Saturday, September 13, 2014

Trails explore Washburn County geology

The Namekagon River cuts through sediment laid down by glaciers.
Two lengthy geological events shaped the terrain of Wisconsin’s Washburn County: the erosion of a vast mountain range and the ice ages of the past million years. Several trails allow modern hikers to explore that geology.

About 600-700 million years ago, the northern third of the county was part of a great Alps-like mountain range stretched. Most of what is now central and southern Wisconsin lay under an ocean.

Over the eons, streams and rivers carried sediment out of these mountains, filling the shallow sea inch by inch. The sandstone found in road cuts and on river banks across the southern part of the county and Wisconsin as a whole are those piles of sediment.

Erosion has worn those mountains down into a relatively flat area, with occasional hills, called a peneplain. While evidence of these mountains doesn't rise above the surface in the county, you can walk through the area where they once rose on the Totagatic Ski Trail.

Then, glaciers during the last ice age (which ended about 10,000 years ago) brought sediment – mainly sand, gravel and boulder clay – that was left across the base of those ancient mountains and the filled-in sea. Because of this, the northern part of the county generally is better for forests than farming, which in our century shapes up to great hiking trails. The Namekagon River cuts through a deep portion of this sediment, visible on the Trego Nature Trail.

The southern two-thirds of the county is largely shaped by ice as well. As the glaciers melted and retreated at the end of the last ice age, they left long narrow mounds of sediment called hummocks. Ice-walled lakes also formed, leaving whole swaths of land fairly flat. You can day hike through such terrain on the Ice Age National Scenic Trail.

The county’s central hilly area – known as the Spooner Hills – were created by till piling up during several glacial advances. The spacing between the hills likely developed when melting ice at the glacier’s bottom formed tunnels so that the water flowed outward into the open plain to the south.

Learn about nearby trails in Day Hiking Trails of Washburn County.