PEALE.] AREA A EIO DOLORES, ETC. 167 



and will be described in his report. Below the mouth of Disappoint- 

 ment Creek the river is flowing toward the northwest, but it soon curves 

 toward the north and east around the northwestern rim of Saucer Vai- 

 led, and a short distance east of Island Mesa emerges into the lower 

 part of Gypsum Valley. Island Mesa is capped with Dakota sandstones, 

 a remnant of the strata forming ftiost of the surface in Saucer Valley 

 (see map of area A, Plate VIII). 



North of the Mesa the river is seen flowing toward the west. It 

 however soon turns to the north, and farther on curves again to the 

 eastward, to the western side of Paradox Valley. In the x)ortiou of its 

 course just referred to, the Dolores is bordered by red sandstones and 

 shales, a portion of which ought probably be referred to the Upper 

 Carboniferous. The canon walls on both sides are bluffy, the upper beds 

 of the bluffs being of Jurassic and Lower Cretaceous rocks. The adjacent 

 country is mesa-like, gashed by streams tributary to the main river. 

 But few of these gashes or caQons carry water during the summer 

 months. 



The Dolores cuts across Paradox Valley at right angles to its direc- 

 tion, and immediately plunges into the canon that continues to its 

 mouth. This portior^ of its course is described in the report for 1875. 



The folds across which the river cuts its way are those of Gypsum 

 Valley and Paradox Valley. Its course was therefore probably outlined 

 before the folding took place, and the cutting of the canon appears to 

 have progressed gradually with the formation of the present folds. 



SAUCER VALLEY. 



At the lower end of the valley of Disappointment Creek is a saucer- 

 like basin which gives name to the valley. 



Through the western rim of this basin Disappointment Creek cuts its 

 way to join the Dolores. The latter is in a monoclinal valley in Jura- 

 Trias and flows around the northern rim of the basin. 



The surface of Saucer Valley is composed mainly of Upper Dakota 

 sandstones. In the centre are remnants of the Colorado shales which 

 prevail so extensively farther up stream in the neighborhood of Lone 

 Cone. Disappointment Creek cuts a deep gully in the soft shales. In 

 September we found water only in pools in this gully. The drainage 

 from the rim bordering the Dolores unites in a stream that cuts across 

 the western rim about three miles north of Disappointment Creek. 

 Near the sources of these streams or gullies, where the dip is greatest, 

 beds of Lower Dakota age are exposed. The eastern, or rather north- 

 eastern rim (for the strike is northwest and southeast}, is the south- 

 western border of Gypsum Valley. 



GYPSUM VALLEY. 



Gypsum Valley is named from the prevalence of gypsum in it, espe- 

 cially at its head. When first seen, the valley seemed to be a simple 

 anticlinal, of which the centre had been eroded away. On the south- 

 west is a hogback-like ridge 400 to 500 feet high. The Dakota sand- 

 stone forms the summit and southwestern slope of this hogback, dip- 

 ping about 15° to the southwest. Beneath this, and presenting the 

 edges of the strata to the northeast, are the shales of the Lower Dakota 

 group, which pass below into the Jurassic. The soft character of the 

 strata has caused the valley to become filled with debris which conceals 

 the greater portion of the underlying strata. 



