Archaeological Discoveries Reveal Value of Santa Cruz River in Prehistory

Return to Fall 2017 AWR

by Sam Potteiger, WRRC Student Outreach Assistant

sunset sites

When people think of Tucson, Arizona, they typically think of our scorching hot summers or the highly-regarded University of Arizona. However, Tucson can also be associated with a rich history dating back to the earliest Southwest Paleoindians. In fact, the Santa Cruz River Valley is one of North America’s longest inhabited regions. The earliest evidence of human occupation dates back 12,000 years, prior to the existence of the Clovis peoples. The Clovis culture is generally regarded by archaeologists to be the ancestors of most Native American tribes. Around 4,000 prehistoric sites have been identified in the Santa Cruz watershed and exciting new discoveries continue to be made. These discoveries could potentially alter how archaeologists view the technological progression of the region’s earliest inhabitants.

The Tucson area is known to have been an important agricultural hub for ancient Native American tribes, and the Santa Cruz River floodplain contains the earliest recorded instances of irrigation in the Southwest. Evidence suggests that it was farmed extensively in the Early Agricultural Period, roughly 2,000 - 3,000 years ago.

Nearly two years ago, construction began to connect West Sunset Road with I-10 and North Silverbell Road. A worker excavating at the site of a planned bridge made an astounding discovery. As Patrick McNamara described in the Tucson Daily Star, the excavator, Dan Arnit, gently scratched away at the dirt, revealing what looked to him to be a heel. He slowly uncovered the rest of the print to reveal the toes and eventually a set of human footprints. The prints belonged to ancient farmers who had tended to fields along the Santa Cruz River, which is thought to have existed up to a mile away from its current location. The rest of the site was excavated to reveal an ancient agricultural field with multiple sets of footprints, field boundaries, planting pits, and irrigation canals.

According to McNamara, these findings were more than just a glimpse into history for Jason Bahe, Pima County Department of Transportation project manager. For Native Americans, the site represents a medium to establish a relationship with their ancestry. Bahe, of Navajo descent, brought his daughter to the site, which provides a 3,000-year-old snapshot of the life of these early farmers. The discovery made there is the earliest evidence of the use of irrigation in the Santa Cruz Valley.

Sunset Road acts as a lens into a transitional period for the Santa Cruz peoples. During this period, societies moved towards larger permanent settlements and increased prosperity. At settlements along the Santa Cruz River, people grew corn, squash, and beans to supplement existing hunting and trapping. Eventually, multiple family groups began to settle together. Populations boomed, and settlements expanded into villages and harnessed resources from a greater area. Other aspects of culture advanced as a result of this expanded wealth. At the site at Sunset Road, the technological advances of the early Santa Cruz societies can be seen. There is evidence of trade with neighboring tribes and even with peoples as far as Mesoamerica. Scholars have posited that as culture flourished and the Early Agricultural Period came to a close, distinct identities began to appear among the Paleoindians. Archaeologists point to this time as the moment when a culture formed that could distinctly be labeled Hohokam. The Hohokam method of irrigation was unparalleled anywhere else in the Southwest. The canals the Paleoindians and early Hohokam built in the Santa Cruz Valley prefigured the complex networks that the Hohokam built in Central Arizona nearly 2,000 years later.

The Hohokam canals built in the Mesa area as long ago as 600 CE are still considered engineering marvels. The irrigation system is simple, but the true marvel of its creation is its monumental scale. The trenches were dug 12 feet deep and diverted water from the Salt and Gila Rivers. The main channels, which drew water directly from the river, were wide at their mouths and tapered as secondary branches drew water from the main channel. By reducing the channel size as the flow decreased, the Hohokam were able to sustain a steady flow rate throughout the different branches of the system. The steady flow rates ensured that the irrigation system would function correctly. If the flows were too fast, sediment would be brought into the trenches and hinder flow. Water that was too slow might not reach the fields at the ends of the branching canals. By meticulously crafting their canals, the Hohokam were able to support an estimated population of 80,000 through the irrigation of more than 100,000 acres of land between 1,100 CE and 1,450 CE. The much earlier sites on the Santa Cruz River indicate that the Hohokam had perfected their irrigation techniques over the course of several millennia.

Archaeological discoveries provide evidence that the Santa Cruz River acted as the heart of all life in the Tucson area for thousands of years. In historic times, Europeans encountered Native American societies built around the bounty the river provided, although by that time the ancient irrigation canals had long since been abandoned and lost under layers of sediment. Father Eusebio Kino, a Spanish missionary, was the first European to set foot into the Santa Cruz Valley. He founded Mission San José de Tumacácori in 1691, and over the course of the next century, the Spanish established other missions in the region where orchards and gardens were irrigated by diverting water from the river.

At the time of American settlement in the 19th Century, the river still had a beneficent aspect. Julius Froebel, German journalist and world-traveler, was astounded by the natural beauty of the river during his visit in the mid-1800s. “The banks of the river, and the valley itself, are covered with poplars and willows, ash trees and plantains, oaks and walnut trees.” Froebel was enchanted by the stark contrast between the bountiful river valley and the harsh surrounding desert. The meadows and grasses of the river valley also supported a diverse range of wildlife. Gold-hungry settlers rushing to California mentioned catching turkeys and hunting pronghorn along the riverbanks. The history of the Santa Cruz River describes a river of plenty. For early inhabitants, it was the source of life in an otherwise challenging environment. The Hohokam constructed sophisticated canal systems to divert its water and support a thriving community. Long after the times of the Hohokam, European settlers saw how the river breathed life into the desert. Although the river may not flow in Tucson anymore, discoveries like those made at Sunset Road act as reminders of the Santa Cruz as a living river.