Muir Woods National Monument is a unit of the National Park Service on the Pacific coast of southwestern Marin County, California, 12 miles (19 km) north of San Francisco and part of the Golden Gate National Recreation Area. It protects 554 acres (224 ha), of which 240 acres (97 ha) are old growth Coast Redwood (Sequoia sempervirens) forests, one of a few such stands remaining in the San Francisco Bay Area.
The Muir Woods National Monument is an old-growth coastal redwood Forest. Due to its proximity to the Pacific Ocean, the forest is regularly shrouded in a coastal marine layer fog, contributing to a wet environment that encourages vigorous plant growth. The fog is also vital for the growth of the redwoods as they use moisture from the fog during the dry summer.
The monument is cool and moist year round with average daytime temperatures between 40 and 70 degrees Fahrenheit (4 to 21 °C). Rainfall is heavy during the winter and summers are almost completely dry with the exception of fog drip caused by the fog passing through the trees. Annual precipitation in the park ranges from 39.4 inches (1,000 mm) in the lower valley to 47.2 inches (1,200 mm) higher up in the mountain slopes.
The redwoods grow on brown humus-rich loam which may be gravelly, stony or somewhat sandy. This soil has been assigned to the Centissima series, which is always found on sloping ground. It is well drained, moderately deep, and slightly to moderately acidic. It has developed from fine-grained sandstone and shale. More open areas of the park have shallow gravelly loam of the Barnabe series, or deep hard loam of the Cronkhite series.
The star attraction of the Muir Woods is the Coast Redwood (Sequoia sempervirens). These relatives of the Giant Sequoia are known for their height. While redwoods can grow to nearly 380 feet (115 m), the tallest tree in the Muir Woods is 258 feet (79 m). The trees come from a seed no bigger than that of a tomato's. The average age of the redwoods in the Monument are between 500 and 800 years old with the oldest being at least 1,200 years old.
Redwood Creek provides a critical spawning and rearing habitat for coho or silver salmon (Oncorhynchus kisutch), coastal cutthroat (Oncorhynchus clarki clarki) and steelhead trout (Oncorhynchus mykiss), each of them threatened species. The creek is near the southernmost limit of coho habitat and the fish have never been stocked, so they have a distinctive DNA. The Redwood Creek salmon are Central Coast Coho Salmon which have been listed as federally threatened species since October 2006 and as federally endangered species in June 2005.
Muir Woods is home to over 50 species of birds. This relatively low number is due to the lack of insects. The tannin in the trees repels the insects and the volume of flowers and fruits produced by plants below the canopy is limited by the shade of the redwoods.
The monument is home to a variety of mammals ranging in size from the American Shrew Mole to much larger deer. The majority of the mammals are not seen as they are nocturnal or are burrowing animals living under the ground or the dense litter on the forest floor. Most commonly seen are Sonoma chipmunks, and Western gray squirrels. Bears historically roamed the area but were largely exterminated by habitat destruction. In 2003 a male black bear was spotted wandering in various areas of Marin County, including Muir Woods.
Muir Woods, part of the Golden Gate National Recreation Area, is a park which caters to pedestrians, as parking of vehicles is only allowed at the very entrance. Hiking trails vary in the level of difficulty and distance. Picnicking, camping and pets are not permitted.
Lodging and camping:
There are no camping or lodging facilities in the Muir Woods. The monument is a Day-use area only. There are camping facilities in the adjacent Mount Tamalpais State Park.
Aramark Cafe and Gift Shop – deli food items and souvenirs. Also has a permanent display of historic photographs.
1.5 miles (2.4 km) of paved, wheelchair accessible trails
Visitors Center with permanent and changing exhibits. Also contains a gift shop.
Hiking and biking:
The monument has a number of paved walking trails (Trail Map) where visitors can get a close look at the magnificent giants. Other unpaved walking trails lead up the hills to connect with trails outside of the Monument boundaries. Bicycles are only allowed on fire roads.
The annual Dipsea Race, a footrace which goes between Mill Valley and Stinson Beach, passes through Muir Woods on the second Sunday in June. The Double Dipsea, later in June and the Quad Dipsea, in November, follow the same course.
Ranger-led walks on a number of different topics, including discussions on the watershed, wildflowers, and tidepools are held on weekends. Moonlight walks are held on nights with a full moon. Reservations are required for the moonlight walks. Daily presentations are possible if staffing permits. Special events are held for the summer and winter solstices.
Weddings are allowed in the Monument with a proper permit.