Pueblo, ColoradoJune 1958

On the morning of June 14, 1958, a weather observer at Pueblo, Colorado spotted an unusual object while tracking a pilot balloon with a theodolite (a surveying instrument used to measure angles). The object entered the theodolite's field of view at 10:46 a.m. Mountain time, moving from the northeast across the northern sky toward the southwest. The observer watched it for approximately five minutes before it disappeared into haze.

The object appeared circular with a distinctive flat ring around its middle and a rounded dome at the center, resembling Saturn as seen through a telescope. It was white or silvery in color with no visible metallic shine, noise, smoke, or exhaust trails. The observer, who had 28 years of experience estimating cloud heights, determined that the object was higher than cirrus clouds at 30,000 feet. It passed above some wisps of cirrus cloud, which blurred its outline slightly. The object was moving too fast for detailed measurements with the theodolite, though it reached an estimated elevation angle of 50 degrees or higher before vanishing.

The Air Force investigation included checks against aircraft schedules, radar units, and military operations, all of which came back negative. A local astronomer confirmed that no known satellite was moving in the direction of the object. The observer noted that the object's speed alone ruled out a balloon, estimating a minimum velocity above 500 miles per hour toward the southwest. Upper air winds that day blew from the opposite direction. The Air Force ultimately classified this case as unidentified, unable to explain what the observer had tracked. The full case file of 19 pages is reproduced below as held by the National Archives.