The Casma River, which upstream is called Río Grande, is a river that crosses northern Casma province in the Ancash Region of Peru. It originates in the Black Mountain Range and drains into the Pacific Ocean. Major tributaries include the Sechín River (right).
The valley contains the small, once important town of Casma, which had to be rebuilt after being destroyed by the 1970 Ancash earthquake. The new town has been completed.