Memnonia: It is in a valley between the northern lowland plains and southern highlands. The landing area is on ridged plains lava flows, a globally extensive rock unit of intermediate (Hesperian) age. The ridged plains are overlain to the north by very young (Amazonian) rocks postulated to be ash-flow tuffsor paleopolar deposits. On the south side of the valley are the ridged plains embay ancient (Noachian) cratered highlands. A small young channel of unknown origin is close (6 km) to the landing site. Viking images indicate the area is relatively smooth and free of obstacles. source