Mae chwe rhan i’r Safle Treftadaeth hwn, gan gynnwys tirweddau chwareli ysblennydd fel Penrhyn, Dinorwig, Dyffryn Nantlle a Ffestiniog. Mae hefyd yn cynnwys Amgueddfa Lechi Cymru yn Llanberis, Castell Penrhyn a Rheilffyrdd enwog Ffestiniog a Thalyllyn. Cawsant eu hadeiladu i gludo'r llechi o’r chwarel i farchnadoedd ledled y byd a’u trawsnewid yn ddiweddarach drwy ymroddiad gwirfoddolwyr i reilffyrdd treftadaeth.
The new World Heritage Site is a serial property in six parts including spectacular quarry landscapes such as Penrhyn, Dinorwig, the Nantlle Valley and Ffestiniog. It also includes the National Slate Museum in Llanberis, Penrhyn Castle and the famous Ffestiniog and Talyllyn Railways, built to transport the slate from quarry to markets around the world and both later transformed through the dedication of volunteers into heritage railways.