Could the watercourse-like markings on the surface of Mars have been made by shifting sands or dust?

Not likely. There are plenty of wind-created features on Mars, but the things that look like dried-up river beds are almost certainly dried-up river beds. There's lots of other evidence of past liquid water on Mars, too, much gathered from the Spirit and Opportunity rovers that are still going strong. http://marsrovers.jpl.nasa.gov/home/index.html

No, there was a river on mars about 1,000 yrs ago & we used to white water raft on it.

its possible, but then you would need wind to make it happen, implying an atmoshpere