New Mexico Geological Society Annual Spring Meeting — Abstracts

The Cañada Alamosa Archaeology Project (CA) has documented a 4000-year cultural sequence near the current boundary of the Chihuahuan Desert that is dominated by C3 shrubs and surrounded by C4 grasslands. Given the topographical relief, erodible soils, ¹⁴C-datable charcoal in sediments, stepped sequence of fan terraces, carbon isotopes in both soil organic matter and pedogenic carbonate, and macrobotanical remains in archaeological structures, we tested the hypothesis that the landscape at the CA contains a late Holocene climate change record with implications for making inferences about the expansion and contraction of the Chihuahuan Desert. The results indicate that (1) the greatest expansion was in the late Middle Holocene based on charcoal in “Alamosa I” sediments dating to 3695 cal BP and 3952 cal BP. (2) Following this greatest period of expansion was a period of greatest contraction when a 800 to 1000-year span of landscape stability allowed the formation of a well-developed soil on “Alamosa I” sediments. (3) The last major desert expansion based on charcoal in “Alamosa III” sediments was underway by 1358 cal BP when sedimentation continued for some 800 years throughout the Medieval Warm Period. (4) By 500 cal BP (CE 1450), now within the Little Ice Age period, a last retreat of the Chihuahuan Desert. Pueblo people abandoned the site during this period of time. (5) By the 1770s, before the introduction of domestic livestock, arroyo cutting and fan building were underway, and were soon exacerbated by overgrazing.