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.