An agency in Colorado that tracks avalanches hiked its danger level to "extreme" for a swath of the state, the highest level on its scale.

Crews are working to free multiple cars that are trapped by an avalanche on Highway 91 near Copper Mountain, the Colorado State Patrol has confirmed.

A mysterious malady has killed off nearly one-fifth of Colorado's aspens. But forest ecologists have struggled to explain the widespread die-off, known as Sudden Aspen Decline.

Winter sports tourism pumps about $11 billion in direct spending into the U.S. economy each year but is at risk of being decimated by climate change, according to the advocacy group Protect Our Win…