Spectral investigations revealed layers of hydrated sulfates and clay minerals at the steep slopes. These minerals are indicative of aqueous environments in ancient times. It is very likely that Noctis Labyrinthus experienced an intense hydrological period when these rocks were formed. Elsewhere, long, extensively interconnected linear structures can be observed along the valley slopes. These are sand and dust deposits that have been shaped by wind into extensive ribbed fields whose ridges are separated by distances of 150 and 400 m. These sand ridges are oriented perpendicular to the wind direction and often formed on large bodies of sand or dune surfaces. The almost vertical orientation of the ridges on numerous slopes indicates that sand was transported parallel to the slope, while on the valley floors or on shallower slopes, the wind transported the fine-grained material from different directions along the valleys and also even uphill.