USGS

Fact Sheet 2004-3035

April 2004

Sources of Ancient Maize Found in Chacoan Great Houses

This study was done in cooperation with the Navajo Nation Historic Preservation Department, Chaco Protection Sites Program, the Chaco Culture Natural History Park, Aztec Ruins National Monument, San Juan County Museum Association—Salmon Ruins, and the University of Colorado Sources of Ancient Maize Found in Chacoan Great Houses

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Background

Between the 9th and 12th centuries A.D., Chaco Canyon, located near the middle of the high-desert San Juan Basin of north-central New Mexico (fig. 1), was the focus of an unprecedented construction effort by pre-Columbian Native Americans. It has been estimated that from 2,000 to 6,000 people occupied Chaco Canyon during its heyday (Windes, 1984; Drager, 1976). One indication of Chaco's regional importance is a network of roads that linked Chaco Canyon with other great houses and communities spread throughout a region covering at least 60,000 km2 (fig. 2). At the height of its cultural florescence in the 11th century, Chaco culture was characterized by the construction of monumental great houses (multistory, planned structures) that required millions of pieces of dressed sandstone and tens of thousands of roof beams. By 1130 A.D., Pueblo Bonito (fig. 3), one of 13 greathouses that occupied the canyon, was four stories tall and contained approximately 800 rooms (Neitzel, 2003). The size of Pueblo Bonito, its numerous large rooms, and the richness of its artifacts, which included caches of turquoise, copper bells, and finely crafted projectile points, suggest that it was a location where imported goods were amassed. Given the richness of its artifacts, some view Pueblo Bonito as having functioned primarily as an elite residence (Judge, 1989). Pueblo Bonito was occupied for at least 300 years; however, only 131 burials were found within the site, suggesting a sustained population averaging less than 100 people (Akins, 2003).


location map for the San Juan Basin

Figure 1. Site location map for the San Juan Basin. Possible sources of archeological corn are A, Aztec Ruin; S, Salmon Ruin; N, Newcomb; and C, Chaco Canyon. CTW is Captain Toms Wash. Small filled diamonds indicate sample sites along the San Juan River and its perennial tributaries. Dashed lines indicate ephemeral streams. See Figure 2 for state boundaries.


Prehistoric roads and great houses

Figure 2. Prehistoric roads and great houses in the San Juan Basin.


Pueblo Bonito.

Figure 3. Pueblo Bonito.


Archaeological Maize And The Use Of Strontium Isotopes To Determine Where It Was Grown

Maize, the mainstay of Native American diet in Chaco Canyon, was introduced to the American Southwest about 3,500 years ago. Understanding whether maize was imported into Chaco and exchanged between great houses throughout the San Juan Basin is crucial to resolving questions about whether or not food grown in the canyon was sufficient to support resident populations as well as visitors to the canyon.

This fact sheet summarizes the results of a study that determined the probable sources of archeological maize found in Pueblo Bonito ruin, Chaco Canyon, New Mexico (Benson and others, 2003). Ratios of two isotopes of strontium (87Sr and 86Sr) in corncobs from two great houses (Pueblo Bonito and Aztec Ruin) were compared to 87Sr/86Sr ratios of soil waters produced from four possible agricultural sites (Chaco Canyon, Newcomb, Aztec Ruin, and Salmon Ruin) in the San Juan Basin (fig. 1). Hereafter Aztec Ruin and Salmon Ruins will be referred to as Aztec and Salmon. The two isotopes of strontium (Sr), 87Sr and 86Sr, differ by only one mass unit; therefore, ratios of the two isotopes remain unchanged by physical and chemical processes. Thus, the 87Sr/86Sr ratio of a corncob is identical to the 87Sr/86Sr ratio of the soil water that sustained its growth, which in turn is identical to the 87Sr/86Sr ratio derived from the dissolution of soluble minerals (carbonates) in the soil zone (Benson and others, 2003).

