I got to thinking about your theory and decided to check some dimensions. The gullies average about 7 - 8 pixels in width and NASA says that the resolution of the full size image is approximately 3 Meters per Pixel... ergo, the channels are approximately 21 to 24 meters in width... that's some ice bolder...
Mars ice boulders are knon to be between 18 and 30 meters in width and I was joking.