The site is dominated by a lake formed from the flooded workings, creating the impression of a single vast pit. Waste banks with finely constructed stone inclines and revetments make the landscape visually striking.

To the south of the lake lie the ruins of the main integrated mill, other buildings, hoist gallows, and haulage structures. The Cornish engine house to the west retains its original engine and boilers.

Northeast of the quarry stand remnants of old village buildings, including the Commercial Hotel. On the former Nantlle Railway line, a notable inverted-arch retaining buttress can be found, with a flight of cantilevered steps nearby.

Opened in 1820, Dorothea rapidly became the dominant slate quarry in the area. By 1848 it employed 200 men, producing over 5,000 tons annually; by 1882 this had grown to 533 workers extracting 16,598 tons per year. The operation eventually encompassed six pits, the last sunk in 1891. It remained profitable throughout the nineteenth and early twentieth centuries—unusual for a quarry without land ownership—except when persistent flooding reduced earnings.

At least eight waterwheels provided power for pumping, haulage, and milling. Steam power arrived in 1841 to drive the first of eight chain inclines (including two double and one triple), replacing earlier horse whims and hand-worked turntrees. Additional powered ramp inclines handled waste, while De Winton steam locomotives appeared in 1869.

The first of four steam-powered Blondins was erected on the spoil banks in 1900; these were electrified in 1959 and operated until 1965, when a road to the pit bottom was constructed. By the twentieth century, eight mills housed 66 saws. A large Cornish beam engine installed in 1906 pumped the pit—then 550 feet deep—until replaced by electric pumps in 1951. Most of the slate waste had to be uphauled to be deposited on the vast tips to the east.

Expansion of the quarry consumed the old Talysarn village, repurposing some buildings, and forced the Nantlle Railway to be rerouted northward. Extensive locomotive-powered rail systems operated both at ground level and atop waste banks, using 2-foot and 3-foot-6-inch gauges; some wagons had double-flanged wheels to accommodate either gauge. Final closure came in 1968.