GLACIER NATIONAL PARK, Mont. -- The ice-covered mountaintops are shrouded by fog. A stream gushes against the rocks on a headlong rush to the lake. High above the deserted visitors' parking lot, an elk stared at a lone hiker.
Glacier National Park is a sanctuary from the outside world -- but for how long?
To the west, subdivisions, vacation homes, and large chain stores move closer to its borders.
To the north, bulldozers pause for the winter before pushing deeper through the forests to a planned coal mine in the Canadian Flathead River Valley.
To the south, a debate rages over whether to allow oil and gas interests to explore a sacred Blackfoot Indian plot. From above, gradual warming continues to nibble away at the park's famed glaciers. Once as many as 150, they barely number 35 today.
``If this keeps up, we may be looking at the National Park Formerly Known as Glacier," said Steve Thompson, a Montana program manager for the nonprofit National Parks Conservation Association.
Glacier is not alone. The national parks are facing unprecedented pressures inside and outside their borders from population growth, homeland security concerns, and the insatiable desire for conveniences like hotels, restaurants, stores, cell phones, and vacation homes.
Thirty cell phone towers have been erected inside parks; one is in view of Yellowstone's famed Old Faithful geyser.
At Georgia's Kennesaw Mountain, an emergency radio communications tower has been constructed above Civil War cannons.
At Arizona's Organ Pipe Cactus National Monument, officials have built an $18 million, 30-mile steel-and-concrete vehicle barrier to slow illegal immigration and drug trafficking.
Fifteen sea and lake parks have acquiesced to recreational enthusiasts and are allowing Jet Skis and other personal watercraft, or are expected to do so.
At the Grand Canyon in Arizona, the clatter of tourist helicopters and whine of planes compete with the rush of the river, the warbling of birds, and the whispers of the breeze.
Just outside park borders, the pressures are more dramatic from construction, population explosions, and pollution .
An Associated Press analysis of census data shows that more than 1.3 million people since 1990 have moved into counties surrounding six of the best-loved parks: Gettysburg, Everglades, Glacier, Yellowstone, Shenandoah, and Great Smoky Mountains.
The average number of people per square mile in those counties has grown by one-third.
The four urban counties around the Florida Everglades show the most dramatic gains.
But even in the remote areas of Glacier, the number of people per square mile has risen from eight in 1990 to 11 in 2005.
Likewise, park visitation has soared from 79 million in 1960 to 273 million today.
Pollution that has drifted scores of miles into parks is affecting visitors, plant life, and wildlife.
Last year, the air breathed by park visitors exceeded eight-hour safe levels of ozone 150 times in 13 parks, from California to Virginia.
Overall, air at one-third of parks monitored by the Park Service continues to worsen even as the government puts into place pollution controls aimed at clearing the air by 2064.
Great Smoky Mountains National Park in Tennessee and North Carolina, the most frequently visited park, has air quality similar to that of Los Angeles.
Many others, including Shenandoah in Virginia, Mammoth Cave in Kentucky, Sequoia and Kings Canyon in California, and Acadia in Maine, also have reduced views and damage to natural resources, mostly from pollutants from coal-fired power plants.
Massive new water demand from explosive population growth is draining water aquifers that affect parks.
In Florida, the Everglades are affected by an average of 900 new residents a day who create a daily demand for 200,000 gallons of water, the park service said.
Americans are split on park development such as resorts, housing projects, phone towers, and snowmobile trails.
Joe Westbrook, a coal miner in Corbin, Ky., said he occasionally drives through the heavily forested federal lands in eastern Kentucky and sees missed opportunities for development.
``Folks have got to go some place," he said.
Across the continent near Salem, Ore., Jessie Hankins, 22, said a cross-country drive that included a stop at Yellowstone convinced him that parks ought to be kept free of development. ``To me, the parks ought to be enjoyed for the natural things that make them what they are."