Did you know that the initial survey point for the State of Arizona, where the Base Line and Principal Meridian meet is in Avondale?  This initial point, located on a hill rising to the east of Phoenix International Raceway, at the confluence of the Salt and Gila Rivers, serves as the point of reference for most of the public land surveys conducted in Arizona and as the basis for patents issued by the US government.

1851--Monument Hill was built by the US Boundary Commission, while making a reconnaissance survey for the United States-Mexico boundary under the 1848, Treaty of Guadalupe-Hildago.  

1865--John A. Clark, Surveyor General for New Mexico and Arizona selected Monument Hill as the initial point for surveys in Arizona.

1867--First survey from the initial point was conducted covering 36 miles in five days.

1984--Bureau of Land Management Cadastral Survey team, Arizona State Lands Department, Salt River Project, Gila River Indian Community, Arizona Professional Land Surveyors Association (APLS) and Bureau of Reclamation initiate a project to refurbish the monument.

2002--Monument received status on the National Register of Historic Places.

2006--Phoenix College Survey students, APLS, and the Arizona Cadastral Survey team restore the monument.

History provided by the Arizona State Office of the Bureau of Land Management.

Monument Hill climbs to 1,158 feet (352.96 meters) above sea level and is located at latitude - longitude coordinates (also called lat - long coordinates or GPS coordinates) of N 33.376988 and W -112.306266.

Coordinates provided by MountainZone.com

Below Monument Hill, is the Base & Meridian Wildlife Area.  The approximately 198-acre Base and Meridian (B&M) Wildlife Area is on the north bank of the Gila River at the confluence with the Salt River with the Gila River and contains primarily all riparian habitat in and along the river and its associated upland banks.

Many specifies of bird, fowl, mammal and fish can be found in the Wildlife area.  The B&M area also contains riparian vegetation including cottonwood, willow, salt cedar, seep willow, desert broom and mesquite trees.

The area is so important to Arizona and the preservation of its natural habitat, that the Audubon Society and BirdLife International recently designated the area as an Important Bird Area.

Each year, the Tres Rios Nature Festival is held at the B&M area to celebrate the natural beauty, wildlife habitat and history of the Salt, Gila and Agua Fria Rivers.