In this extremely nice VIS image, taken by the NASA - Mars Odyssey Orbiter on February, 1st, 2015 and during its 58.268th orbit around the Red Planet, we can see that the faint (---> extremely light/hard to see) dark lines, barely visible in the Central/Northern portion of the frame, are caused by the passage of those micro-hurricanes/tornadoes (that, as you know, are very common on Mars) which are known as "Dust Devils".
As the Dust Devils travel along the Surface of the Planet, they scour (---> sweep) away the loose Surface Dust, thus revealing the darker Surface that is lying beneath the aforementioned loose Dust. Furthermore, and if you pay particular attention, you will also be able to see that there are very well defined (and also well illuminated) Gullies located on the Inner Rim of this old and unusually-shaped ("oval", in this case) Unnamed Impact Crater located in the Martian Region known as Noachis Terra.
Latitude (centered): 51,7254° South
Longitude (centered): 17,0688° East
This frame (which is an Original Mars Odyssey Orbiter b/w and Map-Projected frame published on the NASA - Planetary Photojournal with the ID n. PIA 19271) has been additionally processed, magnified, contrast enhanced and then colorized in Absolute Natural Colors (such as the colors that a human eye would actually perceive if someone were onboard the NASA - Mars Odyssey Orbiter and then looked down, towards the Surface of Mars), by using an original technique created - and, in time, dramatically improved - by the Lunar Explorer Italia Team.