Darn - thought I had you covered, until the 5 hour stipulation.
Douthat State Park - Clifton Forge, Virginia. 40 miles of mountain biking trails. 50-acre lake. Great CCC-era log cabins with riverstone fireplaces. Campgrounds.
http://www.dcr.virginia.gov/state_parks/dou.shtml
220 miles southwest of DC.
http://www.singletracks.com/bike-trails/douthat-state-park.html
Description: Excellent single track. Middle Mountain Momma Mt. bike race held here. Stony Run trail is a 2000' climb, Middle Mountain Trail takes you along the top, and there are a number of trails leading down the mountain on very technical singletrack. Mountain side and Mountain view trails are great on the other side of the Park. Staff VERY mt. biker friendly!!!!!!!!! Hs been called the Mountain Biker's Disney Land, and is just a great place to camp, ride and swim!

Douthat State Park - Clifton Forge, Virginia. 40 miles of mountain biking trails. 50-acre lake. Great CCC-era log cabins with riverstone fireplaces. Campgrounds.
http://www.dcr.virginia.gov/state_parks/dou.shtml
220 miles southwest of DC.
http://www.singletracks.com/bike-trails/douthat-state-park.html
Description: Excellent single track. Middle Mountain Momma Mt. bike race held here. Stony Run trail is a 2000' climb, Middle Mountain Trail takes you along the top, and there are a number of trails leading down the mountain on very technical singletrack. Mountain side and Mountain view trails are great on the other side of the Park. Staff VERY mt. biker friendly!!!!!!!!! Hs been called the Mountain Biker's Disney Land, and is just a great place to camp, ride and swim!