At www.jpl.nasa.gov/news/news.php … and https://phys.org/print430401551.html … Martian streaks, dark lines on Mars thought to be evidence of sub-surface flowing water are now thought to be where grains of sand and dust slip downhill to make streaks rather than seeping water. The Mars Renaissance Rover camera has been studying them and found they only occur on steep slopes …
… they behave like sand grains tumbling on sand dunes on Earth.