United Flight 610 originated in San Francisco and was scheduled to Chicago, Illinois, with en route stops, among which were Oakland, Salt Lake City and Denver. The flight, which was carried out by DC-6 “Mainliner Overland Trail”, departed San Francisco on schedule at 19:15 and after stopping at Oakland proceeded to Salt Lake City, arriving there at 23:24. It departed Salt Lake City at 00:11, 26 minutes behind schedule due to the reloading of bulky cargo. The aircraft climbed to the cruising altitude of 15,000 feet. At 01:47, the flight reported having passed the Silver Crown fan marker (located 12 miles west of Cheyenne) and requested a lower altitude. ARTC cleared the flight down to 8500 feet. After crossing the Cheyenne range station at 15,000 feet the crew then executed a right turn to a heading of 210 degrees, descending to 8,500 feet. The correct heading for the airway to Denver however was 168 degrees. At 01:56 the flight reported reaching its assigned altitude. The DC-6 was now flying dangerously close to the mountainous terrain. At around 02:00 it struck the side of Crystal Mountain. After initial contact with the trees the aircraft continued to travel approximately sixty feet, at which point it struck the ground. From here it traveled in a straight line 225 feet, then bounced into the air again, and came to rest 465 feet farther on. One of the possibilities was that the captain made some wrong selections on the audio selector panel, silencing the Denver low frequency radio range signals and receiving the Denver Visual Audio Range (VAR). Such a mistake can easily be made because using the correct switches in a darkened cockpit is difficult and because both radio range signals are difficult to differentiate. Another possibility is that the ADF had been affected by the Fort Bridger radio range. PROBABLE CAUSE: “The Board determines that the probable cause of this accident was that, after passing Cheyenne, the flight for reasons undetermined failed to follow the prescribed route to Denver and continued beyond the boundary of the airway on a course which resulted in the aircraft striking mountainous terrain.”