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Show 29 Briefty ) Me prii1cipal topographic features Are a broad plateau , dissected by the Colorado aiid ( Qrec" Qrec ) Rivers ( photograph 34 , Exhibit 11C ) ( and aild ) their tributaries , whiell , for the ( most niost ) of their courses , flow through ( canyons cailyous ) ( which whicb ) , as has been described by Powell ( Exhibit 51 ) , vary in depth from a few liundred feet to more ( than thail ) 2,500 feet . . The caiiyoiis frequently have ( inner imier ) gorges , , with the higher walls ( rising Tising ) in gigantic steps to a flat divide . . ( Photograph 34 , Exhibit 11B . ) Isolated mountain niasses which rise above the plateau are the LaSalle Moulitailis , ( lying bril-icy brilicy ) 15 to 20 miles ( east cast ) of the Colorado ( Ri-x"er Rixer ) , , slightly southeast of , ( Moab Aloab ) ; the Blue or Abajo ( Mountains Alountaius ) , 25 ( miles udles ) southeast of Cataract ( Canyon Canyoii ) aild 40 ( miles niiles ) ( north noTth ) of the ( San Saii ) Juan River ; ( "I'lid Ilid ) the ( Henry Heliry ) ( Mountains Mouutains ) , from 12 to 25 miles ( northwest iiorthwest ) of Upper ( Glen Gleii ) ( Canyon Caiiyou ) . Although topographically a plateau , each wash aiid stream ( tributary trib-utary tributary ) to the ( main imain ) river has eroded deep caJ137onS , , which finally ( find fiiid ) ( their 1-beir 1beir ) way to the river . . Various geologic ( strata stratzi ) composed of ( saild- saild ) stone aiid shales of various degrees of hardness have ( been beeii ) eroded by the ( elements elemelits ) hito walls , ( benches beiieJies ) , , ( and aud ) terraces , creating a terrain that ( baf- baf ) fles ( description descriptioli ) . . ( Photograph No . 17 , Exhibit 11B . . ) ( No . . 26 , , Exhibit 11B . ) The ( n-ifilor nifilor ) stream channels are ( generally geiierally ) without water , but eiiormous accumulations of coarse alluvium , the product of |