Produced by Stephen Hutcheson, Lisa Corcoran and the Online Distributed Proofreading Team at http://www.pgdp.net [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.