One of the principal goals in sedimentary geology is to identify the environment of deposition by looking at rocks and their characteristics. It is very important to be able to determine if a package of rocks was formed by wave processes pounding on a beach, by river processes, or by gravity flows traveling from submarine canyons to the abyssal plain of oceans. It is important because by doing so, we can understand, for example, past climate (and use it to predict future climate), we can understand the Earth complex systems, we are able to make predictions about the presence (or absence) at a certain location of a certain rock type, etc.
This post shows an example of the difference between fluvial and eolian rocks. Both pictures (above and below) show the eolian Wingate Sandstone, overlying the fluvial Chinle Formation.
The Wingate Sandstone forms the steep, upper pat of the cliff. It is called an aeolian sandstone because it was deposited by the action of the wind in a desert environment, not unlike what the Sahara desert is today.
The Chinle Formation can be seen immediately below the Windgate, it is more heterogeneous from the point of view of the lithology, consisting of mudstone, sandstone and conglomerate. The Chinle was deposited by rivers flowing on a floodplain.
Immediately after hitting the "Publish post " button I saw "Where does desert sand come from?" talking about the Namib Sand Sea, and posted on the AGU blogosphere site by Vivienne. An appropriate present day analogy for the Wingate of the Triassic.