In the Driftless
In the Driftless region of Wisconsin with my family this last weekend, I had a chance to think about the consequences of its geology. Drift-less refers to the relative lack of glacial presence in this region during the last Ice Age, which ended around 12,000 years ago. Glaciers are one of the great earth-moving machines. Some features, like the rock and sand and dirt that make up mountains, are scraped away. They bring new material to the ground they pass over. In Wisconsin this can be hundreds of feet of sand and topsoil1. The old land is both buried and crushed. But the original lime and sandstone bedrock is still present in the Driftless–usually beneath the ground, sometimes on jagged slabs lifted above the trees.
Spared the resetting effects of the glaciers, the Driftless retained traces of the past billion-plus years of geological history. The present-day soil sits right on top of old rocks. These rocks are a book of changes over time, a geological palimpsest written by the movements of water. Water nibbles at the bedrock, creating craggy, spindly passageways for itself. _Dendritic drainage, like the roots of a tree. Smaller channels open up, then larger, like an organic network of underground pipes. Water spouts up from these depths, changing the course of streams each year and the contours of the land over decades, then disappears back into the earth, rejoining the subterranean rivers and lakes. The surface is changeable. What has endured is the foundation–rock–on which the land sits. Water is the messenger between surface and depths.
Water in the Driftless must find its way back into the bedrock. There is nowhere else for it to go. When there is too much it comes back up, piling into the fields and valleys. There is little overflow capacity in the Driftless bedrock, and less of the water-soaking sediments present in the sand counties a few miles over. Floods devastating to human settlement are common in this region.
A patch of earth with stable geology can lead to human flourishing. The Native American groups that moved through the Driftless observed that it was prone to flooding, and lived with the land while avoiding any permanent settlement in the most unstable areas. The first European residents scraped away too much of what little water-absorbing topsoil the area had–and the floods have been accelerating ever since. The Driftless, an area defined by an absence of change on the scale of geological time, experienced it all at once, on human time. There must be some kind of implicit law of causation here: gradual changes are more likely to produce predictable and regular effects. Sudden changes, unpredictable and rapid effects. And a second principle: most of the effects from change are the result of gradual processes, but most of the change that is noticed happens quickly. Perhaps the American way of life is just one more rearrangement of the topsoil, a perturbation on top of bedrock.
The counties in Wisconsin immediately to the east of the Driftless Region, where the glaciers did move through, are known as the Sand Counties, a geological designation made famous by Aldo Leopold’s canonical work of conservation, A Sand County Almanac. ↩︎