38 WILLIS T. LEE 
and that the uplift may prove to be an anticline extending east- 
ward from the mountains, rather than a dome.) The dome, if 
such it be, is in general terms bounded on the north by the 
Arkansas River; on the west by the Rocky Mountains; on the 
south by the eastward flowing part of the Canadian River, New 
Mexico; to the east the dip continues at least to Beaver county, 
Oklahoma. 
The Dakota sandstone occurs throughout this region. It is 
an easily recognized formation, and conspicuous wherever 
exposed at the surface. It is, therefore, a convenient reference 
horizon. Overa large part of this elevated region —perhaps 
the eastern four-fifths—the Dakota is either the surface forma- 
tion or lies so near the surface that it is exposed in the numer- 
ous canyons. Over the western fifth, the Dakota is buried 
beneath the younger formations to reappear along the mountain 
front in a nearly perpendicular reef known as ‘stonewall.’ 
The greatest elevation at which I have identified the Dakota is 
6,300 feet,* at the point where I crossed the Mesa de Maya. 
Over a considerable area in the vicinity of Mesa de Maya, the 
elevation of the Dakota is practically the same. From this 
region northward there is a gradual descent until the Dakota 
drops beneath the younger formations near the Arkansas River.? 
The westward dip of the strata is indicated by Mr. R. C. 
Hills in the geological maps of the folios just referred to. A 
study of these maps shows that the Dakota lies about 2,200 feet 
beneath the surface at Trinidad, Colo., z. ¢., it lies 3,800 feet 
above sea level, while twenty-five miles to the east it lies at an 
elevation of 5,300 feet, and sixty miles east of Trinidad, where I 
crossed the Mesa de Maya, it lies at an elevation of 6,300 feet. 
There is then a westward dip of the strata in this region of 2,500 
feet in sixty miles, or about forty-one feet per mile on the 
average. The dip of the strata in the southern, eastern, and 
*See U.S. Geol. Surv., Mesa de Maya Sheet. 
7G. K. GrtBErT, U.S. Geol. Surv., Seventeenth Annual Report, Pt. II, “ Under- 
ground Waters of the Arkansas Valley in Eastern Colorado,” sections following 
P. 574- 
