Abstract

Studies of the Quaternary alluvium of Upper Grand Gulch, San Juan County, Utah, were initiated in conjunction with the Cedar Mesa Project of the Museum of Northern Arizona. A series of stream terraces and their relationship to prehistoric utilization and abandonment of the canyon floor were investigated.

Initial results reveal the development of three terraces representing two major periods of degradation, one being contemporary with, or post-dating the occupation of the canyon floor. The oldest alluvial unit, terrace 2, was the unit most relied upon for farming activity by Basketmaker and Pueblo peoples. Arroyo cutting destroyed much of the arable land, or lowered the water table to the point that farming the upper terrace could no longer support the population. Abandonment of the canyon floor took place in Pueblo III time. Terrace 1 represents a period of post-occupation aggradation, followed by degradation and minor development of terrace 0 along some parts of the stream.