Arizona Initial Point

Monument Hill, at the base of the Sierra Estrella in Avondale, is today perhaps best known for providing cheapskate seating for those unwilling to pay admission for the Phoenix Raceway. However, its name comes from its far more important role in mapping out Arizona.

Originally, a survey monument was placed here in 1851 to mark what was the US-Mexican border. It lost this importance just two years later thanks to the Gadsden Purchase, but a new role was found for it after the Arizona Territory was created. To survey such a vast area, an initial point was needed from which to start. In 1865, the United States Geological Survey chose here due to the preexistence of a survey marker as well as its location close to the confluence of two major rivers, the Salt and Gila. Although the original monument is long gone, a concrete cross was built to commemorate the spot's importance in 1984.

From here, almost the entire state of Arizona is surveyed out, including the Phoenix and Tucson street grids. The only part not surveyed from here is part of the Navajo Reservation, which is instead surveyed from a point in New Mexico. From here, one can see how the cross lines up perfectly with Avondale Road, which serves as the meridian (line of longitude) for Arizona. Likewise, Baseline Road in Phoenix is named after its location along the same latitude as the initial point.