Located about 10 miles southwest of Denver, Colorado, the Red Rocks Amphitheater is one of the most beloved concert halls in the world. Classic symphonies and the Beatles to John Denver and U2the list of artists who have performed at the Red Rocks since it began hosting concerts in 1908 is almost as long as the amphitheater’s 2.5 miles of seating.
The reason for his high esteem? A combination of natural geology, man-made architecture and nearly perfect acoustics. But let’s start with the rocks themselves, which took hundreds of millions of years to form.
Benjamin Burke, an affiliate professor at the Colorado School of Mines, explains that Red Rocks is essentially an ancient delta — a 300-million-year-old accumulation of sedimentary rock that once belonged to what is known as the Ancient Rockies. Like the current Rockies, these mountains were very high. But the forces of erosion (wind, precipitation and temperature) have driven silty, sandy and muddy waters downstream along a series of major rivers.
These materials have created many deltas in the region, including the Flatirons area west of Boulder, Roxborough State Park near Littleton, and the Garden of the Gods west of Colorado Springs. Together, Red Rocks and the rest of these areas form the Fountain Formation. Although the composition of the area varies, the material that forms Red Rocks is mostly sandstone of the missorted variety; it ranges from grains of sand to large pebbles, Burke says.
After ancient storms sent mud and sand tumbling down the mountains, they slowly compressed into rock through the geological process of lithification. Subsequent erosion of this rock carved out the area where the amphitheater stands today. “The two rocks on either side of the amphitheater are a little more resistant [to erosion], for some reason,” Burke explains, referencing Ship Rock — the iconic red stone face to the left of the audience — and Creation Rock to its right. The two stunning tilted vertical rock formations are higher than niagara falls.
(Credit: Megan Mahoney Photography/Shutterstock)
The top of the Red Rock seating area, which offers the amphitheater’s best views of Denver and the surrounding landscape, features a bronze plaque marking where Fountain Formation rock collides with age-old Precambrian rock. 1.7 billion years old that forms the bottom of the Denver Basin, Burke said. The oldest rocks in this area were mined for silver and gold during various precious metal rushes between around 1858 and 1893, he adds.
In 1911, three decades before it opened to the public in its current architectural form, the famous Scottish opera singer Mary Garden gave the first solo concert at Red Rocks. She remarked that she had never heard more perfect acoustic properties in any opera in the world.
Burke, who attends at least one show a year on the site, admits he’s not a sound engineer. But he offers a basic explanation: Creation Rock and Ship Rock, combined with the stage infrastructure built directly in front of the disc-shaped rock known as Stage Rock, create an ideal sound transfer.
“The front building and rocks really send the sound out to the audience,” he says. “The [rock] the walls essentially retain this sound, without there being a roof where it would have to be soundproofed. So you get a lot of outward projection without the reverberation, if you will, of the enclosed space for [sound] to bounce back.
The role of the rocks in the acoustic profile is probably due more to size and angle than to composition, he continues. While sandstone generally lacks special acoustic powers, it may have marginal sound absorption properties compared to a harder rock such as granite. “On the whole, rock is still rock,” Burke says. “Having those walls there allows the sound to stay in the amphitheater but not get trapped and bounce back and forth.”
The Beach Boys perform in concert on July 9, 2012. (TDC Photography/Shutterstock)
There is also the elevation aspect. At 6,450 feet, sound actually travels slightly slower than at sea level, thanks to both atmospheric pressure and temperature. Although not perceptible by itself to the human ear or brain, a singer’s performance in a finer tune might be.
“It’s always fun, as a Denver resident, to see artists rise from sea level,” Burke says. “If the performer doesn’t know what to expect, that changes the performance a bit. They end up being a little out of breath.