Elsewhere, however, air traffic was light as people celebrated together, watched football or took in events such as the annual re-enactment of George Washington's Revolutionary War crossing of the Delaware River to attack the British at Trenton, N.J.
Residents of parts of Florida had to take time out from observing the holiday to clean up after storms that destroyed at least two homes and damaged others. Tallahassee reported more than 5.5 inches of rain.
No serious injuries were reported. "We are incredibly blessed today," said Columbia County, Fla., sheriff's department spokeswoman Laurie Windham.
Denver International Airport officials said some passengers stranded or delayed by last week's blizzard were still trying to get flights out of the city Monday but they did not know how many. They also did not know how many people had spent Christmas Eve camped at the airport but said it was "down significantly" from the peak of 4,700 on Wednesday night, when the storm barreled into Colorado.
The airport reopened Friday.
"We're pretty much at some semblance of normalcy," said Joe Hodas, a spokesman for Denver-based Frontier Airlines, the airport's second-busiest carrier. "We're running on schedule. No real delays."
Officials of United, the airport's No. 1 carrier, did not immediately return a call seeking comment.
The storm dropped up to 3½ feet of snow, halting mail deliveries.
On Christmas Eve and Christmas Day, postal carriers trying to clear out the backlog delivered up to 100,000 packages across Colorado and Wyoming, U.S. Postal Service spokesman Al DeSarro said.
About 500 carriers were delivering mail in the two states Monday, with up to 500 more workers on duty in mail processing centers, Desarro said.
In suburban Aurora, mail carrier Doug Fischer donned a Santa suit to deliver packages on Christmas.
"It's awesome. Everybody's surprised," he said.
Elsewhere, travelers passing through New Jersey's Newark Liberty International Airport enjoyed short waits and plenty of space on their flights on the day that is normally a lull in the busy two-week holiday travel period.
"It was very quiet," said Keri Potts, 29, of Hoboken, N.J., returning from a holiday trip to Chicago. "There were no babies on the plane. It was perfect. I would do it again. I don't know why the rush to get there beforehand if the 25th is much more convenient."
From Dec. 17 to Jan. 1, some 4.4 million passengers, up 4.1 percent, will pass through John F. Kennedy International, Newark Liberty International and LaGuardia airports, estimated the Port Authority of New York and New Jersey, which operates the airports.