Access: Not easy, unless you're at least reasonably fit. Close-ish to Dolmen de la Claie-de-Driolle 4 & 6 a good few hundred metres along the same path. (You will also pass various less definite but suspicious bits of possible wrecked sites.)
In Dolmens et Menhirs en Languedoc et Roussillon Bruno Marc refers to 'le grand dolmen de l'Olivier', which from http://www.t4t35.fr seems to be a little further along the same path, but I must have stopped just short of it before giving up for the day & turning back. (Gah!)
Bare remains of the chamber uprights & cairn only here, possibly with a fallen capstone at the front of the chamber according to some sources. As far as I can tell, Le Grand Dolmen de l'Olivier which I didn't find seems to be similar, but larger and with more of its cairn. It also has an additional small (later?) cist in what remains of its chamber.