Santa Monica Mountains

The Santa Monica Mountains have more than 1,000 archeology sites of significance, primarily from the Californian Native American cultures of the Tongva and Chumash people.[3] The mountains were part of their regional homelands for over eight thousand years before the arrival of the Spanish.[4] The Spanish mission system had a dramatic impact on their culture, and by 1831 their population had dropped from over 22,000 to under 3,000.[5]

Azimuth Marker, Mount Allen (Sandstone Peak), Southern California, USA.

Geologists consider the northern Channel Islands to be a westward extension of the Santa Monicas into the Pacific Ocean. The range was created by repeated episodes of uplifting and submergence by the Raymond Fault, which created complex layers of sedimentary rock, some containing fossils of invertebrates and fish. Volcanic intrusions have been exposed, including the poorly named andesitic[6] "Sandstone Peak", which is the highest point in the range at 3,111 feet (948 m). Malibu Creek, which eroded its own channel while the mountains were slowly uplifted, bisects the mountain range.

Snow in the Santa Monica Mountains in 2007.

The Santa Monica Mountains have dry summers with frequent coastal fog on the ocean (south) side of the range and rainy, cooler winters. In the summer, the climate is quite dry (except for the coastal fog), which makes the range prone to wildfires, especially during dry "Santa Ana" wind events.

Snow is unusual in the Santa Monica Mountains, since they are not as high as the nearby San Gabriel Mountains. The lower slopes of the range average between 15 and 20 inches (380 and 510 mm) of rain per year, while the higher slopes of the central and western Santa Monica Mountains average 22 to 27 inches (560 to 690 mm) of rain per year. The bulk of the rain falls between November and March. The higher rainfall in the central and western parts of the range results in more widespread woodlands (with oak, sycamore, walnut, bay laurel, alder and other trees) than the eastern part of the range, where trees are usually restricted to the stream courses.

On January 17, 2007, an unusually cold storm brought snow in the Santa Monica Mountains.[7][8] The hills above Malibu picked up three inches (eight centimeters) of snow - the first measurable snow in fifty years. Snow was reported on Boney Peak in the winter of 2005; and in March 2006, snow also fell on the summit of the mountain. Snow also fell on the peak of Boney Peak in late December 2008. The latest recorded snowfall in the area was in February 2019, when an unusual amount of snowfall accumulated in low passes in the mountains. That storm system also brought rare snowfall to the Los Angeles area. Heavy graupel was recorded in Malibu Canyon on January 23, 2021. It accumulated as low as 400 feet in elevation.

Deep graupel in Malibu Canyon in 2021.

In the Santa Monica Mountains, when the fuels, seasonal drought, wind, and terrain combine with an ignition, a major wildfire occurs. These fires are large, wind-driven canopy fires that consume the above ground vegetation and often cause major property damage and home losses.[9]

In 2018, the Woolsey Fire burned through 88% of the federal parkland resulting in trails being closed for months.[10] The fire, which was three times larger than the biggest fire ever before in the mountains, burned over 40% of the natural area in the Santa Monicas.[11] A restoration plan was developed to plant 100,000 trees, shrubs and grasses of 25 different species.[12]

Over twenty individual state and municipal parks are in the Santa Monica Mountains, including: Topanga State Park, Leo Carrillo State Park, Malibu Creek State Park, Point Mugu State Park, Will Rogers State Historic Park, Point Dume State Beach, Griffith Park, Marvin Braude Mulholland Gateway Park, Charmlee Wilderness Park,[17] Franklin Canyon Park, Runyon Canyon Park, King Gillette Ranch Park,[18] and Paramount Ranch Park.[19]

The Satwiwa Native American Indian Culture Center in Newbury Park, California is located within the Santa Monica Mountains National Recreation Area. The area was purchased by the U.S. National Park Service in 1980.[20] The Rosewood Trail near Stagecoach Inn, which leads to Angel Vista is an access point in Newbury Park.

