Fort Union’s parade ground comes to life in a broad stereograph view of the daily guard mount ceremony. Companies stand in formation near the tall flagstaff with officers gathered at center while onlookers dot the margins of the field. A lone dog trots into the scene, an unplanned detail that gives the military pageant a human note.<br><br>Guard mount marked the change of sentries and the inspection of the new detail. The photograph records the choreography of ranks and files against the open plains that surrounded the post, with quarters and post buildings faintly visible beyond the formations. Depth is strong across the paired images, inviting the viewer into the space of the parade ground.<br><br>Period pencil caption on the verso reads “Guard Mount Ft. Union N.M.” Date likely in the 1880s, when Fort Union served as a major supply depot on the Santa Fe Trail and a center of military life in territorial New Mexico. An evocative document of ceremony, routine, and the small interruptions that make real history, including the fort’s unofficial canine participant.