the team is led by veteran archaeologist scotty macneish. they are seeking evidence of the first inhabitants of the valley. when macneish first excavated here in 1962 he discovered a time capsule of human occupation at a site called purron cave. macneish: here we are back at purron cave. we really haven't dug in it in almost 30 years. walls all preserved. even the trowel marks we made to mark off strata are still preserved and we have all sorts of neat floors of charcoal one on top of the other. the amazing thing about this cave is that we really have unbelievable preservation. the reason we have preservation is it's so dry in this area that the bacteria of decay that destroy things can't live so anything that's dropped in here it dries up and dehydrates and lasts forever. keach: as macneish dug deep into the cave traces of an early people emerged from an archaeological stratum he called el riego. macneish: here is our el riego layer, 8,600 years old. now, in it we not only have a date in terms of the year, but we have some idea of what part