The floor of Hellas is a fascinating and unusual terrain. Some of the apparent features are deceptive.

I include my own rendering of the Hellas area, based on MOLA topography.

This is colour-coded to emhasise differences in elevation of the basin floor, and I have tried to render the basin in near-true geometry (it often appears very elliptical on some maps due to projection problems).

Red represents all elevations higher than about -5000m. Yellow is ~-6000m, pale blue -6500m and dark blue 6800m and deeper.

The floor of the basin has suffered several hundred metres of erosion, and this is uneven with some areas and structures being deeper eroded than others.

The apparent "pedestal" in the basin centre is actually lower in elevation than all the rest of basin, other than a half-annulus in the West, which has suffered greater erosion than the rest of the basin (note the cliff-like boundary of this eroded area, in the north of the basin)

The standard ideas are that this western half-annulus was originally finer-grained sediment that has been more easily eroded by winds and blown away, out of the basin, over geologic time.

Note that in the east, the outer annulus is actually HIGHER than the inner basin, not lower.

The centre of the basin has more extreme relief between the ridges and peaks than does the outer part of the basin. Again, this may be due to wind erosion of the "flats" between the ridges and peaks, or could be due to stronger ridge development than elsewhere. We just don't know.

Note that the ridges make patterns of overlapping circles, indicating that large impact craters exist at basement level. The ridges are contractional wrinkles, which tend to break-through to the surface at locations of basement hights, like buried crater rims.

In the south-east of the basin is a noticeable yellow area that appears to be a seperate, smaller (and hence younger) impact basin.

Hellas is a fascinating area and there is much yet to discover here. Personally, I'd like to see a lander visit the area, but there are problems with solar power in this often-cloudy area which is tilted away from the Sun when Mars and Earth are close. In a few decades, this will change, and nuclear power offers a tidy solution, anyway.