This movement to protect America's natural resources and wilderness is known as the conservationist movement.
This has been part of America since the 19th century, but did not gain national recognition until the presidency of Teddy Roosevelt in the early 20th century. Teddy Roosevelt was known for his "3 C's" policy which included consumer protection laws, controlling of corporations, and conserving natural resources.
Thanks to Teddy Roosevelt's commitment to this policy, the US now has millions of acres of land that are protected by the federal government. This includes many famous national parks and forests that attract millions of citizens yearly.