Junction Butte basalt (2.1 Ma, Yellowstone National Park, USA)
Columnar jointing at base of Junction Butte basalt (2.1 Ma), Yellowstone Plateau volcanic field. The flow overlies fluvial sands and gravels. Yellowstone National Park, USA. Photo by L.B. Aspler.
See Christiansen, R.L., 2001. The Quaternary and Pliocene Yellowstone Plateau Volcanic Field of Wyoming, Idaho, and Montana: U.S. Geological Survey Professional Paper 729-G, 145 p.