Among the scattered mesas in Cydonia is a famous one whose appearance earned it the nickname "The Face." Despite fanciful theories, the mesa is simply a hill about 300 m high. Other mesas nearby have generally similar shapes.
High-resolution images of The Face, however, reveal its northern and eastern sides have a smooth covering material. Where it occurs on slopes, scientists have dubbed it "pasted-on terrain" because that's just what it looks like. The material likely has the same origin as the mantles of dust-covered snow and ice seen elsewhere.
The pasted-on material lies on the sides of The Face that point away from the greatest solar heating, much like the snow that survives into summer lies on the poleward-facing slopes of mountains on Earth. Thus the material may still contain water (as snow or ice) just below the surface. On the warmer sides of this and other mesas, however, the material has eroded away.
The flat ground around the mesas shows several small impact craters. There are also a number of features that look like cones with dimples in the top. (See at the foot of the other mesa in the picture.) These might be what geologists call "rootless cones" - basically, places where volcanic heat met subsurface water and the resulting steam blasted through the surface, creating a cone.
Yet other signs of volcanism - obvious lava flows, for example - are rare in Cydonia, so scientists think a more likely explanation is a pingo. Pingoes are found commonly on Earth in polar regions. Essentially, a pingo is a gigantic frost heave or a kind of ice-blister. This would fit in with the spacecraft observations of a water-rich ground.
