Desert pavement occurs only in the drier parts of the Sonoran
and consists of large, flat areas that are free of vegetation and covered with
tightly packed, small stones. Pavement forms when large rocks on the surface
weather away to form smaller stones. These smaller stones then tend to
accumulate in the lower depressions on the soil surface eventually forming a
Desert Pavement takes several tens of
thousands of years to form.
Desert pavements are usually dark in color due to a thin
coating of desert varnish on the surface of the stones. Desert varnish consists
of clay minerals and manganese oxides which impart the dark color. How varnish
forms is not well understood. It is thought that bacteria which reside on the
surface of the rock plays a major role in concentrating the mineral ingredients
of varnish, perhaps as a means to protect themselves from the extreme
environment of the desert..