Denver ? The city’s airport hummed with activity on Christmas Day as airlines struggled back from a paralyzing blizzard, and mail carriers stayed on the job delivering thousands of storm-delayed packages.

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.

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.

The storm dropped up to 3 1/2 feet of snow, halting mail deliveries.