The Beginning

Starting more than 23 million years ago, at the beginning of the
Miocene epoch, in what is now North America, the climate was hot
and wet. Much of North America was covered with huge seas and
there was no land bridge between North and South America. It was
a time of mountain building and great upheaval in the world. The
India tectonic plate smashed into the Asian plate forming the
Himalayas. Similar events took place in Europe forming the Alps and
in the United States, the Rockies began to grow.

For millions of years during this epoch, water deposited sand and
gravel, making a sedimentary layer called the Ogallala formation
over what is now the Great Plains. In places the Ogallala formation
is 650 feet thick and commonly in the upper layer there is a
protective shell made of Caliche. Caliche is an extremely hard,
non-porous sedimentary rock that takes about one million years to
form after the sediment is laid down.

Later, water and wind covered the Ogallala formation with as much
as 150 feet of sand while continuing tectonic plate activity raised
much of the plains to a higher level, further protecting the water
pooling below.

Ogallala Aquifer

The Great Plains are in dark orange
stretching from Mexico to Canada