You made me curious, so I watched Fuerte perdido today. I could find neither a DVD release nor an English-language edit of the film. What I found is a Spanish television version, running 88 minutes and 30 seconds.
Fuerte perdido is basically a traditional (cavalry) Western. Like, for example, in John Ford’s Sergeant Rutledge (1960) or Sidney Salkow’s The Great Sioux Massacre (1965), the main narrative is framed by the trial or inquiry of one the protagonists and related through flashbacks. The film’s story is standard fare: Geronimo and his Apache braves are on the warpath. They lay siege to Fuerte perdido (the “lost fort”), which is held by a handful of soldiers and a wild assortment of civilians, among them the movie’s hero, Paul Driscoll (Germán Cobos), a gang of despicable gunrunners and whiskey peddlers (Aldo Sambrell et al.), a Sioux woman, Tabali (Ethel Rojo), and, later in the movie, Driscoll’s wife Mary (Marta May). Tension in- and outside the palisades gradually builds to a horrific climax.
Prolific Madrid-born director José María Elorrieta (1921–1974) delivers well-staged violent action and dramatic romance; composer Fernando García Morcillo (1916–2002) an eclectic, catchy score; and crooner extraordinaire José Guardiola (1930–2012) two heartrending songs, “Caravana” and “Camino del sur.” A third canción, “Volveré” (“I Will Come Back”), is interpreted by a female singer whose name the credits give as Maruchy Taylor (I guess – the version I watched is cropped on both sides, so her last name appears as “Taylo”). Among the cast are familiar faces such as Lisbon-born Cris Huerta or omnipresent Frank Braña.
In Any Gun Can Play, Kevin Grant mentions Fuerte perdido as part of a first wave of European Westerns, “a rash of westerns with cavalry heroes and Indian villains. […] That the likes of […] Massacre at Fort Grant […] trespass on such well-travelled territory indicates the timid thinking and lack of adventure behind this first wave of films. All repeat the stock situations […] and […] show little interest in Native Americans as people” (p. 41).