At the eastern end of the Santa Monica Mountains are Griffith Park and Elysian Park. Griffith Park is separated from the rest of the Santa Monica Mountains to the west by the Cahuenga Pass, over which the 101 Freeway (also called the Hollywood Freeway) passes from the San Fernando Valley into Hollywood. Elysian Park is in the easternmost part of the mountains and is bordered by the Los Angeles River to the east and Downtown Los Angeles nearby to the south.

The Rim of the Valley Trail is a plan in progress for accessing and connecting the parkland and recreational areas of the mountains surrounding the Conejo, San Fernando, Simi, and Crescenta Valleys. With trailheads in the mountains and valleys, it would link them through existing and new: walking, hiking, equestrian, and mountain biking trails; parklands; and conservation easements. The Rim of the Valley project also has the goal to protect flora and fauna habitats and wildlife corridors between the Santa Monica Mountains and the inland ranges.[21][22][23][24]

Bobcat kitten 327, SMMNRA

The range is host to a variety of wildlife. Common mammals in the range include mule deer, coyotes, bobcats, striped skunks, raccoons, several native bat species, brush rabbits, and many rodents including California voles, western gray squirrels, dusky-footed and desert woodrats, western harvest and California pocket mice, Botta’s pocket gophers, and pacific kangaroo rats.[25]

The mountain lions population is challenged because the Santa Monica Mountains are isolated and not big enough for weaned cubs to find their own territory.[26][27][28][29] The primary cause of the decline is due to a combination of traffic-related mortality,[30][31] anti-coagulants ingested from human poisoned prey, and attacks by other, more dominant mountain lions.[32] The Wallis Annenberg Wildlife Crossing will bridge the Ventura Freeway which acts as a barrier in the wildlife corridor between the Simi Hills to the north and the Santa Monica Mountains to the south.[33] The National Park Service has recorded a dozen mountain lions struck and killed by motorists on this section of freeway since 2002 when they began a study.[34] Mountain lions approach this particular area and turn back without attempting the hazardous crossing of the freeway as shown by GPS tracking collars fitted to them by the researchers.[35] In 2020, wildlife biologists found the first evidence of physical abnormalities in the isolated population.[36] Newcomers would bring new genetic material into the mountains where the lack of genetic diversity is a serious threat to their long-term survival.[37] It would allow young mountain lions, born in the Santa Monicas, a chance to find a new territory before possibly being killed by one of the more dominant, older males.[38] P-22 was a wild mountain lion residing in Griffith Park in the eastern end of the range, until his death in 2022.[39]

A three to four year old black bear was captured, examined, and collared in 2023. Designated BB-12, he is probably the only bear in the Santa Monica Mountains National Recreation Area and it is estimated that he has been living there for two years.[40] However, in July 2023, BB-12 was killed while crossing the 101 Freeway. This is not uncommon for animals living in and around the Santa Monica Mountains; a common cause of bobcat and mountain lion fatalities is being struck by vehicles.[41]

Over 380 native bird species call the Santa Monica Mountains home.[42] Abundant native song birds species include the Bushtit, California Scrub Jay, House Finch, Lesser Goldfinch, Cliff Swallow, Red-winged Blackbird, Oak Titmouse, Song Sparrow, California Towhee, Spotted Towhee, House Wren, and Black Phoebe. Red-Tailed Hawks, Sharp-shinned Hawks, Red-shouldered Hawks, Northern Harriers, American Kestrels, Great Horned Owls, and Western Screech-Owls are among common raptors in the area. White-tailed kites, Bald Eagles, Golden Eagles[43][44], and Burrowing Owls have also been sighted.[45] In addition to these residential species, many bird species pass through the Santa Monica Mountains as they travel along the Pacific Flyway including Brown Pelicans, Rufous Hummingbirds, Canada Geese[46], Bonaparte’s Gulls, and Elegant Terns. [47][25]

