Groundwater Information Center
Wells monitored by the Department of Water Resources and cooperating agencies are identified according to the State Well Numbering system. The numbering system is based on the publicland grid, and includes the township, range, and section in which the well is located. Each section is further subdivided into sixteen 40-acre tracts, which are assigned a letter designation as shown in the figure below. Within each 40-acre tract, wells are numbered sequentially. The final letter of the State Well Number refers to the base line and meridian of the public land grid in which the well lies. "M" refers to the Mount Diablo base line and meridian; "S" refers to the San Bernardino base line and meridian; "H" refers to the Humboldt base line and meridian.
For additional information, click here DWR Water Fact Sheet Numbering Wells in California (PDF 35KB).