Large pit working with tunnels, buildings, workshops, infirmary, inclines, drum houses.***

The main pit is the amalgamation of two separate workings: Ellen and Eureka. There are also two smaller pit workings to the south and east.

Today, the quarry pits are partially filled with rubbish and no longer reach their original depth, though several access, investigation, and drainage tunnels remain intact throughout the site.

The upper level preserves surviving mill structures along with the remaining Blondins, which feature complex pulley systems that allowed for tower repositioning during operations. Various other artifacts from the quarry’s working life can also be found scattered across this level.

The middle level contains a collection of office buildings alongside the remains of two mills that once processed the slate extracted from below. The workshops that served the quarry’s maintenance needs are still present, along with a ‘specials’ department where custom slate products were prepared.

On the lower level stand further buildings including a mill that still retains its shafting and machine remnants, providing tangible evidence of the mechanical systems that once powered the slate-working processes. Some structures across the site show signs of late renovation work.

The drum houses and inclines remain in fair condition, with some track still in place along the routes where slate once traveled between levels. These inclines feature hinged wooden crimp spargs and largely conventional drum gear, though they incorporate an unusual feature in the form of pulley-and-weight brake-lever counterbalances. Attractive “entry box”-style brakeman’s shelters have survived the years.

At the Nantlle Railway terminus, visitors can still find the line’s stables where the horses that once hauled slate wagons were housed. Adjacent to these stands a building with a wheel-pit that was used for preparing horse feed.

Among the quarry’s unique or unusual features were saw tables built to a De Winton hydraulic-feed pattern, though these ultimately proved unsuccessful in practice. Perhaps most innovative was an arrangement where one mill was powered by another through belt drive.

The quarry’s development began in 1816 as a four-pit operation reaching the valley floor, dewatered by a dedicated drain system. The first mill opened in 1860, followed by an integrated mill in 1870, and by 1898 four mills operated across three levels. Production in 1882 stood at 8,251 tons with 230 workers, rising through the 1890s to peak at up to 350 men before the Second World War, with nearly 200 employed immediately after.

Transport connections evolved significantly over time. Initially linked to the Nantlle Railway via Pen-y-Bryn, this route was replaced by inclines to an extended line after tipping blocked the original path. The three mill levels connected via two incline pitches, with a third descending to the railway. The quarry operated extensive tramways in 2-foot and 3-foot-6-inch gauges, with a De Winton locomotive surviving until 1960. A proposal to haul material up to the North Wales Narrow Gauge Railway at Y Fron failed due to the need for a new bypass loop, and lorry transport via Y Fron only began in 1963 after the Nantlle Railway’s closure under Beeching.
The quarry pioneered technological advances, with six Blondins replacing earlier chain inclines and water balance systems. Initially steam-powered, these were electrified when the quarry became an early customer of Cwm Dyli power station, remaining in use until the 1970s when a lorry road reached the last working pit. The site featured large maintenance workshops.

Decline set in during the 1970s with only twelve men and the top mill operating. A brief late-1980s reactivation ended with a major rockfall. The quarry distinguished itself as one of few Nantlle operations providing extensive workers’ housing, and Nantlle village today largely comprises former quarry dwellings. The on-site war memorial has been re-erected in the village. Some small-scale late reworking, although as of 2025 site looks to be finally abandoned.

The site is still nominally at work, reprocessing tip material, but access by locals is tolerated.

One Blondin tower still stands. At least three Blondin control systems in good condition in three separate buildings.