Arcadia Planitia (Mars)

From classical albedo feature at 45N, 120W.

Arcadia Planitia is a smooth plain with fresh lava flows and Amazonian volcanic flows on Mars. It was named by Giovanni Schiaparelli in 1882 after the Arcadia region of ancient Greece. It dates from the Amazonian period's Arcadia formation's lava flows and small cinder cones. It includes a more recently developed large region of aeolian materials derived from periglacial processes. (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.