Capulin Mountain National Monument, in the northeast part of the state,
is an area of geologic interest that presents still another aspect of
the science of the earth. It contains the cone of an extinct volcano,
one of the most symmetrical of the geologically recent cinder cones in
the United States. Its conical form rises more than 1000 feet above its
base. The irregular rim is about one mile in circumference, and the
crater is about 415 feet in depth, as measured from the highest part of
the rim. Some 40,000 people a year visit the Monument.
The mountain consists chiefly of loose cinders, ash, and other rock
debris of volcanic explosions. These materials were spewed out by a
series of successive eruptions, probably of considerable duration. The
coarse materials fell back around the vent, piling up to form the
conical mound. Dust and other fine materials were carried away by the
wind. After the eruptions, vegetation gained a foothold on the steep,
unstable flanks of the cone, so that in time the slopes became
stabilized. Geological studies indicate that the volcano probably was
active about 7000 years ago.
Capulin Mountain is of special interest, partly because it represents
the last stages of a great period of volcanic activity that was
widespread throughout western North America. Evidences of this older and
more intense activity can be seen from the top of Capulin Mountain in
the scores of other nearby volcanic hills and peaks. The largest of
these is the Sierra Grande, an extinct volcano rising 4000 feet above
the surrounding plain; it is ten miles to the southeast. Northwest of
Capulin are a number of mesas that are capped with black lava, the
largest of which are Barella, Raton, and Johnson. Fishers Peak, south of
Trinidad, Colorado, is on a similar mesa. The famous Spanish Peaks,
northwest of Trinidad, are a pair of extinct volcanoes.
In this great volcanic area, the lava erupted in a succession of flows.
The series of eruptions were separated by long periods of inactivity.
During these inactive times, erosion cut valleys and wore down parts of
the old lava sheets. This action formed new channels and lower terrain
over which succeeding lava flows spread. This process was repeated at
least three times. The oldest lavas, which have been exposed by erosion,
are found on the tops of the highest mesas. The last series of eruptions
created Capulin Mountain; they were ejections mostly of cinders and ash,
with less lava flow than in the preceding volcanic activity. These
cinder-and-ash eruptions were so recent, geologically, that some of the
nearby, bare, steep-sided cinder cones appear as if they had just
cooled.
The National Park Service has constructed a road up the mountain to the
rim of the crater. And from the parking area at the rim, two trails lead
to the most interesting points on the mountain. One trail, self-guiding,
makes the complete one-mile circuit of the crater along the rim. A guide
booklet, keyed to numbered stakes that have been set at places along the
trail, explains the features of particular significance—both on the
mountain and in the distance. The other trail, less scenic, provides a
rare opportunity to see a volcanic mountain from the inside out, for it
leads down to the bottom of the crater.
[Illustration: View of Chaco Canyon National Monument]