Crests and Troughs

This microscopic image taken by the Mars Exploration Rover Spirit shows the troughs between the waves of windblown soil that characterize the surface of Gusev Crater, Mars. The fine-grained soil in the troughs, combined with the coarse grains observed in a similar microscopic image taken of the waves' crests, indicate that the waves are geologic features known as ripples, and not dunes. Dunes contain a more uniform distribution of material. This information helps scientists better understand the winds that shape the landscape of Mars. The image was taken on the 41st martian day, or sol, of the rover's mission by its microscopic imager. The observed area is 3 centimeters (1.2 inches) across.

Image credit: NASA/JPL/Cornell/USGS

Can someone describe to me their conceptualization of the tiny 'trails' across the photo which are tending to be upper right to lower left in general. There are many of these, and my observation is that they do not follow a strick downhill path, nor do they follow only one basic direction or gradient. The markings at current viewing range show a pattern of repetitious 'tread' markings with a central trough and the side by side furrowing making the trough. In this range of time we saw much of this adhesion quality of the soil and the grains, combined with a corrosive and erosional contact quality between grains. It appeared much of the soil was a product of the alterations taking place at the grains as they appear to have a 'shaggy' coat of tufted powdery soil all around them wherever they are not in physical contact with other grains. This activity is not observed to the same rate of effect in other areas devoid of the ripples.