Treen Cliff is a Site of Special Scientific Interest (SSSI) located on the Penwith Peninsula in Cornwall, England, UK, 6 miles (9.7 km) south-west of Penzance.

[1] Designated for both for its biological and geological interest, part of the site, Treryn Dinas, is a Scheduled Ancient Monument consisting of a "cliff castle" with four ramparts and ditches and the Logan Rock.

Maritime grassland occurs on the steeper cliff slopes and is dominated by red fescue (Festuca rubra), with spring squill (Scilla verna), wild carrot (Daucus carota), kidney vetch (Anthyllis vulneraria) and sea plantain (Plantago maritima).

The spectacle of all these flowers strewn along the cliff edge, with the classically beautiful Pednevounder beach below and the rugged headland of Treryn Dinas in the distance, must be one of the loveliest in Cornwall.

[8] There are butterfly colonies of the silver-studded blue (Plebejus argus), small pearl-bordered fritillary (Boloria selene) on Cribba Head in the eastern part of the site as well as the thrift clearwing (Synansphecia muscaeformis) a day–flying moth.