This is a moderate hike that will take you from the oak scrub along the Graham Hill trail, through the verdant Redwood jungle along the Powder Mill Creek and finally down to the San Lorenzo River bottom on the steep Buckeye trail. Most of the hike is sandy single track that holds up well even after a good wash, but as it's in the shade most of the time, it would be a great hike on a hot day.
The San Lorenzo River doesn't live up to its name after months of dry weather, but during the rainy season it gets quite full.
The fee at the Campground entrance to the park is $10 and a trail map costs another $3. You can park for free at the southwest corner of the park off of Graham Hill Road and do the loop from there. There is poison oak along some of the trails but it's not as prevalent here as it is at many bay area parks. Bring water a snack and your camera and enjoy the hike!