Multitechnique dating of earthen irrigation canals at the La Playa site, Sonora, Mexico

Abstract

La Playa (SON:F:10:3) is an archaeological site in Sonora, Mexico that contains the remains of an extensive preceramic earthen irrigation canal system. Modern floodplain erosion has destroyed the majority of these canals, but geoarchaeological investigations on areas of the system that remain reveal much about this early agricultural technology. Comprehensive dating using accelerator mass spectrometry 14 C on gastropods, charcoal, and soil humates and single-grain optically stimulated luminescence (OSL) dating on canal sediments revealed that multiple irrigation systems were used at La Playa during at least two periods during the Early Agricultural period (~750-350 B.C. and~A.D. 50-250). 14 C and OSL age estimates from canals are in agreement with the earliest direct dates on maize from La Playa (A.D. 20-240), indicating that the introduction of maize corresponds to a significant investment in the modification of the floodplain environment for canal irrigation. The late phase of canal use (~A.D. 50-250) occurs before destructive floodplain erosion at the site. This is contemporaneous with local cultural changes, including the development of a new ceramic tradition, changes in burial practices, and changing subsistence strategies. These results demonstrate the utility of the combined 14 C and OSL approach for dating ancient earthen canals.

Early Canal Systems in the North American Southwest

“…Canal irrigation in the prehistoric Southwest was long believed to have been a relatively recent technology introduced by migrants from Mesoamerica around 300 BC (e.g., Haury 1976:150). However, the large scale and complexity of Hohokam canals relative to their Mesoamerican counterparts challenged that hypothesis (Doolittle 1990:79–81); subsequent discoveries of Early Agricultural canal systems in the Tucson area and in northwestern Sonora (Cajigas et al 2020; Carpenter et al 2015) have confirmed that water management in support of agriculture has a much deeper history in this region. Evidence of early canal irrigation is likely preserved in multiple Southwest alluvial floodplains, but the challenge is how to find and recognize it.…”

“…Through time, canals at Las Capas increased in size (Figure 3) with subsequent Cienega-phase systems supporting more regulated flow (Palacios-Fest and Davis 2008) and a greater diversity of crops for larger irrigation communities. Similarly, Cienega-phase canal systems up to 2 km in length were constructed along the Río Boquillas and supported multiple generations of farmers at La Playa (Cajigas et al 2020; Carpenter et al 2015). In Las Capas and La Playa, canal system size was likely constrained more by available river discharge than the amount of irrigable land, labor, and technological skill.…”

“…Through time, irrigation canals increased in channel capacity and length. By the first millennium BC, Indigenous farmers were constructing canal systems more than 1 km long that comprised hierarchical channel networks and gridded fields in southern Arizona (Griset et al 2018; Mabry et al 2008; Vint 2015) and northwestern Sonora (Cajigas et al 2020; Carpenter et al 2015).…”

Relict canals of the Tehuacán Valley, Mexico: A Middle- to Late-Holocene dryland socio-hydrological system

“…Recent studies in other parts of the Americas have directly dated irrigation canals in association with incipient agriculture. For example, Dillehay et al (2005) directly dated an irrigation canal in Southern Peru to cal 5728–5482 BC, canals in Morelos have been dated to as early as cal 1204-932 BC (Borejsza et al, 2014), while canals contemporaneous with the expansion of agriculture into Southern Arizona and Northern Mexico date to as early as ~cal 750–100 BC (Cajigas et al, 2020; Huckleberry and Rittenour, 2014).…”

Geoarchaeology virtual issue: Ancient water management

“…Canal systems are particularly challenging due to the constant modifications associated with cleaning and repair. Cajigas et al (2020) discussed some of these challenges and demonstrated the value of combining different chronometric methods, such as single-grain optically stimulated luminescence and accelerator mass spectrometry radiocarbon, for dating prehistoric earthen canals in northwestern Mexico.…”