We tried to find out some information about these stones but have mostly failed.  The very few sources we found mention there are around 30 of them (some with fossils) and they are probably about twenty years old and was "the impressive gateway into the south entrance to the Parish".  There are two areas of stones - one either side of Thamesdown Drive.

It appears they were found covered in brambles by Pokemon Go players and Haydon Parish Council's Parks and Open Spaces Team undertook to clear the site and reveal the stones once again, which they completed in February 2019.  That must have taken a lot of hard work to clear such a large area - well done them.