Élisée Reclus,
The Earth and its inhabitants, Volume 1…
“ Huge bridges span the ravines, though for more than half the year not a drop of water passes over their pebbly beds.The Sierra de Guadarrama and its western continuation, the Sierra de Gredos, separate this central plateau of Spain into two portions, lying at different elevations. Old Castile and Leon, which lie to the north, in the basin of the Duero, slope down from east to west from 5,600 to 2,300 feet; whilst New Castile and La Mancha, in the twin basins of the Tajo and the Guadiana, have an average elevation of only 2,000 feet. ”
