Site formation and disturbance are evaluated for two open-air sites of the Middle Stone Age (MSA)--Florisbad, South Africa, and $\not=$Gi, Botswana. Artifact assemblages are analyzed by methods appropriate to each site: re-fitting of conjoining artifacts, classification of major and minor artifact damage, on-site distribution of patination, size-profiling, vertical distribution plotting, artifact
... [Show full abstract] dips and orientations. Analysis of artifact attributes suggests predominant functions and demonstrates a highly curated/reduced industry for $\not=$Gi, while Florisbad tools are used expediently because of readily available raw materials. Sixteen sedimentary units at Florisbad contain Holocene Later Stone Age, a late Pleistocene hiatus, and 12 units of MSA antiquity, three of which have assemblages large enough to evaluate: (1) The basal units contain an earlier MSA, broadly associated with the Florisbad archaic Homo sapiens and the Florisian Land Mammal Age fauna. (2) Unit M has a highly retouched form of MSA. (3) Unit F (above) contains a large assemblage of manufacturing debris, plus a small number of formal tools and more numerous utilized flakes used predominantly in butchering. These horizons accumulated during a series of brief visits to the site. Debris was buried gently by spring sediments with no loss or significant disturbance. Two units at $\not=$Gi contain MSA similar to the Bambatan of Zimbabwe. The industry is highly retouched and reduced. Points are the most heavily curated and most abundant type. Edge-wear shows that cutting is the predominant function at the site which, like Florisbad, was used for a specialized activity. The industry represents a long-term accumulation along a river margin. Its condition indicates some exposure to trampling and a relatively slow rate of sedimentation. The main unit shows only minor hydrological disturbance but the assemblage below accumulated under a mix of more turbulent and quiescent conditions. This study demonstrates that open sites can make a greater contribution to MSA studies than is currently appreciated if in-depth investigation of site history is attempted. It further concludes that some variation in MSA industries is related to the expedient or conserved use of raw materials.