HOLMES.] ABA JO MOUNTAINS. 191 



easily traced by a number of monoclinal valleys that follow its axis 

 from the base of the Abajo group to the San Juan. The ridges that 

 separate these valleys have smooth, slopiug faces to the east, and one 

 of them, which presents a continuous line of white or pinkish faces, can 

 be traced south to the San Juan, and far beyond into Arizona. Macomb 

 and Epsom Creeks on the north, and the Eio de Chelly on the south, 

 occui^y the more prominent of these valleys. 



Beyond the San Juan, to the southwest, the wonderful forms of 

 Monumental Valley can be seen ; beyond this the outlines of a broad 

 table-land can be made out, which extends eastward from Navajo 

 Mountain toward the Eio de Chelly, and southward toward the Moqui 

 country, probably connecting there with the " Great White Mesa." 



West of our station, which is near the eastern border of the Abajo 

 group, are a number of small partially isolated groups of mountains, 

 which obscure portions of the plateau country beyond. The formations 

 near the west base of the mountains are certainly of the Jura-Trias Red 

 Beds; beyond these we have glimpses of the caiioned region of the 

 Eio Colorado, with its almost infinite series of red, gray, and whitish 

 cliffs. Eising out of this broken plateau region are the Henry Mount- 

 ains. Their outlines, as well as much of the detail of form, could be made 

 out by aid of the field-glass. They appeared to resemble very closely the 

 vorious groups of trachytic mountains that lie along the eastern border 

 of the Colorado Plateau. The nearest peak of this group is distant 

 about 70 miles from this station. 



The Sierra La Sal is a large group of mountains that lies directly 

 north of the Abajo at a distance to the central peaks of some 40 miles. 

 There are a number of finely-shaped summits, somewhat conical in 

 shape, that fall off to the level of the surrounding plateau in long, steep 

 slopes. This group stands quite alone, and is surrounded for the most 

 part by red rocks, but a series of shelving-spurs on the east and west 

 probably retain a cai)ping of the Lower Cretaceous rocks. 



Between the Abajo and Sierra La Sal is a broad valley of rather ex- 

 traordinary configuration. It is drained by the CaQon Colorado of Dr. 

 Newberry, but from this point no particular caiion can be traced. We 

 see only a broad, depressed area, which falls off in a succession of 

 irregular cliffs from the western border of the Sage Plain to the Eio 

 Colorado, over the whole surtace of which are a multitude of masses of 

 naked rock, white, red, and gray ridges, hillocks, and monuments 

 smoothed and rounded by the winds and water, the whole being as 

 monotonous, except for the occasional lines of cliffs, as a chopped sea. 



The eastern rim of this valley extends considerably to the east of a 

 line drawn between the two groups of mountains, and in the middle 

 part two or more caiioned valleys penetrate the plateau-face of the 

 Sage Plain, and extend many miles eastward toward the Eio Dolores. 

 A glance at the panorama will make the topographic features of this 

 region clear. 



The Abajo group, as will be readily seen, lies on the western border 

 of the Great Sage Plain. The western limit of the Lower Cretaceous 

 formation is uniform with that of the plain ; south of the Abajo it 

 terminates against the eastern base of the Bear's Ears Plateau, while 

 north of the Abajo it breaks off in the high escarped cliffs that overlook 

 the valley of Canon Colorado. The dip of the strata of the plain is 

 almost uniformly to the south and southeast, so that the drainage is 

 turned back in those directions from the western and northern borders, 

 leaving but little surface tributary to the Colorado and Dolores Elvers. 



The Sierra Abajo consist of a number of small groups of volcanic 



