"The hilly, wooded area of southwestern Wisconsin where frac sand mining has exploded goes by the romantic name of the Driftless Area..."

"... so called because it was bypassed by the glaciers that ironed flat the rest of the Midwest during the last Ice Age. 'It is the most beautiful part of the state,' said Kevin Lien, the director of the Trempealeau County Department of Land Management. It is also, thanks to its unique geology, the best source in the nation for diamond-strong kernels of silica sand: smooth, round grains of almost pure quartz that can be found in lower Wisconsin’s sandstone bluffs."

From a New Republic article with the polemical title "Scott Walker's Sand Grab: Wisconsin Wants a Piece of the Fracking Boom, No Matter Who Gets Hurt."