There are many reasons why this is just a regular landform like the ones we have on Earth. One reason is the shadowing of the landform, the second is that there are clouds and clouds could tamper with the camera, and the third s that there have been multiple pictures and only one shows a face.

The first reason is shadowing. When ever you look at something you could think its someone or something else. This can be because shadowing. Sometimes you cant see all the features, or shadows make there own. This is the case with the Face on Mars. There might be crater in the mesa that could look like eyes far away and a curve could make a mouth shape. "Only this one had unusal shadows that made it look like an Egyptian Pharaoh".

"...Revealing... a natural landform". These both give evidence on how there was a change in shadow on the mesa.

The second is the clouds. Some clouds on the red planet could have gotten in the way and make it look more like a face then a mesa. "... April '98 - a cloudy time of year for the Red planet. This gives evidence that there are more clouds then ususal on the Red Planet.

The third thing is the amount of pictures. THere have been multiple pictures of the mesa. And only one looks like a face. The other pictures show a mesa or a butte type area. " Scientist figured it was just another Martin mesa, common enough around Cydonia. This gives evidence that there are other mesas in the area its just this one looks like a face. And as technology got better It would start to show, or take away all of the features the face had.

And those are the reasons why it is just a mesa and not a secret Face on mars. The three things I mentioned where shadowing, the clouds in the area, and the pictures and how they got better over the years. So imust conclued it is just a normal mesa