Possible Source Areas Of Archeological Maize

There are four possible areas that could have supplied maize to Pueblo Bonito: Chaco Canyon, Newcomb, Aztec, and Salmon. Today, Chaco is climatically marginal for the production of maize, and paleoclimatic reconstructions demonstrate that sustained production of maize in this area always was precarious (Toll and others, 1985). Newcomb, located at the base of the Chuska Mountains (hereafter referred to as the Chuskas), has a longer growing (frost-free) season than Chaco. Unlike the Chaco area, the Chuskas accumulate winter snow that melts and runs off during spring and early summer and flows down Captain Toms Wash (fig. 1). Both the longer growing season and the existence of a relatively reliable source of irrigation water enhance the agricultural potential of Newcomb. In addition, abundant maize was documented as having been grown here in the middle 19th century. For example, during a military expedition to Navajo country in 1849, Lt. J. H. Simpson noted "very extensive and luxuriant cornfields" in the Newcomb area (Simpson, 1852).


Aztec Ruin

Figure 4. Aztec Ruin. Photo courtesy of Aztec Ruin National Monument, National Park Service.


The other two sites (Aztec and Salmon) are located near perennial river systems that provide a reliable source of irrigation water. Aztec (fig. 4) is located on an alluvial fan adjacent to the Animas River floodplain, and Salmon (fig. 5) is situated on a low terrace adjacent to the San Juan River floodplain (fig. 1).


Salmon Ruin

Figure 5. Salmon Ruin. Photo courtesy of the San Juan County Museum Association-Salmon Ruins.


Construction Histories

The construction histories of the four archeological sites indicate that exchange between the sites could have occurred during specific time intervals. Major construction episodes at Pueblo Bonito indicate that it was occupied between approximately 850 and 1150 A.D. (Windes, 2003). Numerous great houses in the Newcomb area began construction during the early 800s, and some were occupied until 1300 A.D. (Marshall and others, 1979; Fowler and Stein, 1992). Thus, exchange between Newcomb and Pueblo Bonito could have occurred during the entire time interval that Pueblo Bonito was occupied. Construction of Salmon and the immense Aztec Ruin began 220 and 260 years after the initial occupation of Pueblo Bonito (Robinson and Cameron, 1991; Stein and McKenna, 1988); therefore, exchange between Pueblo Bonito and the two northern great houses could only have occurred late in the occupation history of Pueblo Bonito.

Sample Collection And Processing

The sampling strategy was guided by what is known or conjectured about pre-Columbian agricultural practices. In Chaco Canyon (fig. 6), it is possible that some fields were irrigated with runoff from side-canyon tributaries whose waters were diverted to field-irrigation systems located on alluvial fans (Vivian, 1990). Floodwater irrigation of crops on the Chaco Wash floodplain also may have occurred when the channel was not incised; however, this is not likely, given the high salinity of Chaco Wash water and floodplain soils.


Soil and water sample sites in Chaco Canyon

Figure 6. Soil and water sample sites in Chaco Canyon. The Lizard House Arroyo (LH) and Weritos Rincon (WR) soil sample sites are labeled. Canyon walls are hachured.


The Newcomb area is a site where maize could have been grown on floodplain deposits, and in the Salmon and Aztec areas, maize could have been grown on both floodplain and alluvial fan deposits. Therefore, soil samples were collected from a variety of topographical features—principally alluvial fans and floodplains—by augering eolian, floodplain, and alluvial fan sediments or sampling sediment exposures on the banks of washes and arroyos.

Because stream water used for irrigation also contains Sr, samples were collected from the San Juan River drainage and its tributaries, including the ephemeral Chaco, Captain Toms, and Skunk Springs washes. The latter is a tributary to Captain Toms Wash.

