84 GUIDEBOOK OF THE WESTERN UNITED STATES, 
in the character of the canyon of the Arkansas is not yet understood, 
but it could probably be satisfactorily explained if the history of 
the river were thoroughly known. 
Above the mouth of Oak Creek the canyon of the Arkansas for 
some distance is irregular in width and the sides are low, indicating 
considerable age, though it is generally narrow, and farther on it 
becomes more precipitous, until in the vicinity of Cotopaxi it is a 
veritable canyon, though it is wider than the part of the canyon below 
Texas Creek. 
*Cotopaxi is a small settlement, hemmed in on all sides by high 
granite walls, but fairly good roads lead from it southwestward to 
a rich agricultural region at the foot of the Sangre de Cristo Range. 
mall quantities of the precious metals as well as 
Cotopaxi. some copper have been found near the town, but 
Elevation Bats feet. none of the mines are now in operation. Limestone 
Pehvel'208 aes was once quarried here in large quantities for use as 
flux in iron furnaces, but most of the limestone now 
so used at Pueblo is quarried near Howard, farther up the valley. 
The quarries near Cotopaxi were about 3 miles north of the rail- 
road, at the southern end of the belt of Carboniferous rocks. (See 
sheet 3, p. 100.) The limestone has been preserved here by being 
downfolded into the granite, and on the east side of the downfold 
the rock has been broken by a fault and replaced by the granite. 
For some distance west of Cotopaxi the sides of the canyon are 
composed of massive granite, which in places stands up in nearly 
vertical walls (see Pl. XL, A), but the valley bottom is generally 
wide enough to afford ams accommodation for the railroad and 
for the Rainbow Highway. The canyon maintains this width for 
some distance, but beyond milepost 194 the river passes through the 
narrowest and most rugged part of the canyon west of Parkdale. 
About three-quarters of a mile beyond milepost 194 the railroad 
emerges suddenly from the granite canyon into a broad valley at the 
foot of the Sangre de Cristo Range. The course of the railroad, 
which for a long distance has been nearly southwest, here veers to 
the northwest along this valley. The change from seemingly end- 
less vistas of rocky canyon walls to a broad valley in which there are 
farms and green trees is striking and exceedingly restful and is one 
of the surprises that are constantly awaiting the traveler in this 
mountainous region. 
The change in scenery and in the general character of the country 
is due to a difference in the underlying rocks, but for some distance 
this fact is not apparent, as the rocks are not visible from the train, 
the land near the river being composed of sand and gravel washed 
