It is easiest to start at the top of the road and descend. The road starts where the Ranger's Grade portion of the Summit Trail - Mt. Diablo
intersects Summit Road at about 2700ft elevation. It is quite a climb to get there.
The road starts as a degraded paved road and turns into a loose and slippery fire road. Most of the ride is through the area that was burned by the Morgan Fire in 2013.
About 1 mile in you'll run into the ruins of the Green Family Ranch including the foundations and chimneys of several buildings, a tennis court and a swimming pool. You can find some of the property's history here:
The descent into Curry Canyon is loose and steep on a road that is often covered in small sharp rocks (sharp enough to cut my rear sidewall). It really isn't that fun except the views are incredible in every direction. You can see the top of Mt. Diablo, the burn area and all of Curry Canyon and beyond. It is well worth the effort!
Note: Some maps refer to the last mile or so of the trail as Alder Creek Rd.
The road ends at Frog Pond Road
which will take you the rest of the way to Curry Canyon Road
and your exit.