Henry Cowell Redwoods State Park preserves mainly forest and riparian areas in the San Lorenzo River watershed, including a grove of old-growth coast redwood. Established in 1954, this 4,623-acre park is located near the town of Felton in Santa Cruz County and includes the non-contiguous Fall Creek Unit.
Activities at the park include hiking, seasonal fishing and camping, bird watching, and some bike- and dog-friendly trails. It's an incredibly popular spot for locals, as it can be accessed from the highway on foot, and pedestrians do not pay for access.
The park includes over fifteen miles of trails, the most popular of which is the Redwood Grove trail. The Redwood Grove trail takes visitors through an old-growth "virgin" redwood grove, the oldest trees of which are between 1,400 and 1,800 years old and can grow to be 300 feet tall and 16 feet in diameter. The grove is a self-guided tour, supplemented by pamphlets available on loan or for keeps with a donation of 25 cents. These can be found at the entrance to the grove or for download online.
The self-guided tour has 15 stops, including the "Giant" and "Fremont" trees. The Giant is 270 feet tall nad has a diameter of 17 feet, almost as high as a 25-story building.
The Fremont tree is even more interesting. Named after the explorer and general John C. Fremont, the Fremont tree used to be the honeymoon suite at Welch's Big Tree Resort; the Welch family acquired the grove in 1867. If you go inside the tree with a flashlight, you can see rectangle carved into the side which used to be a window. Imagine staying the night inside a living, breathing tree!
Coast redwoods are not the only trees to be found in the area. There's also the deciduous dawn redwood (a tree thought to be extinct until 1940), a giant sequoia, douglas fir, and the California bay.
Just FYI dogs and bikes are not allowed in the grove.
Branching off near the Fremont tree is the River Trail. I recommend following it to at least the railroad bridge as a quick side excursion. The River Trail follows the San Lorenzo River to a number of river beaches and swimming holes. The trail branches off into other trails that go deeper into the park.
Fall is one of the best times to visit Henry Cowell. The summer crowds have died down and it's not as chilly as it would be in the winter, or as wet as the spring can get.