Large preceramic site of c 2500 BC on north central coast of Peru with two large pyramids, rectangular ground level and subterranean structures. It dates to the Pre-Ceramic Period VI and the earliest structures were an isolated group of house compounds. Some of these were later filled with rubble and two pyramids were built over them. These were subjected to further reconstructions. Caches of offerings were buried in shell refuse around the bases of the pyramids. Rio Seco had a population of 500 to 1000 at its height and was abandoned before the onset of the Initial Period.