The group of 15 backcountry skiers was on a three-day trek organized by Blackbird Mountain Guides into pristine wilderness near Frog Lake in California’s Sierra Nevada near Lake Tahoe.

The skiers set out on Sunday, carrying their own food and overnighting in huts situated at 7,600 feet (3,415 meters) in Tahoe National Forest, where a winter storm arrived and an avalanche watch was issued that morning.

“If you’ve booked the Frog Lake Huts in Truckee, trust our guides to elevate your trip to the next level,” the business said on its website, advertising the trip. “We’ll navigate in and out of the huts, manage the risks, and find the best terrain and snow quality for you and your group!”

On Tuesday, the group was trapped by an avalanche. Authorities said Wednesday that eight people were killed and one person remained missing. Six skiers were rescued after sheltering in place for hours as crews battled blizzard conditions.

Blackbird Mountain Guides said in a statement that it was coordinating with authorities. It said the group, including four guides, was returning to the trailhead when the avalanche occurred near Castle Peak. Three of the guides were among those killed, officials said.

The company, with offices in California and Washington state, offers mountaineering and backcountry ski trips across the U.S. West Coast as well as in Europe and Japan. The tour outfit also offers safety courses like wilderness skills and first aid.

The rugged terrain where the skiers died had been closed to the public for a century before the Truckee Donner Land Trust bought it and opened the huts, which are outfitted with basic accommodations such as sleeping pads, gas stoves and flush toilets.

An avalanche watch had been issued Sunday morning as a powerful winter storm moved into the state. The Sierra Avalanche Center issued a more severe avalanche warning for the Central Sierra Nevada, including the Greater Lake Tahoe region, starting at 5 a.m. Tuesday with large slides expected into Wednesday.

Nevada County Sheriff Shannan Moon said investigators would look into the decision to proceed with the trip despite the concern over potential avalanches.

“We’re still in conversation with them on the decision factors that they made,” Moon said at a Wednesday news conference announcing the deaths.

The sheriff said the search occurred during “horrific conditions” in an area where rescue missions are common.

The tour, which cost $1,165.00 per person, was rated for intermediate-to-expert skiers with at least 20 days of backcountry experience who should be prepared to climb up to 2,500 vertical feet (760 meters) throughout the course of a day, according to the company’s website. Guides carry first aid kits and “wag bags” for human waste disposal, but participants must bring their own ski equipment and avalanche gear, including a beacon, shovel and probe.

“Generally our guides are able to find excellent backcountry snow conditions, but often we need to travel through difficult conditions to access the goods,” the website description said. “This requires riders to be adept with their backcountry touring skills and have a solid foundation of touring before the trip.”

Rapidly accumulating snow piling on fragile snowpack layers, along with strong winds, contributed to the treacherous conditions.

The town of Soda Springs, near where the avalanche took place, recorded at least 30 inches (76 centimeters) of snow during a 24-hour period, according to the Soda Springs Mountain Resort.

___

Associated Press writer Julie Watson in San Diego contributed to this report.