Mars ice boulders are knon to be between 18 and 30 meters in width and I was joking.
I figured that... but except for accounting for where the ice boulders came from, it's not a bad theory that would explain the appearance of the channels/furrows and the disappearance of whatever created them. That's why I thought about it some more... and investigated the size of the channels. By the way, my estimate on the size is based on counting the pixels across the channels on the full size, raw photo... and using NASA's 2.9 to 4 meters/pixel resolution they give for the two raw photos published.