The Gila and Salt River Meridian is the principal meridian that governs all land surveys in the state of Arizona. First monumented by John R. Bartlett in 1851, the initial point lies on the south side of the Gila River at 33°22' 37.82733"N latitude, 112°18' 21.99931"W longitude on a natural landmark known as Monument Hill in Avondale, Arizona approximately 14 miles southwest of downtown Phoenix. Baseline Road is an east-west arterial road in the Phoenix metropolitan area that coincides with the controlling base line for the Gila-Salt River survey. Ranges were run both east and west of the Gila-Salt River Meridian. Survey townships were run both north and south of Baseline Road.
