The Pinar del RÃ o province has one of Cuba 's three main mountain ranges , the Cordillera de Guaniguanico . The mountains are divided into the easterly Sierra del Rosario and the westerly Sierra de los Organos . The Pinar del RÃ o province is Cuba 's westernmost province and contains one of Cuba 's three main mountain ranges , the Cordillera de Guaniguanico , divided into the easterly Sierra del Rosario and the westerly Sierra de los Organos .