Many Barcelona westerns were indeed shot in Fraga, Aragón. That was for the landscape scenes. The town scenes were shot in Balcázar's low-grade western town in Esplugues de LLobregat. This was a tottering town with houses seemingly made of plywood.
Iquino, the main competitor of the Balcázars, shot his westerns in the Balcázar town (it looked better in his movies, actually), or in a ranch of his property in Castelldefels, Barcelona. Iquino was too cheap at times to even go to Fraga for the locations, so he'd shooot it all outside Barcelona. Four Candles For My Colt, ot whatever it's called in English, was shot in a military camp outside Castelldefels. Castelldefels also served as a location for Manuel Esteba's westerns.