La Sociedad Protección Mutua de Trabajadores Unidos (united workers' mutual protection society) was founded in Antonito in 1900 by seven Hispanic laborers, including Celedonio Mondragon, the first president. The SPMDTU promoted Spanish language and culture, fought discrimination, and provided social activities and low-cost group insurance. From this headquarters, the organization established sixty-three other chapters throughout Colorado, New Mexico, and Utah, with a peak membership of around 2,500. About a dozen chapters remain active.
Members constructed this two-story Mission Revival hall of adobe with a bright white concrete stucco finish. It includes a 100-by-49-foot meeting hall with a stage, in addition to offices. Shallow-arched steel trusses span the hall. A mural on the back wall of the stage of a field worker offering the valley's produce was painted by two Adams State College students who signed themselves Los Muralistas del Valle. In 1981, a mural depicting boxers was painted on the south exterior wall by Edward Chacon.