President Abraham Lincoln signed a bill establishing Yosemite Valley and Mariposa Grove as protected wilderness areas. It was the first time in U.S. history that land was designated for public use and preservation, and is viewed by many as the birth of the national parks system.
You can see the actual bill here.
I’ve just updated and revised The Best Sites For Learning About Yosemite & Other U.S. National Parks.
— US Dept of Interior (@Interior) June 30, 2017