SAN FRANCISCO (AP) — California workplace safety officials have fined a guide company that was leading backcountry skiers down a mountain in February when an avalanche was triggered, killing nine members of the group in the deadliest avalanche in the state’s modern history.

The California Division of Occupational Safety and Health, or Cal/OSHA, issued $151,300 in fines against Blackbird Mountain Guides for seven alleged violations it found. The largest fine, $81,000, was for “failing to correct the imminent hazard posed by traveling in avalanche terrain when the avalanche danger was rated high.”

The agency issued the fines earlier this month.

Blackbird Mountain Guides said it has filed a formal appeal and that it believes it was in “full compliance” with all regulatory requirements.

A separate investigation by Cal/OSHA’s Bureau of Investigations, which reviews workplace deaths for possible criminal charges, is ongoing, the agency said in a Friday statement. The Nevada County Sheriff’s Department has forwarded results of its own criminal investigation to the district attorney’s office for review of possible criminal charges, Capital Public Radio reported. The sheriff’s department and the DA’s office did not immediately respond to a request for comment.

The nine people who died were part of a group of 15 backcountry skiers headed out on a three-day trek organized by Blackbird Mountain Guides into pristine wilderness near Frog Lake in California’s Sierra Nevada as a powerful winter storm moved into the state. Three of the dead were guides.

The skiers made their way to remote huts located at 7,600 feet (2,316 meters) in Tahoe National Forest, carrying their own food and supplies. Two days later, on Feb. 17, the group was attempting to ski down the mountain when an avalanche hit near Castle Peak, trapping them. Six skiers, including one guide, were rescued after sheltering in place for hours as searchers battled blizzard conditions to reach them.

Cal/OSHA, which issued the fines on Aug. 12, found the company allegedly failed “to correct the imminent hazard posed by traveling in avalanche terrain when the avalanche danger was rated high.” The other five violations are related to alleged workplace violations, including not providing employees with effective training and failing to report the three employees’ deaths to the agency in a timely manner.

“The citations do not reflect the reality of our profession or the safety program we have built,” Blackbird Mountain Guides said in a statement. “Mountain guiding takes place in dynamic wilderness environments where conditions change minute to minute — it’s not a controlled setting such as construction sites. We welcome the opportunity to work with Cal/OSHA to contextualize the unique realities of operating in backcountry environments.”

The guides on the trip had years of experience in backcountry skiing and certifications from the American Mountain Guides Association, which offers the highest level of training in the industry, the company said.

“Guides pursue knowledge and excellence as a lifelong responsibility and the guides on this trip approached their work with care and professionalism,” said Blackbird Mountain Guides owner Zeb Blais.