IOWA ACADEMY OF SCIENCE 
157 
ARID PLATEAU-PLAINS AS FEATURES OF EOLIC EROSION. 
By Charles Keyes. 
Of all geographic features peculiar to arid areas plateau-plains have long 
remained explicable. They stand out prominently among the many geologic 
phenomena of deserts which have been either greatly misinterpreted or not 
interpreted at all. For such conspicuous and common objects of landscape they 
strangely enough have attracted small critical notice from travelers, llill* is 
almost alone in giving them especial mention and a name. 
Apparently typical water-graved forms of unusual size, they are set in plains 
where stream-corrosion is practically unknown. Mystic features of the desert 
landscape as they have always been, they at this time possess exceptional 
interest, since they appear to offer not only most conclusive proofs of their 
origin by wind erosion, but afford critical data on the eolic sculpture of all 
of the grander physiographic lineaments of excessively dry countries. 
In the arid region plateau-plains appear as even surfaces well elevated above 
the general plains-level about. As broad, flat-topped hills they rise out of the 
vast expanse of level earth after the manner of bold-coast isles out of a glassy 
sea. Mesas, or “tables,” the Spanish-speaking people aptly denominate them. 
The margin of a mesa forms the brow of a precipitous escarpment, which is 
one of its most characteristic features. Indeed, the upper part of the escarp- 
ment is not infrequently a vertical wall 100, 200 or even 500 feet in height. 
Mesa de Maya (armoured table) and Llano Estacado (walled plain) are Spanish 
descriptive terms referring especially to this feature. The talus-like slopes 
below are steep; and their meeting with the general plains-surface is sharp. 
Some plateau-plains are so small in areal extent that they stand boldly out 
of the general plain as conspicuous cones or buttes. The Cameleon, in central, 
and Wagon Mound, in northeastern New Mexico, are illustrations. Others, as 
the Enchanted Mesa and the Covero, in western New Mexico, and the Sunset 
Tanks buttes, in Arizona, are only a few acres in extent. Toyalene is larger. 
From these to the great Chupadera Mesa and the Mesa Jumanes, which are a 
dozen miles across and a score of miles in length, or the vast Mesa de Maya, 
which extends along the southern border of Colorado a hundred miles, there is 
every size. Proportion is mainly a function of geologic substructure. 
The foundation of the plateau-plain is generally some rock-layer more in- 
durated than the rest. Structurally it may be made up of (1) remnants of for- 
mer plains worn out upon the bevelled edges of folded strata, as in the cases 
of the Mesa Jumanes and the Chupadera Mesa; (2) slightly inclined strata of 
hard limestone or sandstone, which are intercalculated in extensive beds of less 
resistant materials, as in the Chaca Mesa and other platform-plains of the great 
Mesa Verde region; (3) nearly horizontally disposed hard beds from which the 
soft superimposed layers have been stripped, as the Toyalane and the Tucum- 
*Final Kept. Artesian and Underflow Investigation, U. S. Dept. Agric., pt. 3, p. 54, 
1892. 
