The Simi Hills are a low rocky

mountain range A mountain range or hill range is a series of mountains or hills arranged in a line and connected by high ground. A mountain system or mountain belt is a group of mountain ranges with similarity in form, structure, and alignment that have ari ...

of the

Transverse Ranges The Transverse Ranges are a group of mountain ranges of southern California, in the Pacific Coast Ranges physiographic region in North America. The Transverse Ranges begin at the southern end of the California Coast Ranges and lie within Santa ...

in eastern Ventura County and western

Los Angeles County Los Angeles County, officially the County of Los Angeles, and sometimes abbreviated as L.A. County, is the List of the most populous counties in the United States, most populous county in the United States and in the U.S. state of California, ...

, of southern

California California is a state in the Western United States, located along the Pacific Coast. With nearly 39.2million residents across a total area of approximately , it is the most populous U.S. state and the 3rd largest by area. It is also the m ...

United States The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country Continental United States, primarily located in North America. It consists of 50 U.S. state, states, a Washington, D.C., ...

Geography

The Simi Hills are aligned east-west and run for , and average around north-south. The Simi Hills are part of the central

System. They lie almost entirely within southeastern Ventura County, with some southern and eastern

foothill Foothills or piedmont are geographically defined as gradual increases in elevation at the base of a mountain range, higher hill range or an upland area. They are a transition zone between plains and low relief hills and the adjacent topograp ...

s within western

. The Simi Hills are on the western edge of the

San Fernando Valley The San Fernando Valley, known locally as the Valley, is an urbanized valley in Los Angeles County, California. Located to the north of the Los Angeles Basin, it contains a large portion of the City of Los Angeles, as well as unincorporated ar ...

. The Simi Valley lies to the north, and the Conejo Valley lies to the southwest. The San Fernando Valley communities of Chatsworth, West Hills, and Woodland Hills are in the eastern hills and adjacent valley floor in Los Angeles city and

county A county is a geographic region of a country used for administrative or other purposes Chambers Dictionary, L. Brookes (ed.), 2005, Chambers Harrap Publishers Ltd, Edinburgh in certain modern nations. The term is derived from the Old French ...

. The cities of Agoura Hills and Westlake Village are also located in Los Angeles County, generally southwest of the Simi Hills. The cities of Thousand Oaks (to the west) and Simi Valley city (to the north) are in the hills and adjacent valleys within Ventura County. The two nearby mountain ranges are: the higher

Santa Susana Mountains The Santa Susana Mountains are a transverse range of mountains in Southern California, north of the city of Los Angeles, in the United States. The range runs east-west, separating the San Fernando and Simi valleys on its south from the Santa C ...

adjacent on the northeast across Santa Susana Pass; and the Santa Monica Mountains running nearby along the south.

Watersheds

The hills provide the complete or partial

watershed Watershed is a hydrological term, which has been adopted in other fields in a more or less figurative sense. It may refer to: Hydrology * Drainage divide, the line that separates neighbouring drainage basins * Drainage basin, called a "watershe ...

s for several year-round creeks and numerous seasonal streams. They include Las Virgenes Creek (tributary of Malibu Creek), Moore's Canyon Creek, Bell Creek, Dayton Creek, Woolsey Canyon Creek, Brandeis Creek, Runkle Canyon Creek,

Arroyo Simi The Arroyo Simi ( Spanish for "Small Stream of Simi", sometimes also referred to as Simi Creek)Appleton, Bill (2009). ''Santa Susana''. Arcadia Publishing. Page 27. . is a westwards-running creek, located in California, United States, running fr ...

, Palo Comado Creek, Cheeseboro Creek, and

Arroyo Calabasas Arroyo Calabasas (also known as Calabasas Creek) is a U.S. Geological Survey. National Hydrography Dataset high-resolution flowline dataThe National Map, accessed March 16, 2011 tributary of the Los Angeles River, in the southwestern San Fernan ...

(northern fork). Bell Creek and Arroyo Calabasas are the headwaters of the Los Angeles River, by name its beginning with their

confluence In geography, a confluence (also: ''conflux'') occurs where two or more flowing bodies of water join to form a single channel. A confluence can occur in several configurations: at the point where a tributary joins a larger river (main stem); o ...

in nearby

Canoga Park Canoga Park is a neighborhood in the San Fernando Valley region of the City of Los Angeles, California. Before the Mexican–American War, the district was part of a rancho, and after the American victory it was converted into wheat farms and ...

. 90% of the Santa Susana Field Lab property drains into the Los Angeles River via tributaries.

Peaks

Peaks in this region include Simi Peak, 2,403 ft (732 m),

Chatsworth Peak Chatsworth Peak is a peak in the Simi Hills overlooking (to the east) Chatsworth and the western San Fernando Valley, in Los Angeles, Southern California. It is southwest of Santa Susana Pass and north of the Chatsworth Reservoir. Chatswort ...

