Recognizing these values, the United Nations has declared Yellowstone a World Heritage Site and International Biosphere Reserve. Another measure of the Park's value is visitation, which has grown steadily. In 1967, about 5,200 travelers visited during the winter months. By the winter of 1991-92, there were 119,762, with many using individual snow machines, exceeding growth projections for the year 2000. The rising human population of Yellowstone, both transient and resident, brings pressure on Park resources.
More visitors demand more facilities.
Recent or proposed construction includes proposed new employee housing throughout the Park and the mining of gravel in the Park for roadbuilding. Other structures have been built or proposed throughout the Park. Their cumulative impact is both large and significant. In some cases the NEPA process was ignored and impacts were not documented, options for meeting Park needs were not explored and the public was not allowed to comment. Over the long term, the integrity of Yellowstone also depends on the environmental quality of lands nearby.