Range.

San Gabriel Mountains: help shield the Leona Valley from the influence of the Pacific.

Tehachapi Mountains: form the geographical border of the Antelope Valley of the California High Desert, forged during the Triassic period and revealed as the seaway subsided.  

Santa Clara River: a significant river system in Southern California that bisects the Sierra Pelona Mountains connecting it to the Pacific Ocean. By doing so, it allows for viticultural areas that are significantly inland, such as the Sierra Pelona AVA, to be cooled by Pacific influences.

Santa Monica Mountains: a coastal range that is part of the east-west Transverse Ranges separating the San Fernando Valley and the Los Angeles Basin. Layers of sedimentary rock and volcanic intrusions are revealed due to activity of the Raymond Fault. Within these hills are located the Malibu appellations, some on steep slopes and others on high valleys.

Soil Diversity

Given that there are six AVAs in the Los Angeles County region, ranging from coastal to desert, the soil diversity is equally varied, although there are some commonalities throughout. The Malibu Coast AVA, which encompasses Malibu-Newton Canyon and Saddle-Rock Malibu, is largely made up of slate, shale and sandstone, with a rocky profile that allows for good drainage along with topsoil made up of clay loam and silty clay loam. 

Sand and gravel on alluvial fans are found in the Sierra Pelona Valley. Soils in the Leona Valley include coarse sandy loam, sandy loam and loam on alluvial fans and terraces. In the Antelope Valley of the California High Desert, alluvium derived from granitic rock on alluvial fans and terraces can be found with very deep loamy fine sand to loam and silty clay.

Climate 

From Mediterranean to Continental Desert climates, Los Angeles County’s AVAs have many distinguishing features that set them apart. What distinguishes the AVAs of Saddle Rock-Malibu and Malibu-Newton Canyon from those of the greater Malibu Coast AVA is largely elevation above the coastal fog line. These appellations tend to be hotter during the day, but due to their elevation, experience significant diurnal temperature shifts.  

In the High Desert regions, Antelope Valley of the California High Desert is drier and hotter than either the Sierra Pelona Valley or the Leona Valley because it is cut off from Pacific influence and is completely Continental. Antelope Valley is located in the rain shadow of the Sierra Pelona Mountains and it extends into the open Mojave Desert, ensuring it is dry and hot. Yet all three AVAs, especially the Antelope Valley of the California High Desert, rely on altitude for their ability to produce distinctive and quality grapes that can still retain acidity.