Pueblo Grande Platform Mound, A Labor Investment Analysis

© 1998 by James Q. Jacobs

Initial Rough Estimate of Construction Time.

Based on a rough estimate of the platform mound size of 300 x 100 x 15 feet, a volume estimate of 450,000 cubic feet was arrived at. Allowing for a diverse material core of rock and earth and diverse distances of source material, I guessed that a cubic foot of average material could be placed per person per hour. Thus, 450,000 / 8 hours per day = 56,250 person days of construction time. Therefore a 100 person crew would have to work, non-stop, for a year, six months and 16 days.

Mound Volume.

Various authors have estimated and/or directly surveyed the size of the Pueblo Grande platform mound. Their results are shown in Table 1 following.


These are sequenced by time, with the later authors last. The last three roughly concur at a size of 300 x 150 feet, the size also published at the museum interpretation. Therefore these figures are used herein. Miller's and Turney's estimates of the height include wall heights. Given their mean of 22 feet, less seven feet for walls, a mound elevation of 15 feet is arrived at. The volume is therefore 450,000 cubic feet.

Percentage of Stone.

The entire perimeter of the mound has a 3-4 feet thick stone retaining wall. This is about 9.2 percent of the volume. Additional stone walls are found in the core. It is not apparent at the site how many of these occur. From the area where they are in evidence an estimate of the percentage can be extrapolated. Also, site interpretations infer that two mounds were joined into one. This fact also adds to the amount of original exterior retaining walls. In conclusion I estimate the stone and stone walls to be 18 percent of the mound's total mass.

Amount of Stone, Earth, and Water Needed.

The total volume estimate is 450,000 cubic feet. Eighteen percent of that is 81,000 cubic feet, the amount of stone. The remaining 82 percent is earthen fill; a combination of soil, ashes, ceramics pieces, and the small stones and gravels found in the local soil. This remainder of the mass totals 369,000 cubic feet. Given that the fill material was treated as adobe, to ensure hardening, 110,700 cubic feet of water would have been added. More would have been employed in stone wall construction, in the making of calinche mortar. Therefore I have increased the water needed to 120,000 cubic feet, or about 900,000 gallons.

Sources and Distances for Materials.

Although the most obvious borrow pits are the nearby ballcourts, they predate the platform mound and are small by comparison. It is also likely that the earth from these digs was already employed in other constructs. An activity that was contemporaneous to the mound construction was canal maintenance. There is a large canal 150 m from the mound. The Salt River is 300 m from the mound. The Salt could have served as a source of stone. The canals could have provided soils. Water could have been delivered to the platform mound via a small branch canal. Therefore only 150 feet is estimated as the carry distance for the water. It is also possible that flotation was used in the procurement of rock and soil, perhaps on rafts or in canoes. But such activity is not in evidence. I therefore have calculated an average distance of 150 m for soil procurement and 300 m for stone procurement. The following person hours (PH) per cubic yard values are used in Figure 2: stone procurement, 5.3; stone moving, 0.71 per 100 ft.; earth procurement, 1.45; earth moving, 0.65 per 100 ft.; earthen adobe making and building, 2.0; water moving, 0.52 per 100 ft.

Labor Estimation.

Labor associated with procurement, moving and building the amounts of materials estimated are shown in Table 2 following.


The total labor in person hours is estimated at 284,445 just for the construction of the platform mound. This is a total of 35,556 eight hour days of actual work time. A crew of 100 persons working an entire year could complete the platform mound if they had ten days off. Additional labor was expended in the construction of rooms atop the mound and a massive adobe wall surrounding the construct.

The Significance of the Mound Construction.

The amount of time expended evidences larger towns than ever before. A system of political organization that had access to hundreds of workers must have existed. Mounds are larger works than ballcourts, and the limited number of mounds in the region relative to ballcourts indicates larger frameworks of social organization. Canal systems require canal-wide organization and coordination. System management requires interconnection and stable social relations. Community well-being is dependent on continued successful maintenance and operation of the system.

