190 REPORT UNITED STATES GEOLOGICAL ' SURVEY. 



tlie ascent of the main summit. A steep ridge, with steep, smooth 

 sides, projects 4 or 5 miles to the east from the main crest, up which 

 we were able to ride to the highest point. This point is only slightly 

 higher than a number of other summits to the west and north, and is 

 by no means a marked peak ; it is simply the highest point of a long- 

 east and west ridge. Here Mr. Wilson made the desired primary tri- 

 angulation station. We were unable, however, to build a monument, 

 as a foot or more of snow obscured the trachytic shingle that abounds 

 near the summit. The latitude of our station was determined to be 

 370 50', the longitude 109° 27'. It is therefore about 23 miles west of 

 the Colorado line, and 58 miles north of the line of Arizona. 



The view from the summit is one of more than ordinary interest, since 

 within the circle of vision there is much that has never passed beneath 

 the explorer's eye. To the eastward the view is only interrupted by 

 the La Plata and San Juan Mountains, 100 miles away. In the south 

 are the iSierra Carriso, in the west the Henry Mountains, and to the 

 north the Sierra La Sal, all in plain view, yet outlining a circle nearly 

 150 miles in diameter, and. including an area of 20,000 square miles. 

 This vast area lies beneath us a silent desert, a plateau land cut by 

 innumerable waterless caSons, and dotted with a thousand fancifully 

 carved and brilliantly colored rocks. 



To the south lies the broad valley of the Rio San Juan, the delicate 

 thread of green that lines its bank being barely visible through the 

 notches cut by the deep side caiions. Beneath us on the west, yet 

 many miles away, is the Rio Colorado, its general course scarcely trace- 

 able through the labarynth of cliffs and caiions. These two streams 

 join in Utah, about 100 miles to the southwest. The lower course of 

 the San Juan can be followed by the eye until it passes the north base 

 of Navajo Mountain, a massive dome-shaped butte that lies a little to 

 the southeast of the junction. In the angle between these streams 

 there is a high red tableland, the Bear's Ears Plateau, which seems to 

 be pretty nearly separated from the surrounding table-lands. It seems 

 to extend to the San Juan on the south, and far out toward the Colorado 

 on the west, while the deep drainage courses that extend north and 

 south from the Sierra Abajo sever it from the Great Sage Plain. It is 

 also severed from the Abajo by a low depression produced by the meet- 

 ing of the northern and southern drainage along the west base of the 

 Abajo group. As far as the eye can reach, the strata, excepting on the 

 eastern border, are nearly horizontal, and there are only a few low 

 buttes that rise above the general level of the plateau. Of these buttes 

 the two known by the Mexicans as Orejos Oso, and two or three inferior 

 ones a few miles further north are distinctly visible. From the interior 

 of the plateau deep caiions open out to the San Juan on the south and 

 the Colorado on the west, which show in their steep faces the brilliant 

 colors of the lower Mesozoic formations. It is probable that the sur- 

 face strata at least are of this age, but the Palaeozoic rocks are doubt- 

 less exposed in the canons of the San Juan and Colorado, as well as in 

 the deeper side caiions. This triangular area comprises nearly 2,001) 

 square miles, and is probably one of the most thoroughly barren districts 

 of the great Colorado basin. 



On the east the Bear's Ears Plateau ends in a great monoclinal.fold, 

 with the down-throw on the east. The Cretaceous floor of the Sage 

 Plain extends westward to the line of this fold, and occupies about the 

 same absolute horizon as the middle portion of the Triassic formations 

 to the west. The throw of the fold would therefore be approximately 

 1,000 feet. Although the amount of displacement is so slight the fold is 



