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[Illustration: Cover: _Columnar rhyolite in the Balanced Rock
area._]
CHIRICAHUA
NATIONAL MONUMENT
Weirdly beautiful pinnacles and columns eroded in volcanic rocks high
in a forested range, which forms a mountain island in a desert sea.
The National Park System, of which this area is a unit, is dedicated to
conserving the scenic, scientific, and historic heritage of the United
States for the benefit and enjoyment of its people.
Unbelievably tall and slender pinnacles, startling likenesses of giant
beasts and men, grotesque and weird figures such as might inhabit
another world--all these and many more, carved by Nature in volcanic
rock, are crowded into 17 spectacular square miles of ridge and canyon
on the west flank of the Chiricahua Mountains.
Rising steeply from the grasslands of southeastern Arizona and
southwestern New Mexico, the Chiricahuas present a verdant, forested
island in a brown sea of desert. Many varieties of trees, shrubs, and
flowering herbs clothe steep canyon walls. Shady glens, alive with
birds, are frowned upon by rows of strange massive spires, turrets, and
battlements in this fascinating wonderland of rocks.
Geological Story
What geological forces created these striking and peculiar pinnacles and
balanced rocks? Geologists explain that millions of years ago volcanic
activity was extensive throughout this region. A series of explosive
eruptions covered the level area with layers of volcanic rock fragments.
Many years elapsed between such periods of activity, resulting in a
series of blankets, layer upon layer. Since the eruptions varied in
magnitude, the resulting deposits were of different thickness.
Finally, the eruptions ceased, and were followed by movements in the
earth's crust which slowly lifted and tilted great rock masses to form
mountains. The stresses responsible for the movements caused a definite
pattern of vertical cracks. Storms and other agencies of erosion,
especially running water carrying small particles of rock, immediately
set to work on the long, slow task of wearing down these mountains.
Shallow canyons became deeper and more rugged as time passed. Weathered
rock formed soil which collected in pockets, and plant life gained a
foothold.
Where previous volcanic activity had spread sheets of lava, the
mountains were now capped with layers of volcanic rock. Along the
vertical cracks and lines of horizontal weakness, erosion began its
persistent work. Cracks were widened to form fissures; fissures grew to
breaches. Undercutting slowly took place. Gradually the lava masses were
cut by millions of erosional channels into blocks of a multitude of
sizes and shapes to be further sculptured by the elements.
Erosion is still going on slowly and persistently among the great
pillared cliffs of the monument. Some of the most exposed portions have
already been worn away. Pedestal or balanced rocks have formed and
fallen; others are tottering; more are just taking shape. Within the
span of a human life, only minor changes may be noticed, but with the
passage of the centuries the face of Nature is ever changing.
Although the spectacular erosional remnants and the massive columnar
structure of the cliffs will impress you even if you hurry through, you
will see much more of geological interest if you can stop and use the
trail. Here and there are exposed beds of volcanic ash and cinders,
indicating the explosive nature of some of the ancient eruptions. Road
construction has uncovered shale which was once the mud of a lake bed.
One trail is strewn with "volcanic hailstones" weathered out of a ledge
composed of millions of marblelike pellets firmly cemented together into
a peculiar "peanut-brittle" rock.