In 1972, Mariner 9 images revealed a variety of branched and networked valleys on Alba Patera, a volcano in northern Tharsis. However, when MOC peered down upon these valleys it became clear that the camera might not help answer the question of their origin. The origin of the textured material is unknown but might result from years and years of wind erosion of surface 'soil' or volcanic ash. However it formed, this covering obscures so much of the details of the valleys that high resolution pictures are unlikely to solve this mystery.
Illumination is from the right.
The picture was acquired in August 1998 during the MGS Science Phasing Orbits imaging campaign, and was presented at the 30th Lunar and Planetary Science Conference in Houston, Texas, March 1999.