The Yellowstone River drops 308 feet over the Lower Falls — nearly twice the height of Niagara — then carves through a canyon of yellow and orange rhyolite rock for twenty miles. The colour comes from iron compounds in the stone, which is why the park is called Yellowstone. The North Rim Trail connects several viewpoints including Lookout Point, which offers the classic view of the Lower Falls from above; the South Rim leads to Artist Point, where Thomas Moran made his famous 1872 painting. Allow at least two hours to do both rims justice, more if you want to hike the steep Uncle Tom's Trail down to the canyon floor.