Excavations at two ancient quarry sites in western Wales suggest how ancient people probably quarried some of the stones now standing at Stonehenge.

The 42 stones in question are some of the smaller parts at Stonehenge, relatively speaking: they still weigh two to four tons each. They’re called the bluestones, and they came all the way from western Wales. Chemical analysis has even matched some of them to two particular quarries on the northern slopes of the Preseli Hills.

One, an outcrop called Carn Goedog, seems to have supplied most of the bluish-gray, white-speckled dolerite at Stonehenge. And another outcrop in the valley below, Craig Rhos-y-felin, supplied most of the rhyolite. University College London archaeologist Michael Parker Pearson and his colleagues have spent the last eight years excavating the ancient quarry sites, and that work has revealed some new information about the origins of Stonehenge.