This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows several dark sand dunes in the north polar region. (website(1))
(2)
1. http://www.msss.com/mars_images/moc/2003/09/30/index.html
2. http://www.msss.com/mars_images/moc/2003/09/30/index.html