, 2,314 ft (700 m), and Escorpión Peak (aka: Castle Peak), 1,475 ft (450 m).

Climate

Because of its low elevation, the Simi Hills typically experience

rain Rain is water droplets that have condensed from atmospheric water vapor and then fall under gravity. Rain is a major component of the water cycle and is responsible for depositing most of the fresh water on the Earth. It provides water f ...

y, mild winters.

Snow Snow comprises individual ice crystals that grow while suspended in the atmosphere—usually within clouds—and then fall, accumulating on the ground where they undergo further changes. It consists of frozen crystalline water throughou ...

is rare in the Simi Hills, even in the highest areas. Summers are warm and dry and

wildfire A wildfire, forest fire, bushfire, wildland fire or rural fire is an unplanned, uncontrolled and unpredictable fire in an area of combustible vegetation. Depending on the type of vegetation present, a wildfire may be more specifically identi ...

s do occur here. Cool winds from the Pacific Ocean come from the

Oxnard Plain The Oxnard Plain is a large coastal plain in southwest Ventura County, California, United States surrounded by the mountains of the Transverse ranges. The cities of Oxnard, Camarillo, Port Hueneme and much of Ventura as well as the unincorpo ...

and blow into the inland areas through the Santa Clara River Valley and the Conejo Valley, though some low hills, such as

Conejo Mountain Conejo Mountain is a in Ventura County, California near Camarillo on the eastern boundary of the Oxnard Plain. At the western edge of the Conejo Valley, it is adjacent to the Santa Monica Mountains. Crossing what was once a formidable barrier fo ...

, block these winds from the Conejo Valley. The Simi Hills further block these winds, which bring cool weather in both summer and winter from the

Flora and fauna

Flora

The southern lower hills are mostly covered in

grassland A grassland is an area where the vegetation is dominated by grasses ( Poaceae). However, sedge ( Cyperaceae) and rush ( Juncaceae) can also be found along with variable proportions of legumes, like clover, and other herbs. Grasslands occur na ...

s and oak savanna. The northern rocky hills area is primarily

chaparral Chaparral ( ) is a shrubland plant community and geographical feature found primarily in the U.S. state of California, in southern Oregon, and in the northern portion of the Baja California Peninsula in Mexico. It is shaped by a Mediterranea ...

shrubland Shrubland, scrubland, scrub, brush, or bush is a plant community characterized by vegetation dominated by shrubs, often also including grasses, herbs, and geophytes. Shrubland may either occur naturally or be the result of human activity. It ...

and oak woodlands. The Simi Hills are part of the

California chaparral and woodlands The California chaparral and woodlands is a terrestrial ecoregion of southwestern Oregon, northern, central, and southern California (United States) and northwestern Baja California (Mexico), located on the west coast of North America. It is a ...

ecoregion An ecoregion (ecological region) or ecozone (ecological zone) is an ecologically and geographically defined area that is smaller than a bioregion, which in turn is smaller than a biogeographic realm. Ecoregions cover relatively large areas of ...

. The oaks (''Quercus spp.'') include: the

evergreen In botany, an evergreen is a plant which has foliage that remains green and functional through more than one growing season. This also pertains to plants that retain their foliage only in warm climates, and contrasts with deciduous plants, whic ...

coastal live oak ('' Quercus agrifolia''), the

deciduous In the fields of horticulture and Botany, the term ''deciduous'' () means "falling off at maturity" and "tending to fall off", in reference to trees and shrubs that seasonally shed leaves, usually in the autumn; to the shedding of petals, ...

valley oak ('' Quercus lobata''), and the scrub oak ('' Quercus dumosa''). Riparian zone plants include California sycamores (''Platanus racemosa'') and arroyo willows (''Salix lasiolepis''). Spring

wildflower A wildflower (or wild flower) is a flower that grows in the wild, meaning it was not intentionally seeded or planted. The term implies that the plant probably is neither a hybrid nor a selected cultivar that is in any way different from the ...

s include the redbush monkey flower (''Mimulus aurantiacus''), Plummer's mariposa lily (''Calochortus plummerae''), and canyon sunflower (''Encelia californica'').

poison oak Poison oak refers to two plant species in the genus ''Toxicodendron,'' both of which can cause skin irritation: *''Toxicodendron diversilobum'' or Western poison oak, found in western North America *''Toxicodendron pubescens ''Toxicodendron pub ...

(''Toxicodendron diversilobum'') is also an important member of the native plant habitat community here.

