To envision a domer, begin with a slick of river riding over and partly submerging a boulder. From upstream, the domer resembles a wet tortoise. On the downstream side, a pourover drops abruptly into a squall of turbulence. It takes a quieter flow to produce a pillow, the cushion of water on the upstream side of a protruding rock, or where the river current hits a wall at an abrupt angle. On his 1869 Colorado River journey, Major John Wesley Powell took a pillow ride: “The river turns sharply to the right and the water rolls up against a rock which from above seems to stand directly athwart its course. As we approach it we pull with all our power . . . but it seems impossible to avoid being carried headlong against the cliff; we are carried up high on the waves—but not against the rock, for the rebounding water strikes us and we are beaten back and pass on with safety, except that we get a good drenching.”

Ellen Meloy