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~;id~'.' 0200ti . monitoring work by NPS had indicated that aeolian sediment may have beet) significant, either as the material underly- ing the site or fonning a protectjve cover. At each sile, the sedimentologists made initial assessments of the depositional environments (aeolian vs. fluvial) on which the sites were located. Although a few of these sites are underlain by :::icdi- ment deposited by slope-wash processes or by side-canyon floods, most sites were built on (or buried by) sand that was transported by wind from Colorado River deposits. Following the May 2003 reconnaissance trip, the list of study sites was narrO\ved to identify areas of highest priority that would then be examined within our budget and time constraints. The Pali- sades, Lower Comanche, and Arroyo Grande investigations described in this report were three of those areas selected for further study. Observations made during the May 2003 reconnaissance trip included the following: I. A preliminary estimate is that roughly 90 percent of the sediment beneath or above these particular archaeological sites is Colorado River sand that was transported from fluvial deposits at the river margins by wind. A few sites were built on or buried by sediment deposited directly by large floods of the Colorado River. (These sites were selected for the purposes of this reconnaissance trip and are not typical of all sites.) 2. Aeolian transport appears to be limited largely by factors such as sediment supply and vegetation, rather than by wind. Reduction in the size of sand bars. increased vegetative cover, and increased submergence of bars can be expected to reduce aeolian transport of sand to the nearby dune fields that contain archaeological sites. Reduced aeolian transport can be expected to facilitate the growth of existing arroyos and estab- lishment ornew arroyos. At many of the sites visited in May 2003. damage to archaeological sites by arroyo development and incision is apparent. Dala and photographs collected hy NPS archaeologists at repeated visits to many sites over a time frame of more than a decade support this observation. 3. Some archaeological sites are threatened by small drainages that might be repaired by modest increases in aeo- lian sand deposition. Examples include sites visited at Lower Tanner and Palisades, where constmction of brush check dams by archeological teams has slowed the incision of some gully systems; all increase in transport of aeolian sand to such areas is anticipated to further stabilize such archaeological features. Other sites (such as Arroyo Grande) are threatened by very large drainages that could only be filled by increases in aeolian transport larger than might reasonably be expected in the short term. 4. The side walls of some drainages showed sedimen- tary structures recording prior gully erosion and prior fill- ing by aeolian sand, but these strucnlres showed filling of paleogullies that were smaller than the modem active arroyo channels. Discussion and Conclusions 29 Beginning in November 2003, six 1110nths after this recon- nnissance river trip, several members of the research group (Draut. Rubin, Dierker. Fairley) installed weather stations at six locations along the river corridor that collect a continuous record of wind conditions and precipitation in the vicinity of selected archaeological sites. The purpose of these stations is to document wind spe~dJdirection and measure aeolian sedi- ment-transport rates using anemometers and sand traps. The work plan for these instrument stations calls for their contin- ued operation until December 2005, after which time they are scheduled to be removed. Data collected at these weather sta- tions will be discllssed in a separate report. Because the relative significance of various sedimentary and geomorvhic processes can differ widely bel\\'een sites, specific causes of archaeological-site erosion. and specific measures needed to rectify erosion, must be determllled on a site-by-site basis. We propose a series of questions that must be answered to detennine the extent to which aeolian sediment deposition affects the preservation potential of archaeological sites. The first two questions in this series are: ( I) What is the depositional context of sediment on which the site is built? (2) Whal is the depositional context of sediment that has buried/protected the site? These two questions require detailed field analyses of the stratigraphic and geomorphic context of each site. using the methods described in this report for the work at Palisades. Lower Comanche. and Arroyo Grande. The results described in this report are intended to answer these research questions for the three locations considered. To move toward developing a plan for mitigation of archaeological-site degradation. addi- tional questions follow. If the answer to question 2 is aeolian sediment. one asks: (3) Is there evidence for loss of aeolian sediment that pre- viously covered the site? Establishing whether or not aeolian-sand cover has been lost from a site provides a means by which to gauge the risk or degree of site degradation. Ifno loss ofaeolian sediment is suspected at a particular site. that site may not be at immediate risk of artifact Joss; in such n case, it may not be necessary to continue with the remaining questions that identify the degree of sensitivity to dam operations that could have contributed to degradation. A loss of aeolian sediment at a site could be most accurately documented using repeated high-resolution survey mapping to quantify aeolian deflation and/or gully incision. If such methods are not available, loss of aeolian sediment can be qualitatively inferred using repeated ground-based photog- raphy and geomorphic and sedimentary evidence of deflation. Evidence for deflation can include pedestal development. lag deposits on the land surface, and exhumation of plant roots. Deflation of aeolian sand in an area that had fomlerly experi- enced aeolian deposition can result from continued wind action