In the Santa Cruz Mountains off the coast of Monterey Bay in California is the Henry Cowell State Park. This park stays cool with all the many redwood trees in the forest. The Henry Cowell Campgrounds has a few camping sites that have been made accessible. In addition to camping, the park has three barrier-free hiking trails.
The most accessible is the Redwood Grove Loop Trail which begins near the Visitor Center. The trail is little less than a mile long (0.8 miles), and includes wooden handrails along the wide trail. Furthermore, the Redwood Grove Loop trail is basically flat and consists of a hard-packed dirt surface mixed with some crushed rock. Natural forest debris is expected on the trail as well.
The first part of the Meadow Trail is barrier-free (approximately 0.5 miles). About 0.2 miles from the trailhead, is another trailhead for the River Trail, which travels through redwoods to the river. The first 4,000 feet of the River Trail is accessible, but you may be able to explore further, especially with a power wheelchair.
You can drive to Henry Cowell State Park in the Santa Cruz Mountains; a few designated handicapped parking spots exist. Or, you can take the Santa Cruz Train from the Beach Boardwalk up to the park.