There are a bunch of loops available from here. Get a map or find a local for best results. As a minimum, the Falcon Guide "Mountain Biking Virginia" has some good info. There are a number of routes up, including Hone Quarry, the paved road, California Ridge, and Lynn Trail to Wolf Ridge, to Timber Ridge. None of these are easy. Even the paved road requires a steep grade over a long distance. Each of the singletrack options are even steeper and all but California Ridge can be highly techncal. At the top, be sure to take the little swirl of a road that goes to the top of Reddish Knob, the highest point in this part of VA, with unobstructed views of the Shanendoah to the east and West Virginia to the west. Any of those brutal singletrack climbs will make a fine downhill. At about 8 miles, the Timber ridge descent is the longest, but will require a few sharp climbs along the way. The last two miles before hitting the dirt road at the bottom are totally primo. The rest can be very rocky or very narrow or both. Much of the trail is covered with leaves or grass so you can't see what's at the bottom of the groove. That makes for some dicey moments if you're flying down at warp speed and you don't know where the roots and rocks are. The Timber Ridge to Wolf Ridge to Lynn trail descent is scary steep in places and has some very tight singletrack. If you take Wolf all the way down, or Timber Ridge, or the Sand Springs Mountain trail that lies between, you will arrive at Tillman road. Take this back north to Briery Branch Road to then head back up a couple miles to the parking area. Tillman Road turns into Tighlman Road, which can be confusing; don't worry, you're on the right path either way. If you want to take Timber Ridge all the way down (recommended for the last couple miles), make sure you don't miss the fork right at the intersection with Sand Springs Mountain. Pick your poison and have a great ride!
From Harrisonburg, take 42 south to Dayton. From Dayton take 257 west, following 257 signs through Montezuma and Ottobine. At Ottobine, follow 257 south. After a few miles, 257 will turn left and take the name Briery Branch Road. After a few more miles, Briery Branch Road will make a left and a right shortly thereafter. When you hit the right fork to Hone Quarry, stay left on Briery Branch. A few more miles you will see a parking area on the left right below the Briery Reservoir dam. This is a popular parking area for the myraid of loops possible from here.
http://www.singletracks.com/item.php?c=1&i=3732