Losing Ground
Photograph by Joel Sartore

At speeds of about 60 miles an hour (97 kilometers an hour), pronghorn—North America's fastest land mammal—race across a section of the Jonah Field near Pinedale, Wyoming, part of the traditional migration route for some 44,000 pronghorn. The pace of energy development in the 30,000-acre (12,140 hectare) field has been just as fast. Since the mid-1990s more than 500 gas wells have been drilled in Jonah Field, estimated to hold ten trillion cubic feet of natural gas. A current proposal would pack in another 3,100 at densities as high as one well every ten acres (four hectares).