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Colorado by Nature: The Geological History of Red Rocks

Coloradans' favorite concert venue was recently designated as a national historic landmark. Here's the story behind those remarkable, perfectly acoustic red rocks.

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This summer, while you’re chilling at Red Rocks, listening to one of 2015’s more retro acts, like the Music of Abba by Arrival From Sweden, Hall & Oates, Neil Young, or the Moody Blues, consider that these timeless rockers have nothing on the venue’s surrounding red rocks, which date back 300 million years.

The Red Rocks are part of the Fountain Formation, a thick stripe of pink sedimentary rocks that stretch along the Front Range’s eastern edge. These colorful rocks form Balanced Rock in Colorado Springs’ Garden of the Gods and Boulder’s fabulous Flatirons in addition to Red Rocks Amphitheatre, one of the world’s most stunning concert venues.

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If you look closely, you’ll see pebble- to fist-sized chunks of other rocks embedded in the amphitheatre’s red rocks. Chunks this large can’t be transported far from a mountain range, so their very presence in the Fountain Formation, which predates the modern Rockies by hundreds of millions of years, indicates that they were shed off an older mountain range. These so-called “Ancestral Rockies” stood in nearly the same spot as today’s imposing peaks, but rose 240 million years earlier.

Piece by piece, swift mountain streams eroded this ancient range and carted away the debris. But where the streams exited the steep terrain, they lost their momentum and dropped a load of sediment, forming a series of cone-shaped piles along the mountain front. Over many millions of years, these sediment piles were deeply buried and eventually cemented and compacted into the dense, hard rock you see today.

Fortunately, geology – like musical acts – often repeats itself. Some 65 million years ago, tremendous forces associated with the uplift of the modern Rockies began to remove the overlying sediments and tilt the Fountain Formation’s layers down to the east. After the red rock was finally exposed at the surface, the elements took over. Water began to seep through the rock, plucking out grains and slowly enlarging cracks through countless freeze-thaw cycles. Fast-forward millions of years, and the cracks became wider and deeper, until all that remained of the ancient rockpile are two major monoliths—Creation and Ship rocks—and the bowl in between, which now contains the prolific Red Rocks stage, rows-upon-rows of steep stone seats, and many nights during the summer months, crowds of screaming, dancing fans.

With its fascinating geological history, Red Rocks Amphitheatre gives a whole new meaning to the term “classic rock.”

Terri Cook, 5280 Contributor

Terri Cook is an award-winning freelance writer based in Boulder. More of her work can be found at down2earthscience.com.

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