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Sedimentology and Stratigraphy of the Palisades, Lower Comanche, and Arroyo G:~iAreas of the Colorado River t!"ti-,f' with respecllo the CfoTada River) margin of the extensive playa deposits behind the dune field. Section 4, 85 m soulh- west of section ], is a pit dug into the surface ofa small playa exposure west of the main playa area. Geomorphic characteristics of the area surrounding each archaeological site studied at Pat1sadcs are discussed in appendix I (figs. 37 Ihrough 39). Stratigraphic data 'llld geo- morphic observations are sUlllmarized in the section below titled "Palisades Site Summary"'. to in 1998 and 1999 showed Ihat aeolian sedimenl deposited after the 1996 BHBF flow had been relained at Palisades, and that arroyo incision in the 3.5 years following the flood had not yet reduced Ihe arroyo flood elevalion to its preflood level (Hazel and olhers, 2000). Medium-formal photographic stations were established before the 1996 BHBF flood at locations where the an"oyo sho\'..:ed filling and erosion after the flow. NPS archaeologists continue to take photographs at those locations. as par! of the site-monitoring program. at selected areas to monitor these processes near the mouths of significant arroyos such as the one at Palisndes (for example, Balsam and Larralde, 1996). Archaeological Significance The wide, relatively flat land in the Palisades area con- tains abundant evidence of prehistoric human occupation. Nine separate prehistoric archaeological sites have been iden- tified, several of which contain multiple habitation and artifact features (Nalional Park Service, 2004). Sites have been dated by radiocarbon methods and artifact identification to Pueblo I and Pueblo II (PI and PII) periods (A.D. 800-1000 and A.D. 1000-1150 respectively: Fairley and olhers. 1994). Several of the sites are affected by the development of an arroyo system in the central Palisades area, which has contributed to the loss of anifacts in some areas. Check dams have been placed in several branches of the arroyo by the National Park Service (NPS) and representatives from the Zuni Tribe to reduce the erosion of arti facts by arroyo incision (Leap and Coder. 1995). To limit damage to archaeological sltes by visltor impact. NPS relocated a section of the Beamer Trail through the Palisades area in 1992. In addition to prehistoric cultural features. historical arti- facts are present at Palisades dating back to mining operations in this area during the late 1800s and early 1900s. Two mine shafts, with tailing piles, are left as evidence of copper ore extraction at the Tanner-McCormick rnine, which ceased to be actively mined in 1920. Historical feahlres include the remains of a cabin (used betWeen 1890 ano 1910) wiih associated metal and glass artifacts; many items have been removed by visitors in the last few decades (Coder, 1994). Stratigraphic and Geomorphic Analyses Locations of stratigraphic sections described below are shown on figure 2. Detailed stratigraphic logs are described in appendix I (see figs. 32 through 36). Section I is a verti- cal face that forms the north \\'311 of the main arroyo trunk at low elevation. Section 2 is located 78 Illlandw~rd (east; up-arroyo) from section 1, and was compiled from sediment exposures in an arroyo wall as well as a shallow pit excavated in the arroyo floor at the base of the naturally exposed wall. Section 3 is located farther up the arroyo, 40 In from section 2, and is a pit dug into the surface at the northem (upstream, Grain-Size Analyses Figure 6 shows the results of grain-size analyses on two horizons from section I. Unit F, an aeolian unit, is shown to be coarser than unit G, a fluvial deposit within this stratigraphic section. Figure 7 shows the grain-size distribution for unit H of section J at Palisades; this horizon contained no diagnostic sedimentary structures, and its depositional environment could not be definitively ascertained in the field. The grain-size plot is ambiguous also; this sample plots between the fields defined by known fluvial and aeolian deposits (fig. 7). The most likely explanation for this horizon is that it is a fluvial deposit that has undergone some degree of winnowing by wlnd, but not enough to remove all of the fine grains that would leave a mahue aeolian lag deposit. Grain-size analyses for three horizons within section 4 are shown in figure 8. Three of these samples were collected from unit B. a flood deposit wirh \....el1-defined fluvial climb- ing ripples. This flood depo,it coarsens upward slightly (fig. 9). Upward coarsening of deposits has been attributed by Rubin and olhers (1998) and Topping and others (2000a) to sediment-supply limitation during the flood that deposited a particular stratum. This inverse grading occurs as fine-grained suspended sediment becomes progressively depleted through- out the duration of the flood (the finer sizes having been transponed downstream earliest and fanhest); given un1im. ited sediment supply, constant bed conditions, and sufficient accommodation space. a flood deposit should first coarsen and - then fine upward. mimicking suspended-sedirllent respon-se to Ihe hydrograph. Unit E of section 4, the poorly sorted distal debris flow sediment. exhibits a coarser overall grain-size profile thanlhe fluviallmils (fig. 8). The one sample analyzed from the fluvial depositullit F in section 4 is finer than any of the Ihree samples from lmil B (fig. 8). Driftwood Elevation Survey: Palisades Stage- Discharge Relationship In order to establish an approximate stage-discharge relationship for flood elevations in the Palisades area, the loca- tion and elevation of driftwood logs were surveyed during field work in May 2004 by D. J. Topping and 1. E. Hazel. Horizont~l coordinates of survey data are referenced (0 the NAD83( 1999) epoch and were projecled into NAD83 Ari-