LATE-HOLOCENE ARROYOS, FLOODS, AND PREHISTORIC SETTLEMENT SHIFTS IN THE ZUNI SALT LAKE AREA, NEW MEXICO

Surficial geologic mapping and twenty-seven ¹⁴C ages from alluvial deposits and soils exposed in modern arroyos near Zuni Salt Lake, New Mexico provide evidence for two episodes of piedmont and valley entrenchment that date A.D. 900-1050 and A.D. 1300-1400. These events correlate to episodes of arroyo-cutting identified elsewhere on the southern Colorado Plateau with each event followed by approximately 200-300 years of aggradation. Synchronous episodes of downcutting and backfilling on small and large basin streams with local base-level controls argue for changes in climate and flood regime as causal mechanisms for floodplain change. Flooding on small basin drainages near Zuni Salt Lake is related to the Southwest summer monsoon, a meteorological event that is poorly linked to El Niño. Periodic entrenchment of ephemeral stream channels in the Zuni Salt Lake area affected indigenous floodwater farming by locally lowering water tables and reducing irrigable area. Extensive arroyo activity in the Zuni Salt Lake area was an important environmental factor contributing to the aggregation of Puebloan communities during the A.D. 1300s.