The rock is a type of gritstone but more featured than Peak grit. 'Tonnau' means waves in Welsh, after visiting the crag you will understand!
Craig Y Tonnau is located in the forest at the bottom of the Crimea Pass. It is one of the better esoteric crags in the Meiroinydd guide book.
I spent the weekend dosing at Play y Brenin on my SPA assessment. Here are a few photos I took in the glorious morning sunshine.