Soils from the ancient Maya site of La Technica, Guatemala were physically and chemically characterized. Soil types were described taxonomically. Stable carbon isotope analysis the humin fraction of the soil organic matter was conducted to search for evidence of ancient maize agriculture. Residues of maize and other C4 plants leave behind a distinct isotopic signature different from the predominating C3 forest vegetation of the Usumacinta valley. Analyses of these flood plain soils improve our understanding of ancient Maya agricultural practices.