The Sierra Menera mining railway entered into operation on July 27, 1907 carrying iron ore from the rich deposits of the Ojos Negros mines (Teruel) to the port of Sagunto. These mines were only 15 km from the broad gauge railway operated by the Compañía del Ferrocarril Central de Aragón (Central Railway Company of Aragon). However, in spite of the short distance, the high rates charged by the Central de Aragón prompted the mining company to build its own railway from the mines to a loading facility on the coast. Thus, somewhat bizarrely, a 205 km long, narrow gauge railway was built, practically all of it running parallel to the Central de Aragón’s lines.

As the line was intended solely for the transport of iron ore, its operational life was always dependent on the output of the mines. Production rose steadily, especially after a steelworks was set up in Sagunto. However, the demand for transport grew at such a rate that the mining company discovered that its railway was causing a veritable bottleneck that stifled any possibility of expansion. This led the company to transfer the iron ore transport business to RENFE.