Thurston Island is an ice-covered, glacially dissected island, long, wide and in area, lying a short way off the northwest end of Ellsworth Land, Antarctica. It is the third largest island of Antarctica, after Alexander Island and Berkner Island. The island was discovered from the air by Rear Admiral Byrd on February 27, 1940, who named it for W. Harris Thurston, New York textile manufacturer, designer of the windproof "Byrd Cloth" and sponsor of Antarctic expeditions. Thurston Island is separated from the mainland by Peacock Sound, which is occupied by the western portion of Abbot Ice Shelf. It divides Bellingshausen Sea to the east from Amundsen Sea to the west. Originally charted as a peninsula, the feature was not recognised an island until 1960.
The easternmost point of the island is Tierney Peninsula, southeast of which is Seraph Bay. Simpson Bluff, a broad ice-covered bluff sits between Levko Glacier and Savage Glacier where they enter the bay. Nearby Baker Knob is a small rounded coastal elevation which has an abrupt east face. Both Simpson Bluff and Baker Knob were named by US-ACAN for personnel from the Eastern Group of U.S. Navy Operation Highjump: Photographer's Mates R.M. Simpson and T.W. Baker, respectively. Operation Highjump obtained aerial photographs of Thurston Island and adjacent coastal areas, 1946-47. Snow-covered Harrison Nunatak stands south of Savage Glacier. It was discovered on helicopter flights from the USS Burton Island and USS Glacier during the U.S. Navy Bellingshausen Sea Expedition in February 1960, and was named by the Advisory Committee on Antarctic Names for Henry T. Harrison, Jr., a U.S. Weather Bureau meteorologist with the Byrd Antarctic Expedition in 1928–30. The southeast point of the island is Cape Walker.
South coast
On the south side of the island are King Peninsula, Williamson Peninsula, Evans Point, and Von der Wall Point, projecting into Peacock Sound. Williamson Peninsula is bordered by Schwartz Cove and O'Dowd Cove. Shelton Head is a headland marked by exposed rock, located west of Long Glacier on the south coast of Thurston Island. It was mapped by the USGS from surveys and U.S. Navy air photos, 1960–66, and named by US-ACAN for John A. Shelton meteorologist at Byrd Station, 1963-64. Prickly Ridge is a rounded ice-covered ridge west of Shelton Head on the south side of Thurston Island. The descriptive name was given by Advisory Committee on Antarctic Names ; small dispersed nunataks rise above the ice surface giving the feature a prickly appearance. Belknap Nunatak, an ice-covered spur, is the largest outcrop on the ridge. It was mapped by the United States Geological Survey from surveys and from U.S. Navy air photos, 1960–66, and named by US-ACAN for William Belknap, a field assistant at Byrd Station, 1964–65.