56 W. CROSS — WIND EROSION IN THE PLATEAU COUNTRY 



the northwest, and it seems reasonable to suppose that they have long had 

 the same direction. While the wind transportation of dust and fine sand 

 is thus demonstrated on the plain, the whole process of deflation, of which 

 the transportation is a part, may be studied in the area lying between the 

 Abajo and La Sal mountains. Here also may be found some measure of 

 the denudation accomplished. 



The Plateau Country East of Grand Eiver, Utah 



If the reader will refer to the Hayden map of this border zone between 

 Colorado and Utah,^ or to the Abajo and La Sal topographic sheets of the 

 U. S. Geological Survey, he will see that the Great Sage plain, floored by 

 the Dakota sandstone, forms the divide between these two mountain 

 groups, wraps around the northern base of the Abajo mountains, and 

 ends in flat-topped ridges reaching out toward the Grand Eiver canyon, 

 but a few miles distant. The scarp by which the plain is terminated on 

 the west and north is the uppermost of a series of cliffs marking the out- 

 crops of the harder, more resistant members of the middle Mesozoic sec- 

 tion which have been cut through by Grand river. The same rocks also 

 form the floor of terraces extending back from these scarps to varying 

 distances. It is this type of topography which characterizes the Plateau 

 country adjacent to the larger canyons, not so overpowering here as in 

 the Colorado Canyon district farther south, yet meriting the glowing 

 descriptions given of it by Newberry^ and Powell.'' The principal sand- 

 stones seen in scarps or terrace floors, as the case may be, occur at various 

 horizons within the White Cliff (Jurassic) or Vermilion. Cliff (Triassic) 

 groups of Powell, or, in the terminology of the southwestern Colorado 

 stratigraphic column, respectively the La Plata and Dolores sandstones. 

 Between the La Plata and Dakota sandstones occurs the McElmo (Juras- 

 sic) formation, some 500 or 600 feet thick, made up of friable sandstones, 

 sandy marls, and clays, so destructible that the formation usually presents 

 a steep debris-covered slope below the Dakota rim of the upper plateau. 

 All these formations are prevailingly reddish in color, varying from light 

 pink to the strong deep red of the Vermilion Cliff sandstone. The White 

 Cliff sandstone forms the "Orange cliffs" of this region, and in many 



5 U. S. Geological and Geographic Survey of the Territories, etc. Geological and Geo- 

 graphic Atlas of Colorado and portions of adjacent territory, by F. V. Hayden, 1881, 

 sheets xiv and xv. 



" J. S. Newberry : Report of expedition from Santa Fe. New Mexico, to the junction of 

 the Grand and Green rivers of the Great Colorado of the West, in 1859. Washington, 

 1876, pp. 93-100. 



' J. W. Powell : Exploration of the Colorado river of the West and its tributaries. 

 Washington, 1875. 



