The largest and closest is North Peak, the other half of the double pyramid, which is nearly as high in elevation at 3,557 feet (1,084 m), and is about one mile (1.6 kilometers) northeast of the main summit.

These include 38 preserves, such as nearby city open spaces, regional parks, and watersheds, which are buffered in some areas with private lands that have been protected by conservation easements.

Its looming presence over much of the Bay Area, delta, and Central Valley, and good visibility even from the Mother Lode, all key regions during the gold rush and early statehood, made it an important landmark for mapping and navigation.

According to Indian historian Bev Ortiz and Save Mount Diablo:[14] "The name Kahwookum was made up in 1866 — with no real Native American connection — referred to the California Legislature's Committee on Public Morals, and tabled.

[15] The conventional view is that the peak derives its name from the reaction of Spanish soldiers to the 1805 escape of several Chupcan Native Americans in a willow thicket some 7 miles north of the mountain.

Thomas Starr King, a Unitarian clergyman, abolitionist, Republican, Yosemite advocate, cultural Unionist, and California's leading intellectual.

[21] In 2005 Arthur Mijares, from the neighboring town of Oakley, petitioned the federal government to change the name of the mountain,[22] claiming it offended his Christian beliefs.

Finally Mijares proposed Mount Reagan,[23] but the board rejected it on the grounds that a person must be deceased for five years to have a geographic landmark named after them.

Significantly, botanist Mary Leolin Bowerman (1908–2005), founder of the Save Mount Diablo non-profit in 1971, published her Ph.D. dissertation in 1936 at the University of California, Berkeley.

Soon after Earth Day in 1971, the nonprofit organization "Save Mount Diablo"[27] was created by co-founders Mary Bowerman and Art Bonwell, barely ahead of real estate developers.

It also adjoins protected areas owned or controlled by local cities such as the Borges Ranch Historic Farm, the Concord Naval Weapons Station (now in the process of being converted to non military use), Indian Valley, Shell Ridge Open Space and Lime Ridge Open Spaces near the city of Walnut Creek, and east to the Los Vaqueros Reservoir watershed.

There are unprotected areas in Arroyo del Cerro, Curry Canyon, the Marsh creek region, and on the northern slopes of North Peak, and in a number of inholdings surrounded by preserve land.

Other large projects are proposed in the northern Black Diamond Mines and Los Medanos foothills, at the Concord Naval Weapons Station, and near Marsh Creek State Park.

Large-scale development of other private parcels is restricted by city and county urban limit lines, by lack of water, excessive slope, and sensitive resources including rare species.

The upper portion of the mountain is made up of volcanic and sedimentary deposits of what once was one or more island arcs of the Farallon Plate dating back to the Jurassic and Cretaceous periods, between 90 and 190 million years ago.

The summit area of Mount Diablo is made up of deposits of gray sandstone, graywacke, chert, oceanic volcanic basalts (greenstone) and a minor amount of shale.

In the western foothills of the mountain there are large deposits of younger sandstone rocks also rich in seashells, severely tilted and in places forming dramatic ridgelines.

(It is best to learn the characteristics of this shrub and its toxin before hiking on narrow trails through brush and to be aware that it can be bare of leaves (but toxic to contact) in the winter.)

The park and nearby Black Diamond Mines Regional Preserve mark the northern extreme of the range of Coulter pine (Pinus coulteri).

Less common wildlife species include the reintroduced peregrine falcon, ringtail cats, and to the east American badgers, San Joaquin kit fox, roadrunners, California tiger salamander, and burrowing owls.

In modern times Mount Diablo art has been most strongly represented in plein aire painting, especially the group Artists for Action, and photography.

Representative work includes books and articles by classical writers such as William Brewer, Richard Henry Dana Jr., Alexandre Dumas, père, Bret Harte, and the Reverend Thomas Starr King, and modern ones such as Mark Allen Cunningham.

Early painters include Thomas Almond Ayres, Eugene Camerer, W. H. Dougal, Eduard Hildebrandt, Charles Hittell, Edward Jump, William Keith, John Ross Key, Charles Koppel, Edward Lehman, Pascal Loomis, Henry Miller, Joseph Warren Revere, through Clarkson Dye and others, to modern painters such as Robert Becker, Frank J. Bette, Ruth Breve, Betty Boggess Lathrap, Paul Carey, Bob Chapla, Mary Lou Correia, Ellen Curtis, Pam Della, Susan Dennis, Warren Dreher, John Finger, Pam Glover, JoAnn Hanna, Peg Humphreys, Don Irwin, Jeanne Kapp, Geri Keary, Chris Kent, Paul Kratter, Eunice Kritscher, Fred Martin, Cathy Moloney, Shirley Nootbaar, Charlotte Panton, Greg Piatt, Kenneth Potter, Robin Purcell, Ocean Quigley, Don Reich, Mary Silverwood, Barbara Stanton, Bruce Stangeland, Marty Stanley, and even the recognized comic book painter Dan Brereton.

Photographers include Ansel Adams, Cleet Carlton, Alfred A. Hart, Scott Hein, Stephen Joseph, Don Paulson, Brad Perks, Robert Picker, Richard Rollins, David Sanger, Michael Sewell and Bob Walker.

A ceremony memorializing the attack on Pearl Harbor on December 7, 1941, is held at the Cal State East Bay Concord Campus, with some of the few remaining survivors who are present.

The summit of the mountain received around six inches (15 cm) of snow at its peak, and the access roads were closed to automobiles at the 3,000 feet (914 m) mark due to the hazardous icy conditions above.

The course record for the Mount Diablo climb currently stands at 43 minutes, 33 seconds, set on October 5, 2008, by Nate English (ZteaM) 4 days after breaking his thumb in a bike accident.

[41] He broke the 44 minutes, 58 seconds record, set in 2004 by former professional cyclist Greg Drake (Webcor Cycling Team) of Redwood City, California.

[42] The previous course record was set by former professional cyclist Mike Engleman (Coors Light Pro Cycling Team) in 1990 with a time of 45 minutes, 20 seconds.

[citation needed] As early as 1806, General Mariano Guadalupe Vallejo (July 4, 1807 – January 18, 1890) reported an encounter with a flying, spectral apparition, while engaged in military operations against the Bolgones band of the Bay Miwok tribe.