A massive block of snow fell from a roof and buried a woman and her seven-year-old son just feet from the front door of their condominium in Northern California, authorities said.
Olga Perkovic and Aaron Goodstein had been skiing in the Sierra Nevada mountains near the Nevada state line, the Alpine County Sheriff's Department said.
They were returning home on Sunday when a chunk about the size of a trailer fell from the roof, burying them under about 3ft (1m) of snow.
"It was a freak accident," Undersheriff Spencer Pace said, adding that warming temperatures often cause snow to slide off roofs, occasionally injuring people.
But he said neither he nor the sheriff could recall sliding snow ever killing anyone in the three decades they have been there.
Mr Pace said Ms Perkovic's mother, who was staying in the condo with the family of five, reported the pair missing at about 6.40pm on Sunday.
Rescuers searched the nearby Kirkwood Ski Resort for hours because the pair's last known location was a ski lift where they had scanned their tickets at about 4pm.
The undersheriff said it appeared the two skied an alternative route home from the slopes which took them between buildings on a path that is unpaved in the summer.
At about 9pm, a neighbour spotted ski gloves next to the condo, realised they were under the snow and called 911.
The 50-year-old mother and her young son, from San Francisco, were airlifted to hospital, where they were declared dead, Mr Pace said.
They were the third and fourth skiers to die at California resorts since a major snowstorm late last week.
The region's largest storm of the winter season dumped more than 6ft (1.8m) of snow in the area over the last week, according to the Kirkwood ski resort, which is about 180 miles (290km) east of San Francisco.
Avalanches have also briefly closed Squaw Valley and Mammoth Mountain in recent days.