This presentation of the Program of the Second MSL Landing Site Workshop shows an image of a "crater" near the equator that is 2.4 km wide and 750 meters deep !
On the Mars Image explorer you can zoom in on the floor of this possible collapse feature and inspect the polygonal patterned ground.
Although on Wikipedia I couldn't find any pattern quite like this, could this mean there's ice in the subsurface of the floor of this "crater"?
No.
This pattern is not directly water/ice-related, it's just dunes - the crater is filled with martian sand and the winds created these ripples.
There are a few other examples of similar patterns - here's a small selection:
https://www.nasa.gov/image-feature/the-dunes-in-mars-wirtz-crater https://en.wikipedia.org/wiki/Proctor_(Martian_crater) https://www.dailymail.co.uk/sciencetech/article-1206382/NASA-captures-vivid-shot-sand-dune-Martian-crater.html
