In 1936, however, a white wall of more than three million cubic yards of concrete rising 726 feet against black rock halted the river in its tracks.  Erected to prevent floods and to provide hydroelectric power, Hoover Dam turned the Colorado into a tame ditch for the last 300 miles of its course to the sea. The Colorado and its tributaries, along with the other major rivers that brought water to the Sonoran Desert, such as the Yaqui and the Mayo, became ghosts of the past, victims of the twentieth-century, carcasses of sand whose lifeblood had been diverted into cotton fields, copper mines, and vast, sprawling cities.

Human groups have shaped the flora and fauna of the Sonoran Desert, including the Colorado delta, for millennia.

Pre-Columbian America was not a "pristine natural kingdom" where "the native people were transparent in the landscape, living as natural elements of the ecosphere" [as Shetler said, 1991, p226].

The most intensive way pre-Columbian Native Americans transformed their environments was through agriculture. Archaeologists are finding evidence that so-called "Archaic" peoples were growing maize (corn) at least 3000 years ago in well-watered areas like the Tucson Basin. Then came pinto and tepary beans, gourds, squash, cotton, and a host of other plants including amaranth and devil's claw. The Cocopas cultivated panic grass in muddy sloughs along the Colorado delta.

They, like the Quechan, Mojaves, Yoemem (Yaquis), and Yoremem (mayos), practiced flood-plain-recession agriculture, planting their crops as flood waters receded. The Hohokam and their successors, the Akimel O'odham (Upper Pimas), on the other hand, dug canals to diver water from Sonoran Desert rivers onto their fields. Hohokam canal systems along the Salt and Gila rivers snaked across the desert floor for nearly 100 miles (160 km) in the Florence area and for 125 to 315 miles (200-500 km) in the Phoenix Basin. Hohokam farmers did not use all sections of these canal systems at any one time. Nonetheless, they still irrigated between 30,000 and 60, 000 acres (12,000-24,000 hectares) in the Phoenix Basin alone.

Hohokam farmers also constructed ditches and brush weirs along alluvial fans to diver runoff onto their fields after summer rains. This form of agriculture, sometimes called ak-chin among Tonoho O'odham in southern Arizona and temporal among mestizos (people of mixed Hispanic and Indian ancestry) in rural Sonora, is still being practiced today. North of Tucson, however, the Hohokam developed an enormously labor-intensive type of agriculture that did not survive into the historic period.

Archaeologist Paul and Suzanne Fish and their colleagues at the Arizona State Museum discovered more than 42,000 rock piles in association with contour terraces and checkdams on the western slopes of the Tortilla Mountains. They also found huge roasting pits containing charred fragments of agave. The rock piles protected young agave plants form predation by rodents and conserved moisture by reducing evaporation around their bases. During the twelfth and thirteenth centuries, more than 100,000 agaves may have been simultaneously growing in these rock pile fields.

In the winter of 1358-59 AD, a massive flood roared down the Salt and Verde rivers, washing out the canals and washing away fields in the Salt River Valley. The flood was followed by two decades of drought and more floods in the early 1380's. Hohokam communities along the Salt may have never recovered from those climatic changes.