SEDIMENTOLOGY AND STRATIGRAPHY OF THREE ARCHAEOLOGICALLY SIGNIFICANT AREAS OF THE COLORADO RIVER CORRIDOR, GRAND CANYON, ARIZONA

This study presents initial results of a joint effort between geologists and archaeologists to evaluate the significance of various depositional processes and environments in the formation and preservation of archaeological sites along the Colorado River corridor in Grand Canyon National Park. Stratigraphic investigations of the Palisades, Lower Comanche, and Arroyo Grande areas of Grand Canyon yield detailed information regarding the sedimentary history at these locations. Reconstruction of past depositional settings is critical to a thorough understanding of the geomorphic and stratigraphic evolution of these three archaeologically significant areas. Examination of past sedimentary environments allows the relative significance of fluvial, aeolian, debris-fan, and slope-wash sedimentary sources to be identified at each site. In general the influence of fluvial sedimentary processes (number and thickness of flood deposits) is shown to decrease with distance from the river, as locally derived sediment becomes more significant. Flood sequences often occur as ‘couplets’ that contain a coarsening-upward fluvial deposit overlain by inter-flood units that reflect reworking of fluvial sediment at the land surface by wind and local runoff. Archaeological features are built on and buried by sediment of various depositional environments, representing a complex interaction between geologic and cultural history. Such field analysis, which combines geological and archaeological information and techniques, can provide a basis for determining of the effects of Glen Canyon Dam on selected areas of the river corridor. This knowledge is essential to the development of preservation strategies for cultural resources in Grand Canyon National Park.