I'm gonna talk about a really, really cool lake, but first, some geology lessons.
On Earth, mountains and valleys tend to be formed by tectonic motions or volcanism, and then shaped by erosion (mostly water and wind erosion) back into their lowest possible forms. This is why the Appalachians are so much more rounded than other, spikier and younger mountain chains...
On Mars, there is some evidence of that process having taken place as well, but mostly only in the distant past. On Mars, there is a very weak atmosphere which can't really do much to erode away mountains or craters, and so they stay, but the tallest mountains, they tend to flatten out just to the force of gravity.
Take the Alba Mons and Olympus Mons for instance, Alba Mons is a much older volcano, and it has been stretched out by gravity, trying to deform the planet back into a sphere, but Olympus Mons is younger, and that process has only just begun for it.
The stresses of weight of Alba Mons on the surrounding lands has caused a series of striking tectonic features, huge rifts where tectonic pressure has deformed the land. Olympus Mons hasn't yet deformed to the same extent that Alba Mons has, but all of the mass of the Tharsis igneous provinces are being deformed in this way.
@patience Venus does have tectonics, just not global tectonic plates like Earth does. Both Mars and Venus have some local tectonic stuff going on. Theories abound as to why Earth has tectonic activity such like it does, mostly it's chalked up to convection of the mantle.
@patience that definitely plays a factor in geology, for sure. erosion is far more efficient at spreading out a mountain chain than gravity alone ever could be... depending on the gravity of the planet that is.