(KRON) -- New photographs of a Northern California avalanche and an investigation report were released this week by the Sierra Avalanche Center. During a Feb. 17 blizzard, the giant avalanche killed a group of six women and their three professional backcountry skiing guides near Castle Peak and Fro g Lake in the Sierra Nevada mountains. Six people, including one guide, survived the disaster. Skiers and guides who died were identified by the Nevada County Sheriff's Office as: Kate Morse, 45, of Tiburon Caroline Sekar, 45, of San Francisco Katherine Vitt, 43, of Greenbrea Carrie Atkin, 46, of Soda Springs, Calif. Danielle Keatley, 44, of Soda Springs and Larkspur, Calif. Lizabeth Clabaugh, 52, of Boise, Idaho Andrew Alissandratos, 34, of Verdi, Nevada (Blackbird Mountain Guide) Nicole Choo, 42, of South Lake Tahoe, Calif. ((Blackbird Mountain Guide) Michael Henry, 30, from Soda Springs (Blackbird Mountain Guide) The six skiers were close friends connected through their love of adventure, skiing, and the outdoors, family members said. "They were passionate, skilled skiers who cherished time together in the mountains," family members wrote. Victims were swallowed up by an avalanche that was as large as a football field. Before rescuers could reach the site, some of the survivors scoured the snow and found three lifeless bodies, officials said. Three more skiers were "completely buried" under snow until they were rescued by survivors, an investigation report released by the Sierra Avalanche Center revealed. After the first 911 call, several hours passed before a search and rescue team was able to reached the dangerous site. The avalanche site is seen on the right side of the mountain. (Photo courtesy Sierra Avalanche Center) SAC's report states, "A group of 15 backcountry travelers were involved in an avalanche below Perry's Peak around 11:30 a.m. 12 people were caught in the avalanche. Remaining members of the party performed a companion search and were able to rescue 3 buried individuals." The skiers were up at 8,260 feet of elevation when snow and ice fell 400 feet down, the report states. The report continues, "Search and Rescue arrived on scene in the late afternoon and excavated 8 of the 9 remaining deceased victims, working into darkness in high intensity storm conditions. Search and rescue teams evacuated 6 survivors from the scene that night under their own power to Frog Lake Huts. After the storm ended, avalanche mitigation efforts were performed on the slope on the afternoon of Friday, Feb 20. Following avalanche mitigation, search and rescue was able to remove 5 of the deceased and found the 9th buried victim before nightfall. Rescue operations concluded on Saturday Feb 21, following the retrieval of the last 4 deceased." A helicopter conducts avalanche mitigation after nine victims were killed. (Photo via Nevada County Sheriff's Office) The avalanche's trigger is listed in the report as "unknown." David Lerach, a professor of meteorology, said weather conditions on February 17 created the four elements necessary for an avalanche: a steep slope, a weak layer of snow at the bottom, a heavy layer of snow at the top, and a trigger. "That trigger can be human ... a skier, snowmobile ... or it can be natural. If you just add a lot of stress to the snowpack in a short amount of time, that stress can create the fracture, and you can have natural avalanche cycles," Lerach said. The six skiers were fully equipped with avalanche safety equipment, experienced in backcountry skiing, and deeply respected the mountains, victims' family members said. Sheriff Shannan Moon described the incident as a "catastrophic event." Moon said, "There are no words that truly capture the significance of this loss and our hearts mourn alongside the families of those affected." ...read more read less