UTAH ACADEMY OF SCIENCES 33 
A GENERAL SURVEY OF THE JURASSIC IN 
SOUTHEASTERN UTAH. 
By J. B. FORRESTER. 
I shall make no mention of the Jurassic west of the 
Wasatch Range. I do not wish to imply, however, that it 
is not to be found there. I shall limit my observations to 
the occurrence east of that Range, with special reference to 
that portion bounded on the north by the Book Cliffs, on 
the east by the Utah-Colorado Line, and on the south by 
the Utah-Arizona Line. I shall discuss it under the fol- 
lowing heads: (1) Geographical Distribution. (2) Geo- 
logy, and (3) Economic Features. 
The exposure at the Uinta Mountains forms a fringe 
along the slopes, and partakes of the attending phenomena 
of the Uinta Uplift, namely faulting and folding. A good 
section and discussion of its occurrence in this region can 
be obtained from J. W. Powell’s “Geology of the Uinta 
Mountains.” With this note I shall pass on to the more ex- 
tensive exposures farther south. 
The Jurassic strata constitute the greater part of 
Emery County, Grand County south of the Denver and Rio 
Grande Railroad, Wayne County, west half of Garfield and 
Kane Counties and practically all of the large county of 
San Juan. This makes a total of about twenty thousand 
square miles. In this area there are small isolated regions 
covered with strata of earlier or later age. A small area 
‘of Upper Aubrey is found in the western end of Wayne 
County, also in the Cataract Canon of the Colorado River. 
The famous Natural Bridges in San Juan County occur in 
the northern extremity of an exposure of Upper Aubrey 
that extends south to the San Juan River. 
GEOLOGY. 
For convenience I have divided the Jurassic into three 
series, Upper, Middle, and Lower. This division is based 
upon lithological characters. The characteristic rocks of 
each are as follows: 
Lower, 1205 feet of sandstone, massive and cross- 
bedded. 
Middle, 1866 feet of Argillaceous strata and Lime- 
stones. 
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