Yellowstone National Park is one of the jewels of the National Park System. As more and more travelers visit the park, some conservationists are concerned that we may be ruining the very place we long to preserve. This hour, we’ll talk about America’s first national park with David Quammen, whose reporting on Yellowstone appears in the May issue of National Geographic magazine. Last month, when “Think” was in Washington D. C., we talked with National Park Service director Jonathan Jarvis and took a tour of the Washington Monument with a ranger from the National Mall. You can listen to that entire show here.