A hundred years ago another powerful force entered the Yellowstone scene. Man, arriving in ever increasing numbers, came armed with the power to choose between preserving or destroying the wonders that nature has taken more than 2.5 billion years to create. Sensing this grave responsibility, he took the necessary steps to insure that these irreplaceable natural features would be preserved and protected. Today, Yellowstone National Park indeed exists “for the benefit and enjoyment of the people,” a fitting and lasting symbol of a great national heritage that now includes more than 275 places of natural and historical interest. On the eve of the 100th anniversary of our first National Park, we are again reminded of that continuing responsibility we all share in preserving these unique places for the benefit and enjoyment of all future generations of visitors.