The Oligocene in Utah
33.9 - 23.0 Ma
The Oligocene Epoch was subsequent to the Eocene Epoch and antecedent the Miocene. During this time the planet was starting to change into the planet we know today. The name Oligocene comes from the Greek word oligos, which means few. The start of this epoch began 34 million years ago and ended 24 million years ago.
South America had detached from Antarctica and ice was starting to accumulate on the landmass. The continents were starting to move towards their current positions and the seas were cooling. Mountain building was occurring in Western North America and the Alps were just staring to form in Europe. La Garita Caldera, a volcano located in southwestern Colorado, erupted leaving a volcanic crater that was about 22 by 47 miles. During this time, an asteroid struck Nunavut, Canada and left a crater that was about 15 miles in diameter.
Tropical Forests were starting to be replaced by savannahs and grasslands. There were also roses and cashew trees. Much of North America was prairie like, giving rise to animals such as camels, rhinoceroses, and horses. There were also terror birds and carnivorous marsupials. The largest land mammals ever known walked the earth at this time.
Utah Geology During the Oligocene
Utah during the Oligocene, experienced significant igneous activity. Some of this activity is still visible in southern Utah. Volcanic activity produced intrusive igneous rocks in northern Utah as well as in southern Utah. Those southern intrusions created the Henrys, La Sal, and Abajo mountain ranges.