The Upper Herto Member is a sandy fluvial (deposited by rivers) unit recording a freshwater lake environment, and has yielded archaeologically relevant remains across a stretch. Locality BOU-A19 preserved 71 artefacts, BOU-A26 331 artefacts, and BOU-A29 194 artefacts, a total of 640. Additionally, BOU-A19B has 29 artefacts, and BOU-A19H 15 artefacts. The tool assemblage contains tools made using the Levallois technique (associated with the African "Middle Stone Age"), as well as cleavers and other bifaces (associated with the earlier Acheulean). Though bifaces and blades are rare (respectively less than 5% and 1% of the tools), it is more likely these tools were frequently made by Herto Man at a different location than that they were indeed rarely produced at all. Such an assemblage is typically labelled as the vaguely defined "Transitional Acheulean", which is found as far back as 280,000 years ago. The Herto site thus indicates the transitional phase was long-lived, and the actual derivation of what is considered "Middle Stone Age" proper was not gradual nor simple.