The group of quarries served by the Rhiwbach tramway are situated on bleak moorland to the east of Blaenau Ffestiniog. All the quarries here are at the fringes of the slate deposits, and never were big producers. They were therefore more vulnerable to the ups and downs in the price of slate on the open market. Periods of total closure were common as were frequent changes in ownership. Their production costs were also higher.
Rhiwbach Slate Quarry, along with Blaen y Cwm, differed from all other quarries in the slate industry in one important respect. The exit incline from the quarry for the finished product led up and not down. The classic balanced incline, by which the outward loaded slate wagons brought up the empty wagons by gravity, was not possible. The quarry had therefore to build a substantial engine house to power the incline from the bottom, with the haulage wire passing over a pulley at the top. This engine house also powered the quarry machinery and the underground inclines.
The quarry was started at the beginning of the 19th century on a site to the South of the later main workings, but part of the quarry was worked out by the 1880's . The pit working on the main site started in the 1860's, was later developed extensively underground to encompass eight levels. Drainage of the underground workings was through a tunnel which began 350 feet below the surface and emerged onto the side of Cwm Penmachno. When the quarry first opened, the slate was taken down on horseback. The Rhiwbach Tramway opened in 1863 and revolutionised the transport arrangements for the quarry. A wharf was opened in Porthmadog and from then on all slate went out along the tramway and down the Ffestiniog Railway.
This quarry was one of the most remote in the industry and it was frequently cut off for long periods in bad weather. Because of this, the living quarters almost reached village status. It included family accommodation, a shop and a school house as well as the barracks for the single men.
Although the quarry occupies a large area, the annual tonnages scarcely exceeded 6000 tons and it was closed down several times. The quarry finally closed in 1951 and all the machinery was removed.