The letter was written by Darwin to thank an American geologist, Dr.Ferdinand Vandeveer Hayden, for sending him copies of his research into the geology of the region that would become Yellowstone National Park.

After years of heated debate, gray wolves were reintroduced to Yellowstone national park.

As early as 1966, biologists asked the government to consider reintroducing wolves to Yellowstone park.

At some time in the past Yellowstone must have blown up with a violence far beyond the scale of anything known to humans.

But Christiansen couldn't find the Yellowstone volcano anywhere.

By last year, the Yellowstone wolf population had grown to more than 170 wolves.

By the 1920s, wolves had practically disappeared from the Yellowstone area.

Fish and Wildlife Service carefully monitors and manages the wolf packs in Yellowstone.

Gray wolves once were seen here and there in the Yellowstone area and much of the continental united states, but they were gradually displaced by human development.

In the 1960s,while studying the volcanic history of Yellowstone national park,bob christiansen became puzzled about something that,oddly,had not troubled anyone before：he couldn't find the park's volcano.

It had been known for a long time that Yellowstone was volcanic in nature — that's what accounted for all its hot springs and other steamy features.

Just at this time nasa decided to test some new high-altitude cameras by taking photographs of Yellowstone.

The reintroduction of wolves to Yellowstone Park.

The Yellowstone wolf project has been a valuable experiment to help biologists decide whether to reintroduce wolves to other parts of the country as well.

Today, the debate continues over how well the gray wolf is fitting in at Yellowstone.

Yellowstone obviously was of this second type, but Christiansen couldn't find the caldera anywhere.