The great boulder piles along Park Boulevard weren't stacked by anyone. This stop follows the rock from deep underground through cracking, rounding and flash floods, then looks at what has vanished from these valleys, the pronghorn that once ran here.
Nobody stacked the rock piles out here. The answer starts about fifteen miles down. This began as molten rock that cooled there and never erupted. The park's own pages put that anywhere from eighty-five million to more than a hundred million years ago. Erosion reached it about twenty million years ago, and everything that once lay above is gone. Cracks cut it into rectangular blocks. Groundwater worked down them and rotted the corners first, the way an ice cube rounds under a tap, turning cubes into spheres over millions of years, in a much wetter climate. Then the climate dried. Flash floods washed away the rotted ground, and the spheres settled onto one another. They weren't stacked. They were unpacked. This country has lost something else. In nineteen forty a Park Service biologist saw the clumps of native grass in the western half and called it what once must have been good antelope range. The pronghorn have not returned. Try seeing it the way it was. Grass to the rocks, and something fast moving through it.
Photo: NPS / Brad Sutton · Public domain (NPS staff photo)