Mount Tamalpais, the highest point in Marin County, rises steeply above Richardson Bay. The ridges of Mount Tamalpais, shape the upper reaches of the watershed. They are protected as public open space and support a rich diversity of plant and wildlife communities.
The watershed drains to Richardson Bay, a shallow and biologically-rich wildlife preserve.
Richardson Bay is considered one of the most “pristine estuaries on the Pacific Coast in spite of its urbanized periphery.” The Bay is recognized as an Important Bird Area (IBA) and is located on the Pacific Flyway, an important migratory bird corridor. During the winter months, the Bay supports hundreds of thousands of waterbirds, including shorebirds and waterfowl.
Historically, the myriad of habitats in this watershed were connected to one another through the streams cascading down from Mt Tamalpais. Creeks overflowed onto floodplain marshes and these wetlands transitioned into extensive native forests and grasslands.
Today, the upper slopes and ridges of the watershed remain largely protected from development. The hills are dominated by:
- Redwood and Douglas fir forest
- Oak woodlands
These plant communities provide wildlife with natural movement corridors. The diverse vegetation is a reflection of the soils, availability of water and micro-climates in the watershed. The creeks and adjoining forest lands support steelhead trout and northern spotted owls.
The baylands and Richardson Bay still support a diverse array of native plants and animals. Great blue heron and great egret nesting colonies are found along the Bay’s shoreline.
Bothin Marsh Open Space Preserve protects the largest salt marsh at the northern end of Richardson Bay. Surrounded by cordgrass and pickleweed, the marsh supports many birds including the endangered Ridgway's rail, as well as the endangered salt marsh harvest mouse.
The watershed supports a number of special-status plants and animals. Occurrences of species found in coastal marsh in the lower watershed are of particular interest:
- California black rail
- San Pablo song sparrow
- Salt marsh harvest mouse
- Point Reyes bird’s-beak
At higher elevations, northern spotted owl territories occur in wooded areas along several creeks.
On the Tiburon Peninsula, there is a small population of California red-legged frog. The population was discovered in 1997 at a small pond, formerly a lagoon, at Keil Cove. A second sighting was made in 2000 in coast live oak woodland to the northwest of the Keil Cove sighting. This is probably the last remaining population on the peninsula.
The Arroyo Corte Madera del Presidio watershed still supports a steelhead trout run. Old Mill and Cascade Creeks support the healthiest remaining fisheries habitat in the watershed. Due to their seasonal nature, the small creeks draining directly to Richardson Bay do not support sustainable fisheries.
The Arroyo Corte Madera del Presidio subwatershed is known to support nine fish species. Seven are native and two are introduced.
Native species include:
- California roach
- Sacramento pikeminnow
- Coho salmon
- Steelhead trout
- Threespine stickleback
- Staghorn sculpin
- Prickly sculpin
Recorded observations of Coho date from the 1940s to 1960s. Coho were last seen in 1981.
Steelhead are federally listed as a threatened species. They continue to inhabit Arroyo Corte Madera del Presidio in reduced numbers.
Introduced species include:
- Rainwater killifish
- Western mosquitofish
Barriers to fish passage in our local creeks can consist of road crossings and undersized culverts when they block passage for fish at any life stage. Fish passage considerations must be made for the young fish as well as adults.
Richardson Bay itself supports the second largest surviving eelgrass bed in San Francisco Bay. Eelgrass beds provide important shelter for fish and shellfish, and a food source for many water bird species.
Richardson Bay has many fish species including:
- Bay pipefish
- Bat ray
- Black surfperch
- Northern anchovy
- Pacific herring
- Striped bass
- Threespine stickleback
In the winter, the Bay supports hundreds of thousands waterbirds including ducks, geese, grebes and shorebirds.
The Richardson Bay Audubon Center and Sanctuary manages a small upland parcel, supporting beach, bluffs, grasslands, oak woodland, coastal scrub, and riparian woodland, and 900 acres of submerged baylands. The Center operates a Monitoring Avian Productivity and Survivorship (MAPS) bird-banding station during the breeding season. The Center is also working on eelgrass bed restoration, native oyster restoration, fish monitoring, water quality monitoring, and waterbird surveys.
Species captured and/or observed during the breeding season include:
- Cooper’s hawk
- Anna’s hummingbird
- Pacific-slope flycatcher
- Black phoebe
- Western scrub-jay
- Chestnut-backed chickadee
- Bewick’s wren
- Swainson’s thrush
- Northern mockingbird
- Wilson’s warbler
- Spotted towhee
- California towhee
- Dark-eyed junco
- Black-headed grosbeak
- Red-tailed hawk
- Mourning dove
- American crow
- Common raven
- Barn swallow
- Cliff swallow
- House finch
Mill Valley, Tam Valley, Homestead Valley, and Almonte
Mill Valley land use is mostly medium to low density residential with clusters of commercial areas on the valley floors. The upper slopes and ridges are largely owned by Marin County Open Space, Marin Municipal Water District, and state and federal park agencies; these lands provide habitat connectivity between adjoining watersheds.
The Coyote Creek area is bounded by Bothin Marsh and Richardson Bay to the east and the Arroyo Corte Madera del Presidio subwatershed to the north. The ridges to the south and west are protected as part of the Golden Gate National Recreation Area. The Coyote Creek subwatershed includes the unincorporated communities of Tamalpais Valley, Tamalpais Valley Junction (Tam Junction), Manzanita, and Almonte.
Most of the development is single-family residential, with limited commercial development and services. The upper watershed is mostly rural and semi-rural, while the lower watershed is developed with greater densities near Bothin Marsh. Commercial development is largely concentrated in a small area at the junction of Highway 1 and Almonte Road.
Sausalito and Marin City
Sausalito and Marin City both have a mix of residential and commercial areas. The upper hillsides are almost entirely residential and there is a substantial houseboat residential area at along the bay front. Marin City has less waterfront; commercial development is in the lower bayfront areas and the residential development is in the hills.
Tiburon, Belvedere, and the Peninsula
In addition to Tiburon and Belvedere, the Peninsula supports Bel Aire, Paradise Cay, and Strawberry Point. Development is largely residential, with small commercial areas. The largest preserve in the watershed is Ring Mountain Preserve, located on Tiburon Ridge.
- Richardson Bay Audubon Center & Sanctuary
- (Oncorhynchus mykiss) in Streams of the San Francisco Estuary, CA
- Ecology, Assemblage Structure, Distribution & Status of Fishes in Streams Tributary to the San Francisco Estuary