Casa Grande: the USA’s first archaeological reserve

Submitted by Sammy Smith (sammy@thesga.org)

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View from walkway exiting visitor center, 2009.

Between the modern cities of Tucson and Phoenix are the famous crumbling prehispanic architecture now central to the Casa Grande Ruins National Monument. This archaeological zone became the USA’s first archaeological reserve in 1892 by order of President Benjamin Harrison, and was declared a National Monument in 1918 by President Woodrow Wilson.

As visitors wander forth from the park’s air-conditioned museum, their eyes are, not surprisingly, drawn to the towering multi-story ruin beneath the large flat roof that was built to protect it in the early 1930s.

But, this monumental architecture was only a small part of the footprint of this amazing Sonoran desert community.

Irrigated fields and homes were scattered for miles on a tongue of land between the Gila River, to the north, and McClellan Wash to the southwest. The canals drew water from the Gila River, upstream to the east-northeast. The park area is within the McClellan Wash drainage, but the area is fairly flat, a plain with low vegetation that remains after years of ranching.

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Cut-away model displayed in visitor center, showing walls and beams in Casa Grande ruin, 2009. Note that the lowest doorways were above the exterior ground surface, necessitating entry via ladders.

The largest ruin, under the roof, is made of local subsoils called caliche, processed into mud, then dried in place on the structure. Builders imported wooden beams from higher, forested elevations at least fifty miles away. The beams support the floors, and allow this building to be built so tall. It also has shaped wood lintels above the doorways. The footprint of the Casa Grande ruin is about 59×42 feet. It is known as a platform mound, because it was built atop an artificial terrace that was up to about 4 feet high.

The interior walls had a smoothed clay surface that was treated like plaster. Probably, the exterior also had a smoothed surface, but none of it survives. The desert peoples who designed and built Casa Grande most likely planned to collect whatever rainfall ran off the building’s flat roofs.

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Plan map of Compound A, Plate 6 in Fewke’s 1912 report, showing the exterior wall and interior structures. North is to the right, and the large Casa Grande ruin is the black-walled structure northwest of the middle of the compound. The diagonal line is an old stagecoach road that went between the railroad station at the town of Casa Grande, about twenty miles to the west, and the town of Florence about ten miles to the east. The Southern Pacific Railroad’s line was completed in the winter of 1889–1880.

The Casa Grande building had a wall approximately 420×230 feet surrounding it and several residences. This walled area is called Compound A. Jesse Fewkes, who worked there in the early 1900s, estimated that Compound A’s wall was originally about 7 feet tall. The wall also had a ditch along its exterior.

Construction of Casa Grande, and also the walls and residences of other structures in this community, would have required “mining” caliche from below the surface, crushing it to the proper granularity, and mixing with water to use as a construction material. The main ruin shows horizontal layers that would have been constructed, then left to dry for several days before adding to the wall.

Researchers estimate that the large Casa Grande ruin would have required about 1545 cubic yards of caliche soil. No borrow pits of that size have been found near the ruin, so we assume that multiple deposits of caliche soil were extracted and processed to make the walls. Since wetting the caliche deposits would have made them easier to extract, perhaps some of the caliche came from construction of nearby irrigation canals.

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Plate 4 in Fewke’s 1912 report, showing an aerial view of prehispanic architectural remains scattered near the Casa Grande ruin (lower left). Photograph appears to have been enhanced to emphasize structures and compound walls.

Within and outside the compound wall surrounding the Casa Grande ruin were residential compounds, also with surrounding walls. Communities may have clustered residences, with little space among the buildings. Other communities are like this one, with the residences scattered at some distance from each other. Researcher Jesse Fewkes (1912, p. 86) noted:

The limits of this prehistoric settlement are difficult to determine. The whole plain was dotted at intervals with houses similar to those of Casa Grande, from the point where the Gila leaves the mountains to its junction with its largest tributary, the Salt, the valley of which is also marked by the remains of many similar prehistoric buildings. Not all the mounds…, however, contain ruins of great buildings; many walled structures, formerly homes of the inhabitants, have fallen, leaving but slight traces of their existence—no vestiges of walls above the surface of the ground, merely broken metates or fragments of pottery scattered over a limited area.

In historic times, the first stabilization activities at Casa Grande took place in 1891–1892, which significantly slowed deterioration of the big ruin. Ruins of smaller buildings around the monumental architecture have been covered in a more durable material to enhance preservation.

Archaeologists working in southwestern North America can observe people using construction techniques similar to the ones that builders used to make Casa Grande, because some people still know and use them. That’s not true in the Southeast—here in Georgia. Still, are there lessons to be learned from the construction techniques used in building and maintaining the Casa Grande buildings that are informative in considering construction methods for ancient buildings that once stood at Kolomoki, the Leake site, or Etowah, for example?

NOTE: In January 2010, the Society for American Archaeology sent a letter to the Ruins’ superintendent supporting expansion of the park to include more ruins along the Gila River, noting:

Addition of these ruins to the Monument would greatly add to its value as an interpretive center of Hohokam culture, bring more heritage tourism into local communities, and protect these irreplaceable ruins for future generations.

References

Del Bono, Elisa Maria. 1999. Characterization and Analysis of the Caliche Walls of the Great House, Casa Grande Ruins National Monument, Coolidge, Arizona. Unpublished MS thesis. Philadelphia, University of Pennsylvania.

Fewkes, J. Walter. 1912. “Casa Grande, Arizona,” in Twenty-Eighth Annual Report of the Bureau of American Ethnology to the Secretary of the Smithsonian Institution: 1906–1907, pp. 25–179. Washington, D.C.: Government Printing Office.

Both are available as PDFs from the Internet Archive. The NPS website includes a link to a 1992 history called “Casa Grande Ruins National Monument, Arizona: A Centennial History of the First Prehistoric Reserve, 1892–1992, An Administrative History” by A. Berle Clemensen, including a synopsis of Hohokam archaeology and many pictures and drawings.

Where to find it