140 GUIDEBOOK OF THE WESTERN UNITED STATES. 
Near milepost 367 the valley opens and is irrigated, and the deep 
red of the sandstone is relieved by the bright green of alfalfa, sugar 
beets, and apple orchards, which are irrigated by water taken from 
the creek that comes in from the right. Below this point the river 
turns more toward the west, and it soon cuts through the red sand- 
stone that has bordered the valley most of the way from Glenwood 
Springs. 
As all the beds here dip toward the southwest the river cuts 
through a formation from bottom to top and then passes into the 
overlying formation. The top of the Triassic system is crossed at 
milepost 369, or about three-quarters of a mile beyond the siding of 
Chacra. The Gunnison formation, the next formation in the series 
above the Triassic, is only about 300 feet thick, and as it dips at an 
angle of about 45° it is soon crossed. It is characterized by a variety 
of colors, but maroon, green, and white predominate. Across the 
© river on the left there 
sw. Gtana F Ne, are some small conical 
E hills composed of this 
formation, which are 
capped on the far side 
by massive beds of the 
Dakota sandstone, 
which marks the base 
Horizontal sca of the Upper Creta- 
. ceous series and is one 
of the most persistent 
and widespread formations in the Rocky Mountain region. It is 
generally thin, at few places exceeding 80 feet in thickness. It was 
deposited on the surface of the Gunnison formation. During the 
deposition of the Gunnison formation the region was land, though 
probably of low relief, but the deposition of the Dakota marks the 
end of land conditions and the beginning of the occupancy of the 
region by the sea, which continued during the deposition of the suc- 
ceeding thick shale. The Dakota sandstone is generally massive and 
very resistant to erosion, so that where it is upturned at any con- 
siderable angle it makes hogbacks, such as those seen back of Canon 
City. Although the Dakota is not exposed near the railroad its beds, 
concealed beneath the surface, are crossed by the track about halfway 
between mileposts 369 and 370. The relation of the Dakota to the 
rocks above is shown in figure 36. 
The rocks above the Dakota for a long distance are very soft shale 
or shaly limestone, so they have been eroded into a wide valley that 
lies between the little hogback formed by the Dakota sandstone and 
the mountainous ridge on the left, which trends nearly parallel with 
. the line of the railroad and is composed of the Mesaverde forma- 
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