Mount Diablo isn't especially tall, State Parks points out on its park page: just 3,849 feet. But because it rises from low rolling hills and flat valleys, the view from the top is remarkable, and it has made the mountain the East Bay's best-known landmark.

The view

On the best days you can see almost 200 miles, State Parks says. Summer is often hazy, so the clearest viewing usually comes the day after a winter storm, when you can look west past the Golden Gate Bridge to the Farallon Islands and southeast to the Lick Observatory on Mount Hamilton.

The mountain has also mattered to surveyors. In 1851 it was made the initial point of the Mount Diablo Base Line and Meridian, used for land surveys covering two-thirds of California and all of Nevada. The peak is sacred to the Bay Area's Miwok and Ohlone peoples, and Wikipedia notes that the park covers about 20,000 acres.

The Summit Visitor Center

The visitor center sits in a stone building on the highest peak, built in the late 1930s from fossil-bearing sandstone quarried in the park. Visitors can see ancient marine fossils in the walls on the way up the circular stairway to the observation deck. Exhibits cover the mountain's geology, ecosystems and cultural history. It is open daily from 10 a.m. to 4 p.m., but the park says the elevator is out of service until further notice.

Other stops

Rock City, about a mile north of the South Gate kiosk, has the Wind Caves, Elephant Rock and Native American grinding rocks, and it makes a good picnic spot. On the north side, Mitchell Canyon (reached from Clayton) is known for spring wildflowers and has a small visitor center open on weekends and holidays. Near Juniper Campground, at 2,900 feet, you can already see the Golden Gate Bridge.

Sharing the road

South Gate, North Gate and Summit roads are popular with cyclists, and the park has 67 bike turnouts. Cyclists should use them, and drivers should pass only when it is safe and never across double-yellow lines. Drones are not allowed. Carry plenty of water: the park recommends at least a quart every two hours.

More on the mountain: where to spot tarantulas this fall and Morgan Territory, Diablo's backcountry.