Location: Mount Diablo State Park in the East SF Bay area
Tidbits: The view from the summit is the second most expansive view in the world (#1 is Kilimanjaro). On a clear day you can see about 25,000 square miles.
Summitted, Numerous times starting in 2000
When to go:
Anytime. If you're lucky, the summit will be covered with snow. This only happens once a year on average.
You can drive from the base to the summit in 45 minutes. There is a toll station where a small fee is collected to access Mount Diablo State Park. Since my old home was on the base of this mountain, I usually walked the 7 miles from the base trail that starts in the town of Blackhawk. There are numerous other trails located on all sides of the mountain. If starting from the base, I strongly advise you to get a map. The mountain is deceiving and it is incredibly easy to get lost on the hundred+ miles of trails on the mountain and in the adjoining foothills.
Hotel and Climb Reservation:
No guide, permit, or trail reservations are required. There are numerous hotels located throughout the San Francisco Bay area. Mt. Diablo is about a one hour drive from San Francisco. Camping is available in designated areas by permit. Check with the State Park for regulations and availability.
Standard light hiking gear and water for a day hike. There is water and a phone at the summit, as well as an interpretive center.
State Park Website: http://www.parks.ca.gov/?page_id=517
State Park Brochure and Map: http://www.parks.ca.gov/pages/517/files/mountdiablo.pdf
Mount Diablo dominates the skyline in the East Bay of San Francisco. It was created by a "thrust fault"...basically the earth pushing the mountain "UP" during earthquakes over millions of years (it is not an extinct volcano as some people incorrectly think).
Since the area is relatively flat in all directions (the Pacific Ocean to the West and the Central Valley to the East), the mountain can be seen from the Sierra Nevada Mountains, to points far out at sea. The early settlers took advantage of this and used the summit at the meridian marker which nearly all local surveys were based. This geographic anomaly created numerous interesting features on this mountain from sulpher springs, to coal mines, to meadows, to unusual rock towers (which are popular with the local children and climbers).
One popular trail that I recommend is taking the access road into the park and leaving your car at Curry Point and walking on the Oyster Point Trail to the overlook (about 4 miles round-trip, taking a side-trip to balancing rock (you can see west toward the Sierra Nevada Mountains on a clear day), and then walking to "Rock City" to admire (and free-climb?) some of the unusual sandstone rock formations. You can then drive or walk a few miles to to the summit. I have seen Eagles, Wild Boar, Lynx, Deer, Coyote, Hawks, and a variety of other wildlife during my trips. In the spring months, there are several small waterfalls located throughout the park...they are somewhat difficult to find, so I suggest contacting a ranger station for directions.