GEOMORPHOLOGY OF DUNE LANDSCAPES TO UNDERSTAND ARCHAEOLOGICAL SITE DISTRIBUTION IN PETRIFIED FOREST NATIONAL PARK

The Petrified Forest National Park in northeastern Arizona contains extensive Quaternary sand sheets and dunes, as well as abundant archaeological sites in the dune landscape. This paper investigates soils and geomorphology of these dunes to better understand archaeological site distribution. Past and recent archaeological research in the area has shown apparent correlation between archaeological site locations and dune geomorphology, and it has long been hypothesized that prehistoric inhabitants frequently targeted dunes for habitation and agricultural purposes.

Eolian sands are not typically conducive to dry-farmed agriculture; however, dune farming is known ethnographically among the Hopi, and has been inferred in archaeological contexts on the southern Colorado Plateau. Understanding the underlying landscape conditions will help to demonstrate what geologic conditions allowed for eolian deposits in Petrified Forest to be conducive to dry-farmed agriculture during prehistory.

Eolian deposits in the Petrified Forest include semi-stabilized dunes and sand sheets. Previous investigation estimated the timing of eolian deposits based on soil development; however, numerical ages on the eolian deposits were lacking. This paper presents Optically Stimulated Luminescence ages for 12 samples at 8 locations. These ages show that eolian activity has been high during the late Holocene, and confirms earlier work suggesting multiple periods of deposition. Soil geomorphic studies have demonstrated high clay content and weak soil development. The high clay content, combined with young ages of deposition, suggests that clay within eolian sediments is likely due to deposition from local sources. In addition, it is hypothesized that high clay content may have contributed to increased water holding capacity, improving sediment conditions for prehistoric agriculture.