Dates from Cerro Mejia were collected during the 1999-2000 season and both the 2008 and 2009 seasons. The plot below was created using Oxcal 4.2 and the ShCal04 calibration (McCormac et al. 2004).
Based on the initial sample of dates it appeared that Cerro Mejia was only occupied for a brief period of time, however in the 2008 and 2009 field seasons excavations found that many structures had several occupation floors and that the site was occupied over a longer period of time. Also, using the southern hemisphere calibration has made some difference in the results, all dates are later, however the difference in time ranges from 25 to 110 years.
The majority of dates are derived from carbonized wood. On the site of Cerro Mejia carbonized wood was exceptionally rare. It is likely that dung was the primary fuel and that wood found its way into hearths when architectual elements or other wooden items were no longer fit for thier intended use. This means that the dates likely indicate the initial felling of trees for construction, as well as random inclusions. In one case we were able to date a seed from Unit 17. Sample number AA90356 has an uncalibrated intercept date of 1152BP and an error of 35. The calibrated two sigma range is 880-1020 AD. This sample was collected from the latest floor and indicates that the site was likely occupied during the second half of the Middle Horizon.
The last date on the figure above is a clear outlier. Unit 8 was a somewhat circular structure located in the agricultural fields on the slope of Cerro Mejia. The hearth may represent use of the structure as a shelter after the site was abandoned. Other areas of Mejia exhibit shelters for pastoralists because Mejia routinely sprouts grass in La Nina years. Today people often bring goats to graze on the site. In the past the site may have been used in a similar fashion.