The two access tunnels into the upper pit survive, with the former Treflan Uchaf farmstead nearby, which was reused as an office and workshop during the quarry’s operational years. A long incline links the high level of the northern (upper) quarry to a surprisingly extensive working platform that has now been almost completely cleared. Perched on the spoil tips of the lower quarry stands a mysterious structure measuring approximately 10 feet by 6 feet by 13 feet, open at the front on the ground floor and open at the rear on the upper level; its original purpose remains unknown. Although water is still present across the site, no physical evidence suggests it was ever used to power machinery, and what appears to be a leat is merely a drainage ditch. The exit incline remains an obvious landscape feature, with its upper section now serving double duty as a farm track, though no drum survives from its working days. A small smithy can be found at the point where the incline once crossed the access road to Gareg Fawr. Beyond this, the incline continues as a public footpath towards the former river crossing, where a steel girder bridge built in 1902 stood until the 1990s. Along this route, concrete foundations from an unsuccessful 1920s granite-crushing venture remain beside the incline.

Treflan Slate Quarry consisted of two pits that were at one time under different ownership. Activity at the site probably began well before the 1800s, though the 19th century marked its busiest and most productive period. At its peak, around 30 men may have been employed, producing approximately 700 to 800 tons of slate annually. The quarry originally relied on water diverted from the “Factory Stream,” which later broke its bank and flooded into the lower pit. Material from the pits was carried through tunnels to a hand-worked dressing area where it was prepared for market. Once finished, the slate was transported by incline down to a branch line of the North Wales Narrow Gauge Railway. Operations gradually dwindled over the following decades, and the quarry finally shut down in the 1920s.