Brown's Ravine:
I believe that technically it is only legal from
Dyke 8 to the Marina... although many people ride out to the
"Spanish House" and back. Check with CA State Parks.
Salmon
Falls:
This ride is 100% legal for MT biking. It is a bit bumpy and
technical, not a good beginners trail. There are other
versions of this ride, the below GPS tracks are for the pretty
standard out-n-back, including the Sweetwater trail.
Download the GPS tracks for these
four trails
HERE.

East end of Salmon Falls using Garmin Mapsource
and Google Earth.
Auburn area
Forest Hill
Divide:
This is 100% legal for MT bikes,
it is a multiuse trail so watch for horses. This is a great
intermediate+ loop about 10.5 miles long. Great single track,
good parking. To get there go I-80 to the Forest Hill road exit,
head East approx. 4.5 miles to the parking area. you will head
out and about the .6 mile mark you will hit a split. The
"normal" direction is counter-clock wise, so go right. GPS
tracks
HERE.

Forest Hill Divide loop - Auburn, CA
Stagecoach, Manzenita and
Mossy Rock: