Ross Valley land use and habitat

The watershed includes 44 miles of stream channels. Ross Creek drains the northern slope of Mt. Tamalpais. San Anselmo Creek and its tributaries drain the northwestern portion of the watershed. The two channels join to form Corte Madera Creek in Ross. Corte Madera Creek flows through more than a mile of concrete-lined channel past the confluences of Larkspur and Tamalpais Creeks and into the lower earthen section out to the salt marsh at the mouth.

Despite the dense development in the valley floors, the Corte Madera watershed supports a great diversity of habitats including:

• Redwood forest
• Serpentine outcrops
• Chaparral
• Oak woodlands
• Grasslands
• Riparian forest
• Tidal wetlands

It is home to many protected species including:

• At least 17 plants
• Steelhead trout
• Northern Spotted owl
• San Pablo Song Sparrow
• Ridgway's and black rails
• Salt marsh harvest mouse

Corte Madera Marsh Ecological Reserve is recognized as an Important Bird Area by the Audubon Society.

The Corte Madera Creek watershed originates in the foothills of Mount Tamalpais and flows through steep, narrow valleys on its way to San Francisco Bay. The watershed supports diverse habitats, from hilly headwaters to salt water marshes.

Upper watershed

Habitat in the upper watershed is mostly oak-bay woodland, coast redwood and Douglas fir forest, grassland, chaparral, northern coastal scrub, and serpentine outcroppings. The upper stream reaches' relatively natural channels provide rearing and spawning habitat for steelhead trout.

Middle and lower watershed

Urban areas dominate the middle and lower reaches of the watershed. Developed urban uses often abut the creek bank. Commercial buildings, fences, and backyards of residences are close to the creek bank in some areas. Near the confluence with Ross Creek, one mile of Corte Madera Creek runs in a concrete-lined channel through residential and commercial uses.

Tidal marshes

Due to its steep topography, tidal marshes have always been limited along Ross Valley's bayshore. Today, only a few tidal marshes remain in the watershed. The largest is the 1000-acre Corte Madera Marsh Ecological Preserve, recognized as an Important Bird Area (IBA). Just south of the marsh, the San Clement Creek tidal channel provides haul-out habitat for Harbor seals.

Special status species

• Salt marsh harvest mouse
• California clapper rail
• California black rail
• Point Reyes bird’s-beak
• Marsh microseris
• Northern spotted owl

Native fish species

• California roach
• Sacramento pikeminnow
• Sacramento sucker
• Steelhead trout
• Chinook salmon
• Longjaw mudsucker
• Pacific lamprey
• Threepine stickleback
• Starry flounder
• Staghorn sculpin
• Riffle sculpin
• Prickly sculpins

While Corte Madera Creek watershed supports a steelhead trout run, fish migration barriers exist throughout the watershed. This includes the concrete-lined channel running through Ross and Kentfield.

Common herpetofauna species

• California newt
• Pacific giant salamander
• Arboreal salamander
• California slender salamander
• Yellow-eyed salamander
• Pacific tree frog
• Western fence lizard

Introduced species

• Rainwater killifish
• Western mosquitofish
• Black crappie
• Common carp

Incorporated municipalities

• Fairfax
• San Anselmo
• Ross
• Larkspur
• Corte Madera

Unincorporated communities

• Greenbrae
• Kentfield
• Sleepy Hollow

Local land managers

Marin County Opens Space District protects and manages several areas, primarily along the ridgelines. Additionally, Marin Municipal Water District manages watershed lands in the south and west. San Quentin federal prison manages lands on point San Quentin. The College of Marin operates a campus in Kentfield.

Changes to the watershed

The Ross Valley watershed was by the intensive timber harvesting and livestock grazing of the 1800s and urbanization in the 20th century. Field studies show severe creek channel incision started in the mid 1800s. To this day, the watershed continues to respond to this land use history.

Ongoing disturbances to watershed processes

• Headward advance of 1st order tributaries
• Reduced bed incision and bank erosion in the upper alluvial channel network
• Slowing of channel aggradation in the lower reaches of the watershed

Problematic channel incision has been slowed by bedrock outcrops and manmade grade-control structures. Nearly 50% of the watershed's creek banks are stabilized by rock or concrete to protect landowners' property from bank retreat.

Dense urbanization along streambanks and unnaturally narrow channels limit available space in the watershed for channel widening. Channel widening is a natural process of reestablishing inset floodplains. These floodplains provide important habitat and increased flood capacity.

Loss of native wetlands

In addition to heavily developed creek banks, the watershed's tidal areas have been heavily modified. In the 1960s, the Army Corps of Engineers designed and constructed an earthen trapezoidal channel on the lower 4.5 miles of creek through the towns of Corte Madera, Larkspur, Kentfield, and Ross. This project widened and straightened the creek, with the goal of improving flood water conveyance. The project was also intended to store sediments delivered from upland during water flows and daily from the tide.

Changes to sediment delivery

Upland sediment sources such as gullies, overland flow, and landslides are the main sediment load into stream channels. In stream channel bed and bank erosion account for only a small fraction of the annual bedload transported in the system. Together, the San Anselmo Creek and Sleepy Hollow Creek subwatersheds generate 55% of the total annual bedload, while Ross Creek and Fairfax Creek subwatersheds only generate about 10% of the bedload each. These differences are due to variations in geology, topography, vegetation types, and land use.