Ride Type: Jeep trail / Single track Location: Grindstone OHV trail area. Length: 28 mile loop - 4 1/2 hours Difficulty: Intermediate with a few expert sections Directions: Take M-10 west out of Stonyford Gas: In Stonyford or on I-5 See online USFS OHV trail map at: Grindstone.pdf Beautiful single track trails winding back and forth across fire roads. The trails cover a lively mixture of rocky ridge tops, forested hillsides and deep canyons. Plenty of bail-outs if things get rough. We attempted to take Trail 28 for it's entire length and turned around in two different places due to steepness becoming more than my rusty, underdeveloped skills can handle. The only caution is don't go down anything you're not sure about getting out of. There are no secondary access points the deep canyon crossings. Four hours doesn't sound like much, but the trails were all strenuous. One good time after another! The Stonyford area is exceptional for interesting terrain and well kept trails. Watch out on hot days. Dust can be a problem in Summer and Fall. Very few other bikers around, so take a buddy. I'm sure there are other routes equally as nice as the ones we took. When the map says expert, they mean it. Even some of the intermediate trails are very steep. Green trails should work for heavy bikes. We trailered in two dirt bikes deciding to do this one as a day trip rather than camp. There is plenty of decent camping available however. Left San Francisco at 6am and arrived by about 9am with a stop to buy sandwiches for the trail. Got back home at 6pm. Two GPS files with identical tracks are available for down load. Mapsource (.gdb) version 2 and GPS eXchange format (.gpx) The turns are approximately marked by waypoints with trail numbers. Both of the places we turned around do go through if your balls are bigger than mine. Also included is a track following a great back-road way from Stonyford to Williams.