Human-set fires pose a major threat to many parks. When O'Shaugnessy Dam was completed it flooded Hetch-Hetchy Valley. Traffic congestion and other symptoms of over-use plague Yosemite, the most popular national park. Immediately after the Giant Sequoia trees were discovered some of the largest were cut down and sections shipped east as curiosities. The Disney corporation planned a huge recreational development for this valley, which has since been added to Sequoia National Park.
Parking is a problem in many popular parks.
Many of the redwood parks consist primarily or entirely of cutover land. The limited size of their protected habitat, and proximity to highway 101 have in the past posed threats to the elk herd at Prairie Creek. Natural disasters pose special problems for managers of open space. Power generation lakes occupy the heart of North Cascades National Park. All land for miles around Olympic National Park has been clearcut.