To the north east of the town of Blaenau Ffestiniog is the valley of Cenunant y Diphwys.

The exact location of this original quarry has been obliterated by subsequent mining activity, but it is likely that it was part of what became Diphwys Casson.

[1] The quarry was successful in the period 1820–1880, but it ran into difficulties and production ceased in 1890.

Working restarted in 1920, but this lasted only seven years before the quarry was again abandoned.

This incline operated by Rhiwbach Tramway was also used by the Votty & Bowydd Quarry.