Yuba Expidition has maps. Head East up old Camptonvile road. Trailers, dags, rusted cars and over the top. nice downhill to cool down. On the flat there is trail head north side. fast down hill(rips) at all trail weys stay north. Until overlook and Marysville road. Head East Along north side of road and watch for trail. It will cross road once then back.
Hwy 49 to Downiville from Nevada City. Left on Marysville road Park at bar/store.
http://www.singletracks.com/item.php?c=1&i=1269