The Corte Madera Creek watershed is located in the eastern urbanized corridor of Marin County, California, and reaches from San Francisco Bay into the foothills of Mount Tamalpais, in the Coast Range. It is bounded on the west by a steep, forested ridge running northwest from the East Peak of Mt. Tamalpais (elevation 2,571 ft) to Pine Mountain and then north-northeast to White’s Hill (elevation 1,430 ft).
San Anselmo and Fairfax creeks rise along these ridges and drain steep upland areas onto relatively steep and narrow valley flats; these creeks combine as San Anselmo Creek in the town of Fairfax. San Anselmo Creek then flows southeast through Ross Valley, bounded by a sandstone ridge running southeast. Several intermittent tributaries rise on the grassland and grass-oak woodland-covered hills along the northern and eastern edges of the basin. Sleepy Hollow Creek joins San Anselmo Creek in San Anselmo near Saunders Avenue. Ross Creek is a major tributary descending from the northern flank of Mount Tamalpais to join San Anselmo Creek in Ross. The channel is called Corte Madera Creek from the Ross Creek confluence to San Francisco Bay Estuary, and for a mile of its length it is encased by a concrete-lined channel. It drains into a tidal salt marsh at Kentfield, and then into San Francisco Bay near Corte Madera. Larkspur Creek and Tamalpais Creek are the only major tributaries to Corte Madera Creek that enter downstream from the concrete channel. Corte Madera Creek has approximately 29 named tributaries, with an aggregate length of approximately 44 miles. In addition to these streams, Phoenix Lake, which covers 28 acres, is located above Ross, and is an impoundment of Ross Creek.