One hundred and fifty years ago this summer, amid a civil war that had torn his nation apart, President Abraham Lincoln signed a law that changed history. It had nothing to do with preserving the Union; instead, it preserved forever a beautiful valley and a grove of trees Lincoln had never seen, thousands of miles away in California.The law Lincoln signed on June 30, 1864, set aside the Yosemite Valley and the Mariposa Grove of giant sequoias for "public use, resort and recreation ... for all time." The idea of national parks — what the historian Wallace Stegner called "America's best idea" — essentially was born in that moment. http://usat.ly/1vmubjA http://bit.ly/1fJ5yqZ