On March 22, 1912 the City of La Mesa Board of Trustees adopted Ordinance No. 8 establishing a city base plane of reference for survey elevations and fixing the elevation of the primal bench mark. Elevation surveys are necessary when constructing a building to make sure that the building will not flood when it rains. They are also necessary to make sure that sewer pipes flow properly. Establishing a base plan of reference ensured that adjacent projects could be linked together and surveyors would be speaking the same language with respect to elevation. Most of La Mesa is between 500 and 600 feet above mean sea level.
Benchmarks are located around the City. They are small bronze monuments or disks that form a network of elevations. Each is labeled with an elevation based on the reference plane so that a surveyors could find a bench mark near to a project for their use.
The Primal Benchmark was a bronze tablet set in the wall of the brick building at the southwest corner of Lookout and Railroad Avenues now known as La Mesa Boulevard and Nebo Drive. Its elevation was five hundred forty and six one-hundredths (546.06) feet above city base or mean sea level.
Unfortunately, over time, the primal bench mark was lost.
On October 22, 2012 in honor of La Mesa’s 100th birthday a new Centennial Benchmark was set at the Southeast corner of the intersection of La Mesa Boulevard and Nebo Drive (North of the Pacific Southwest Railway Museum). And on October 23, 2012 the City Council adopted an ordinance establishing and fixing the elevation of the Centennial Benchmark.