Shonkin Sag, Glacial landform near Highwood Mountains, Montana, United States.
Shonkin Sag is a glacial channel in Montana, cut through the hills and valleys of the Highwood region by ancient floodwaters. Its walls drop steeply, and the deep erosion marks stretch across a wide section of the landscape, clearly visible from the road.
Around 15,000 years ago, Glacial Lake Great Falls overflowed and its waters cut through the existing valleys to form this channel. The scale of that flood was large enough to leave marks that are still easy to read in the terrain today.
The name Shonkin comes from the Blackfoot language and refers to the Highwood Mountains or carries the meaning of being brave. Travelers passing through the area will notice the name used for the valley and the surrounding region alike.
The clearest views of the channel come from the roads that pass through the area, so a drive is enough to take it all in. Highway 331 north of Belt, heading toward Highwood, is a good starting point for following the channel by car.
Beneath the floor of the channel sits a laccolith, a lens-shaped body of syenite and shonkinite rock that geologists study closely for its unusual composition. Shonkinite is a rare type of igneous rock that takes its name from this very valley.
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