Ride back up the road you drove down and take a signed right onto the Plum Valley Ditch Trail. This is a singletrack with numerous technical sections and a couple of dropoffs that are quite dangerous -- at least I can't ride down them.
In about 6 miles you'll reach Oregon Creek Road, where you should turn right (i.e., downhill). Cross the creek on foot, and, if I recall correctly, soon cross it again to the north and continue slightly uphill on the "O" trail (actually a fire road), which isn't marked. Warning: there are opportunities here to take a wrong turn. At this point it is advisable to have an up-to-date map and a GPS marked with a waypoint for Forest. Better yet, ride with a local rider.
The "O" trail takes you back to Forest City, a good place for a break.
Continue up Forest City's main street and turn left at the top. You're looking for a trail that begins past (again, if I recall correctly) an abandoned Datsun automobile. It turns into a singletrack, which I think is the Sandusky Trail. That takes you to Sandusky Road. Climb the road (unfortunately it can be very loose and rocky; it's much more work than its slope would suggest) to Henness Pass Road.
There look to the right; the Truckee Flume Trail begins maybe 20 feet up the road, off to the right. It climbs along a cliff, then wends its way through forest, eventually reaching an outlook high on the western slope of Yomana Mountain. From nearby vantage points you may be able to see Forest City some 1,000 feet below. Continue south on the trail until you reach South Fork Trail. Turn right to go downhill.
This downhill section is very rough and quite capable of causing a nasty accident. Proceed down it slowly. I'm told that if you'd rather avoid South Fork Trail, you can go uphill at the intersection mentioned in the prior paragraph and soon reach Ridge Road, where you ride downhill (i.e., west) on pavement back to the intersection with the road to Forest City, i.e., where you turned left in your car to reach the trailhead.
If you do go down the South Fork Trail, you'll reach relief from the rock gardens in a mile or two. Turn right on another dirt road and in short order you'll reach the top of Forest City's main street.
I can't guarantee that this description will be detailed enough to find your way. You may wish to stop at a bike shop in Grass Valley or Nevada City, or go to the BONC link below, for more detailed directions.
From I-80 take Calif. Hwy. 49 north to Grass Valley. Between Grass Valley and Nevada City the highway is a freeway. Watch for the left-hand Downieville exit. Continue north on Hwy. 49 about 23 miles, passing through North San Juan about mile 16. Look for a right turnoff with a sign to Alleghany. This is the Ridge Road. It's paved all the way to Forest City.
Take the Ridge Road about 16 miles until you see a left turn signed for Forest City (or just Forest). Take it, and go downhill a couple of miles to the hamlet of Forest City. Park in town. Do not run low on gasoline, food, or water. There are no services of any kind there, and no store.
Note: A number of recently published map editions, e.g., DeLorme's Northern California Atlas & Gazetteer, and AAA-CSAA's Bay and Mountain Section map, incorrectly show the turnoff for Forest City as occurring right after crossing the Middle Yuba River and entering Yuba County. Do not follow those maps, or you will end up on a bad road. Continue driving a couple of miles north on Hwy. 49 until you see the Alleghany sign. If you reach the Camptonville turnoff, you've gone too far.
Summary: Alot of hard work went into building these trails including the fancy trail bridge and alot of really well designed switchbacks. Unfortunately it just wasn't all that much fun to ride. Aside from the switchbacks, the trails are just pretty boring and lack flow. Not enough high speed sections that allow you to carry speed for any distance to speak of or put a grin on your face. There was alot of forest litter on the surface because they don't seem to get ridden enough to disperse it that was probably part of the problem on my visit. Sure would have been nice to include some high speed swooping sections on the downhills. Alot of climbing and not alot of payoff on the backside IMO. A good fitness loop, but not really worth the drive. Even the Pioneer Trail along Hwy 20 has better flow and more grins per mile.
Other recommended trails in the same area: Downieville shuttle runs, Mills Peak
Summary: Those directions sure bring back fond memories but no longer bear any relation to reality for this gem of an XC system. Check here for the most up to date description (scroll down on the left to find the one for Forest City). http://mtbsingletrack.com/ There is more new singletrack on the way, including ultimately a downhill trail to the Downieville system. Kudos to Forest Trails Alliance for building and maintaining this sweet, sweet goodness!
Recommended Route: Lots of options. Explore! (My "Difficulty Rating" below is relative, of course.)
Review Date October 14, 2003
Overall Rating 4 of 5
Aerobic Difficulty 3 of 5
Technical Difficulty 4 of 5
Ridden Trail: Once a year
Reviewed by: imtnbke
Cross Country Rider
, from Oakland, Calif., USA
Summary: I wrote the introductory information, so I'm not going to add much here. It's a nice ride overall, and if you're in Downieville it may be worthwhile to head over to Forest to do it. (Check in Downieville for the fastest way to drive or ride to Forest.)
I hope that the trail builders will continue to improve the route, as they've been doing recently. There are still some loose, unstable sections on the lower part.
Also, be ready for lots of deep powder on the upper portion if it hasn't rained lately.
Recommended Route: As stated in the introductory information.
If you follow that route, the total climbing is about 2,500 feet. But it will feel harder than that.
Other recommended trails in the same area: Downieville, of course.