Looks more like sort of gravel to me. And note the apparent wind scouring of this possible sediment around the one "rock." If indeed it's gravel and not sand, that is one heck of a wind that made such scouring.
The rocks are rounded. It seems unlikely to me that with such extreme weather, there is no liquid.
Maybe, maybe not. I don't know what the atmospheric density is on the surface, but with temps that low it could be very high. If the atmospheric density is higher than Earths, heavy scouring could take place with a much smaller amount of wind than you would expect on Earth.