This is a great loop ride that visits an interesting and beautiful historic site and follows some amazing singletrack down to and along the south fork of the Yuba River. The shortest loop is about 17 miles while some fun add-ons exist that can make it more like 25-30 miles. Probably two-thirds singletrack, most of the climbing on this ride is on rolling trails or moderate fireroads, but it can be plenty strenuous depending on your speed.
Good camping is $5 a night down the hill
How to get there:
From I-80, take 49 north or 20 south to Nevada City. Turn off 49/20 onto 49 towards Downieville. About a mile up the road, turn right onto North Bloomfield Rd. Follow this for a few miles - it drops steeply down to the Yuba river, turns to dirt after the bridge, and climbs the other side of the canyon. Follow signs for N. Bloomfield until you see the sign for the camping/parking area (1-2 miles past the river.) Park in the day-use lot.