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<br />-"'i <br /> <br />, <br /> <br />-...:~~- ..;,.:::...... ....: " <br />.." <br /> <br />~".... . <br /> <br />.~ .~-~ <br /> <br />J <br /> <br />- <br /> <br />..:..--._ '~'. .M.o... <br /> <br />C.F. Waythomas. R.D. Jarrett / Geomorphology II (/994) JS-ro <br /> <br />23 <br /> <br />T:lble2 <br />Radiocarbon d:ncs from alluvial and flash. flood deposits, Arthurs Rock Gulch <br /> <br />S~p[e No.. Lab no. Reported age Dlibl'3ted ageb <br />location and (C-14 yr BP)' <br />m::lteriald:uerJ yr BP yrAD <br />I !/14/89-4 , GX-15640 465 = 160 644.517.314 1306.1433.1636 <br />Site I. Unit e <br />'Wood <br />1111.1189-5 GX.15641 240 i: liO 500.297.0 1450.1653. 1955 <br />Site I. Unit C <br />wood <br />1111",39-11 GX-15643 .1320:t 225 5289.4868.4566 3340.2919.2617< <br />Site :.CnirA <br />charco:ti <br />IIIi.1i90-CI.1.! GX-I669:J 215 ~75 311.289.0 1639.1661.1955 <br />Site ..;., FE) <br />wo'~(~ <br />[J,' i~/90.C[4-2 GX-16692 260 = 75 .132.302.0 1518. 1648. 1953 <br />3::~ .:.. FB3 <br />'",'cod <br />1 1/:0/90-CI4-2 GX.I6694 430 = 75 531. 509. 457 1419.1441. 1493 <br />Site:. FB3 <br />wood <br />III:Oi9Q-CI4-3 GX-I6695 99,6=2.3% <br />Si(~:.. FaJ of 1950C-14 <br />wood activity <br />~BP .lges reported with respect to year AD 1950. <br />~D:{~ ~libnl.[ed using method of Stuiverand'Reimer (1987), reponed 3S (-1 (j (age) + 10-). <br />'BC "ges, <br /> <br />(%1 <br />.17 <br />28 <br />:!5 <br />36 <br />64 <br />0 <br />25 <br />24 <br />51 <br />45 <br />55 <br />69 <br />31 <br />65 <br />35 <br />35 <br />65 <br />73 <br />27 <br />56 <br />44 <br />100 <br />0 <br />63 <br />37 <br />1!4 <br />16 <br />72 <br />28 <br />63 <br />37 <br /> - <br /> ,.;' <br />:3 the ~ <br />i <br />,ath- <br />lage , <br />~ <br /> <br />I <br />4.2, Process identification and c/asrfabric <br /> <br />In steep mountain catchments like AnhutS Rock <br />Gulch. coarse bouldery sediment is delivered to the <br />valley bottom by several processes. Flash floods, debris <br />flows. debris avalanches, and rockfalls are all important <br />geomorphic processes in the Colorado Front Range <br />foothills (Costa and Jarrett, 1981). Deposits produced <br />by the last three processes are probably the primary <br />sources of sediment for flash floods. In the westernpan <br />of the foothills zone (in the sub-alpine ecotone). above <br />2100 to 2300 m, rainfall-induced flash floods are less <br />common than they are below this elevation and rainfall. <br />discharge. and paleofloOd data indicate no substantial <br /> <br />flooding above 2300 m (Jarrett. 1990). However. <br />debris-flow deposits are recognized throughout the <br />foothills zone. and commonly are found below the ele- <br />vation limit for flash floods in the Colorado Front <br />Range. Thus, in a paleoflood investigation it is impor- <br />tant to diiferentiatebetween depOsits fonned by flash <br />flooding and deposits formed by debris-flow or other <br />mass-movement processes because paleoflood recon- <br />structions would be erroneous if made on deposits other <br />than water-flood deposits (Costa and Jarrett, 1981), <br />Criteria for differentiating between debris-flow-and <br />water-flood deposits are described by Costa and Jarrett <br />(1981) and Costa ( 1988). Such criteria are most'tlseful <br />for deposits that are fresh ( < 100-200 years old) and <br />