Lightning struck a tree where seven mountain hikers were resting, seriously injuring a 15-year-old and sending all seven to a hospital, authorities said Tuesday.

The hikers, from two parties, had stopped near the tree Monday on 11,850-foot Marble Mountain when lightning hit it, the Gunnison County Sheriff's Department said in a statement.

Four people in the group were able to walk to Marble, about 4 miles away, and call 911.

The 15-year-old was in serious but stable condition Tuesday, the sheriff's department said. The six others were treated at a hospital and released.

The injured included two young children, ages 5 and 9, officials said. A dog that belonged to one of the hikers was killed.