Hohokam Canals: Prehistoric Engineering
Nobody in the New World moved water more efficiently than the Hohokam Indians. The canals they built to sustain their large and complex agricultural society are still considered an engineering marvel.
The Hohokam people lived around the Mesa area of Central Arizona for almost 1,500 years. They appeared around 1 CE and disappeared about 1450. Their agricultural society flourished around the middle Gila River and Salt River. These sources allowed them to farm beans, squash, corn, and cotton. The Hohokam were skilled agrarians, managing the soil to replace lost nutrients. Additional food came from extensive gathering of wild plants, dry farming agave, and hunting deer and small animals.
Around 600 CE the Hohokam people began to construct irrigation canals. They excavated trenches up to 12 feet deep by hand, using a digging stick. The trenches drew off Salt River water and fanned into a network of smaller canals that brought a steady supply of water to fields. Between 1100 CE and 1450 CE, 500 miles of canals irrigated 110,000 acres. The food produced by this advanced irrigation system is believed to have supported up to 80,000 people—the highest population density in the prehistoric Southwest.
Hohokam canals possessed remarkable features that still stand as examples of engineering genius. First, they were wide at the mouth and carefully tapered, getting smaller as secondary branches drew water from the main channel. By shrinking the channel size as the flow decreases, the Hohokam were able to stabilize flow rate. A steady flow rate is key to creating a functional irrigation system. Water that moves too fast carries sand and silt that will eventually block the canal. Water that moves too slowly will not reach its destination. Second, canals covered miles of territory on a relatively steady grade, avoiding hills and valleys that could affect flow rate.
Though the Hohokam people are most celebrated for their canals, they made fire-hardened pottery and figures and jewelry from shell and turquoise. They built increasingly elaborate structures, such as the Big House in Casa Grande Ruins National Monument. The society also constructed large earthen platform mounds of unconfirmed purpose. Located in the center of villages, the mounds may have been used for housing elite members of the society or for ceremonial activities. Hohokam rock art, in the form of petroglyphs and pictographs, is found in mountain ranges and rocky areas throughout the region.
The Hohokam disappeared from their villages near the Salt and Gila Rivers in 1450 CE. Their descendants survive as members of the Tohono O’odham Nation.
The three centuries leading up to the Hohokam's disappearance around 1450 CE had been a period of migration and social change, with old settlements and prestigious structures constructed in the Salt and Gila Basins being abandoned. The reasons for this mass abandonment remain unknown to this day. Perhaps disease or war threatened the population. Perhaps flood damaged the canal infrastructure, or drought brought hardship. There is also speculation that a great leader died, causing the people to drift away and migrate. We may never discover why the Hohokam decided to leave the area they had lived in for almost 1,500 years. But their descendants live on as members of the Tohono O’odham Nation.