Complex sentence: In Chaco Canyon between 1020 AD and 1120 AD, the chert accounted for more than 20% of the material used for making stone tools, apparently imported in its raw form rather than as manufactured tools.
Split into simpler sentences: In Chaco Canyon, to the east, Narbona Pass Chert accounted for more than 20% of the material used for making stone tools in the Chaco era between 1020 AD and 1120 AD. It seems to have been imported in its raw form rather than as manufactured tools.