Chemical analysis of cacao residues in archaeological ceramics from North America: considerations of contamination, sample size and systematic controls Mary Ann Pelleymounter, Petia A. Shipkova, William N. Washburn, D.K. Washburn • 2014
Cacao consumption during the 8th century at Alkali Ridge, southeastern Utah Petia A. Shipkova, William N. Washburn, D.K. Washburn • 2013
The prehistoric drug trade: widespread consumption of cacao in Ancestral Pueblo and Hohokam communities in the American Southwest Petia A. Shipkova, William N. Washburn, D.K. Washburn • 2011