26 GUIDEBOOK OF THE WESTERN UNITED STATES. 
hill surmounted by a thick, square block of rock. ‘This mesa was first 
mentioned in the report of the exploration of Maj. Long, in 1820, and 
on account of its resemblance to an old ruin was called Castle Rock. 
As the train approaches milepost 32 the traveler may see that the 
railroad is built around the foot of Castle Rock mesa, which is about 
300 feet high and has a cap rock 60 or 70 feet thick. 
Castle Rock. This mesa is shown in Plate XJ, A, and in figure 7. 
Elevation 6,218 feet. The lower part of the mesa is composed of soft, fri- 
Sears oaTte es able beds of the Dawson arkose, but the cap rock is 
a coarse conglomerate of pebbles and boulders of 
crystalline rocks of all sorts that have been washed out from the 
mountains and of a volcanic rock (rhyolite) which caps also some of 
the adjacent mesas. These materials were washed out of the moun- 
tains by streams of water and dropped as sheets of gravel and boul- 
ders upon the surface of the land. The county seat of Douglas 
Figure 7.—Castle Rock from the north. 
County, named in honor of Stephen A. Douglas, stands at the base 
of the mesa and bears the name Castle Rock. It was formerly noted 
for its stone quarries, the remains of which still disfigure the mesas, 
but the increasing use of cement in construction work has so de- 
pressed the market for ordinary building stone that the quarrying 
industry has nearly disappeared. Samples of the stone may be seen 
in the Douglas County High School building, on the right as the 
train enters the town, and in the station building of the Denver & 
Rio Grande Western Railroad.*? 
This stone was once molten lava 
*According to Richardson the rhyo- 
lite is said to have boen first quarried 
about 1876, and it is reported that up 
to 1914 about 30,000 carloads had been 
marketed. The stone has been exten- 
sey used for building in Denver, Colo- 
prings, and Pueblo, where it has 
Saat general satisfaction. The quar- 
ries, to which railroad spurs have been 
constructed, are near the town of 
Castle Rock. The stone is readily 
accessible, is easily worked, is of pleas- 
ing gray to pinkish color, stands the 
} weather well, and is sufficiently strong 
for ordinary purposes, although the 
more porous varieties are not adapted 
for use where great strength is desired. 
In recent years the production of this 
stone has fallen off because of the com- 
petition of other building materials. 
