by Pileated

Created on: April 18, 2008   Last Updated: December 04, 2008

The City of Phoenix and the surrounding valley is a reflection geologic evolution and a blending of diverse human cultures. Few would believe that this arid valley hundreds of miles from the ocean was once a sea much closer to the equator. The Salt River Valley has experienced numerous different human cultures that combine to produce the rich and diverse array of cultures we see today.

Two hundred to three hundred million years ago, the Phoenix valley and most of the southwest consisted of a large marine shallow sea. It seems difficult to imagine today, but the tectonic plate upon which Phoenix sits was once below sea level and approximately 14 degrees from the equator. Lime depositions from the accumulation of shell fish and sand within this shallow sea formed underwater limestone and sandstone formations. As the tectonic plate moved, they collided with other plates, causing an uplifting of the land area that is now Arizona. The plates moved progressively northward. The vast sea that covered most of the western states was transformed into vast areas of salt marshes, and mud flats. Sandy beaches and estuary sand deposits, now above sea level, were blown by the wind to form sand dunes. Progressively, as the land mass continued to move northward and rise, climates changed becoming drier, mountains formed along fault lines, eventually creating the flat arid Salt River valley and surrounding mountains that we see today.

Prehistoric humans first entered the Salt River Valley about 40,000 years ago. They were migratory people that followed herds of game. It is believed that the first permanent human occupants arrived about 2,500 years ago. They farmed the valley, digging canals from the Salt River to irrigate their crops. Water was more plentiful then and the native people were able of farm most of the valley. Then, in the 1400s, they disappeared leaving only empty structures and the irrigation canals as evidence that they once existed. Other Native Americans eventually moved in, found the empty dwellings of their predecessors and named them "Hohokam", or "those who vanished".

Roughly 100-200 years later, in 1521, the early Spanish claimed the area for Spain and named the land Arizona, which described the dry desert they found. In the 1600's, small Spanish communities established. But in 1680 Native Americans temporarily drove the Spanish out of Arizona. Eventually, Spanish settlements re-established throughout Arizona. When Mexico separated from Spain and became an

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