If you're going to fish Western Wisconsin, you'll undoubtedly spend some time in the rolling hills of SW Wisconsin, also known as the Driftless Area. About the best explanation I've ever encountered of what this actually means was penned by Jeff Erickson in "Minnesota's South Branch of the Root River," Fly Fisherman, December 2006 issue, beginning on page 44.
"Unlike much of the Midwest...the Driftless Region was missed during the last period of glaciation in North America, 12,000 years ago. The area was deprived of glacially-deposited drift (hence the term "driftless), but its sedimentary bedrock was deeply dissected by streams carrying enormous volumes of runoff from retreating glaciers along its perimeter.
The calcium and carbonate-rich limestone that stimulates...high aquatic productivity acts as an enormous sponge, absorbing moisture and then releasing it in steady, trout friendly increments. Innumerable springs percolating through the limestone moderate stream temperatures and PH levels, producing excellent conditions for aquatic insects and the trout that hunt them. The glacial runoff left relatively steep stream gradients, crating numerous riffles and short rapids that supercharge the water with dissolved oxygen. As a result of these natural factors (the Driftless Area) offers suberb wild trout habitat."
For more information on fishing Wisconsin's Driftless Area, check out the excellent fly shop, The Driftless Angler and its website, driftlessangler.com or stop by at 106 S. Main Street Viroqua, Wisconsin 54665 :: (608) 637-8779