Here's the googlemaps satellite image:

http://maps.google.co.uk/maps?f=q&source=s_q&hl=en&geocode=&q=stonehenge&sll=53.800651,-4.064941&sspn=13.857722,27.685547&ie=UTF8&hq=Stonehenge&hnear=Stonehenge,+Amesbury,+Salisbury,+UK&t=h&ll=51.176949,-1.818967&spn=0.007587,0.01929&z=16

I presume you mean the circle of uncultivated land to the south of the A303. It's three bowl barrows:

http://www.magic.gov.uk/rsm/10319.pdf