PETERSON AIR FORCE BASE, Colo. (AP) -- Volunteers at a Colorado Air Force base monitoring maps showing Santa Claus' progress have answered more than 41,000 phone calls from children asking about the jolly old elf.

Phones have been ringing nonstop Monday at Peterson Air Force Base, headquarters of the North American Aerospace Command's annual Santa-tracking operation.

Hundreds of helpers at NORAD are taking calls and tracking Santa's location on large projection screens. They're posting updates for nearly 1.2 million Facebook fans and more than 120,000 Twitter followers.

The maps show Santa is nearing Denmark on his journey west. NORAD says he has delivered more than 3.5 billion presents so far.

The volunteers started taking calls at 4 a.m. Mountain time and will keep updating until 3 a.m. on Christmas morning.