[Bernard Marx]

It's a subsidence sinkhole of some kind. Something created a cavity beneath it and overburden collapsed into it. It bears an uncanny resemblance to the subsidence holes let after underground nuclear tests at Frenchman's Flat in Nevada:

?

[dr_lew]

It's a subsidence sinkhole of some kind.

I believe there a number of these holes on Mars, and the caverns are essentially lava tubes. Here, it looks like the date of the initial collapse is recorded by the secondary rim, formed by additional accumulation after the collapse, although I couldn't explain the exact mechanism. I think there is a lot of crusty material on Mars formed from compacted windblown dust.