Although most people think of Nebraska as one flat stretch
of land, the Northwestern corner of the state is considered to be the beginning
of the Badlands with its toadstool rock formations that are composed mainly of
sedimentary rock. This area was starting to form over 20 million years ago, by
a combination of erosion and minor plate movements.
During the Tertiary period, the White River (which still
exists) was what could be considered a paleoriver that carried sediment from
the West, which contained ash from volcanic eruptions and deposited course
sands that would later become sandstone. As the wide river raged on, silt was
deposited in the plains that would later become rocks that alternated layers—or
cross-bedded layers of siltstone and sandstone. As millions of years passed and
the land began to rise, erosion would prove to have much more of an effect on
the soft siltstone layered between the harder, more dense sandstone. As the
strata lithified, it provides valuable information and documentation to
sedimentologists who look at the effect of the sea level changing.
Erosion over a long period of time in this location has
created rock formations that are referred to as toadstools based upon their
mushroom-esque shape. Images taken of Toadstool State Park in the past show how
erosion continues to effect these rock formations--the stronger sandstone has
fallen on top of the softer siltstone—or the cap of the mushroom has crushed
its stem.