Evidence at Marana indicates that several communities centered on ballcourts became integrated into one, centered on the platform mound and a canal system. The platform mounds can be seen as evidencing a redefinition of social systems and community. Greater populations and wider integration made possible a social hierarchy and development of a more important and/or powerful class of people. Construction of rooms atop the platform mounds after 1250 and walled enclosure of the mounds reinforce the view of the platform mound as an elite space. The platform mounds are also surrounded by the most developed residential compounds, indicating the centrality of the mounds to the community. These factors indicate an important public or elite function for the mound complexes, such as center of a polity and government of a canal system. Certainly the platform mounds were connected to an important aspect of the lives of many Hohokam people. This much is plainly evidenced by the numbers required for the construction.

Comments from Readers.

Mr. Jacobs, I saw your piece on the labor estimates for the Pueblo Grande mound. You asked for comments and I thought I would pass these on, hoping that they are helpful. I think the level of effort was actually much greater than you suggest.
1. I don't know what you mean by saying that mound fill is "treated as adobe." If you mean that the fill is an adobe mixture, it is incorrect. Mound fill may have been water settled at times, but it is almost always, in my experience, loose fill.
2. Your speculations on material is also incorrect. The major stone material for the outer stone masonry walls at PG are not river rock and it does not come from the Salt River. Although like all coursed caliche construction in the Classic Period, odd river rocks and cobbles do occur in the walls. River rock, which is not tabular in nature, does not work well (if at all) in a stone masonry construction. The major rock in the Pueblo Grande is indurated caliche, a caliche that has hardened to a soft stone and is roughly tabular in nature (but still quite crummy). There are several outcroppings of this material (which we use in the stabilization work at PG) to the north of the mound. Also, canal sediment is not used. Canal sediments have been size sorted by the fluvial processes found in the canals. It is not a good construction material. Here you can get clays, but more often, particularly in the headward areas of the canals (I have excavated quite a few canals at the Pueblo Grande head area) you generally get sands and silts, few clays. The fill in the mound is a matrix of Estrella Loam (or the equivalent basin alluvial sediments around PG) with rocks, old construction materials and cultural debris. The old construction material, including fragments of old walls, comes from tearing down existing rooms and walls during rebuilding events. At the Mesa Grande mound I have found huge deposits of wall material, daub and even buried roofs.
3. Concerning the references to adobe making, the actual process at Pueblo Grande is a coursed caliche construction. This relies on the use of caliche and the binding of calcium carbonates rather than the use of adobe (soil with 20% or more of clay) and the binding of clays. I do not believe that ballcourts were used as borrow pits, certainly not for mound construction. Usually borrow pits are near the mounds. At the site of Los Hornos, Wilcox and I found one of the borrow pits for that platform mound. It was 60 meters long, 40 meters wide, and over 4 meters deep (we never found the bottom). Pueblo Grande undoubtedly had numerous borrow pits, probably arrayed in areas around the mound. Mesa Grande had one to the northeast of the mound about 30 to 40 meters away.
4. In terms of your overall labor estimates, I think the truth is much more complex. There are many building episodes at Pueblo Grande and other major mounds. Taking the final product and using it as a basis for labor estimates is a short-cut and leaves out much of the history of mound development and the labor involved. Although this approach has been used by many people, Nietzel for one, Doug Craig and others for another. Also, as one who has worked to rebuild walls at a major mound, you missed the most labor-intensive part of the process, as everyone else has. Rebuilding walls is an incredibly difficult process and I think you have to do it to really understand how much effort it really is. While I will not give away what I think is the most labor intensive part, I will note that all mounds are also part of a larger complex, one that has a compound wall (usually a massive compound wall) and, in the case of Mesa Grande, a huge plastered eastern plaza; a great labor feat in and of itself.
5. Finally, if by the mounds being "elite space" you are referring to the mounds as containing living quarters of elite members of Hohokam society, I don't agree. But then, that is too long of a debate to discuss here.
Again, I hope these limited comments help.  Jerry Howard.

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