The Forest > Eo/Oligocene
The Eocene and Oligocene Periods
of Geologic History
The Eocene occurred from 63 million
until about 36 million years ago the Oligocene continued
to 25 million years ago. Oregon's major mountain ranges
still hadn't formed, so fossil records are similar across
the state and show the presence of palm, cinnamon, fig,
avocado, trees, giant ferns, and the dawn-redwood.
By the Oligocene, land mammals and plants
bagan looking like what we see today (although the trees
now might be found in the temperate eastern United States
or Asia). In central Oregon the trees were maple, oaks,
elm, basswood, sycamore, gingko, katsura, and dawn-redwood
(the latter three are now only found in parts of Asia).
Three-toed horses, camels, giant pigs,
saber-toothed cats, and tapirs prowled the landscape. Oregon
was definitely changing from a more tropical climate to
the temperate one we know and love today.