Chimani is the best app that allows you to find public land in the United States. 

Chimani National & State Parks provides access to information on 3,000+ national parks, wildlife refuges, forests, and monuments. You can find the best places for camping, hiking, biking, climbing, paddling, and more.

You can access hundreds of parks for free, Yellowstone, Yosemite, Grand Canyon, Zion, Grand Teton, Mount Rainier, Great Smoky Mountains, Rocky Mountain, Olympic, Bryce Canyon, Joshua Tree, Cuyahoga Valley, Death Valley, Cape Cod, Zion, Acadia, and many more.