These rocks have been weathered away
over millions of years.
boulders sometimes appear to be peeling away layer by layer. This
is called exfoliation and is an example of a physical rock-weathering
process. Water moves into cracks in the rocks, freezes and expands,
causing the rock to flake apart. Expansion and contraction from
hot desert days and cold nights can also cause the rock to split.
As the edges of the coarse-grained monzonite rock break away, it develops
into rounded boulders. The process of exfoliation is the first step
in soil formation from these large boulders. Physical, chemical,
and biological processes will continue to break down the flakes of exfoliated
rock into soil-sized particles.
The formation of the different rock types and the mountainous topography within the
Chihuahuan Desert Nature Park resulted from two different volcanoes.