KIRKWOOD, Calif. (AP) — A mother and her 7-year-old son died after they were discovered buried under snow just feet from their front door in what Northern California authorities are calling a “freak accident.”

The Alpine County Sheriff’s Department said that Olga Perkovic, 50, of San Francisco and her son Aaron Goodstein had been skiing in Kirkwood, which is in the Sierra Nevada near the state line. They were returning home from the slopes Sunday when a chunk of snow about the size of a trailer fell from the roof of their vacation condo, burying them under about 3 feet of snow.

“It was a freak accident,” said Undersheriff Spencer Pace. He said warming temperatures often cause large chunks of snow to slide off roofs, occasionally injuring people. But he said neither he nor the sheriff can recall deaths from such an incident in the three decades they’ve been there.

Pace said Perkovic’s mother, who was staying in the condo with the family of five, reported the pair missing at about 6:40 p.m. Sunday.

Rescuers searched the nearby Kirkwood Ski Resort for hours because the pair’s last known location was a ski lift where they scanned their tickets at about 4 p.m. Sunday.

Pace said it appears the two skied an “alternate” route home from the slopes that took them between buildings on a path that is unpaved in the summer.

At about 9 p.m., a neighbor spotted ski gloves next to the condo, realized they were buried beneath the snow and called 911.

The mother and son were airlifted to a hospital, where they were declared dead, Pace said.

They were the third and fourth skiers to die at California resorts since a major snowstorm late last week.

Aaron was a first grader at French American International School in San Francisco’s Hayes Valley, according to ABC7 News, the Bay Area News Group’s media partner.