The transition from the Fountain Formation into the overlying Lyons Sandstone is marked by a fairly abrupt change from feldspar-rich fluvial (river-deposited) sandstone beds to quartz-rich, windblown, fossilized sand dunes. Frequently you can see spectacular bedding features in the rock, representing the fossil sand dune. You may discover the trackways of small amphibians or even the fossil impressions of raindrops preserved on the solidified sandy surfaces. The sand dunes existed during the Permian. The Lyons Sandstone ranges from about 100 to 200 feet in thickness. It is named after the town of Lyons north of Boulder, where you can purchase slabs of ancient dunes for building walls and as ornamental rock. Look for good exposures of these sandstone beds at many of the parks and open-space areas near Lyons.
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