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<br />1496
<br />
<br />W, L. GRAF
<br />
<br />mained unaffected by the tamarisk invasion
<br />a, (Figs. 4, 5). Field evidence suggests that the
<br />Wsurface has been stable for 1,000 yr or
<br />more, as indicated by the presence of Fre-
<br />mont Indian petroglyphs on nearby walls
<br />
<br />
<br />Ie
<br />
<br />il(, ,
<br />1\:
<br />fie'
<br />'ii'
<br />il
<br />
<br />~J,11
<br />r'
<br />: Ii
<br />
<br />! !':j
<br />i!
<br />!U
<br />
<br />, I
<br />
<br />, l
<br />I! 1
<br />
<br />i!~ ,;
<br />
<br />r,'t
<br />
<br />~
<br />!.,!rl e
<br />kJ;
<br />~~! ~
<br />
<br />iT
<br />
<br />~
<br />
<br />~
<br />f/)
<br />~ 600
<br />~
<br />0
<br />Z
<br />~
<br />a:
<br />C)
<br />::l!: 500
<br />0
<br />a:
<br />LL.
<br />.-
<br />::l!: E
<br />~
<br />IU
<br />a: 400
<br />l-
<br />f/)
<br />Q.
<br />::)
<br />IU
<br />0
<br />Z 300
<br />~
<br />I-
<br />fJ)
<br />0
<br /> 200
<br />
<br />that would be accessible only if the terrace
<br />were stable at the time the artwork was done.
<br />Anasazi artifacts and a few Anasazi struc-
<br />tures on the surface provide further evi-
<br />dence of stability since the period 1075 to
<br />
<br />90
<br />
<br />
<br />1400
<br />
<br />1200
<br />
<br />1000
<br />
<br />800
<br />
<br />600
<br />
<br />400
<br />
<br />200
<br />
<br />o
<br />
<br />E
<br />oM.
<br />
<br />Figure 8. Spread of tamarisk through Colorado and Green River systems as indicated
<br />by historical photography. Locations plotted in Figure 6; sources of data given in Table 2.
<br />
<br />H, MANILA,UTAH
<br />
<br />800
<br />
<br />F., LOWER SPLIT MOUNTAIN CANYON
<br />
<br />700
<br />
<br />E. GREEN RIVER (Town),
<br />UTAH .
<br />
<br />D,CONFLUENCE OF THE
<br />GREEN AND COLORADO
<br />RIVERS
<br />
<br />C, MOUTH OF THE
<br />SAN JUAN RIVER
<br />
<br />. 8, LEE'S FERRY
<br />A,HEAD OF MARBLE CANYON
<br />
<br />100
<br />
<br />o
<br />1890
<br />
<br />1910
<br />
<br />1930
<br />
<br />1950
<br />
<br />1970
<br />
<br />Site' Probable
<br />approximate
<br />invasion
<br />date
<br />
<br />
<br />1250 A,D. (see Mutschler, 1969, foCa
<br />cussion and precise locations of some ~,
<br />tures). Talus blocks that have falle~'L
<br />overhanging cliffs since the cessan~n i
<br />deposition of desert varnish about'2
<br />B,P, rest on the surfaces of many of i
<br />upper terraces. Cabins built by settletsll
<br />the upper surfaces do not appear to~
<br />sustained flood damage, suggesting thaI:
<br />least in the past 80 to 90 yr the surfa~,II;
<br />not been flooded, ,il:
<br />The most obvious response of the ma.:
<br />channels to the influx of tamarisk has" ,i
<br />channel restriction by encroachment i:
<br />stabilized materials and low terraceS"
<br />ered by tamarisk thickets. Figure' 9 sh~!1
<br />the changes over the past century in a 'I
<br />section of the Green River at mile 67,91,
<br />frequently photographed site on Bawk,:,
<br />Bend (see Fig. 7 for location; mile marksi~
<br />measured upstream from the confluenlt]
<br />the Green and Colorado Rivers and
<br />shown in detail by Herron, 1917, and"
<br />Belknap and Belknap, 1974). Before the!
<br />rival of tamarisk, the cross-river distao"
<br />between stable bank materials was co,_
<br />tent, suggesting that the bank-tocba,
<br />width was in equilibrium with the discha
<br />of the stream. After the establishmento(,
<br />plant and anchoring of materials';i
<br />bank-to-bank width was substantiallYj, .
<br />duced, and apparently a new equilibrl
<br />situation prevails, with no substall"
<br />changes in the last 25 yr. .ii,
<br />The changes in cross section at Bow
<br />
<br />TABLE 2, SOURCES OIi
<br />DATA FORFlGURE 8 !
<br />
<br />.Jl
<br />Kolb brothers' photo (19~1
<br />E. C. LaRue photo with,;
<br />tamarisk (1914-192TIl"."".,."I,I,',
<br />exact date not kno ,
<br />H, D. Miser phot~ with'
<br />tamarisk. (1921) ,,' .
<br />H. D. Miser photo withil
<br />tamarisk (1921)t; H.Ei
<br />Gregory phot~ with,
<br />marisk (1923)
<br />E. C. LaRue photo with'
<br />tamarisk (1921)\ .
<br />C. Eddy photO with'
<br />tamarisk (1927)jl
<br />Christensen (1962),!li i
<br />Maurie and "Penfold. (
<br />,,/.)'
<br />Thomas (1952) '"III
<br />Robinson (196S) ,II ,II
<br />1 '~ ~: L JI;
<br />. See Figure 8. ,. ,.~i [I
<br />t Photos in U,S. Geological Survey A .
<br />Denver, Colo. . "
<br />
<br />A
<br />B
<br />
<br />1910
<br />1921
<br />
<br />c
<br />
<br />1922
<br />
<br />D
<br />
<br />1924
<br />
<br />E
<br />F
<br />G
<br />H
<br />
<br />1931
<br />1955
<br />1952
<br />1961
<br />
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