Project Blue Book Case #2173. On October 17, 1952, an unidentified object was observed over Tierra Amarilla, New Mexico — a remote community in Rio Arriba County in the state's mountainous north. Tierra Amarilla sits at approximately 7,500 feet elevation in the Chama River valley, surrounded by the Carson National Forest and the Sangre de Cristo Mountains.
While far from any military installation, Tierra Amarilla lay within the broader New Mexico nuclear corridor. Los Alamos National Laboratory was approximately 60 miles to the south, and the entire state was crisscrossed by military flight paths connecting the various weapons facilities, testing ranges, and research laboratories that made New Mexico the most militarily significant state in the country.
The remote mountain setting provided dark skies and clear air, ideal for observation. The limited population and absence of commercial air routes meant that any aerial object was immediately conspicuous. The high elevation also placed observers closer to overflying aircraft, potentially improving visual detail.
October 1952 was in the declining phase of the great wave. Reports continued at elevated rates in New Mexico, consistent with the state's status as one of the most active regions for UFO sightings throughout the Blue Book era.
No conventional explanation was found for the Tierra Amarilla observation. The case was classified "Unknown."