Thanks TXnMA. I think your earlier posting on these structures is the best suggestion -- that at least the longer ones were laid down to channel water, and the "rooms" could be pools or ponds to retain the runoff, as the rainfall declined thousands of years ago. BTW, the geographical description given in the Old Testament for the location of Eden may refer to two now-vanished rivers that flowed out of Arabia and met the other two in a now-flooded spot under what is now the Persian Gulf.
Whoa!
Again!
I have my own theory, but this time, I’ll keep it to myself, since it’s not quite formed into something recognizable by others.