We now know that pre-modern human tool use dates back far beyond we previously might have thought, each discovery proving that our early ancestors showed sign of intelligence and early social evolution. A recent finding in central China of a prehistoric tool mill dating back 600,000 years ago used by Homo Erectus in the Lushi Basin, South Luo River, supports this hypothesis. The discovery was dated using pedostratigraphic analysis, optically stimulated luminescence, and magnetostratigraphic analysis which authenticated the aforementioned period.
Basically, the Lushi Basin site shows that Home Erectus actually had some sort of tool factory (100 stone implements were found), where flake and core technology, similar to other tools used by Home Erectus and found in China at other sites, proving that they actually were organized at a greater level of sophistication then previously thought.
Prof. Huayu Lu has co-authored a thesis on the finding with researchers from the Henan archeological institute and La Trobe University of Australia. The thesis was published on the latest issue of Journal of Human Evolution, where you can read more about the discovery (for 19.95$ unfortunately).