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. R . __..__.~ __._, _. ....___..._...,_ - _ _ .1 _ ~2i it crosses in an independent manner. Gregory {l"950, p. iS7j stated ". these streams so completely out of accord with regional slopes, originated on surfaces no longer represented in the landscape." In .the canyons of Zion, Parunuweap, i.a Verkin and North Creek the streams -often follow sinuous meanders characteristic of a mature stage while the topography of the canyons is youthful. The streams once flowed . over "old surfaces" where meandering was characteristic. 1rl;th regional uplift the streams incised without much change in pattern (Gregory 1950). In contrast to the major river valleys, the minor valleys are o,`ten controlled by the~rock structures through which the smaller streams, .both perennial and annual, f]ow:~Ash Creek follows the Hurricane fault; the Santa Clara River skirts a lava ridge; the North Fork in Zion Canyon and the East Fork in Parunuweap Canyfln have trellis drainages contro]-led by fractures in the Navajo sandstone (Cook 19bQ). . The divide between .the Virgin River basin and the Bonneville basin lies along the southern edge of the Markagunt Plateau. Rivers to the north of the divide, including the Sevier River, are characteristically north-trending and post mature while those to the south, including the Virgin River; are youthful and head in steep -walled gorges of high gradient. These youthful streams are extending headward while the north-trending streams are becoming correspondingly .shorter (Gregory 1950). Ash Creek has worked its way headward a few kilometers into the loose basin fill north of Kanarraville. Gardner (i94i~) states that waters from the adjacent plateaus flow sometimes north into the Great Basin or sometimes south into Ash Creek depending on which distributary they follow across the.a]luvium.