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 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.
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. 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.