This trail continues on a bit further than mapped here, but this is the only section open to bikes.
Starting at the parking lot at Tennessee Valley, enter Miwok on the north end where the road meets the lot. The singletrack begins immediately. About 0.5 miles in, there are some steps and switchbacks to negotiate. After another quarter mile, there is a short but very steep section. At the 1 mile point, the trail drops down to an intersection.
Miwok continues as a fire road through the other trails. After a few hundred yards, take the sharp uphill left past the water tank. If you hit pavement, you missed the turn. The climb past the water tank is steep but short.
Continue along on Miwok, and you'll have views of Tam Valley to your right. At 2 miles the fire road splits, with Miwok continuing to the right. A hundred yards later, the climb ends, and you begin a 1.5 mile descent, which ends at Highway 1. You'll pick up the singletrack to Diaz Ridge
about 50 yards to the left across Highway 1. After a 0.25 mile climb, you'll reach the Diaz Ridge Trail
Another option is to take the left fire road (Coyote Ridge) back at the 2 mile split.
Coyote RIdge reaches its peak (amazing views) in another 0.25 miles, and can lead you down to Tennessee Valley Beach or Muir Beach (via Coastal Fire Road
The singletrack lower portion of Miwok is a great descent as well for your return to the Tennessee Valley parking lot.