Missouri River Corps of Rediscovery: Gates of the Prairie

"This evening we entered much the most remarkable clifts we have yet seen. These clifts rise from the waters edge on either side perpendicularly to the height of [about] 1200 feet. every object here wears a dark and gloomy aspect. the tow[er]ing and projecting rocks in many places seem ready to tumble on us. the river seems to have forced it's way through this immence body of solid rock for the distance of 5 3/4 miles and where it makes it's exit below has thrown on either side vast collumns of rock mountains high. the river appears to have woarn a passage just the width of it's channel or...