As you proceed toward Moab along Highway 128, you reach the Colorado River, a name derived from the red colour of the water's load of iron mineral based silt.
Along each side of the river all the way to Moab, and beyond along Highway 279, you follow he river's edge and are contained by steep red cliff walls rising several hundred meters. The river has cut itself deeply into the surrounding rock formations.
Large sections of the older cliff walls are covered in a dark deposit. This thin blueish black material is a thin layer of manganese rich clay acted on by bacteria and is called “desert varnish”. It only covers areas which have been stable for a long time and have not had significant water erosion. The dark coating is a stark contrast to the underlying red rock, a characteristic used by Native Americans.
In some areas, the cliffs have been more eroded and form slightly dome shaped formations, whose vertical faces have been further eroded by wind, rain, and freeze-thaw cycles. In such cases, the hollowing out is a precursor to arch formation and can be seen in these images. The ones shown here are along Highway 279.
