Park at the Bald Mountain parking lot. The trailhead is across the Mount Umuhnum Road.
The trail goes through a forest with a variety of trees such as oak, madrone, manzanita and pine. Ride through the forest for 3.5 miles with lots of hairpin switchbacks. The average slope is about 6%. The last 0.2 miles is open only to hikers. To reach the summit, ride for 0.2 miles on the paved road.
The views from the summit are great: Silicon Valley lies below you, and (on a clear day) one can see all the way to San Francisco, Monterey Bay, and the Pacific Ocean. There are great views of all the mountains in the area, including Mount Hamilton and Mount Diablo.
Get more info and download a free audio guide describing the natural environment, the scenery, and the rich history of the area, here