Are you sure about that? According to the article/s it doesn’t have the radio range or the flight range to fly 1,200 kilometers.
The article and Wiki say the radio range is 125 Km. As others have stated, it probably flew on a straight trajectory after it lost radio contact. As for flight range, it can fly for 8 to 9 hours. Wiki says its cruising speed is 81 mph, with a 127 mph max speed.
By car, the shortest distance between Ft. Huachuca and Evergreen, CO is 831 miles. That distance by air would be considerably shorter. If it can fly 81 mph for 9 hours, it can travel 729 miles at cruising speed. This would only be a difference of 102 miles based on the driving distance, which is not in a straight line. I'd say given a tail wind, and its original flight altitude, that it is quite conceivable that it made it there under its own power. We get very strong winds up here in the Rockies.