Evidence of quarrying for Stonehenge’s bluestones is among the dramatic discoveries leading archaeologists to theorise that England’s greatest prehistoric monument may have first been erected in Wales, reports.

It has long been known that the bluestones that form Stonehenge’s inner horseshoe came from the Preseli hills in Pembrokeshire, around 140 miles from Salisbury Plain.

Now archaeologists have discovered a series of recesses in the rocky outcrops of Carn Goedog and Craig Rhos-y-felin, to the north of those hills, that match Stonehenge’s bluestones in size and shape. They have also found similar stones that the prehistoric builders extracted but left behind, and “a loading bay” from where the huge stones could be dragged away.

Carbonised hazelnut shells and charcoal from the quarry workers’ campfires have been radiocarbon-dated to reveal when the stones would have been extracted.

Prof Mike Parker Pearson, director of the project and professor of British later prehistory at University College London (UCL), said the finds were “amazing”.

“We have dates of around 3400 BC for Craig Rhos-y-felin and 3200 BC for Carn Goedog, which is intriguing because the bluestones didn’t get put up at Stonehenge until around 2900 BC,” he said. “It could have taken those Neolithic stone-draggers nearly 500 years to get them to Stonehenge, but that’s pretty improbable in my view. It’s more likely that the stones were first used in a local monument, somewhere near the quarries, that was then dismantled and dragged off to Wiltshire.”

The dating evidence suggests that Stonehenge could be older than previously thought, Parker Pearson said. “But we think it’s more likely that they were building their own monument [in Wales], that somewhere near the quarries there is the first Stonehenge and that what we’re seeing at Stonehenge is a second-hand monument.”

There is also the possibility that the stones were taken to Salisbury Plain around 3200 BC and that the giant sarsens – silicified sandstone found within 20 miles of the site – were added much later. “Normally we don’t get to make that many fantastic discoveries in our lives,” Parker Pearson said. “But this is one.”