On Earth, snowy weather is more common in the upper regions of the Northern Hemisphere and the lower regions of the Southern Hemisphere. A similar situation seems to exist on Mars, where seasonal frost made of carbon dioxide commonly appears in the rocky gullies of its middle and high latitudes.
Snapped in April by NASA's High Resolution Imaging Science Experiment (HiRISE) attached to the Mars Reconnaissance Orbiter, this detailed photo shows the frosty nooks and crannies in a crater on the Northern plains.
The amount of frost that forms within the alcoves differs according to the materials in the ground and the gradients of the surfaces on which the frost forms. So where there are craggy, uneven surfaces we see dark, shadowy features, while the tips of alcoves appear bright and illuminated because of the frost.
Steep slopes are not very common on the Northern hemisphere of the Red Planet. Most fluctuations in frost appearance occur within chasms along the Southern plains, where there are more slopes and surface variations.
HiRise is continually observing the changes in frost levels within these valleys on Mars to better understand its behavior.