Great Blue Spring of the Lower Geyser Basin, Firehole River, Yellowstone

Those three tiny figures on horseback near the middle of the picture are doing important work: they tell you how enormous everything else is. Thomas Moran painted this scene of the Lower Geyser Basin along Yellowstone's Firehole River after traveling west with the 1871 Hayden Geological Survey, the first official expedition to document the region. The deep blue pool at the center is real, and so are the bands of yellow and orange spreading across the foreground, which come from heat-loving bacteria and mineral deposits left behind by the steaming water. Moran worked in watercolor here, letting the paper show through in the sky and steam so the whole landscape feels half-dissolved in mist.

Moran's Yellowstone pictures had real consequences. Congress saw his watercolors alongside William Henry Jackson's photographs while debating whether to protect the area, and in 1872 Yellowstone became the world's first national park. Moran later added a Y to his signature and went by "Thomas Yellowstone Moran," which tells you how closely he tied his name to the place. He belonged to the later generation of American landscape painters connected to the Hudson River School, though his loose handling of light and vapor owes a clear debt to the English painter J. M. W. Turner, whose work he studied carefully. The rocky butte on the left, solid and reddish against all that haze, is one of the few things in the painting with firm edges.