Casma River in the context of 1970 Ancash earthquake

The Cordillera Negra (Spanish for "black range"), Yana Walla in qechua is part of the Cordillera Occidental, one of three mountain ranges in the Andes of west central Peru. It is almost entirely located within the Ancash Region.

The range extends over an area about 230 km long and 25–40 km wide, stretching in a NNW-SSE direction parallel to the Pacific coast, its ridge is about 60 km from the coastline. It is part of the Andes mountain range which inland borders on the Costa, the narrow strip of coastal deserts along the South American coast. In the north and east the range is bordered by the Santa River which crosses the coastal ridge at 8° 45' S and runs parallel to the Cordillera Negra for almost all its length. In the south the range is bordered by the Patiwillka River at 10° 30'. In the central part of the range near Huaráz, Casma River breaks through the ridge of the range.

The Sechín River is a seasonal river about 55 km (34 miles) long in the Ancash department of Peru that remains dry for long seasons, increasing its volume at times of rain in the mountains at its source. It is of irregular regime, due to this is known as Loco River. It rises at an altitude of 4,385 m (14,386 ft) in the Cordillera Negra and it ends by flowing into the Casma River about 10 km (6.2 miles) inland from the Pacific Ocean. The Casma-Sechin basin runs down the western slopes of the Andes mountain range - one of the world’s driest deserts. The city of Casma, population 30,000, is located near the junction of the two rivers. The Pan-American Highway crosses the Sechin River at Casma.

Historical records showed that the Sechín was severely affected by flooding in 1925 from an extremely strong El Niño cycle. Elders alive at the time recounted that the rains of 1925 were significantly stronger than those in 1871 and 1891, although the rains from 1891 were considered "calamatious."