Dark Sand Cascades on Mars

They might look like trees on Mars, but they're not. Groups
of dark brown streaks have been photographed by the Mars
Reconnaissance Orbiter on melting pinkish sand dunes covered
with light frost. The above image was taken in 2008 April near
the North Pole of Mars. At that time, dark sand on the interior of
Martian sand dunes became more and more visible as the spring
Sun melted the lighter carbon dioxide ice. When occurring near the
top of a dune, dark sand may cascade down the dune leaving dark
surface streaks -- streaks that might appear at first to be trees standing
in front of the lighter regions, but cast no shadows. Objects about 25
centimeters across are resolved on this image spanning about one kilometer.
Close upsof some parts of this image show billowing plumes indicating
that the sand slides were occurring even when the image was being taken.