This is an excellent park where you can easily see some of California's great giant redwoods. Most of the big trees in the state were cut down in the late 1800s, and in this part of California groves of old growth trees are not too common. Big Basin State Park, up near the town of Boulder Creek, has many more, but this park is closer and has a nice walking path close to the parking lot for visitors short on time or who can't hike very much.
That being said, there are miles and miles of great hiking trails for more serious hikers. Check out the park website and you will see that there are two separate sections of the park. The main one is where the campsites, redwood grove, ranger office and shop are. A little further, on Felton Empire Road, is a trailhead that goes to much less traveled sites up toward the ridge of the Santa Cruz mountains. You can follow a trail along the creek up to old abandoned lime kilns and likely have the place to yourself.
Henry Cowell Redwoods State Park consists of 1,800 acres of towering redwoods, steep canyons, and chaparral-covered ridges. It features 15 or 20 miles of trails and limited access roads, for use by horses, bikes, and hikers, with the most famous trail is the short, easy 0.8 mile circular walk called the Redwood Grove Loop Trail through some impressive towering redwoods. The park also offers camping, a visitors center and store, seasonal fishing, and day-use picnic areas. The maximum elevation in the park is 802, and this point features an observation deck on top of a water tower. Animals in the park include raccoons, mule deer, coyotes, silver salmon, steelhead, and the rare but deadly banana slug.
The park is named after Henry Cowell, a Santa Cruz land baron who arrived in California in 1849. By 1865 he had made his money moving supplies during the gold rush, and he moved to Santa Cruz. By 1886 he owned 6,500 acres including what is today the campus of UC Santa Cruz. In 1930, a small section in the middle of the Cowell property was given to the county as a park, and in 1954 this county park and 1600 acres of Cowell's land were converted into a State Park.
This is one of the more southerly stands of redwoods you will find in the state. It's a great place for either a short (1 mile) hike through a redwood grove or a longer (5 mile) hike by the river.