In images of Jezero crater on Mars, it looks like the delta fan is higher than the surrounding crater floor.
This indeed seems to be the case with closer-up images from the Perseverance rover taken from the edge of the delta.
Intuitively, I would guess that a river flowing would dig a kind of trench in the ground where it flows, so the ancient river bed would be lower than its surroundings. So how did the delta end up higher than its surroundings?
My hypothesis is that sediments were deposited, and erosion wore off the rocks around the delta, but somehow, the sediments from the delta were harder and didn't wear off as fast. Is this indeed the case, or is some other mechanism at play?