I posted about my camping trip to Lake Somerville SP on the 4th weekend, in the Camping Forum. Here is a report on the biking trails:
Several nice hiking trails, much under canopy of low tree branches, for shade. Same trails used for biking. Some parts were a little hard to peddle through, but otherwise, fun for biking. You can bike on the roads too, if watching for traffic.
There is a 26-mile round trip trailhead connecting this park with one on the other side. Some of the roadway is soft dirt or loose rock which makes it hard to peddle through (it is also used for horses). I did about 4 miles of it, then turned around and came back. It was just too hot in the middle of the day to do the whole thing. It would be nice in the fall.