In August of 1916, the United States was on the brink of joining World War I. But instead of looking overseas, some Americans were worried about a battle breaking out on the home front: the fight for conservationism.
This was when president Woodrow Wilson created the National Park Service. While few parks had already been created and maintained across the country, this was huge step toward preserving the nationally-organized system of recreation areas, historic landmarks and unique geological formations that stand today.
Monday marks the National Park System's 98th birthday and many parks are offering free admission to note the occasion.
Check out the map below to see what sites can be visited for free in the state of California.