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'. , 30 Sedimentology and Stratigraphy of the Palisades. Lower Comanche. and Arroyo Grande Areas.of the Colorado River t' accompanied by reduced sediment supply in the source area from which the sand is derived. Therefore, if it can be estab- lished thai degradalion of the archaeological site is related to a loss of aeolian sediment cover, the next question that arises is: (4) What is the source of the aeolian sedimenllha! has buried the site? Positive identification of the source area for aeolian sedi- ment can best be made by documenting wind conditions at this location over a representative period of time. In this river corridor, the most prominent sources of nev..' sediment from which the wind can mobilize sand are sand bars created by flu- vial deposition of sediment (see, for example, Schmidt, 1990). It is also possible for large aeolian dune fields (which have developed by accumulation of windbome sand from fluvial deposits) 10 serve as source areas for other, secondary aeolian deposits located farther from the river. Records of wind speed and direction can be llsed to generate vector sums that demon- strate the potential for aeolian transport of sediment over time; this is the primary objective of data collection at the weather stations now in operation at six locations along the river cor- ridor (mentioned above). Because wind conditions may vary widely from season to season, and even from year to year, the longer the time interval from which data are lIsed. the more accuratc net sediment-transport calculations and predictions will be. Once a source area has been identified on the basis of local wind conditions. it is necessary to ask: (5) Has there been a demonstrated reduction in the source area from which this aeolian sand is derived? Aerial photography and repealed high-resolulion map- ping can be used to identify historical changes in the amollnt of sand available in the source area for aeolian transport. A demonstrated redut:tion in the open-sand area at the source indicates that less sand would therefore be available for trans- port toward and redeposition at the archaeological site in ques- tion. The definition of"open sand" (sa!1d that is availab_le t~ be tran-sported by wind) is somewhat loose, because multiple fac- tors affect the entT3inment of sand by wind to varying degrees. Aeolian sand transport is limited by the presence ofvegeta- tion (Olson, 1958; Bressolier and Thomas, 1977; Ash and Wasson, 1983; Wasson and Nanninga, 1986; Buckley, 1987; Bauer and others, 1996), interstitial moisture in the sediment (Sarre. 1988, 1989; McKenna Neuman and Nickling, 1989; Namikas and Shennan. 1995; Wiggs and others. 2004). trap- ping of sand by gullies (Bauer and others, 1996), nonerodible surface objects such as rocks (for example, Gillette and Stock- ton, 1989). and cryplogamic soil cruSls tLeys and Eldridge. 1998; Belknap, 200 I; Goossens, 2004). A reduced potenlial for aeolian entrainment of sand from a given source area could therefore be manifested in the fonn of increased vegetation on the source-area sand bar, an increase in the moisture content of the exposed sand area (caused either by flow fluctuations or precipitation), increased exposure of rocks that obstruct \vind, or development of cryptogamic soil cmst on the source-area sediment. If a loss of open sand in the identified source area is inferred. one needs to ask: (6) Could renewed deposition of aeolian sand have a sub- stantial restorative effect on this site? Sites at which renewed aeolian deposition would "sub- stantially" improve the preservation of cultural features would be those at which the greatest threat of degradation is from deflation of sediment cover by wind, from incision by gullies small enough to be healed by wind-blown sand (those on the order of gullies observed on the land surface and in stratigraphic sec- tions by this research group: see also Thompson and Potoch. nik, 2000). Aeolian sedimentation is not expected to protect (in tenns of its ability to prevent complete loss of the site) archaeological features that are more threatened by incision of a major gully, arroyo, or side-canyon channel than Ihey are by the loss of aeolian sediment. In the case of sites that have been compromised by migra- tion of aeolian dunes, leading to the destabilization of surfaces on which the sites were fonned (for example, fig. 48), renewed deposition of aeolian sand during dune migration could rebury artifacts but would not lead to preservation of the site in its original, intact state ifartifacts have migrated downslope. If the answer to question 6 is 'yes,' a final additional question that begins to involve larger-scale management decisions should be asked: (7) How could this be accomplished') This final question is obviously broad, but given that increased deposition of aeolian sediment at a particular site would (in our line of reasoning) be linked to an increase in sand available for aeolian transport from the source area, the question could be rephrased to ask, how could the source area for aeolian sediment at this site be enhanced? Because river- level sand bars constitute the largest SO!1Tce of flew sediment that could be mobilized by wind, an increase in the area of open sand available on river-level sand bars would enhance the potential for aeolian sand transport and redeposition in the vicinity of the archaeological site considered. In Grand Canyon. management options include restoration of open.sand area on river-level sand bars throughout the river corridor using BHBF flows (Bureau of Reclamation. 1995). Behavior ofa particular sand bar that is of interest as an aeolian-sedi- ment source during a BH BF flow may be gauged using aerial photographs or mapping conducted before and aner Ihe 1996 BHBF. However, future BHBF flows may induce local aggra- dation or degradation pattems that arc not identical to those of the 1996 flow, if sediment concentration and flow operation are dinorenl from Ihe 1996 controlled flood experiment. Additional management considerations related to the observations of this study are discussed below~ as they involve processes not limited to aeolian sedimentation.