Plaster City is an unincorporated community in Imperial County in the U.S. state of California. It is located 17 miles (27 km) west of El Centro, at an elevation of 105 feet (32 m). United States Gypsum operates a large gypsum quarry and plant there and owns the town. The quarry was started in 1920 and was acquired by United States Gypsum in 1945. It is the site of the last industrial narrow gauge railroad in the United States. The 3 ft (914 mm) gauge line runs north to the gypsum quarry and brings gypsum from the quarry to the plant. The first post office at Plaster City opened in 1924.