They were: The quarries operated internal railways of 2 ft (610 mm) gauge and were served by Glynrhonwy Siding off the LNWR's Caernarfon to Llanberis branch.

[3][4] Lower Glynrhonwy was acquired by the Air Ministry in 1939 for munitions storage.

[5] During the Second World War the site generated two extra trains per day on some occasions.

[7] A 100 MW pumped storage project, marketed as a "quarry battery", received approval in 2017 and as at 2019 had reached the "detailed engineering design" stage.

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