The hunt for the boar Troynt is almost certain to be the hunt for the Trwch Trwyth1 ("Boar King-Boar"* - the prouncation is similar) which is described in the medieval tale of Culhwch and Olwen (Details). In the tale, Arthur tells his warriors that the pig was once a sinful king, transformed by god into a boar as punishment2. Arthur has to collect a number of treasures fixed to the pig in order to help Culhwch win Olwen.
First, however, he has to kill a preliminary boar Ysgithrwyn Ben Beidd ("White Tusk Chief of Boars"*). He is helped in this by his dog Cavall (previously written Cabal) who, infact, kills the boar. Cavall then goes on to help Arthur hunt the Twrch Trwyth.
Unfortunately there is no mention of the wonder in Culhwch and Olwen, and, indeed, as can be seen on this Map, the route of the hunt as given in the tale goes nowhere near Carn Gafallt. This suggests the myth of the hunt, for whatever reason3, took in a broader range of areas than that in the story.
Footprints in stone are a classic wonder4, reported across Britain. Bord* has collected over a hundred of them, forty-three from Britain alone, and details of the footprints of Arthur's various animals from around Britain can be found at Thomas Green's Arthurian Gazetteer.