Who built these craters? They are not natural! Once, a meteorite fell to the floor of Mars. With great speed. He made a crater.
In this neighborhood, no one stone remained upon another.
Instantly there came another meteorite, similar in speed, diameter, angle of impact, and no stone survives.
Evaporated and disappeared. Now they are part of the atmosphere, newly super-heated from the incoming meteorites. Only two holes remain.
Both meteorites have the same diameter, and produce two twin craters with walls as dinner plates. That happened million years ago. Other meteorites collide.
Volcanic activity erodes many parts of Mars. The freeze and the next heating did not affect these walls. Neither the wind blew some parts. Very rare, or very well built. Possibly they were used as water deposit. Or they were used to tackle water when it rained. I do not know. But they are not natural and have something to do with water.
Why do not drop the first crater wall in the other? Concrete can only maintain this walls firm. Who is using constructions material on Mars?
image of Lunae Planum