Mount Diablo, sacred to Native Americans who lived and worshipped there for over 5,000 years became a critical reference point for Spanish explorers in the 18th century, and American trappers and early California settlers in the 19th. In 1851 Colonel Leander Ransome established the crossing of the Mount Diablo Base and meridian lines from which most of California and Nevada are surveyed.

California Registered Historical Landmark No. 905

Plaque placed by the State Department of Parks and Recreation in cooperation with the San Ramon Valley Historical Society, April 23, 1978.

Marker is on Summit Road, on the right when traveling north.

Courtesy hmdb.org

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