The seaside sites of Huaynuná and Las Haldas are found about 20 kilometres (12 miles) north and south of the mouth of the Casma River on the coast.

A frieze located at Sechin Bajo dated at 3600 BCE is the oldest example of monumental architecture discovered thus far in the Americas.

[9] The amount of irrigable land is the narrow valleys is not large, although some population lived outside the agricultural area in the coastal sites.

The waters of the Pacific Ocean off Peru are extremely rich and some of the earliest settlements were on the desert coast and depended upon fishing rather than agriculture or hunting and gathering for subsistence.

[10] The Casma/Sechin culture was located about 130 kilometres (81 mi) north of the northern outposts of the Norte Chico civilization, believed by archaeologists to be the oldest in the Americas.

[12] By 3000 BC, at a few locations in coastal Peru, including the Casma/Sechin valleys, a sizable population was present and undertaking large projects such as building pyramids and other ceremonial and monumental structures.

The location of Sechin Bajo inland from the sea and from marine resources suggests that agriculture had become a significant contributor to the livelihood of the builders and nearby occupants.

The labor requirement for construction also implies a numerous sedentary or semi-sedentary population nearby with a mechanism of control to gather and supervise workers.

[17] Both Huaynuná and Las Haldas are located more than 12 kilometres (7.5 mi) distant from the irrigable lands of the Casma River Valley and thus fishing was their principal means of subsistence.

Floodplain agriculture seems to have been the most common means of raising crops although small-scale canal irrigation was probably also used in the Casma and Sechin valleys during this time.

Technological developments included woven textiles and pottery, the adoption or expansion of canal irrigation for agriculture in the river valleys, and the construction of many large monumental pyramids and plazas.

[23] Many industrial and food plants were cultivated by the inhabitants of the Casma and Sechin Valleys, but evidence of maize, the most important crop of the Americas, is absent during the Initial Period and earlier.

Maize and domestic animals, llamas, alpacas, and guinea pigs, were introduced during the Early Horizon period and the dependence upon marine resources for protein declined, suggesting that the invaders (if such there were) came from the highlands of Peru rather than other coastal cultures.