The Driftless Region serves as home to these two rivers, and many, many more, and is in a deciduous forest biome.  Most of this part of southwestern Wisconsin was not touched by the last glaciers and displays a very rugged landscape dominated by limestone bluffs rising above the two main rivers.  Valleys carved by smaller rivers and streams abound, but anything resembling a lake is the result of human intervention.  The predominant vegetation is mixed hardwoods such as oak, aspen, and maples.  With the abundant spring fed streams in every valley, the trout fishing in this biome is world class.  The big river is one of the main flyways for bird migration and plays host to birds using that flyway, including huge concentrations of Tundra Swans in the spring and fall. Timber Rattlesnakes are timid venomous snakes that inhabit those rocky bluffs.