Geomorphology, hydrology, and alluvial stratigraphy in lower Chaco Canyon do not support the possible existence of prehistoric sand-dammed ephemeral lakes

Abstract

Sand dunes 1–5 m high accumulate on the downwind side of the confluence where Chaco Wash and Escavada Wash form the broad, braided, sandy Chaco River at the northwest end of Chaco Canyon. Sand dunes derived by reworking channel sands are common next to the river and washes. Recently Force et al. (2002) and Force (2004) proposed that a similar set of sand dunes dammed Chaco Wash during Pueblo II occupation (a.d. 900–1150) of Chaco Canyon, forming a small lake. The dynamic geomorphology of the sand dunes and canyon floor, the hydrology of Chaco Wash, and stratigraphic analyses of the locality where lake beds were thought to exist all nullify the hypothesis. The sand dunes at the canyon mouth and nearby have changed in historic time, so it is likely that the configuration of dunes has changed during the past thousand years. To create a set of dunes across the entire mouth of Chaco Canyon requires that sand be trans