An open creek that should have been buried under snow forced backcountry ski guides to change course directly into the avalanche path that killed Tiburon resident Kate Morse and eight others near Castle Peak in February, according to a newly released report.

The 56-page preliminary report, compiled by avalanche expert Don Sharaf for Truckee-based Blackbird Mountain Guides, found that guides had planned to cross the creek to reach a safer, pre-mapped route that would put distance between the group and known slide paths descending from Perry's Peak, according to CapRadio's reporting on the findings. GPS data from guide Nicole Choo's Strava account shows the group tried two to three times to get across.

They couldn't.

A six-week snow drought had left the creek running as open water between vertical banks. In a normal winter, consolidated snow bridges the gap.

"Based on the group's tracks from the preceding days, they would not have known about this impassable barrier before their exit on Tuesday morning," the report states, according to the Mercury News.

Unable to cross, the group remained on the near side, closer to the avalanche terrain. The report found they were buried roughly 50 feet from the mapped safer route.

Morse, 45, was vice president of commercial strategy at Septerna, a South San Francisco biotech company, and a mother of three whose children ski for Sugar Bowl Academy, as The Ark reported in February. She and her husband Eric purchased their Tiburon home in 2015. She was among six clients and three guides killed when the slide struck between 11 a.m. and 11:30 a.m. on Feb. 17 during a blizzard. It remains the deadliest avalanche ever recorded in California.

The report, which reflects information available as of July 15, does not assign blame. Sharaf concluded the group was not traveling through avalanche terrain when the slide hit but was trying to reach the pre-mapped escape route. A subtle gully channeled debris through a gap in otherwise dense timber onto the drainage floor where the group stood at roughly 7,850 feet elevation. Dense tree cover blocked any view of the start zone above.

A senior Blackbird guide had labeled the planned route "High danger UP" on his digital map a month before the trip, designating it as simple, low-exposure terrain appropriate for high-danger days.

The report does not explain why the group left Frog Lake Huts that morning despite a "high" avalanche danger rating, or why they did not turn back when the creek proved impassable. Blackbird did not respond to Mercury News questions on those points.

The Nevada County Sheriff's Office said it would investigate possible criminal liability, the Marin IJ reported Aug. 7. The case has since been turned over to District Attorney Jesse Wilson for review. Cal/OSHA also opened a workplace safety investigation into Blackbird two days after the avalanche.

Blackbird said in a statement accompanying the report's Aug. 10 release that much remains unknown and expressed hope the information would help the community heal.

Two other Southern Marin residents were among the nine killed, the Mercury News reported: Danielle Keatley, 44, of Larkspur, and Katherine Vitt, 43, of Greenbrae. Caroline Sekar, 45, of San Francisco, was also killed.