87Sr/86Sr ratios of soil waters from sediment where maize may have been grown were compared the 87Sr/86Sr ratios of archeological maize (cobs). To produce 87Sr/86Sr ratios characteristic of soil water, Sr was extracted by leaching the soil samples with a weak acid, and 87Sr/86Sr values of the simulated soil waters were obtained using isotope mass spectrometry. To ascertain the source of maize found in Pueblo Bonito, seven cobs were analyzed that were found during the excavation of the structure by George Pepper, between 1886 and 1899, as part of the Hyde Exploring Expedition (fig. 7). Ten cobs from Aztec also were studied to determine whether they possessed 87Sr/86Sr ratios similar to those in simulated soil water produced from samples of nearby alluvial fans and floodplains. Prior to mass spectrometric analyses, the cobs were ashed and dissolved in nitric acid to eliminate their organic content.


Areal view of room and kiva layout of Pueblo Bonito

Figure 7. Areal view of room and kiva layout of Pueblo Bonito. Rooms in red are in older part of structure where cobs were found. Room in blue is in younger part of structure where cob H-10648 was found. Kivas are circular structures.


Results

87Sr/86Sr data for soil and surface waters have been plotted together with 87Sr/86Sr ratios for archeological cobs from Pueblo Bonito and Aztec (fig. 8). Comparison of the 87Sr/86Sr ratios of the Pueblo Bonito cobs with 87Sr/86Sr ratios in soil water from Newcomb and Chaco Canyon indicates that six cobs were probably grown in Newcomb area fields close to the base of the Chuskas. In particular, the 87Sr/86Sr ratios of simulated soil waters from upper parts of the Captain Toms and Skunk Springs drainages and the 87Sr/86Sr ratios of surface water from the two drainages are similar to the 87Sr/86Sr ratios of the six cobs (fig. 8).


87Sr/86Sr ratios

Figure 8. 87Sr/86Sr ratios of eolian (sun), floodplain (bullet), and alluvial fan (Δ) sediments; surface waters (square); and cobs (arrow). Abbreviations: SS and SSW (Skunk Springs Wash), CTW (Captain Toms Wash), BMS (Basketmaker site on CTW), CC (Casa Chiquita), PDA (Pueblo del Arroyo), CK and CKF (Chetro Ketl Field area between LH and the Chetro Ketl Greathouse), LH (Lizard House Arroyo), CR (Casa Rinconada), ST (Section 10 site), WR and WER (Weritos Rincon), AZR (Aztec Ruin), AR (Animas River), SR (Salmon Ruin), and SJR (San Juan River). The red rectangles enclose the 87Sr/86Sr ranges of Pueblo Bonito cobs. The blue dashed rectangle encloses the 87Sr/86Sr range of Aztec Ruin cobs. 87Sr/86Sr ratios from Animas River tributaries range from 0.7097 to 0.7099 (double-headed arrow)(Benson and others., 2003).


One surface-water sample from Chaco (a sample derived from flow in Fajada Wash) has a 87Sr/86Sr ratio that falls within the 87Sr/86Sr range of the six cobs. Fajada Wash is usually a minor contributor of water (and Sr) to Chaco Wash, and the87Sr/86Sr value of Chaco Wash water is unlike that of Pueblo Bonito cobs (fig. 8). Two simulated soil waters from Weritos Rincon and Lizard House Arroyo also have 87Sr/86Sr ratios that fall within the range of Pueblo Bonito cob 87Sr/86Sr ratios. Benson and others (2003) used soil water and cob trace-element ratios to demonstrate that these two sites could not have been the source of cobs found in Pueblo Bonito.

Pueblo Bonito cob H-10648 has a 87Sr/86Sr ratio similar to that of cobs found in Aztec and also similar to that of a soil water produced from a floodplain sample at Aztec (AZR#2) (fig. 8). Aztec cob 87Sr/86Sr ratios indicate that some of the cobs probably were grown in Aztec soils. Most of the cobs with larger 87Sr/86Sr ratios probably were grown in Salmon soils. Cobs with smaller 87Sr/86Sr ratios may have been grown in the Animas River floodplain (AR#1), using water from the Animas River for irrigation. The 87Sr/86Sr ratio of Animas River water indicates significant variability with the highest 87Sr/86Sr ratio having nearly the same value as two cobs from Aztec (fig. 8). In fact, the Animas River may have experienced higher 87Sr/86Sr ratios from time to time, depending on the relative flux of Sr from its tributaries whose 87Sr/86Sr values range from 0.7097 to 0.7099 (Benson and others, 2003).

