To reach black mountain, there are three prominent trails. One is via hidden villa, second one is via Rhus ridge and the third one is via PG&E trail.

This trail (3rd) is less common due to the elevation gain being close to 3200 feet and is 12 miles total hiking distance. It is a good hike and gets challenging on the last two miles of ascent i.e. 5th and 6th mile. This hike is a must do in bay area before going to Yosemite hikes like upper yosemite waterfall hike or four mile hike etc.

When you reach the top, don't get dishearten by the communication towers. Rather, take the monte bello road towards the opening and you will be pleasantly surprised with the view of pacific ocean to west, San Francisco city to north, Lick's observatory in the east and mnt umunhum in the south. Also, you will get a good view of the silicon bay area.

I recommend this hike.