I will swear I've seen similar objects.
It was backpacking and I was crossing a large area which was all river until last summer. Then the edges kind of dried. This was on the edge, and in a spot where it had dried a bit, then rained and the stream washed away some of the silt, dried a bit more, same thing happened, and then dried.
I don't remember where it was, but in the periphery of my mind I noticed the area. These were soft, and would have been washed away as the water rose again.
I doubt they are related to Mars, where they probably took a long time to form.