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<br />Journal of Geology <br /> <br />LARGE FLOODS ON THE COLORADO RIVER <br /> <br />5 <br /> <br />'- <br />0,1 <br />" <br />~, <br /> <br />80 <br /> <br />Crevice Deposits '4,000 m) sec" <br />12000 <br />10000 <br />8000 <br />6000 <br /> <br />75 <br /> <br />In <br />~ 70 <br />~ <br />CI> <br />E <br />,565 <br />r: <br />o <br />.~ 60 <br />a; <br />W 55 <br /> <br /> <br /> <br />Figure 4, Distribution of flood sed- <br />iment and calculated water surface <br />profiles near Axehandle Alcove, All <br />of the undescribed sections are <br />capped by G1 deposits, The eleva- <br />tion datum is arbitrary, The sur- <br />veyed water surface rises down- <br />stream because river stage was <br />rising during the course of the sur- <br />vey, Flow is right to left, <br /> <br />;',' <br /> <br />" <br /> <br />Surv.yod WsW Surface (3/14190) <br /> <br /> <br />50 <br /> <br />- G1'(lll84?) <br />. Described stratigraph6c sections <br />n Undoscrll9d sits <br /> <br />,., <br /> <br />45 <br /> <br />400 <br /> <br />800 <br /> <br />SOO <br /> <br />200 <br /> <br />o <br /> <br />Distance, in meters <br /> <br />cent cliffs, and charcoal accumulations from hu- <br />man occupation between floods, Limits on the <br />chronology of floods were determined by several <br />radiocarbon analyses of (J I charcoal from the sedi- <br />ment at Axehandle Alcove (figure 31 and (21 plant <br />fragments and fecal pellets of Neotoma (pack ratsl <br />incorporated into the highest crevice deposits (ta- <br />ble JI. The oldest dated material was a charcoal <br />accumulation near the bottom of the exposure, <br /> <br />Table 1. Radiocarbon Analyses <br /> <br />1,000 <br /> <br />1.200 <br /> <br />The age of this sample requires that 14 of the 15 <br />flood deposits exposed at Axehandle Alcove were <br />emplaced by floods after 4518-4239 cal yr B,P, A <br />date from a hearth in the middle of the section <br />indicates that there were ten flooda large enough <br />to overtop the section after 2307-2062 cal yr B,P, <br />In a correlative sequence of flood deposits across <br />the river, radiocarbon analysis of plant fragments <br />preserved immedistely below Gl requires it to <br /> <br />~..! <br />~.. <br />~ <br /> <br />:~.. <br />~: <br /> <br />~::" <br />",: <br /> <br />~ :" <br /> <br />':1 <br /> <br />(" <br /> <br /> Calibrated <br />Material I4C Date' At,eb <br />Analyzed 613C (%0) (14C yr BP) lcal yr BP) <br />Neotoma fecal -21.8 1425 :t 130 1517-1187 <br />pellets, plant <br />frogments <br />Charcosl -25,8 2150 :t 140 2340-1994 <br />Charcosl -25,9 2155 :t 75 2307-2062 <br />(hearth) <br />Charcosl -22,2 2470 :t 85 2715-2384 <br />(hearth) <br />Charcosl - 24.4 2930 :t 165 3323-2888 <br />Charcosl -14,2 3530 :t 80 3919-3704 <br />(hearth! <br />Charcosl -21.6 3915 :t 85 4518-4239 <br /> <br />Laboratory <br />Number <br /> <br />GX-I6055 <br /> <br />GX-I6052 <br />GX-I6053 <br />GX-I6049 <br />GX-I60SO <br />GX-I6054 <br />GX-I6051 <br />Right Bank <br />GX-I6012 <br />GX-16024 <br /> <br />Plant Frogments <br />Neotoma fecal <br />pellets <br /> <br />!< <br /> <br />~. . <br />K::,' <br />~ <br />~ ..... <br />,. <br />:<;. <br /> <br />:\. <br />;;, <br /> <br />~~~ <br />::~) <br />1 <br />.y. <br /> <br />-25,7 <br />-23,3 <br /> <br />330 :t 120 <br />1470 :t 190 <br /> <br />520--280 <br />1595-1179 <br /> <br />. Radiocarbon ageslin "c yr 0,',) are baaed upon the Libby hall We 15570 yearsllor "e. The error stated ia :t 1<1 aa judged by the <br />analytical data alone, The age ia referenced to A,D, 1950, <br />b Calibrated agea are dendrologically calibrated {Stuiver and Reimer 19861, with resulta presented in calender years belore present, <br />"Present" is A.D. 1950. Reponed ranges reflect :t: 10' uncertainty and no laboratory error multiplier. <br />