Marin’s Southern Coastal watersheds include Webb Creek, Lone Tree Creek, Cold Stream, Redwood Creek, Alder Creek, Rodeo Lagoon, and Tennessee Valley.
The lower watersheds of Webb Creek, Lone Tree Creek, and Cold Stream are primarily coastal scrub. The upper watersheds contain Douglas fir and redwood forest. Oak-bay woodland and redwood forest occur along the drainages, with patches of grassland habitat.
The Redwood Creek watershed contains a variety of habitat types including:
- Coastal chaparral
- Old-growth redwood forest
- Mixed hardwood forest
- Seasonal wetlands
- Riparian woodlands
A large intermittently tidal lagoon occurred at the mouth of Redwood Creek before the land use changes that followed European colonization of the watershed. This lagoon once covered an area of approximately 25 acres. Only a remnant of the lagoon remains today.
- Mt. Tamalpais manzanita
- Tamalpais oak
- Tiburon buckwheat, and Mount Tamalpais jewel-flower.
The Alder watershed is predominantly composed of residential and rural residential development. Undeveloped areas are primarily annual grassland and coastal scrub, with small groves of eucalyptus and Monterey pine.
Duxbury Reef is considered the largest shale reef in North America. It provides an extensive system of rocky intertidal and subtidal habitat that supports large areas of kelp beds and many marine invertebrates and fish. It is an important haul-out site for harbor seals. Steep, unstable cliffs separate the reef and a narrow strip of sandy beach from the Bolinas Mesa.
The Tennessee Valley watershed is largely composed of grassland and coastal scrub habitats. It has a small freshwater marsh near the lower watershed. Similar habitat types occur within the Rodeo Lagoon watershed
Northern spotted owls have been recorded along Webb Creek, and Tamalpais oaks occur at the top of Webb Creek and Lone Tree Creek watersheds. There are no historical or current records of special-status fish species in these watersheds.
- Coho salmon
- Steelhead trout
- California red-legged frog
- Monarch butterflies
- Northwestern pond turtle
- Northern spotted owl
Redwood Creek was previously considered the southernmost stable population of Coho salmon. However, no returning adults were recorded for the first time since the 1940s in winter of 2007-2008. Redds were also not observed.
An 80% decline in spawning salmon was observed in most western Marin County creeks that year. One cause of the decline may have been the lack of local coastal upwelling in 2006. This normally brings nutrient-rich waters to Coho salmon smolts in late spring and early summer.
One Coho salmon redd with adult Coho salmon was observed in Green Gulch Creek in the winter of 2006-07.
Monarch butterflies have been observed roosting in eucalyptus trees in the Alder Creek watershed.
Harbor seals haul out at Duxbury Reef. In addition, six species of algae and marine vascular plants, and 89 species of invertebrates, have been identified at Duxbury Reef. No fish have been observed in the seasonal drainages of the Bolinas Mesa.
The Tennessee Valley watershed is largely composed of grassland and coastal scrub habitats. It has a small freshwater marsh near the lower watershed. Similar habitat types occur within the Rodeo Lagoon watershed. Rodeo Lagoon is an important aquatic resource for a variety of native fish and wildlife species.
- Salt marsh common yellowthroat
- Monarch butterfly
Species recorded in Rodeo Lagoon
- California brown pelican
- Salt marsh common yellowthroat
- Monarch butterfly
- Mission blue butterfly
- Point Reyes jumping mouse
- Tidewater goby
- Franciscan thistle
Webb Creek, Lone Tree Creek, and Cold Stream watersheds occur within state and federal lands, including Mt. Tamalpais State Park and Golden Gate National Recreation Area. In the Webb Creek watershed, there is a small military complex and a campground perched on the rocky bluffs along the ocean.
95% of the land within the Redwood Creek watershed is in public ownership. Within the watershed boundaries lie:
- Mt. Tamalpais State Park
- National Park Service lands, including Muir Woods National Monument and portions of Golden Gate National Recreation Area
- Marin Municipal Water District lands
Three private communities occupy a small portion of the watershed: Green Gulch Farm, Muir Woods Park, and the Muir Beach community.
The Alder Creek watershed is primarily composed of urban and rural residential areas in and around the town of Bolinas. Wastewater is handled in part by the Bolinas Community Public Utility District’s sanitary sewer system and treatment ponds, and in part by on-site septic systems.
Many residents have small numbers of livestock on their property. A few commercial gardens and other small businesses, and portions of livestock ranches, also occur in the Alder Creek watershed.
Agate Beach is a popular tidepooling spot open to the public; facilities include a parking lot and portable restrooms.
Conservation and restoration
A water service moratorium set by the Bolinas Community Public Utilities District and Marin County land use restrictions limit the likelihood of future development in the watershed.
Aside from a concrete culvert where a seasonal tributary joins Alder Creek near Agate Beach, there are no stormwater management facilities for Bolinas. Most surface runoff flows to ditches and channels paralleling roadways and into Alder Creek.
Marin County Stormwater Pollution Prevention Program (MCSTOPPP) has applied for funding to reduce nonpoint source pollution into Duxbury Reef and Point Reyes Headlands. As part of the Tomales Bay Integrated Coastal Watershed Management Plan, a watershed assessment for Duxbury Reef and other local Areas of Special Biological Significance was completed.
In 2003, a Redwood Creek Watershed Vision for the Future was developed through a collaborative effort between public and private landowners and resource managers to successfully manage the Redwood Creek watershed. The public agencies involved in the vision included:
- California Department of Fish and Game
- Marin Municipal Water District
- County of Marin
- Muir Beach Community Services District
- National Park Service.
Golden Gate National Recreation Area has also been working since 2003 to restore areas along lower Redwood Creek.
The Tennessee Valley and Rodeo Lagoon watersheds are located within the Marin Headlands, part of GGNRA. Fort Cronkhite, an old Army mobilization post, is adjacent to Rodeo Lagoon and is also part of GGNRA. In the early 1990s, a draft watershed management plan for Tennessee Valley was completed by Golden Gate National Recreation Area.
A 1998 study, The Landscape History of Tennessee Valley, describes the land use history of the watershed, ecological impacts of those land uses, and implications for park planning in the watershed.
- Salmonid Trends in Redwood and Lagunitas Creeks
- California Water Boards strategic Plan Updates 2008-2012