All national parks in the USA. will be accessible admission-free from April 16 through April 24. The week of free admission during National Park Week is to mark the 100th anniversary of the National Park Service. This year’s celebration brings the grand total of free-admission days at America’s national parks to 16—well above the nine free days offered in 2015.
"It’s about making great connections," the parks service says on its website announcing the celebration, "exploring amazing places, discovering open spaces, enjoying affordable vacations, and enhancing America’s best idea—the national parks!"