PEALE] GEOLOGY GRAND EIVEE PLATEAU CREEK. 91 



valley. It rises among low hills, and has a much more gradual fall to 

 its mouth. It is about 24 miles iu length, and forms a portion of the 

 boundary-line of the plateau of station 48. Between the parallel por- 

 tions of the two streams just described there is a terrace, the height of 

 which is about SO feet, at the bend of the first branch. It is about a 

 mile wide here and slopes to the forks, where it terminates in a point, 

 the entire length of the bench being about seven miles. It is covered 

 with good bunch-grass, and has evidently been used by the Indians as a 

 ^raziug-ground for cattle. The plateau between this creek and the 

 Grand Eiver is approximately triangular in shape, the base being on the 

 eastern side. Here it is 15 miles in width. To the west it gradually 

 terminates in a' ridge, which extends between the two streams. Its 

 length is 15 miles, and its mean elevation, where the general level is 

 best preserved, is about 10,200 feet. It was once, doubtless, continuous 

 with the mesa or plateau which still exists to the southward. Erosion 

 has isolated it. The covering of basalt which once covered it has been 

 partially removed. The remnants left reach from 200 to 250 feet above the 

 general level, forming monument-like points that are visible from a great 

 distance. Station 48 was located on one of these points, a conical mass 

 248 feet high. The eastern edge of the plateau, as I have already men= 

 tioued, has steep bluffs, overlooking a broad valley. On the north side, 

 also, are bluffs, which as we go down the Grand become less steep, a num- 

 ber of small streams cutting them into small hills. Toward the eastern 

 side the beds are nearly horizontal, but as we go west we find that there 

 is -a slight dip to the east, or perhaps a little north of east. The south- 

 ern side of ^e plateau, near station 48, has a number of creeks draining 

 it, the courses of which are nearly parallel, flowing south. Between them 

 are sharp ridges, at the base of which gray and pinkish sandstones 

 outcrop. On top are light clayey beds and iuterlaminated hardened 

 shales, weathering a white color, thus giving the bluff's a unique appear- 

 ance, as seen from a distance. Underneath the basalt, the beds are 

 concealed even on the edges of the plateau. As we go down the creek 

 the valley widens on both sides. On the south are drift-covered ter- 

 races sloping from the divide. On the north side are low bluffs, close 

 to the river, in which pink and yellowish strata outcrop. These beds 

 are cut into terraces, beyond which are bluffs of variegated sandstones, 

 passing above into light colored shales. On the latter, station 50 is 

 located. From station 50 to the Grand the descent is at first rather 

 abrui)t. Then there is a gradual slope broken up by the drainage into 

 low buttes. The Grand has a broad bottom, through which it flows 

 sluggishly. 



South of the station the country is very nearly the same. There are 

 magnificent«exposures of the strata, which are inclined but slightly. On 

 the north side of Plateau Creek are bluffs of sandstone, through which 

 the stream cuts rapidly to soft shales, which weather in the most pecu- 

 liar manner, as shown in one of the illustrations, Plate Y. Above the 

 black argillaceous columns are yellow sandstones, And the debris from 

 them has fallen down, capping the summits of the pillars. Below, still 

 lower beds are shown, until a belt of red sandstone is seen opposite 

 Mesa (a) Creek. It here enters a caiion, in which it keeps until it joins the 

 Grand. Almost all the creeks in this region cut profound cailons ; even 

 the smallest rivulets cut gullies from eight to twenty feet deep. 



The terraces are covered with basaltic bowlders, and are almost des- 

 titute of vegetation. Good grass, however, is found in the alluvial bot- 

 toms bordering the creek. Scrub-oak and stunted cedars are found on the 

 hills. The caiiou on Plateau Creek is eight miles long. Below its mouth, 



