The regolith at the Apollo 16 landing site, the only Apollo landing site in the central lunar highlands, contains material derived from a number of sources. A model that accounts for the introduction of basin ejecta and mixing of the megaregolith is used to estimate the abundance of basin material in the Apollo 16 regolith. Megaregolith mixing model estimates of the abundance of primary ejecta from the Imbrium, Serenitatis, and Nectaris basins are found to be present in roughly equal (8--10%) proportions. Additionally, the presence of mare-derived material in the Apollo 16 regolith suggests that a significant component of the regolith (15--23%) is derived from lateral transport. There are inherent difficulties in directly comparing model results with ground truth at Apollo 16. Results suggest shallower mixing during ejecta emplacement than predicted by Oberbeck et al. (1975).