Downieville Classic is a 14.1 mile heavily trafficked point-to-point trail located near Sierra City, CA that features a river and is rated as difficult. The trail is primarily used for mountain biking and is accessible from April until November.
This is a very popular descent north of Lake Tahoe which you can shuttle from the Mountain Bike town of Downieville. The trails are very well maintained. Some of the time you will be on forest roads so a regular mountain bike will be fine, but if you want something really fun, splurge and rent a full suspension rig from one of the town bike shops for a truly epic ride. The shuttle vans run several times a day and take you up over 4,000 feet into the mountains for a really long descent.
This was without question the most fun I've ever had mountain biking. I'm only an intermediate, so it was terrifying in a few spots, but that's the point. What fun would mountain biking be if you were at ease all the time? Do not attempt if you aren't in good physical condition. If you become too exhausted you could hurt yourself on this trail. It requires the utmost focus. Also make sure your bike is tuned up well. Be aware, for some ridiculous reason, motorcycles are allowed on this trail, and they are usually coming uphill! This creates some dangerous situations at times.
Super fun area to mountain bike it's a world class destination. The Butcher trail is just one of many trails that lead back to the town of Downieville. These trails are old gold mining trails that are still used for claims. The Yuba river is usually not fair from the Butcher trail, 2nd divide, 3 divide is a super fast flowy DH with loam, rocks and tree roots. Plan on a at least a 14 mile plus ride back to town depending on what rout you take.