Project Blue Book Case #5852. On June 14, 1958, witnesses in Pueblo, Colorado, observed a bright object in the sky above the city. Pueblo was home to the Pueblo Army Depot (now the Pueblo Chemical Depot), a major military installation that stored chemical weapons and conventional munitions — one of the Army's most sensitive storage facilities.
Pueblo's position at the edge of the Great Plains, where the Arkansas River emerges from the Rocky Mountain foothills, provided a geographic setting with clear sightlines to the east and dramatic mountain terrain to the west. The city's elevation of approximately 4,700 feet placed observers above the denser lower atmosphere.
Colorado's military significance extended well beyond Pueblo. The state hosted the North American Air Defense Command (NORAD) at Cheyenne Mountain, the Air Force Academy in Colorado Springs, Lowry AFB in Denver, and the Rocky Mountain Arsenal. The entire Front Range corridor was one of the most militarily significant regions in the country.
The 1958 timing fell during a relatively quiet period for Blue Book, between the dramatic 1957 wave and the mid-1960s resurgence. Cases from this inter-wave period received thorough investigation.
The object over Pueblo could not be identified as any military or civilian aircraft operating in the area. Weather data did not support atmospheric explanations. The case was classified "Unknown."