Summary

The oldest maize found in Pueblo Bonito probably was grown in an area at the base of the Chuska Mountains 80 kilometers (km) to the west. One maize sample (H-10648) found in Pueblo Bonito came from the San Juan or Animas river floodplains 90 km to the north. This study has demonstrated that maize was transported over considerable distances in pre-Columbian times.

—Larry Benson


For more information about this fact sheet and supporting files contact:

Larry Benson
lbenson@usgs.gov
U.S. Geological Survey
3215 Marine Street
Boulder, CO 80303
(303) 541-3005

References Cited

Akins, N. J., 2003, The burials of Pueblo Bonito, in Neitzel, J. E., ed., Pueblo Bonito center of the Chacoan world: Washington, D. C., Smithsonian Books, p. 94-106.

Benson, L., Cordell, L., Vincent, K., Taylor, H., Stein, J., Farmer, G., and Kiyoto, F., 2003, Ancient maize from Chacoan great houses: where was it grown?: Proceedings of the National Academy of Sciences , v. 22, p. 13111-13115.

Drager, D. L., 1976, Anasazi population estimates with the aid of data derived from photogrammetric maps, in Lyons, T. R., ed., Remote sensing experiments in cultural resource studies: Reports of the Chaco Center no. 1, Albuquerque, New Mexico, National Park Service, p. 151-171.

Fowler, A. P., and Stein, J. R., 1992, The Anasazi great house in space, time, and paradigm, in Doyel, D. E., ed., Anasazi regional organization and the Chaco system: Albuquerque, New Mexico, Maxwell Museum of Anthropology, Anthropological Papers no. 5, p. 101-122.

Judge, W. J., 1989, Chaco Canyon-San Juan Basin, in Cordell, L. S., and Gumerman, G., J., eds., Dynamics of Southwest prehistory, Washington, D. C., Smithsonian Institution Press, 209-261.

Marshall, M. P., Stein. J. R., Loose, R. W., and Novotony, J. E., 1979, Anasazi communities of the San Juan Basin: Santa Fe, New Mexico, Public Service Company of New Mexico, Albuquerque and New Mexico Historic Preservation Bureau.

Neitzel, J. E., 2003, Three questions about Pueblo Bonito, in Neitzel, J. E., ed., Pueblo Bonito center of the Chacoan world: Washington, D. C., Smithsonian Books, p.1-9.

Robinson, W. J., and Cameron, C. M., 1991, A directory of tree-ring dated prehistoric sites in the American Southwest: Tucson, Arizona, the University of Arizona.

Simpson, J. H., 1852, Journal of a military reconnaissance from Santa Fe, New Mexico, to the Navajo country: Philadelphia, Pennsylvania, Lippincott.

Stein, J. R., and McKenna, P. J., 1988, An archeological reconnaissance of a late Bonito phase occupation near Aztec Ruins National Monument, New Mexico: Santa Fe, New Mexico, National Park Service.

Toll, H. W., Toll, M. S., Newren, M. L., and Gillespie, W. B. , 1985, in Mathien, F. J., ed., Experimental corn plots in Chaco Canyon: the life and hard times of Zea Mays L., Environment and subsistence of Chaco Canyon, New Mexico: National Park Service Archeology 18E, p. 247-278.

Vivian, R. G., 1990, The Chacoan prehistory of the San Juan Basin: New York, Academic Press.

Windes, T. C., 1984, A New Look at Population in Chaco Canyon, in Judge, W. J., and Schelberg, J. D., eds., Recent research on Chaco prehistory: Albuquerque, New Mexico, Reports of the Chaco Center no. 8, National Park Service, p. 75-87.

Windes, T. C., 2003, This old house construction and abandonment at Pueblo Bonito, in Neitzel, J. E., ed., Pueblo Bonito center of the Chacoan world: Washington, D. C., Smithsonian Books, p.14-32.

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