22 THE BOOK CLIFFS COAL FIELD. 
The rocks in the foothills at the northern end of the Uncompahgre 
Plateau, near Grand Junction and Mack, dip northeastward at angles 
varying from 5° to 45°. Near the mouth of Gunnison River the 
Dakota sandstone dips 5°; west of Fruita the dip is 40° N. 40° E., 
and east of Mack it is 30° N. 55° E. Several miles west of Mack the 
direction of the Dakota outcrop turns and trends southwestward and 
the sandstone dips northwestward at angles ranging from 2° to 15°. 
Between the Uncompahgre Plateau and the San Rafael Swell the 
rocks are irregularly disturbed, but little is known of the structure. 
South of the railroad between Cisco and Thompsons the Dakota out- 
crop trends almost east-west and dips northward. Seven or eight 
miles southwest of Thompsons the trend turns abruptly southward, 
forming the nose of a northwestward-pitching anticline. The axis of 
this fold is eroded and the vari-colored shales of the Jurassic are 
exposed between ridges of Dakota sandstone which on the north dips 
10° N. 25 ° E. South of the town of Green River the dip of the Dakota 
indicates the presence of another low northward-pitching anticline, 
the dips varying from 5° to 15°. 
West of Green River the San Rafael uplift causes the highland to be 
fringed by prominent hogbacks formed by steeply dipping strata. 
The Dakota outcrop constitutes the outermost belt of foothills, in 
which the sandstone west of the town of Green River dips almost due 
east and in the vicinity of Price River northeast, the angles averaging 
about 10°. 
The Mancos shale underlying the valley between the Dakota hills 
and the Book Cliffs doubtless conforms to the general structure of 
this region, but there are few opportunities for measuring the dips. 
Locally, however, especially where interbedded limestone and sand- 
stone outcrop, the dip is shown to be low, and throughout the valley 
it probably ranges between 1° and 5°. 
On the other hand, the structure of the rocks that form the cliffs 
is well exposed. Between Palisades and Carbonera the general dip 
is northeastward, the usual angle being about 4°. But in the vicinity 
of the Book Cliff mine, north of Grand Junction, the dip is locally 
steep, amounting to 25° or 30° N. 50° E. This dip continues down 
the northeastern side of the Little Book Cliffs, forming a dip slope; 
the steep inclination soon changes, however, to the prevailing low dip. 
Two miles north of Carbonera a local fold is exposed which causes 
a southwestward dip of 15°, but the extent of this disturbance was 
not determined. It is south of the zone of doming found by H. S. 
Gale a in the White River valley in 1907. From Carbonera to the 
vicinity of Thompsons the dip in the face of the cliffs is about 5° NW., 
but, as is general throughout the field, it becomes less toward the 
a Gale, H.S.. Coal fields of northwestern Colorado and Utah: Bull. U. S. Geol. Survey No. 341. 1909. 
