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Grand Mesa was created by a unique series
of geological events. A hundred million years ago the area was on the swampy
shore of an inland sea. As sediments were deposited in and around the sea,
they buried huge amounts of trees, ferns and other plant matter growing in
the swamps. The plant matter was turned into coal and has been mined for many
years in the valleys beneath Grand Mesa. Living in these swamps were large
numbers of dinosaurs and their tracks can be found in the rocks above the
beds of coal. Time passed and the sea slowly disappeared, the area began to
rise and experience volcanic activity. The rocks deposited by the inland sea were covered
with lava flows and broken by fissures filled with lava. The lava cooled forming
a flat surface that today is the top of Grand Mesa. Fissures that provided
channel-ways to the lava today can be seen along Crag Crest Trail and on Leon
Peak. Beginning about fifteen million years ago a glacier pushed across the
top of the lava. Marks left by the glaciers as they moved across the surface
of the hardened lava can be seen today. These marks are called glacial striations.
The glaciers also scooped out large shallow depressions that formed lakes.
Today many of these lakes have been modified with dams and provide valuable
water storage.
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