October 21

Wyoming streams are mad. In several places they run across mountain ranges instead of down their sides. It happened like this. Forty million years ago (mya) in the Eocene epoch, major mountain building occurred in the region. The Laramide Orogeny, geologists call it. The Laramide Orogeny is strange in that it has no obvious relationship to plate tectonic theory. The Uinta mountain range, for instance, runs east-west, which makes little since to a tectonic geologist. And for 25 million years after the Laramide Orogeny, nothing much happened. The existing mountains just eroded, downwasted, buried themselves. Wind and water filed away their peaks and depositied layer upon layer of sediment in the valleys. The valleys filled up to the height of the peaks, which became mere bumps. Then erosion flattened them more. On the basis of this dull topography rivers and streams formed, meandering across the post-Eocene plain. The slow, lazy rivers carved their channels in a slow, lazy fashion. But in the Miocene, when Basin and Range faulting began across the expanses of North America that lay to the southwest, massive uplifting of the entire region occurred. Again, no one is sure why. This is a strange place. Maybe the Yellowstone hotspot had something to do with it. Because of the uplifting the gradient of regional watercourses steepened dramatically, the amount of precipitation increased and the streams that had flowed lazily to their destinations flowed faster. But they stayed in their old channels, incising ever deeper into the rock below. The region eroded, but it did not erode evenly. The sediments that had accumulated since the Eocene washed away first, leaving the recently buried mountains intact. Erosion exhumed the Rockies. And today, with the post-Eocene sediment scraped away to the seas, we have a topographic landscape reminiscent of that which existed before evolution even dreamed of producing Homo sapiens. Miocene rivers lay juxtaposed on Eocene landforms.

But tonight I have left the boisterous geography of Wyoming behind for the placidity of Nebraska, the stable state, the dependable craton, the offensive guard of United States geography. It does its job, day after day, with no fireworks or fumaroles. Tonight I’m camped on a dirt road in the prairie under the sweeping light of the Kimball, NE air tower. Chap and I are settling in for a glass of wine and a cigar. The stars are out tonight and we’re going to enjoy watching them from the stable, lovable craton.