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,. ", ~ CH~'l -r.",,"lAnOr~' . PARK'"' ,J ,; I ' ,/ ..In.,.1 t..... .:....b Bo"om / .~:-"....../. I [RKl // .1 . I G _____/!QJ /......:.1 J ~' ( i~.1 ~ i CAN~~~S I '\'PDI..h REGION 1 ... ...., 'II, PARK : \ .1. S.I Juclion l i 'h'- ........ . ..J \ r--_ ~.......'.J t. REGj>N 2 REGIPN 3 4- -1"::::-'::" ~ L - - /RKl L _ --..,d _ " l.QJ r--- I r- ---..:."':\-_, REGION 5 ---i-~<,~o<' ._._. I REGION 4 l..r":'l__ L. ~'-o I --....--....-J '. - 0; '-,... I.... .- .~& '_'-..' .~ ~..J ,-0 !~'IDI c.~ ~ ! i~ ~ ~ ,'- J . J HliE-'WUNA ,_J~l I ~ I -L11 . ~ ~. GLEN CAHYOtl ;- 'IIA nONAl ... ! RECREATION AREA ,J" r l J'-~: ~:.r J~ . "-\.'\.. . . . . . . I Lllh ''>.': ,< P~tud' Miles 10 r'- Cr...,,' Junction . /RKl ~ .HonklYiUe Region 4-Cataract Canyon (RK 326-344); and Region 5-Lake Powell innow (RK 316-326). The river in region I was low-gradient, meandering, and lined with tamarisk (Tamarix spp.) and willow (Salix spp.), with a primarily sand and silt substrate and intennillent deposits of alluvial cobble and rock outcrops. The river in region 2 was similar with a greater proportion of sand substrate. In region 3, the river was a continuation of this channel geomorphology between the connuence and Cataract Canyon, whereas in region 4 (Cataract Canyon), the river was unique for the only extensive rocky habitat for more than 150 km upstream. It was also the deepest region in the upper basin, with a maximum water depth of 30 m at RK 341 (Valdez et a!. 1982). Region 5 consisted of deep deposits of silt and sand, which filled lower Cataract Canyon in the Lake Powell innow. Fish habitat in each region was largely detennined by shoreline type, because much of the main channel had a shifting sand bollom with Iillle cover for fish. Five types of shorelines were classified including (I) tamarisk- willow, (2) talus-scree, (3) rock ledges, (4) vertical walls, and (5) sand beaches. The tamarisk-willow habitat was the most common, particularly along silt and sand banks in regions 1,2 and 3. This habitat was characterized by dense growths of tamarisk and willow with overhanging and submerged branches and root wads. Talus-scree habitat was present below steep uncon- solidated slopes where boulders and other colluvial materials had spilled into the river, sometimes fonning large whitewater rapids. This habitat was preva- lent in region 4 and occurred intennillently in regions I, 2, and 3. The boulder and cobble jetties fonned by these talus slopes created large eddies with sandy reallachment bars and associated eddy return channels (backwaters) that were important fish habitat. Rock ledge habitat was present where low walls of metamorphic or igneous rock overhung the river in the lower reaches of regions I and 2. These ledges were characterized by depressions and pockets worn by water action and were good fish habitat when associated with rock substrate. Shifting sand substrate provided Iillle cover and low productivity; reducing the fish habitat value of rock ledges, particularly for native roundtail chub (Gila robllsta)-a species with close affinity for rock substrate (Valdez et a!. 1982). Vertical wall habitat was prevalent in the lower reaches of regions I and 2 and throughout region 4. This habitat was created by steep, high walls of sedimentary or metamorphic rock that emerged from below the water surface. These smooth walls had few irregularities, and the absence of an associated rock substrate negated their value as lateral cover for chubs. Sand beach habitat generally had an associated shifting sand bOllom and usually fonned the banks of nursery backwaters. This shoreline habitat was common in regions I and 2 but occurred intennillently in regions 3, 4, and 5. Flow and temperature of the Colorado and Green rivers varied dramati- cally during our investigation. Before the study, record high nows of about ,~ lo4ontit-.llo . Fig. I. Five study regions of the Colorado and Green rivers in and adjacent to Canyonlands National Park. of 1,128 m), depending on lake level. The study area was divided into five regions: Region I-Green River, above the connuence with the Colorado River (RK 0-80); Region 2-Colorado River, above the connuence with the Green River (RK 0-80); Region 3-Connuence, to the first rapid in Cataract Canyon (RK 344-350);