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28 Sedimentology and Stratigraphy of the Palisades, Lower Comanche, and Arroyo,Gra~de Areas of the Colorado River at the site of section 5 retreats further and meets the upper ter- race. The proximity of this nickpoint to the upper terrace at this lime (2111) implies that perhaps two or three intense rain stomlS could allow the nickpoint 10 move into the upper terrace area. Although no samples were collecled from Arroyo Grande for radiocarbon dating, numerous stratigraphic horizons in the arroyo walls contain sullicient ash material for radiocarbon dating purposes. Any future efforts to conduct radiocarbon dating work on charcoal (either cultural or noncu1tural ash, such as the apparent grass-fire horizons represented in several stratigraphic sections) could provide valuable age data that could be used to refine the flood history of this area. as well as providing dates for various stages of cultural occupation. Discussion and Conclusions These investigations of Holocene stratigraphy in archaeologically significant areas have been designed as a cooperative effort by geologists and archaeologists to col- lect data to help guide managers on future efTorts to preserve archaeological sites in Grand Canyon. Developing a strategy for preservation of such cultural resources requires a detailed understanding of sedimentary and geomorphic processes with multiple time scales considered. In the shorter teml, field evaluation of geomorphic processes (such as gully incision and dune migration) is essential to the success of erosion-mit- igation elTorts at archaeological sites (for e.xample. checkdam constmction. slope stabilization). The time scales on which these processes and mitigation methods are relevant in a par- ticular location may vary from less than an hour (the duration of a rainfall evenlthat can carve a new gully or further incise an existing one) to decades or more (the time scale on \\'hich the migration distance of large aeulian dunes becomes impor- lant). To develop a far-sighted. longer tenn approach to in situ preservation of sites throughout the river corridor, it is neces- sary to docllment in detail the gcomorphic and stratigraphic context in which these sites were built and in which they were preserved. Such infonnation is essential to the formulation of m3l1agelnent decisi-ons. including those that involve dalll operation, with the aim of maintaining and restoring sedi- mentary deposits in which sites are located. The time scale on which these research topics remain relevant ranges from days (during which the clTect offlow fluctuations. including a beach/habitat-building flow [BHBF]. may be measured) 10 many years or decades. as anthropogenic impact on the river corridor continues. In her recent comprehensive assessment of cultural- resource issues in the river corridor, and of the research approach that is needed to best address the preservation of archaeological sites. Fairley (2003) has posed a series of research questions that encompass complex multi-dimen- sional aspects of geomorphic process and history, paleocli- mate and ecology. and cultural interaction with the Grand Canyon landscape. Fuur of thuse research questions are par- ticularly relevant to the present study: (I) What do the sedimert!ary strucnJres and grain sizes in Holocene deposits re'v'e~r~~'the relative dominance of aeolian versus fluvial processes in prehistory. and how might these processes have influenced the preservation or erosion of archaeological sites in the past'? (2) What types of geomorphic processes were active on the landscape before settlement. and what processes created the landscape on which sites were subsequently located? (3) How have postdepositional processes altered or removed portions of the archaeological record at sites? (4) What do postdeposilional sedimenls [Ihose that post- date site fonnation] reveal about landscape changes since the time of occupation'? Slratigraphic and geomorphic dala such as those collecled during this investigation are essential to fomlulating answers to these and other research questions, which seek to better define the context in which prehistoric people lived in Grand Canyon. Understanding the complex interaction between the people \",ho lived along the river corridor and their physical environment has great significance for enhancing archaeologi- cal studies of this area. The same types of data in turn fonn the basis by which management decisions must be made that have the potential to preserve or restore archaeologically significant sediment deposits. During the course of this study. the importance of answcr- ing the four research questions listed above on a site-by-site basis became particularly apparent. The relative dominance of f1uvml, aeolian. and slope-wash sedimentation can differ widely bet\l./een study sites and can vary substantially between stratigraphic sections within anyone study site. It is difficult. and not necessarily informative, to fonn regionally general- ized conclusions about the geomorphic processes that created the landscape before and after selllement, or to generalize the effects ofpostoccllpation processes on archaeological site preservation. without actual detailed field study at a site in question. For example. the answers to these questions attaincd by our work at Arroyo Grande (dominance offtuvial and slope-wash deposition in various areas of site G:03:064, with arroyo incision having removed portions of features) cannot be assullled-to- affect other sites in western' Grand Canyon~ or even sites directly across the river, in exactly the same manner. Observations Related to Aeolian Sediment Because this research team was originally assembled for the specific purpose of investigating the role of aeolian sediment in the preservation of archaeological sites. we otTer conclusions on that topic based on infommtioll obtained during this stratigraphic study and from earlier reconnaissance work done in 2003. As 11n initial reconnaissance effort for thi~ project, personnel from Ihe USGS. NPS. Hopi and Huala- pai Trib~s, GCMRC, and the Western Area Power Authority (WAPAl participated in a river trip from May 4 to 19.2003. NPS archeologists J. R. Balsom, L. M. Leap, and J. L. Dierker directed visitation of3~ archeological sites at which earlier