San Antonio Creek Watershed
The San Antonio Creek watershed comprises approximately 25% of the Petaluma River watershed; it extends from Antonio Mountain and Chileno Valley in the northwest to Petaluma Marsh and the Petaluma River to the southeast. The creek, which has a seasonal flow, forms a portion of the border between Sonoma and Marin Counties.
Changes to Watershed Processes
Changes to the watershed are described in the San Francisco Estuary Institute survey of stream bank and bed conditions and sediment supply along San Antonio Creek in 2000 (Collins et al. 2000 1).
Changes have included the draining of a shallow lake at the headwaters of the creek was drained for agricultural uses in the late 1800s, which may have increased the magnitude and frequency of peak flows while lowering the water table in the Chileno Valley. This in turn is likely to have accelerated erosion and bank incision.
In addition, the mainstem creek was historically a perennial stream, at least in its lower reaches, and perhaps for much of its length. The tidal channel of San Antonio Creek was diverted from its natural slough through the much smaller and shorter Schultz Slough around 1930. This change in course has also flattened the gradient of the stream and contributed to aggradation in the lower reaches.
The Estuary Institute survey states that relative to pre-European settlement conditions, sediment production in the watershed has greatly increased, the base flow of the creek has been greatly reduced, and peak flows have increased.
The upper San Antonio Creek watershed is dominated by annual grassland and mixed evergreen forest, with patches of oak and bay woodland. The lower watershed includes extensive coastal salt marsh and brackish marsh which provide valuable habitat for fish and wildlife.
Fish and Wildlife
Special status species include California black rail, clapper rail, salt marsh common yellowthroat, San Pablo song sparrow, Townsend’s big-eared bat, California red-legged frog, northwestern pond turtle, and salt marsh harvest mouse have all been recorded in the watershed.
There are limited records of salmonids in the San Antonio Creek watershed. Up until the mid-1900s, steelhead trout were fairly common in the watershed (Collins, et al., 2000). Although steelhead were seen in 2000 (Cox 2), Leidy (2007 3) notes steelhead trout are extinct from the watershed; California roach and threespine stickleback are still found. An evaluation of San Francisco Bay Area watersheds for their potential for steelhead trout restoration efforts noted that potential habitat may exist in the creek from the Point Reyes-Petaluma Road crossing down to Highway 101 (Becker et al. 2007 4).
Human Habitation, Land Use, and Resource Conservation
Land Use Imperviousness
San Antonio Creek watershed lands are primarily in private agricultural ownership. Most of the tributaries flowing from the west and south (on the Marin County side) have steep gradients and incised channels, and the surrounding land is used primarily for livestock grazing (SSCRCD 1999 5). The north (Sonoma County) side of the watershed has moderate slopes, and is used for livestock grazing, vineyards, and dairy production.
Marin Agricultural Land Trust is actively protecting land in the watershed, having purchased agricultural conservation easements on a number of ranches. Public lands include Olompali State Historic Park, on the eastern slopes of Mount Burdell, and a portion of the 1,950acre California Department of Fish and Game Petaluma Marsh Wildlife Area. A 600-acre landfill and recycling center, which handles the bulk of Marin County’s refuse, is located adjacent to a portion of creek channel and marshlands in the southeastern portion of the watershed.
In 1999, the Southern Sonoma County RCD completed The Petaluma River Watershed Enhancement Plan (SSCRCD 1999). The plan includes information on land use, erosion, riparian enhancement opportunities, and fisheries enhancement for each subwatershed draining into the Petaluma River, including San Antonio Creek. In 2008, SSCRCD completed the San Antonio Creek Watershed Plan in collaboration with local landowners and residents.
For more information about San Antonio Creek, please contact Southern Sonoma County Resource Conservation District at 707.794.1242 x5 or at http://www.sscrcd.org/
1 Application of the SFEI watershed science approach to San Antonio Creek, Sonoma and Marin Counties
2 Major Streams in Sonoma County
3 Ecology, Assemblage Structure, Distribution & Status of Fishes in Streams Tributary to the San Francisco Estuary
4 San Francisco Estuary Watersheds Evaluation -- Identifying Promising Locations for Steelhead Restoration in Tributaries of the San francisco Estuary
5 Petaluma River Watershed Enhancement Plan