Badlands west of Terry, Montana, looking westward.
Here Larocque had it easy, traveling on the southeast side (the viewer's right) of the Yellowstone. The following summer (July 29, 1806), Clark recorded his impression of the breaks on the northwest side: "The hills are high and ruged Containing Coal in great quantities." That is all he could see of the stream-deposited, coal-bearing, extensively eroded sediments of the Paleocene Epoch (65–58 million years ago), in what geologists today call the Tullock member of the Fort Union formation.
Badlands in the vicinity of Terry, Montana.
Rainsplash, wind, and runoff erosion have carved the soft, pale gray mudstone and somewhat harder ledges of brown sandstone into fantastic layered shapes.