Stumbled across the first excavation of this site by accident last year (2011), when out blackberry picking. A team from Sheffield university led by Mike Parker Pierce (if you've watched any Stonehenge documentary, Mike PP will be the "Stonehenge expert") were excavating around the rocky outcrop and had began to uncover a large stone.
They have been looking for the sources for some of the non spotted dollerite "blue stones" from Stonehenge (only about half of the so called blue stones are spotted dollerite, the rest are a mixture of stones). Geologists had taken rock samples from the outcrop and one of the samples had come back as a positive match for one of these other stones. They'd therefore come to excavate around the outcrop to see if they could find any evidence of neolithic quarrying. They found flint tools and some "hammer stones" and then as they dug away from the rock face they uncovered a large stone (approx. 14 foot by 4 foot by 30 inches), which appeared to have been abandoned, possibly because a crack had appeared on its top face.
They returned this september (2012) and continued their dig, hoping to find evidence of which way the stones would have been moved (up stream towards the Preselis or down towards the sea) and to pin point the original location of the Stonehenge stone. They didn't find any sign of which way the stone was moved but they did locate the exact location from where the Stonehenge stone came from. They have also found more tools and quite a bit of charcoal around where the Stonhenge stone came from. They are now speculating that the stones may have gone to Castell Mawr before being taken on to stonehenge, they will be back next september to continue their research, focusing on Castell mawr which they believe had two stone circles within the henge and to explore possible sources of the other stones