Mount Diablo State Park

At the mountain's summit, the visitor center was constructed out of sandstone quarried in the park during the 1930s. Exhibits focus on the cultural and natural history of the park, while a gift shop offers books and other park-related items. There is parking and restrooms available. Outside of the visitor center, an observation area features telescopes to allow enjoyment of the panoramic views.

The Mitchell Canyon area is noted for its spring wildflowers and is the starting point for a number of trails.

Rock City offers a short, boulder-filled hike among impressive sandstone formations. The most prominent formation is Sentinel Rock, a sandstone monolith with steps carved into it that provides a tremendous view over the surrounding countryside. Other formations include the Wind Caves, Elephant Rock, Lower Rock City, Gibraltar Rock, and the Grotto Picnic area.

The University of California has been excavating this trove of 9-10 million year old mammal bone fragments since 1926. Specimens found include horses, camels, rhinos, pronghorns, sabre-toothed cats, a fox, and a very large hyena-like dog, although no complete skeletons have been recovered.

In September and October thousands of fuzzy male tarantulas venture out of their burrows seeking mates, and can be observed moving across trails and roads; while they may appear intimidating, the spiders are harmless unless provoked. The Mount Diablo Interpretive Association leads guided hikes to see the spiders during their migration, but these hikes are very popular so advance sign-up is required.

This grueling, 11.2-mile (18-km) annual bike race starts at the Athenian School at the mountain's base and climbs 3,249 feet (990 meters) up Southgate Road to the summit. The race is held in the autumn and draws around 1,000 masochists cyclists of varying ability levels, with the start staggered into waves of about 150 riders. Prizes are awarded, including a special t-shirt for all men who finish in under 1 hour and all women who finish in under 1 hour and 20 minutes. Proceeds from the event benefit Save Mount Diablo’s land conservation efforts.