WSP09906 - Laserfiche WebLink

Home Browse Search

GRAND CANYON ARCHAEOLOGY by Janet R. Balsom, Grand Canyon National Park Archaeologist Beginning in 1983, erosion of archaeological sites located at the old high water mark of the Colorado River was noted. The first site discovered (AZ C:13:10) is located on the right bank of the Colorado River, near Unkar Delta. Arroyo cutting in a dune field capped by mesqui,tes uncovered significant archaeological remains dating back to the Anasazi occupation, sometime between A.D. 800 and 1200. Limited test excavations conducted in 1984 confirmed the existence of extensive archaeological remains buried in the sand dunes. Since that time, numerous other sites have been located eroding from the sand dunes at and above the old high water mark ' For a long time, people assumed that prehistoric remains would not be found below the historic high water mark for two reasons. First, the belief that prehistoric people were smarter than we are and would not build someplace where they would be flooded. Second, that any remains which would have been close to the river would have washed away. The data collected thus far suggests that this is not the case. We have found over a dozen areas along the river where structures or features were built below high water and are still intact; areas where structures were flooded in-place and then built upon later. Flood terraces along the river where dune formations exist seem to hold prehistoric remains, some obvious, some in a state of becoming visible. Research on the cause of the erosion is ongoing. In an I interdisciplinary project, Richard Hereford of the USGS I and Janet Balsam of Grand Canyon National Park are examining sites in the stretch of river between Palisades and Unkar Delta (River mile 65 to 72) for clues of depositional history and subsequent erosion. The initial information suggests that the erosion of sites along the river seems to be directly related to the operation of Glen Canyon Dam, both the peaking power scenario and the depletion of sediments from within the system. The 1983 high water flood may have been the catalyst for the erosion to occur. In the areas which have been studied, it appears as though the archaeological sites were flooded l[lIld encased in fluvial deposits over the last 1000 or more years. The accumulation of river deposits and wind blown sands have buried the sites within the dune formations. With the depletion of sediments on the lower beaches, erosion of the old high water deposits is occurring. The low and fluctuating flows are accelerating the erosion of the beaches, particularly during high run-off seasons. The downcutting we are seeing through the archaeological deposits is from rain water attempting to reach the river. Headward erosion from the base of the dunes which were i steepened during the 1983 high water is beginning to occur. This erosion and erosion within the current beach zone coupled with changes in beach sediments and the need for rain water to reach the river may be the cause of the site erosion. The archaeological site erosion problem is becoming more apparent as more sites are discovered due to continued erosion of additional archaeological sites. 9