Although they are linked in many people's minds, Yellowstone and Grand Teton national parks couldn't be more different. One is an immense wilderness plateau that sits atop a caldera seething with molten lava; the other is a striking set of peaks rising from a broad river plain. One encloses some of the most remote backcountry in the lower 48 and provides crucial habitat for rare species; the other is a short drive from a chic resort town and includes an airport and grazing cattle in its mixed-use approach. What they do share is the affection of millions of visitors who come here annually to renew their ties to nature through the parks' shining mountains, alpine lakes, majestic elk, and astonishing geysers.

Unfortunately, mining, logging, and housing developments have impacted the 19 million acres known as the Greater Yellowstone Ecosystem that includes the parks and the surrounding area. The ecosystem is an interdependent network of watersheds, mountain ranges, wildlife habitats, and other components extending beyond the two parks into seven national forests, an Indian reservation, three national wildlife refuges, and nearly a million acres of private land. It is one of the largest intact temperate ecosystems on the planet; its 18 million acres span an area as vast as Connecticut, Rhode Island, and Delaware combined.

It's also a massive and important source of water. West of the Continental Divide, snowmelt trickles into creeks, streams, and rivers that run through Yellowstone before draining into the Snake River, traveling through Grand Teton National Park and Idaho, and running into the Columbia River, which winds its way west through Oregon and into the Pacific Ocean. Water on the eastern slopes of the divide passes through Yellowstone in the form of the Madison and Gallatin rivers, which meet the Jefferson River west of Bozeman, Montana, and merge into the Missouri, which flows into the Mississippi and, ultimately, the Gulf of Mexico.

As if that weren't enough, the headwaters of the Yellowstone River are in the remote Thorofare country south of Yellowstone Lake. After running north the length of the park, the Yellowstone meanders across Montana as the longest undammed river in America, until it converges with the Missouri in North Dakota.

The Parks Today

It has long been a challenge for park managers to make the parks accessible to three million annual visitors, many with different, even contradictory, expectations of a wilderness excursion. This necessitates the construction of new facilities and ongoing road maintenance and repair. At the same time, the parks are wild preserves, and the National Park Service must cope with the impact of six million feet on the forests, meadows, and thermal areas, as well as on the day-to-day lives of the millions of animals that inhabit the area.

It's a tough balancing act. Some of the pivotal issues in the parks today include the impact of snowmobiles; the reintroduced gray wolves and the resulting livestock losses of ranchers in and around the parks; the inadequacy of the park's infrastructure to cope with three million human visitors each year; invasive nonnative species, such as lake trout and zebra mussels; and the reduction of habitat surrounding the parks, coupled with a growing population of elk and bison seeking forage beyond park boundaries and possibly infecting domestic animals with a disease called brucellosis that, when transmitted to cattle, causes cows to abort fetuses. And that's just the short list.

Possible solutions are often "too little, too late," layering complex management strategies on an ecosystem that might do better if it were allowed to work things out naturally. The problem is that Grand Teton and Yellowstone have already been altered significantly by humans, so "natural" becomes a relative concept.

A good example is the reintroduction of a natural predator of the overpopulated elk: gray wolves, which were eliminated in the 1920s. These days, ranchland surrounds the parks, so the Defenders of Wildlife set up a trust to pay anyone who loses a calf to a wolf -- and ranchers do because the wolves haven't read the management plan. And wolves from Yellowstone have migrated south into Grand Teton and beyond; besides the packs that den in and around the Gros Ventre area, a lone wolf was spotted at the Wyoming-Colorado border, and two others turned up dead in Colorado in 2004 and 2009.

Yellowstone's artificial boundaries also cause problems for bison. The state of Montana now allows hunters to shoot bison when they stray outside the park. Because ranchers fear brucellosis, over 1,600 animals were killed when they left the park for low country in Montana in the winter of 2007-2008 alone, and over 250 have been killed since then -- although so far there are almost no documented cases of bison or elk infecting livestock.

As for snowmobiles and cars, most people agree that changes must be made as park visitation continues to grow. Currently, snowmobilers flock to the park as soon as the snow starts falling and remain until late February. While the popularity of the sport has had a positive effect on the tourism industry in the gateways of West Yellowstone, Jackson, and Gardiner, park officials are concerned about the long-term environmental impact of the machines: They are noisy, and engine emissions create air pollution, which some say presents a health hazard. While technology has reined in the noise and smog to a large degree, snowmobiles still share narrow trails with wildlife during months when the animals' energy levels are depleted by bad weather and a lack of food. A 3-year phase-out of snowmobiles was agreed upon in 2000 but was overturned before park policy could be changed. The compromise resulted in a quota system that limits the number of snowmobiles in the park to 318 per day.

Then there's the traffic issue. Park roads are narrow and twisty, so the intrusion of 30-foot-long motor homes and pickup trucks towing trailers creates congestion, especially during the peak summer months. There have been studies of transportation alternatives to unclog park roadways, even a costly monorail that would wind through Yellowstone, but no decisive action has been taken.

Recently, park scientists have battled to protect the native cutthroat trout in Yellowstone Lake from the impact of lake trout introduced by man. They have also recognized the enormous value of the microbes evolving in Yellowstone's superhot thermal areas, and scientists are using them in new technologies ranging from nanocircuitry to industrial bleaching products. As the world awakens to the accelerating loss of vital species in shrinking wild habitats, it becomes ever more imperative to find ways in which to preserve the relatively unspoiled ecosystems, like that of Greater Yellowstone.

Note: This information was accurate when it was published, but can change without notice. Please be sure to confirm all rates and details directly with the companies in question before planning your trip.