268 FirLp Co_LumMBIAN Mustum—GEo.oecy, VoL. I. 
Approached from the Grand River Valley, the most conspicuous 
landmark is the high and abrupt Triassic bluff which forms the 
valley’s southern confine (Plate XXXIV). For several miles to the 
southward the massive red sandstone has been denuded of its Juras- 
sic covering and so has received the name of Red Mesa (Plate 
XXXV). Some distance from the face of this bluff isolated buttes 
and ridges of Jurassic clays appear, and farther still to the southward 
the whole thickness of this formation is exposed in the fantastically 
weathered shapes of typical bad lands. The top of the Jurassic strata 
is covered with a heavy growth of pines and hence is geographically 
known as Pifion Mesa. All of these strata dip in a general way to 
the northeast and with the Book Cliffs, which bound the valley on the 
north, form a great monocline (Plate XXXIX). This is, however, 
varied. by many local complications. 
Along the lower course of the Gunnison River, the strata forming 
the crest of the Pinon Mesa sweep down to the valley level in a great 
undulating fold. In this the Jura-Trias has been but little broken or 
crumpled, although it is. now deeply furrowed by later cafions of 
erosion. Here the Jurassic clays, protected by a heavy capping of 
Dakota sandstone, extend quite to the river bank. A few miles west 
of Grand Junction however, this fold gives place to a fault of more 
than one thousand feet. Farther along the line of bluffs to the north- 
westward the strata are again continuous in a more or less interrupted 
fold (Plate XXXVI) until at a point sixteen miles west of the mouth 
of the Gunnison the crest of this fold is broken by a fissure through 
which the Grand River has cut its cafion. 
Along the line of this fault the Triassic sandstone is exposed in 
an almost perpendicular bluff standing high upon a bench of igneous 
rocks consisting chiefly of a coarse-grained granite (Plate XXXIV). 
Against this igneous bench occasional masses of Triassic sandstone 
lie tilted at high angles. A short distance toward the river the Trias 
resumes its almost horizontal position and still nearer the river 
appears a series of Jurassic bluffs facing the line of fault and dipping 
in the general direction of the monocline. (Plate XXXVIII.) 
STRATIGRAPHY. 
In this region the Trias is represented by a massive ledge of 
reddish sandstone, slightly cross-bedded, and weathering in peculiar 
pinnacle and dome-like shapes (Plate XXXVII). Below this is a 
softer stratum of vermilion-colored sandy shale resting directly upon 
