Chad Pallansch, 49, has not been heard from since setting off Wednesday from the East Inlet Trailhead near Grand Lake at Rocky Mountain National Park.
On this day in history, December 11, 1972, Apollo 17 astronauts become last humans to walk on the moon
On Dec. 11, 1972, Apollo 17 astronauts Eugene Cernan and Harrison Schmitt became the last humans to walk on the moon