Fauna

The Simi Hills is the principal, and much wider, of only two terrestrial

wildlife corridors A wildlife corridor, habitat corridor, or green corridor is an area of habitat connecting wildlife populations separated by human activities or structures (such as roads, development, or logging). This allows an exchange of individuals between ...

linking the coastal Santa Monica Mountains with the inland

Topatopa Mountains The Topatopa Mountains are a mountain range in Ventura County, California, north of Ojai, Santa Paula, and Fillmore. They are part of the Transverse Ranges of Southern California. Etymology A name for the mountains was first inscribed within ...

, and

San Gabriel Mountains The San Gabriel Mountains ( es, Sierra de San Gabriel) are a mountain range located in northern Los Angeles County and western San Bernardino County, California, United States. The mountain range is part of the Transverse Ranges and lies betw ...

, all of the transverse ranges fauna community. The Simi Hills are a critical wildlife corridor linkage for the Santa Monica Mountains to these and other Transverse Ranges further east. The undeveloped native

habitat In ecology, the term habitat summarises the array of resources, physical and biotic factors that are present in an area, such as to support the survival and reproduction of a particular species. A species habitat can be seen as the physical ...

provides routes that protect larger land wildlife of the Santa Monicas from genetic isolation. The

Wallis Annenberg Wildlife Crossing The Wallis Annenberg Wildlife Crossing is a vegetated overpass spanning the Ventura Freeway and Agoura Road under construction at Liberty Canyon in Agoura Hills, California. The bridge will be one of the largest urban wildlife crossings in the ...

is a proposed vegetated overpass spanning the Ventura Freeway at Liberty Canyon in Agoura Hills, California. Large sections of the Simi Hills are protected by parks and open space preserves. The Santa Susana Field Laboratory property, a crucial wildlife corridor to the Santa Susanas, has been proposed for public open space parkland after the closed site's cleanup completion. The population of red-legged frogs is small and isolated, and was impacted by the Woolsey Fire swept through the area in November 2018.

History

The Simi Hills were inhabited for over 8,000 years by Paleo-indians and Chumash-Venturaño Native Americans for settlements and hunting grounds. The Chumash had the established village of ''Hu'wam'' in ''Cañon del Escorpión'' (Bell Canyon). It was a multicultural 'crossroads' destination, where Chumash,

Tongva The Tongva ( ) are an Indigenous people of California from the Los Angeles Basin and the Southern Channel Islands, an area covering approximately . Some descendants of the people prefer Kizh as an endonym that, they argue, is more historically ...

, and Tataviam peoples traded and lived beside Bell Creek below Escorpión Peak, at the present day Bell Canyon Park. This peak in the Simi Hills (aka: Castle Peak) is one of nine alignment points in Chumash territory and is essential to maintaining the balance of the natural world. Upstream were healing springs and are rock outcrop 'grinding stones.' The Burro Flats Painted Cave, an example of the

Rock art of the Chumash people Chumash rock art is a genre of paintings on caves, mountains, cliffs, or other living rock surfaces, created by the Chumash people of Southern California. Pictographs and petroglyphs are common through interior California, the rock painting tradi ...

, is nearby. The Juan Bautista de Anza expedition passed through the area in 1769, being the first European sighting of the Simi Hills. The U.S.

National Park Service The National Park Service (NPS) is an agency of the United States federal government within the U.S. Department of the Interior that manages all national parks, most national monuments, and other natural, historical, and recreational properti ...

administers the Juan Bautista de Anza National Historic Trail which enters at Moore Canyon in

El Escorpión Park El Escorpión Park is a three-acre (12,000 m²) park located in the Simi Hills of the western San Fernando Valley, in the West Hills district of Los Angeles, California. The park contains the geographic landmark known as Escorpión Peak or Castle ...

and crosses across the southern Hills through Upper Las Virgenes Canyon Open Space Preserve and Cheeseboro/Palo Comado Canyon Park to the Conejo Valley. In 1845 the

land grant A land grant is a gift of real estate—land or its use privileges—made by a government or other authority as an incentive, means of enabling works, or as a reward for services to an individual, especially in return for military service. Grants ...

for

Rancho El Escorpión Rancho El Escorpión was a Mexican land grant in present day Los Angeles County, California given in 1845 by Governor Pío Pico to three Chumash Native Americans - Odón Chijulla, Urbano, and Mañuel.

, beside the Peak and named for it, was issued to one Chumash and two Tongva people and a rare instance of Native Americans being grantees, by Mexican Governor

Pío Pico Don Pío de Jesús Pico (May 5, 1801 – September 11, 1894) was a Californio politician, ranchero, and entrepreneur, famous for serving as the last governor of California (present-day U.S. state of California) under Mexican rule. A member of t ...

