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3) GEOMORPHOLOGY OF MANCOS SHALE TERRAIN W I- 101'.- .:"".J The Mancos Shale terrain between Grand Junction, Colorado and Price, Utah, which is the subject of this chapter, is in its simplest form a high escarpment (Book Cliffs) with a pediment at its base. This ideal situation is achieved near Crescent Junction, Utah where the escarpment, capped by Mesa Verde sandstone rises steeply above a southward-sloping pediment. Toward Price to the west and Grand Junction to the east the landforms become more complex as the Green, Price and Colorado Rivers are approached. Elsewhere dissected pediment surfaces are fringed by badlands, and the base of the Book Cliffs is formed by a zone of rugged Mancos-Shale badlands. Often within a short distance, gently-sloping gravel-capped pediments are replaced by steep rapidly eroding badlands. On a gtoss scale this variability is revealed by a relative relief map that was prepared by Johnson (1982), in an attempt to show landform distribution on the Mancos Shale outcrop between Grand Junction and the Utah-Colorado boundary north of the Highline Canal (Figs. 3-l, 3-2). As relative relief increases, so does the presence of deeply-incised channels, steep channel gradients, and steep hillslopes all of which signify greater erosion and, therefore, greater salt release. The purpose of the map, then, is to visually distinguish areas according to their relative erosional stability and salt production. The relative relief map shows clearly the great variability of relief in the study area. Relative relief ranges from 12 m/km2 along a portion of Big Salt Wash and near East Salt Creek to more than 500 m/km2 along the Book Cliffs escarpment. The steep terrain of the escarpment is obvious, and there is a 2 to 3 km wide zone along the cliffs which has a relative relief of at least lOO m/km2. According to this map, the most stable areas are as follows. between Badger Wash and East Salt Creek, along and to the east of East Salt Creek, the area drained by the lower portions of Big Salt Wash and Lipan Wash, along Little Salt Wash, and near Walker Field. using available topographic maps, aerial photographs and field reconnaissl!ince Johnson (1982) identified three major landform classes within the area shown on Figs. 3-l and 3-2. These are badlands, pediments and alluvial valley floors. A similar classification system was developed by Schafer (l981) in the Woodside, Utah area. Johnson 31 '.~ " , ':1 '1 ,) ~ .! 1 " ,1 ~ ~ ~ '~ 1, ,1 ;: ~; 5 J , :0 , .'~ :~ 1 .j ,-~, , ;{ 'l a " , ) t , 'j , 4 . -,;,--,~-':{,"