TOPOGRAPHY. 9 
Creek, which drains the area between the Little Book Cliffs and the 
Book Pi teau northwest of De Beque. The streams which flow south- 
ward from the Book Plateau are small, and on account of the slight 
precipitation and limited drainage area flow intermittently through- 
out the year. During the dry months the discharge even within the 
highlands almost ceases and the stream beds across the lowlands 
are dry. 
The relation of the through-flowing streams to the lowland indi- 
cates that their general courses were defined before the development 
of the present topography, for there is little adjustment between the 
drainage and the outcrops of the hard and soft formations. Grand 
River conforms only partially with the trend of the lowland; Green 
River maintains its way directly across the shale belt; Price River, 
flowing alternately over hard and soft rocks, instead of continuously 
in the shale lowland, is a good example of superimposed drainage. 
LOWLAND AT BASE OF BOOK CLIFFS. 
The lowland at the base of the Book Cliffs extends in a curved but 
general westerly direction from Palisades, Colo., to Helper, Utah, a 
distance of 190 miles. From Palisades it continues southeastward 
between the Uncompahgre Plateau and Grand Mesa, and from Helper 
the lowland extends southward between the San Rafael Swell and the 
Wasatch Plateau, where it is known as Castle Valley. Throughout 
its extent the lowland is underlain by shale and is not a stream valley 
in the sense of being carved and occupied by a single master stream; 
instead, the lowland has been eroded in soft rock by general subaerial 
action and forms part of several drainage basins. The lowland has 
been widened by the gradual recession of the Book Cliffs northward 
due to the weathering of the soft shale and the undermining of the 
overlying hard sandstone which forms the cliffs. By this process the 
cliffs have retreated, but they have maintained a fairly regular front. 
The average width of the lowland is about 12 miles, having a maxi- 
mum of 23 miles, in the vicinity of Cisco, and a minimum of 4 miles, 
near Woodside. The lowland is an undulating plain that rises gently 
toward the bordering highlands and extends between the Book Cliffs 
on the north and a belt of sandstone hills on the south. It practically 
coincides with the outcrop of the Mancos shale. The small streams 
that head in the Book Cliffs and cross the lowland have carved steep 
arroyos, which impede travel. In the vicinity of the cliffs there are 
outlying buttes and the shale is eroded into badlands. Adjoining the 
cliffs there are local fringing remnants of an old outwash gravel- 
covered plain into which the streams have cut their way 100 feet or 
more, and south of Grand River, near Palisades, a number of terraces 
arc well developed. The largest, about 150 feet above the river, is 
