Fifteen individuals were struck by lightning and a dog was killed after they were caught in a storm on well known Mount Bierstadt Sunday morning.

The Unmistakable Creek County Sheriff’s Office says five individuals were injured seriously enough to be taken to Denver-area hospitals. Their conditions are unknown.

A call first came in about the incident at around 11:30 a.m. MT. Rescue teams at first said the majority of the casualties were en route down the mountain when they were struck.

“The storm came through really fast,” hiker Pete Hunter said. “Didn’t really see the clouds building as we’d expect in the distance. It was kind of like they built right on the summit.”

Madeleine Ripley was on the peak with friends, and shocked by a strike while touching a stone.

“I felt lightning, and I just started running back down, and I kept going,” she said.

Two hikers were missing for a short time, as indicated by the sheriff’s office, however they were later found by a National Guard helicopter that was flown in for the search. Authorities say they were students from out of state.

Various area agencies were involved in the rescue. Victims were not ready to be airlifted specifically off the mountain because of climate conditions, however Flight for Life units were called.

A Blackhawk helicopter was likewise requested.

At 14,065 feet, Mount Bierstadt is one of the state’s most popular “14ers” — mountains more than 14,000 feet in mountaineering parlance. Colorado has 58 such peaks, including Pike’s Peak and Mount Elbert, the state’s tallest. The Peaks pull in a huge number of climbers per season.

Mount Bierstadt sits nine miles southeast of Georgetown via Guanella Pass. The hike to the summit is approximately three miles one-way from the top of the pass, with an elevation gain of 2,391 feet.