"Stewart Udall left an indelible mark on this nation and inspired countless Americans who will continue his fight for clean air, clean water, and to maintain our many natural treasures."—President Barack Obama In his best-selling 1963 book, , Stewart Udall warned of the dangers of pollution and threats to America's natural resources, calling for a nationwide "land conscience" to conserve the nation's wild places. Along with Rachel Carson's , is credited with triggering the modern environmental movement in America.