An army of 1,500 mail carriers fanned out across Colorado and Wyoming on Christmas Eve, making rare Sunday deliveries in a bid to get hundreds of thousands of blizzard-delayed packages to their destinations on time.

"This is an unprecedented effort," Postal Service spokesman Al DeSarro said. They all volunteered for the extra duty, he said.

Normally, about 100 carriers would be working on Sunday, he said.

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A blizzard dropped up to 3 1/2 feet of snow on Colorado and Wyoming last week, disrupting mail service for parts of three days amid the Christmas delivery crunch. The storm also shut down roads, businesses, schools and airports -- including Denver International, the nation's fifth-busiest.

That delayed mail arriving from elsewhere as well as deliveries within the two states.

"There were flights of packages that didn't get in until Saturday morning," DeSarro said, adding that 300,000 packages arrived at post offices in the two states on Saturday and Sunday.

Mail carrier Robin Smith, who was delivering packages in suburban Aurora, said she volunteered for the gratification of helping other people.

"I have two little girls, a 10- and a 6-year-old, and they think it's really cool that I'm playing Santa Claus," she said.

Smith said one elderly woman was overwhelmed when she knocked on her door and handed her a package.

"She looked very lonely and her car was buried" in snow, Smith said. "She was like, 'I didn't know I would see this.' I gave her a great big one. It was to 'Grandma."'

Mail carrier Danny Chavez said some people in Aurora were surprised to see him but others expected it.

"They say 'Thank you very much and Merry Christmas' and I say the same to them," he said.

DeSarro said about 500 carriers would make deliveries on Christmas Day.

"It's going to be a huge load," he said.