Thaumasia Planum is a large volcanic highland plateau, located south of Melas and Coprates Chasma which are part of the giant Vallis Marineris canyon system. It was named after a classical albedo feature and is made up largely of lava flows, at least several thousand meters thick. The flows date back to the Noachian, the oldest of the three Martian geologic time periods, and are about 4 billion years old. It borders to the east on a 900 km long north to northeast trending ridge, informally named Coprates rise.