Richard Bridge-
The national parks exist on Federal Government land; the forest rangers and maintenance staff are government employees. The roads through the parks are built ansd maintained by the government.
Who in hell do you think the "public" is?

Yellowstone National Park spans an area of 3,468.4 square miles (8,983 km2)

For perspective, England occupies 50,346 sq miles (130,395 km²)