Lewis and Clark documented the Yellowstone River and surrounding badlands scenery in 1806. They remarked on the landscape that appeared burnt in many places and the dark and light browns and red rocks; they called the river “Red Stone River.”
Many eastern Montana hills are capped with red rocks and contain coal beds sandwiched between layers of siltstone, sandstone and shale. Over the ages, lightning has ignited the coal which has cooked, fused and melted the adjacent rocks—transforming them. Visible in the sample are examples—sandstone that baked into brick-like rocks, shale that fused into a ceramic-like product, and other rocks that melted and look like hardened lava or glassy slag. The clear to blue/gray grains are likely Montana agates. This sand was collected from an anthill.
NPS public domain
Yellowstone Lake from Eagle Bay