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Shortly after the birth of Christ, an indigenous race started to inhabit the Sonoran desert in southern Arizona halfway between present-day Phoenix and Tucson. Nobody really knows who they were, where they came from or what happened to them. History calls them the Hohokam. Anthropologists prefer a more generic term – ancient Sonoran desert people. Starting out as hunters and gatherers, they quickly advanced beyond that. Over the course of the next 10+ centuries, on the banks of the Gila River, they developed a thriving culture with sophisticated knowledge of agriculture, architecture and astronomy. They achieved all this despite having no tools, no working animals and no livestock. They never knew about the wheel and they had no written language. Then, in the space of one or two generations, they were gone. We know all this because of what they left behind at the Casa Grande Ruins National Monument.
The high point of this ancient Sonoran culture was the construction of a large central building, which Spanish missionaries named “Casa Grande” over 250 years after it was abandoned. Sixty feet square and four stories high, nobody really knows what it was used for. It was built with a substance called “caliche” (cuh-LEE-chee). Hard clay under the desert floor was ground up and mixed with water to create a sticky mud that could be molded like Play-Doh and dried as hard as rock. This was the main construction material used for everything. Casa Grande contained an estimated 3,000 tons of caliche, all hand molded in two foot layers built on top of one another without scaffolding or tools. Floors and internal supports were built with pine and fir logs brought from 50 miles away and imbedded in the wet caliche. Fifty years after its completion around 1350, the Sonoran culture fell apart. For four centuries after it was abandoned, Casa Grande stood mute, ravaged by weather, vandals and souvenir hunters. You can still see graffitti carved into the walls by stagecoach passengers and cowboys. The U.S. Government began preservation efforts in 1891. It became a National Monument in 1918. The protective roof was built in 1932. Preservation efforts are ongoing and have successfully maintained the ruins in their 1891 state.
The achievements of this long gone culture were astounding. The Casa Grande is an obvious one but there were many more. Using only pointed sticks, they dug hundreds of miles of irrigation canals to bring water from the Gila River into the desert. This created an oasis of almost 1,000 square miles of fertile crop land in which they grew corn, beans, squash, tobacco and cotton. Artisans created pots, jewelry and baskets with intricate artwork, some of which have been found in the area. Trade flourished down into Mexico and all the way to the Pacific coast. But, in my humble opinion, the most fascinating part of the culture was their interest in astronomy. The walls of the Casa Grande have tales to tell about that.
The Sonoran culture tracked major astronomical events to guide their planning, activities and religious ceremonies. Key among them were summer/winter solstice and the spring/fall equinox. They did this through a series of “alignments”, which were holes or channels constructed in the Casa Grande walls. On the day of those celestial events sunlight would shine directly through those alignments. There was one other event they tracked – the 18.6 year lunar nodal period. This is a cycle of declination (angle) changes of the moon’s orbit around the earth. Throughout ancient history, it was used for ceremonial religious observances, particularly among pagan religions. However, the lunar nodal cycle is also a key component of eclipse prediction. This cycle is followed at many ancient sites, including Stonehenge. Could the ancient Sonoran desert people predict solar and lunar eclipses? Your guess is as good as anybody’s.
This picture is the west wall of Casa Grande. It is the best preserved and the most interesting. The round portal under the gold arrow was the alignment for the summer solstice – the longest day of the year. The square portal under the blue arrow was the alignment for the peak of the lunar nodal period, which astronmers call the lunar standstill. Other alignments are have been identified but are not readily visible and some are just gone, eroded away with the walls.
Casa Grande was completed around 1350. By 1400, the Sonoran culture was in a steep decline from which it couldn’t recover. Theories abound as to why. There’s no evidence of warfare or conquest. The conquistadors were still two centuries away. One version that seems credible is supported by geological data. In the late 1300’s, the Gila River Valley experienced flooding on a monumental scale. This deepened the river channel to the point where no water could flow into the irrigation canals unless they were rebuilt. This flooding was followed by years of drought, which lowered the water level even more. The desert began to reclaim its land. Unable to sustain themselves, the Sonoran people began to leave. Within 30-40 years, this 1,000 year culture was gone. They most likely dispersed to different areas in smaller groups and formed the genealogical base of today’s southwest tribes.
This National Park Service diagram shows the extent of the Sonoran irrigation system. There were hundreds of miles of canals. Parts of it are still in use today. This entire system was dug with pointed sticks, the most sophisticated tool they ever developed.
At its peak, the Sonoran culture had several thousand people living in compounds over hundreds of square miles on both sides of the Gila River. The Casa Grande was one of these compounds, centered on a one acre site surrounded by seven foot walls. It was just one compound out of many, although it was the biggest. This culture pre-dated other Native American cultures and lived in peace. Today, the Pima, Hopi and Zuni nations consider this culture to be their ancestors
In this 1964 photo, an archaeologist is standing in an excavated section of a Sonoran culture irrigation canal. They were built with steps for gravity flow and lined with caliche. Not bad for pointed sticks.
Casa Grande Ruins National Monument is located in Coolidge, AZ – about 20 miles due north from Exit 211 on I-10. It’s small. You can see the entire thing in 60-90 minutes. Nevertheless, it is one jaw dropping discovery after another. If you get out to Arizona, make sure you take the time to visit.
Cheers … Boris and Natasha