Our Watershed

 

 

A watershed is the physical area draining to a particular body of water like a creek or a Bay, in this case the Tomales Bay.

 

Located in western Marin County, California, approximately 40 miles northwest of San Francisco, the Tomales Bay Watershed encompasses almost 220-square miles bounded by the slopes of Mt. Tamalpais to the south, the Inverness Ridge to the west and the agricultural lands to the east. Tomales Bay itself is an approximately 12 miles long flooded valley, covering 10.8 square-miles, straddling the San Andreas Fault. The Bay is less than a mile wide, and has an average depth of less than 20 feet.

 

The Tomales Bay watershed is remarkable for its beauty, wildlife, and diverse human history.

 

At the juncture between the ocean and the land, Tomales Bay is created by the San Andreas Fault and underlying geology.  Extraordinary vistas of rolling pastoral hills rising on the east and rugged wildlands rising on the west surround Tomales Bay – one of the most biodiverse estuaries on the

western coast of North America.  These vistas are cherished by the residents of the Tomales Bay Watershed and draw millions of visitors to the region each year.

Here, some of California’s finest seafood grows wild, and we produce healthy and award-winning beef, dairy, produce and cultivated shellfish. Today, this region has a resident population of approximately 11,000 people, mostly clustered in eleven villages.

 

Residents continue to share in a continuation of food production and local self-reliance through local creameries, cheese makers, organic farms and other agricultural production systems; the local oyster industry; and the collection of firewood, berries, herbs and other goods.  Additionally, much of the local economy has shifted and is predicated upon the demand for recreation-oriented goods and services ranging from over-night accommodations to kayak rentals to numerous eateries that serve approximately 2.5 million visitors annually.

 

The waters that drain into Tomales Bay and are exchanged with the Pacific Ocean come from two major subwatersheds, the Lagunitas Creek watershed which covers over 90 square miles and delivers approximately 66% of the freshwater flow to the Bay; and the Walker Creek watershed which covers over 75 square miles and delivers about 25% of the freshwater to the Bay.  The remaining freshwater comes from the many small coastal drainages along the east and west shores of Tomales Bay.

 

Learn more about each of the major subwatersheds below.

Coastal Watersheds

First-Valley Creek

An important coastal tributary meeting the bay just north of the Inverness store, this perennial watershed receives water from fog-drip and the valleys of the Inverness Ridge, and provides drinking water for local residents.

Watershed Area: 0.79 square miles

Major Land-Uses: residential, IPUD water supply, open space

Stream type & Important Tributaries: Perennial stream

 

White Gulch

Flowing through "windy gap" at Pierce Point and into a picturesque cove, this intermittent stream is a west-shore reference tributary watershed with minimal human influence.

Watershed Area: 0.26 square miles

Major Land-Uses: Nat'l. Park lands, Tule Elk Preserve, hiking and horse-back riding

Stream type & Important Tributaries: Intermittent stream

 

Millerton Gulch

Meeting the Bay just south of Millerton Point, this intermittent stream represents small east-shore tributary watersheds with characteristic influences.

Watershed Area: 3.8 square miles

Major Land-Uses: Ranching

Stream type & Important Tributaries: Intermittent stream

 

East-Shoe Reference Tributary

Meeting the Bay just south of the Marconi conference center, this watershed represents small east-shore perennial watersheds with minimal human influences.

Watershed Area: 0.44 square miles

Major Land-Uses: Minimal human influence

Stream type & Important Tributaries: Perennial stream, spring-fed

 

San Geronimo Creek

At the downstream end of the San Geronimo Valley, this site represents the watershed of an important head water spawning ground of Coho and Steelhead.

Watershed Area: 9.44 square miles

Major Land-Uses: residential, open space

Stream type & Important Tributaries: Perennial stream

 

Mid-Lagunitas Creek

On Lagunitas Creek in Samuel P. Taylor State Park, this site represents the mid-watershed, below Kent Lake and the other drinking water reservoirs.

Watershed Area: 43 square miles

Major Land-Uses: residential, MMWD water supply, State Park, open space

Stream type / Important Tributaries: Perennial stream / Lagunitas Creek headwaters, San Geronimo Creek, Devil's Gulch

Lower Lagunitas Creek

On Lagunitas Creek just south of Point Reyes Station, this site represents nearly all of the water from the upstream watershed, except Olema Creek, before it flows through the wetland, and into the Bay.

Watershed Area: 92.9 square miles

Major Land-Uses: ranching, residential, open space, state and federal park lands

Stream type / Important Tributaries: Perennial stream / Upper and Mid Lagunitas Creeks, Nicasio Creek, Olema Creek, Bear Valley Creek, Tomasini Creek

Major Land-Uses: ranching, residential, open space, state and federal park lands

Stream type / Important Tributaries: Perennial stream / Upper and Mid Lagunitas Creeks, Nicasio Creek, Olema Creek, Bear Valley Creek, Tomasini Creek

 

Olema Creek

A major tributary to Lagunitas Creek, this watershed represents the water flowing through the Olema Valley in an important Coho stream.

Watershed Area: 14.69 square miles

Major Land-Uses: ranching, federal park lands, open space

Stream type / Important Tributaries: Perennial stream / John West Fork, Quarry Gulch, Davis Boucher Creek, Randall Gulch

 

Wetland-Bay Interface

Situated just north of the old north levee, downstream of the Giacomini wetland restoration, this site is where Lagunitas Creek meets Tomales Bay. This is our innermost Bay sampling site (see below for description of the others)

 

Inner Bay Site

Situated near Millerton Point, this site is heavily influenced by Lagunitas Creek, the inner coastal tributaries, and the long residence time of water in the inner part of Tomales Bay.

 

Mid-Bay Site

Situated in the middle of the length of Tomales Bay, this site represents the water of the Bay under the influence of both Walker and Lagunitas Creeks and the tidal exchange of the Bay itself.

 

Outer Bay Site

Situated near the mouth of Walker Creek, at an oyster farm lease, this site is heavily influenced by the quality of upstream runoff from Walker Creek, and the tides at the mouth of the Bay.

 

Walker Creek Upstream

On the mainstem at Walker Creek Ranch, this site represents the upper portion of the Walker Creek watershed.

Watershed Area: 40.22 square miles

Major Land-Uses: ranching, open space

Stream type / Important Tributaries: Perennial stream - Arroyo Sausal, Salmon Creek

 

Walker Creek Downstream

At the highway 1 bridge over Walker Creek just south of Tomales, this site represents the mixing point of fresh water from Walker Creek and Bay waters.

Watershed Area: 70 square miles

Major Land-Uses: ranching, residential, open space

Stream type / Important Tributaries: Perennial stream / Upper Walker Creek, Chileno Creek

 

Keys Creek

Meeting Walker Creek just south of the Highway 1 bridge, this intermittent creek receives water flowing through the town of Tomales and from the valley along the Tomales-Petaluma Road.

Watershed Area: 4.7 square miles

Major Land-Uses: ranching, residential

Stream type / Important Tributaries: Intermittent stream

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