Recent construction of an irrigation canal across the Batán Grande -- Poma archaeological complex of northern Peru provided an opportunity for inspection of soil profiles and detailed sampling along a five km transect bisecting an important concentration of ceremonial structures built during the past 3000+ years. From laboratory analysis of 80 soil samples, it is concluded that no long-term irrigation agriculture was practiced in this area and it was unimportant as a resource base. Stratigraphic studies indicate few sediments survive from the 1925 El Niño event, but a massive bed attributable to prehistoric slack-water flood sediments has been identified and can be bracketed between ca. 650-1000 by associated diagnostic funerary ceramics. Other flood deposits representing the same or different events are described, but it is concluded that intervalley correlations will be difficult until more precise dating methods are available.