Native fish found in the Santa Monica Mountains include tidewater gobies, arroyo chub, and pacific lamprey. Additionally, Malibu creek is home to the southern steelhead trout, which is an endangered species. [48][49]

Snakes are common but only occasionally seen: the Southern Pacific rattlesnake (the only venomous species), mountain kingsnake, California kingsnake, gopher snake, and garter snake. The mountains are also home to the western fence lizard and the coastal whiptail. The population of red-legged frogs is small and isolated, and was impacted by the Woolsey Fire that swept through the area in November 2018.[50]

Heart leaf penstemon, Keckiella cordifolia, along the Backbone Trail in the Santa Monica Mountains

The Santa Monica Mountains are in the California chaparral and woodlands ecoregion, and includes the California oak woodland and southern coastal sage scrub plant community, and are covered by hundreds of local plant species, some of which are very rare or endemic, and others which are widespread and have become popular horticultural ornamentals. Dudleya verityi is a rare species of succulent plant known by the common name "Verity's liveforever". This species is endemic to Ventura County and is found only on one edge of the Santa Monica Mountains, where it occurs in coastal sage scrub habitat.[51] The most common trees in the mountains are oak and sycamore. The California black walnut, endemic to California, grows on the northern side of the mountains in the Valley and Griffith Park. Other species include willow and alder (along stream courses) and bay laurel. Several species of ferns (including large sword ferns) are found in wetter, shady areas throughout the range, especially near streams.

Many invasive weeds have colonized the mountain habitats which can bring about significant changes in the ecosystems by altering the native plant communities and the processes that support them. These non-native plants include annual Mediterranean grasses, Spanish broom (Genista juncea), and yellow starthistle (Centaurea solstitialis). In creekside riparian habitats are found plants such as giant cane (Arundo donax), German ivy (Delairea odorata), blue periwinkle (Vinca major), and ivy (Hedera spp.).

More frequent fires have created conditions favorable to invasive plants. The 2018 Woolsey Fire burned through 88% of the federal parkland.[52] The fire, which was three times larger than the biggest fire ever before in the mountains, burned over 40% of the natural area in the Santa Monicas.[53] The fire created a challenge to native plants as black mustard with bright yellow flowers quickly established itself as a wet winter followed the fire.[54] The mustard plants will also provide fuel for the next fires.[55]

The New Zealand mud snail is an invasive species found in the Santa Monica Mountains, that pose a serious threat to native species, complicating efforts to improve stream-water quality for the endangered steelhead.[56] Within a period of four years, the snails expanded from their first known population in Medea Creek in Agoura Hills to nearly 30 other stream sites. Researchers at the Santa Monica Bay Restoration Commission believe the snails' expansion may have been expedited after the mollusks traveled from stream to stream on the gear of contractors and volunteers.[57]

Haze in the Santa Monica Mountains near the west edge of Los Angeles County, 1975. Photo by Charles O'Rear

The eastern end of the range, located in the City of Los Angeles, is more intensively developed than the western end. The city of Malibu runs between the coast and the leading mountain ridge, from Topanga Canyon in the east to Leo Carrillo State Park in the west.

Communities along the north slope of the mountains include (from east to west):

• the Los Angeles communities of:
  • the unincorporated area of Universal City
  • Studio City
  • Sherman Oaks
  • Encino
  • Tarzana
  • Woodland Hills
  • West Hills
• Calabasas
• Bell Canyon
• Agoura Hills
• Westlake Village
• Thousand Oaks
• Newbury Park

Communities along the south slope of the mountains include (from east to west):

• the Los Angeles communities of:
  • Los Feliz
  • Hollywood Hills
  • Bel-Air
  • Benedict Canyon
  • Brentwood
  • Pacific Palisades
• Beverly Hills
• Santa Monica
• the unincorporated community of Topanga
• Malibu
• Solromar