The 'face' in Cydonia Mensae was imaged by Mars Global Surveyor on 8th April 2001, a couple of months into its extended mission. MGS obtained the highest resolution image of the landform to date. (See the full-size 155 KB image here.) Although it is undeniably an unusual landform, owing to the odd symmetry and erosion patterns of its flanks, the 'face' is merely a small-scale geological structure containing pronounced areas of subsidence. It is just over 2 miles (~3.5 Km) long.
Cydonia Mensae is a small region located near the border between Chryse Planitia and Arabia Terra in the northern hemisphere, just above the datum line (Mars' equivalent of Earth's sea-level).
