Elysium Planitia (Mars)

This feature is named after an earlier feature.

Elysium Planitia, located in the Elysium and Aeolis quadrangles, is a broad plain th in the Elysium and Aeolis quadrangles, is a broad plain th. It lies to the south of the volcanic province of Elysium, the second largest volcanic region on the planet, after Tharsis. The largest craters in this Elysium Planitia are Eddie, Lockyer, and Tombaugh. Elysium contains major volcanoes named Elysium Mons and Albor Tholus and river valleys--one of which, Athabasca Valles may be one of the youngest on Mars. (wikipedia entry)

A planitia is a low plain. On Mars they are named after the nearest named albedo feature on the Schiaparelli or Antoniadi maps.