sentences:  The Callejón de Huaylas has become narrow between the highest and vertical walls of rock, without any vegetation and, in this stretch, the rocks of the Cordillera Blanca and Cordillera Negra come closer (less than 5 m of distance).To arrive to Huallanca, at the north end of the Callejón de Huaylas, 33 tunnels must be passed in a trip of 25 km, in which the Santa River breaks, roaring, the Cordillera Negra, to flow to the sea.In Huallanca, 1,410 msnm, the hydroelectric power station of the Cañón del Pato is located.