Rainbow Falls is a broad waterfall on the Missouri River in Great Falls, Montana, and one of the five Great Falls of the Missouri. Nearly spanning the river at 1,320 feet wide, it drops 47 feet over sandstone and was named for the rainbows once common in its year-round spray. Meriwether Lewis admired it during the Lewis and Clark Expedition, though it later received its present name in 1872 from railroad engineer Thomas Paschall Roberts. Seasonal flows and operations at upstream Rainbow Dam, built in 1914, now greatly affect its appearance, yet it remains closer to its natural condition than most other Missouri falls at Great Falls.