Basalt Over Sandstone

February 04, 2004

Basalt_over_sandstone copy

Provided by: Paul Grimshaw
Summary authors & editors: Paul Grimshaw

The above photo shows an example of the interesting geological processes that continue to shape our planet. The red rock is Navajo sandstone, deposited as sand dunes in southwestern Utah around 180 million years ago. The darker rock is Tertiary-Quaternary basalt that erupted as lava from a flank volcano associated with the Pine Valley Laccolith, the largest such intrusive body in the United States. Note the horizontal banding of redder and whiter sandstone indicating sand with differing iron compounds and the bedding planes of the ancient sand dunes, part of a vast Jurassic desert. Also note the large "crystals" of columnar basalt at the upper left where the lava cooled into columns.

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