Cities in California, Texas, and Arizona are expecting air quality to become unhealthy for sensitive groups on Thursday.

Scientists have found previously undocumented ash deposits buried beneath the Lava Creek Tuff in Wyoming — and at least one ...

A new trail in this southern Arizona city plots the most visitor-friendly astronomy stops—and there are plenty to choose from ...

In the open savannah grasslands of southern Arizona near Sonoita, Walter Vail and Herbert Hislop bought 160 acres, a quarter ...

If your destination is Flagstaff, the Grand Canyon, or even Las Vegas, add a pit stop to see another National Park Service ...