Mount Diablo State Park

Mount Diablo is sacred to many Native Americans and was considered the point of creation by the Miwok Indians. Today, evidence of Native American presence on the mountain can be seen at Rock City and elsewhere in the park, with grinding holes in the stone showing where the Miwok once smashed acorns and other nuts into powder.

In 1851 the mountain played a vital role in the initial survey of the Western United States when Colonel Leander Ransom chose the south peak of the mountain as his starting point. Subsequent surveys in much of California, Oregon and Nevada were located with respect to this point.

Protection of the mountain began in 1931 when the state acquired land around the peak and created a park. The Civilian Conservation Corps made many improvements to the area during the 1930s, including roads, trails, ranger residences, maintenance buildings, campgrounds and picnic facilities. The CCC also constructed the Summit Visitor Center using stone quarried from the mountain, and visitors today can view shells and other fossils embedded in this natural building material.

On December 8, 1941, the day after the attack on Pearl Harbor, the beacon on Mt. Diablo was turned off to prevent enemy aircraft from using the light to establish their location. On December 7, 1964, there was a ceremony held at the visitor's center on Mt. Diablo which included jets flying overhead and local dignitaries speaking. The purpose was to once again turn on the beacon. On cue, Admiral Chester W. Nimitz, the United States' last surviving fleet admiral, flipped the switch turning on the beacon. Ever since and only once a year, the beacon is on at night on December 7.

In 1971 a push to expand the park and to protect the mountain from development began with the formation of the Save Mount Diablo organization. Since that time the park has increased in size from 6,788 acres (27 km²) to approximately 20,000 acres (80 km²). In addition, there are more than 80,000 acres (300 km²) surrounding the park that are now protected by a series of preserves, parks, and open spaces stretching from Suisun Bay all the way south to Interstate 580 near Livermore.

As a geologic feature, Mount Diablo is relatively young, having been formed about one million years ago. The mountain lies between converging earthquake faults and was created by uplift that continues today, pushing the mountain higher by 3-5mm each year. The mountain's summit and core are composed of greenstone, an igneous rock that is 90-190 million years old, while the mountain's slopes include large sandstone deposits, formed in ancient seabeds and swamps and filled with deposits of fossils.

Commonly seen mammals include coyote, bobcat, black-tailed deer, California ground squirrels, fox squirrels and grey foxes. Mountain lions, peregrine falcon, ringtail cats, badgers, San Joaquin kit fox, roadrunners, tiger salamanders, and burrowing owls are also present but rarely seen. During the winter bald eagles and golden eagles can be found in the park.

Snakes in the area include the Northern Pacific rattlesnake, and visitors should be cautious to avoid startling one, particularly in rocky areas where the snakes often warm themselves. Visitors should also be cautious to avoid poison oak, fleas, ticks and mosquitoes.

In spring, the upper parts of the mountain see a rainbow of wildflowers: purple lupines, pink thistles, red larkspurs, orange California poppies, and yellow goldenbushes scattered around the trails.

Temperatures vary greatly with elevation; snow can often be found at the summit during winter, but is extremely rare at the lowest elevations. The climate data below is from the National Weather Service station at Mount Diablo Junction, which is at an elevation of 2,170 feet (660 meters), far below the 3,849 foot (1,173 meter) summit.

Summer is the dry season, when the landscape is a pale brown of dry grass, scattered with green trees. At this time of year, hikers and bikers can be confident they won't get rained on. Winter brings rain, and in rainier years, the mountain is a vibrant green through early spring.

The park is filled with trails and fire roads that interconnect, providing a practically infinite number of possible routes. Carry extra water when hiking as it is easy to get lost, and especially on the higher slopes the trails can be strenuous so plan extra time. Many hikers will want to hike to the summit, but be aware that since there is a road to the mountain's top, traffic and crowds can make that trek less rewarding. An alternate option is to hike in the northern part of the park around Mitchell Canyon, which contains fewer people, or to trek to the North Peak, which at 3,557 feet (1,084 meters) is only slightly less high than the 3,849 foot (1,173 meter) summit, but since it lacks crowds it is a more peaceful spot to enjoy the view.

• Annual tarantula migration. 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. 
• Diablo Challenge. 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. (updated Jan 2017)

There are no hotels inside the park, but neighboring communities such as Walnut Creek and Concord offer plenty of options.

The park offers three family campgrounds that can accommodate tents and RVs up to twenty feet (six meters) in length. There are also five group camps catering to groups of 20-50 people. Note that the park gates close at sunset, so campers are locked into the park for the night. Campground quiet hours are from 10PM-6AM, and generators may not be used from 8PM-10AM. Checkout time is noon. Campground reservations are recommended but generally only necessary on busy holiday weekends.

• Junction Campground. 6 sites, first-come, first-served only. $30 per night. (updated Jan 2017)
• 🌍 Juniper Campground. 36 sites. Showers are available at no additional charge. $30 per night. (updated Jan 2017)
• 🌍 Live Oak Campground. 22 sites. Showers are available at no additional charge. $30 per night. (updated Jan 2017)

Camping is permitted only in designated campgrounds.

Remember that Mt. Diablo is largely wild — there are rattlesnakes, mountain lions, and black widow spiders. Be careful to avoid poison oak. Ticks are present in the park, some of which may carry lyme disease, so exercise appropriate cautions.