. The Rancho El Conejo was to the west, and included that end of the Simi Hills. In the first half of the 20th century, there were four large

movie ranch A movie ranch is a ranch that is at least partially dedicated for use as a set in the creation and production of motion pictures and television shows. These were developed in the United States in southern California, because of the climate. The ...

es in the Simi Hills for filming motion pictures on location. The gated community of Bell Canyon began development of geographic Bell Canyon in the 1968. To the north of U.S. 101, east of Thousand Oaks, and west of Simi Valley the early 1960s suburban expansion of metropolitan Los Angeles brought the development of small to significantly sized parcels of land in the Simi Hills. Hillside subdivisions regraded natural contours into terraced lots, changing the Hills viewshed, drainage patterns, and habitats in those areas. The extensive planned new community projects at Jordan Ranch and Ahmanson Ranch were eventually stopped by local citizens and the

Santa Monica Mountains Conservancy The Santa Monica Mountains Conservancy is an agency of the state of California in the United States founded in 1980 and dedicated to the acquisition of land for preservation as open space, for wildlife and California native plants habitat Natur ...

keeping extensive Hills acreage natural in open space parks. The Simi Hills were home of the Rocketdyne Santa Susana Field Laboratory (SSFL) for open-air testing of rocket engines from 1947 to 1990, and the site of experimental

nuclear reactor A nuclear reactor is a device used to initiate and control a fission nuclear chain reaction or nuclear fusion reactions. Nuclear reactors are used at nuclear power plants for electricity generation and in nuclear marine propulsion. Heat fr ...

experiments with four nuclear accidents between 1959 and 1969; these projects and accidents were declassified in 1989. The first accident, in 1959, was the most serious with a full meltdown. The extent of the accident is unknown due to instrument limitations, other than that it released extensive radiation. More radiation was released in the 1959 event than in the

Three Mile Island accident The Three Mile Island accident was a partial meltdown of the Three Mile Island, Unit 2 (TMI-2) reactor in Pennsylvania, United States. It began at 4 a.m. on March 28, 1979. It is the most significant accident in U.S. commercial nuclea ...

20 years later. The groundwater under portions of the Simi Hills, contaminated with toxins and radionuclides that were also historically used at SSFL, has been and is a key concern in new development decisions and the SSFL property's future limited to parkland use after an impending cleanup, initiating preservation of more open space in the range. The NP
Rim of the Valley Trail Corridor
is in the planning stages and includes the Simi Hills open space parklands and proposed new areas.

Parks

* Bell Canyon Park with Bell Creek; West Hills and Bell Canyon * Challenger Park *Cheeseboro/Palo Comado Canyon Park - in the Santa Monica Mountains National Recreation Area, western Simi Hills in Ventura County. *

and the Moore's Canyon Juan Bautista de Anza National Historic Trail segment; West Hills, Los Angeles * Rocky Peak Park - ''adjacent and above Santa Susana Pass'' *

Ronald Reagan Presidential Library The Ronald Reagan Presidential Library is the repository of presidential records from the administration of Ronald Reagan, the 40th president of the United States, and the burial place of the president and first lady, Nancy Reagan. It is the larg ...

complex with museum *

Sage Ranch Park Sage Ranch Park is a and wildlife corridor located at a height in the northwestern Simi Hills on the northwestern plateau of the Simi Valley, bordering Los Angeles County and its San Fernando Valley.Stone, Robert (1998). ''Day Hikes in Ventur ...

- near the Santa Susana Field Laboratory with trails and camping. * Santa Susana Pass State Historic Park - with the Old Santa Susana Stage Road in the rocky northern Simi Hills. * Upper Las Virgenes Canyon Open Space Preserve - (previously the Ahmanson Ranch Park), 3,000 acres (12 km²) Park in the southern Simi Hills, managed by the

Nearby ranges

* Chalk Hills *

* Santa Monica Mountains * Verdugo Mountains

References

External links

;Parks
SMMC: Upper Las Virgenes Canyon Open Space Preserve
(formerly Ahmanson Ranch)
SMMC: Sage Ranch Park
* ttp://venturacountytrails.org/TrailMaps/Cheeseboro/CheeseboroTrails.htm Ventura County Trails.org: Cheeseboro-Palo Commado Parks
Ventura County Trails.org: Wood + Lang Ranches Regional Parks
;Park finders
Santa Monica Mountains Conservancy (SMMC): Simi Hills Park-Finder
— ''interactive website''.

— ''interactive website''.
Santa Monica Mountains Conservancy (SMMC): All local ranges Park-Finder
— ''interactive website''. {{Authority control Hills of California Transverse Ranges Mountain ranges of Los Angeles County, California Mountain ranges of Ventura County, California Geography of the San Fernando Valley Geography of Simi Valley, California San Fernando Valley Agoura Hills, California Hidden Hills, California Thousand Oaks, California West Hills, Los Angeles Woodland Hills, Los Angeles