Four starch granules were recovered from two ground stone tools: FS689, Sample SS281 (n=2) and FS689, Sample SS281-2 (n=2). The date was made on associated charcoal from the same layer and context (Zarrillo et al. 2008).
Zarrillo, S., D. M. Pearsall, J. S. Raymond, M. A. Tisdale and D. J. Quon 2008 Directly dated starch residues document early formative maize (Zea mays L.) in tropical Ecuador. Proceedings of the National Academy of Sciences, USA 105(13):5006–5011.