I'm thinking there may be some sort of geological phenomena round there that produce juicy looking tumps (there's another near Kinver). Sandstone?

I don't have a photo to hand but another one a few miles South and on the other side of the Motorway looks very similar - but that one is topped by a genuine barrow - http://heritageaction.wordpress.com/2010/02/28/barrow-hill-worcestershire-landscape-art-vandalised/