Two composite radiocarbon dates on wood beams from a unique prehistoric building in southern Arizona are the result of growth series subsampling of the beams and statistical evaluation of radiocarbon dates on the subsamples. This procedure avoids some of the problems caused by secular variations in the biospheric carbon-14 activity and by the dating of specimens grown over a range of years. This procedure yields results similar to more precise tree-ring dates from other sites in the southwestern United States. The procedure illustrated here is applicable to any archaeological tree specimen consisting of at least the last 40 growth rings.