San Geronimo Creek

San Geronimo Creek is a stream in Marin County, California, United States, which feeds into Lagunitas Creek below Kent Lake.

Course
The creek rises in the hills west of the town of Fairfax. It descends northward to Woodacre, where it turns westward and parallels Sir Francis Drake Boulevard through the villages of San Geronimo, Forest Knolls, and Lagunitas. It then turns southwestward and joins Lagunitas Creek at the eastern edge of the Samuel P. Taylor State Park.

Ecology
The 6000 acre San Geronimo Creek watershed is within the 60,000 acre Lagunitas Creek Watershed, which is home to the largest-remaining wild run of coho salmon in central California. These coho are part of the "Central California Coast Evolutionarily Significant Unit," or CCC ESU, and are listed as "endangered" at both the state and federal level.

Efforts are also being made to protect and restore streams and habitat in the San Geronimo Valley, where upwards of 20% of the Lagunitas salmon spawn each year and where as much as 1/5 of the juvenile salmon (or fry) spend their entire freshwater lives.

Spawning salmon and trout may be viewed at Roy's Pools, located about 5 mi west of Fairfax. There are jump pools and a fish ladder.

Bridges
At least seven bridges span San Geronimo Creek:
 * at Meadow Way, 0.5 mi south of Sir Francis Drake Boulevard, a concrete continuous slab 70 ft long, built in 1965.
 * at Lagunitas Road, 0.03 mi south of Sir Francis Drake Boulevard, a prestressed concrete tee beam 67 ft long, built in 1964.
 * Mountain View Road at Sir Francis Drake Boulevard, a steel bridge 51 ft long, built in 1962 and reconstructed in 1974.
 * at Montezuma Road 0.03 mi south of Sir Francis Drake Boulevard, a concrete culvert 33 ft long, built in 1938.
 * at Sir Francis Drake Boulevard 7.6 mi east of State Route 1, a concrete tee beam 32 ft long, built in 1929 and reconstructed in 1993.
 * at Creamery Road, 0.04 mi south of Sir Francis Drake Boulevard, a concrete Tee Beam 23 ft long, built in 1948.
 * at San Geronimo Valley Drive, 0.04 mi east of Nicasio Valley Road, a concrete tee beam 22 ft long, built in 1929.