You can google this, but there were several incidents that led to the ban. They included drones chasing Big Horn Sheep at Zion's, An award ceremony at Mount Rushmore that was interrupted by a drone, A drone crash into Yellowstone's Grand Prismatic Spring (which could destroy the beauty of the spring as the lipo battery dissolves, according to experts), and several other incidents. I just read that people continue to fly their drones in NP, despite having the fines.I am wondering why national parks in the States are NFZ's.