When John Williams penned the gritty, Colorado-set novel “Butcher’s Crossing” in 1960, he faced a herd of Western writers stampeding in the other direction. Seminal novelists of the genre such as Zane Grey and Louis L’Amour had already idealized the American Frontier in hundreds of best-selling books and stories. But Williams, a University of Denver professor for 30 years, took a darker view of U.S.