Lower Falls Of The Yellowstone River, Yellowstone National Park, Wyoming - This Is Nearly The Same View Depicted In The 1872 Sketch By Thomas Moran, And Printed For The 150th Anniversary Commemoration Of The Department Of The Interior. The Splendid Yellow-brown Walls Of The Canyon Consist Predominantly Of Rhyolite Tuff And Lava (Sulfur Creek Tuff And Canyon Flow, Respectively), Which Were Erupted Nearly 500,000 Years Ago. Both Units Have Been Intensely Altered By Hydrothermal Fluids. Location: Yellowstone National Park, WY, USA Photographer: Stewart Tomlinson, USGS Photo