The epistolary relationship between Joan Coromines (Barcelona, 1905 - Pineda de Mar, 1997) and Joan Sales (Barcelona, 1912 - 1983) documents how Sales actively collaborated in the collection of toponymic materials for the Onomasticon Cataloniae in municipalities and parishes of the Camp de Tarragona, Muntanyes de Prades and the Segarra. Joan Sales reported to Coromines his routes and the difficulties that he encountered in these areas. A result of the surveys carried out in these sites is the collection of Vallclara (Tarragona) presented in our work.