In reply to pancakeandchips:
From what I can make out, there are 6 quarrying areas included.
1. Penrhyn Quarry (Bethesda) and the Ogwen Valley down to Port Penrhyn.
2. Dinorwig Quarry and the mountain quarrying landscape.
3. Dyffryn Nantlle Quarries.
4. Gorseddau and Prince of Wales Quarries (Cwm Pennant) including the tramway and mill.
5. The whole of the Ffestiniog district and the railway to Porthmadog.
6. Bryneglwys Quarry, Abergynolwyn village and the Talyllyn railway.
Can't see any mention of Aberllefenni or Corris, which I think is odd.