City of Santa Clarita General Plan-- 
Significant Ecological Area Overlay

Significant Ecological Area Overlay

Significant Ecological Area Overlay (SEA) category is used to designate areas of prime importance to the City and the Valley for protection and preservation. It consists of the Santa Clara River, the Santa Susana Mountains, San Francisquito Canyon, Lyon Canyon and the Valley Oaks Savannah. Other areas which are found to have community-wide, City, Valley and/or regional importance may be designated. Development in these areas is severely limited. Specific environmental studies must be performed to assess the potential for damage or destruction of an SEA prior to approval of any plans for development in an area identified with an SEA overlay. The intent of the SEA designation is to ensure the continued viability of the biota contained within the SEA. It is the City's desire that the SEAs eventually be acquired and protected as a public trust.
 

Significant Ecological Areas

Los Angeles County has designated five locations in the Santa Clarita Valley as Significant Ecological Areas (SEAs). These are ecologically fragile or important land, and water areas that are valuable as plant or animal communities. The SEAs include the Santa Clara River, the Santa Susana Mountains, San Francisquito Canyon, Lyon Canyon, and Valley Oaks Savannah. The Santa Clara River SEA and the VaIley Oak, are the only SEAs that occur within the City boundaries. The five SEAs are described below and their locations are shown in Exhibit OS-2.

1. Santa Clara River SEA. This is the largest SEA in the Santa Clarita Valley, extending through the City of Santa Clarita and along the entire Santa Clara River watershed. It supports a variety of natural. habitats including freshwater marsh, coastal sage scrub, oak woodland, and riparian woodlands. A great portion of the river channel, through the planning area, remains dry for most of the year. In scattered areas, however, the water table under the stream bed is high, and lush riparian. vegetation provides refuge for birds and wildlife. For example, the red-shouldered hawk (Buteo lineatus) is restricted to this community and is becoming increasingly uncommon in Southern California due to habitat destruction. This assemblage of vegetation described as a broad wash association in the SEA descriptions is unlike that found in steeper mountain canyons and is rare in the Los Angeles basin. It is the only major river drainage from the San Gabriel Mountains that remains unchannelized for most of its length. This area was designated as an SEA primarily because of the threat of loss of suitable habitat for the unarmored threespine stickleback (Gasterosteus aculeatus williamsoni), a federally and state-listed endangered species. This species formerly occurred in the Los Angeles, San Gabriel, and Santa Ana rivers but is now restricted to San Francisquito Canyon, three areas in the Santa Clara River, and San Antonio Creek on Vandenberg Air Force Base. The stickleback requires clean, free-flowing perennial streams and ponds surrounded by natural vegetation. The adjacent floodplain of the Santa Clara River is included in this SEA in order to preserve this habitat. The natural vegetation along the intermittent portion of the stream slows heavy runoff during rainy seasons and thus decreases destruction and siltation of stickleback habitats downstream.
2. Santa Susana Mountains SEA. The western-most portion of the planning area encompasses a portion of this SEA which covers 12,000 acres. These mountains are one of several relatively small ridges (dominated by Oat Mountain at elevation 3,840 feet) that form the western end of the transverse ranges and blend eastward into the larger San Gabriel and San Bernardino Mountains. The Santa Monica Mountains are also part of this system. Vegetation within this SEA consists of coastal sage scrub on the south facing sunlit slopes and dense chaparral on the north facing slopes. Riparian and oak woodland vegetation is found along, stream drainages, and within canyons, along with Bigcone Spruce, Bigleaf Maple, and California Walnut. The oak woodland habitat is extremely diverse containing six species of oaks, one of which (Dunn’s Oak--Quercus dunnii), is found only in this area of Los Angeles County. The interior portions of the Santa Susanna Mountains are largely undisturbed by the urbanization that has occurred both to the south (San Fernando Valley) and to the north (Santa Clarita). These wilderness areas are important for maintaining gene flow and wildlife movement between the Santa Monica and the San Gabriel mountains, which are now largely isolated from one another by urban development.
3. San Francisquito Canyon SEA. San Francisquito Canyon SEA contains an intermittent stream that drains the hillsides north of the planning area in the Angeles National Forest. Riparian vegetation is located in the canyon bottom along the stream channel, while grasslands and chaparral are found on the walls. This SEA was designated because it supports populations of the Unarmored Threespine Stickleback, a federal and state-listed endangered species. The San Francisquito Canyon SEA is currently maintained to prevent downstream siltation of the Santa Clara River and provide constant water flows to preserve designated critical habitat for the Unarmored Threespine Stickleback. The San Francisquito floodplain is included in the SEA in order to preserve downstream stickleback habitats.
4. Lyon Canyon SEA. The Lyon Canyon SEA is located in the southwest portion of the planning area, west of 1-5, and covers approximately 150 acres. This SEA is a relatively narrow canyon that contains both an oak woodland community and a substantial chamisal chaparral community. The oak woodland, found in the southern portion of the SEA contains both the Coast Live Oak (Quercus agrifoli) and the Valley Oak (Quercus lobata). The northern region of the SEA contains the chaparral community consisting of Sugarbush, Ceanothus, Black Sage, Mule Fat, and Charmise, which is the dominant shrub.
5. Valley Oaks Savannah SEA. The Valley Oaks Savannah SEA covers approximately 400 acres and is located west and east of 1-5, south of the Valencia interchange. This area contains one of the last remaining stands of Valley Oak in the Santa Clarita Valley, and it represents the southernmost limit of large, contiguous Valley oak savannah in California. Although the stand is quite extensive, little regeneration is occurring, possibly due to grazing or other disturbances. The vegetative land cover consists mainly of weed-dominated grasslands. Scattered Coast Live Oaks occur throughout the site as well.

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