These are the trails local guru Carl Ringler has been building specifically for mountain biking. The ones near the overlook are thrashed. Moderate to Difficult. There are a number of places you can access the trails, but I recommend driving into the State Park and parking at the west end in the boat ramp parking lot. From there you will see entrances on the wooded side of the lot.
Trails run in all directions from there.
Take the second left where the Clinton State Park sign is. You won't actually enter the state park by car, but this area's hours are 8 a.m. to 10 p.m. However, as I mentioned, the trails at this end are overused. Paying to enter the State Park is noble because those funds keep the park open to its largest user group, off-road cyclists, and you get to the good areas with enough energy to enjoy them. It's even better if you can save the 30 bucks to buy a year pass to Kansas State Parks.