Cuarteron Reef (Huayang Jiao 华阳礁 in Chinese; Calderon Reef in Filipino; đá Châu Viên in Vietnamese) is a reef at the east end of the London Reefs in the Spratly Islands of the South China Sea.
It is controlled by China as part of Sansha, and claimed by the Philippines as part of Kalayaan, Palawan. It has a supply platform and a reef fortress. The supply platform has anti-aircraft guns, naval guns, search radars and radio communications equipment.
Coordinates: 8°53′00″N 112°51′05″E / 8.88333°N 112.85139°E