For millennia, Colorado's Yampa River Valley has followed the rhythms of wildlife mating and migration, the habits of elk and grouse and bear. The arrival of ranching in the 1880s altered the pattern a little, but radical change didn't occur until the last half of the 20th century. That's when the big ranches began to be broken up into small ranchettes and vacation-home lots, the kind of low-density exurban sprawl responsible for habitat fragmentation across the West.