We have a house across from the state park, one of the only houses there. I know this park like the back of my hand. There are easy rides along the shores of the patuxent river, including 2 beaches. The gravel paths are easy, but as you explore more of the Park you will find some more difficult hills. If you go across the street from the remote controlled airplane field you will find some paths that go through the thick woods. On these trial there are some really fun hills like a roller coster up and down. This is where I got into Moutain biking, there are many trails all over the place, and no one really knows about this place. If you enjoy the area there is also an old plantation from the time of the revolution just down the road called Sotterly.
Greenwell State Park is located in St. Mary's County. Take Route 235 towards Hollywood. Turn on to Route 245 East (Sotterley Road) and travel 2.5 miles. Make a right on to Steerhorn Neck Road. The park entrance is the second drive on the left (approximately 8/10 of a mile).
http://www.singletracks.com/item.php?c=1&i=1335