Public Land Survey System
Mount Diablo Meridian
The Initial Point of the Mount Diablo principal meridian and base line was established in 1851 atop Mount Diablo which rises above the surrounding valley, east of the San Francisco Bay area. This point was chosen from which to survey most of the northern part of California, and all of the state of Nevada, due to its excellent vantage over the surrounding areas for surveyors. The meridian—in 121°54.845’W longitude—runs from a point on the California coast, south of the San Francisco Bay at its southern terminus to the California-Oregon state border at its northern terminus. The base line—in 37°52’54”N latitude—runs both east and west from the initial point, terminating at the Pacific Ocean in the west and the eastern border of Nevada in the east. The initial point for the Mount Diablo meridian has the most elaborate commemorative architecture of all the initial points in the U.S. with a small museum and tower structure atop Mount Diablo housing the marker.