One of the quietest places in California: The Eureka Valley and Inyo Mountains. | Photo: Dustin Blakey, some rights reserved It's a gorgeous day in the California desert. An autumn breeze, cool for the desert at 80 F, makes the dry leaves of big galleta grass rustle. Two hundred yards or so off to the south, the raucous song of a cactus wren echoes off the rocks. It seems loud, despite the distance: it's just that everything else is so quiet that hearing a bird from a tenth of a mile away is pretty easy.
Eyes closed, you listen for more: the hum of a passing dragonfly; the chatter of a pair of antelope ground squirrels; the pulsing blood in your ears. You can't remember when you were in a place this quiet. You start breathing more deeply. Your shoulders drop down lower and away from your ears. You feel at peace.
And then the dirtbikes show up.
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Noise is one of the least-recognized forms of pollution that people cause. And we cause a lot of it. According to a study done last year by the National Park Service, human activity has radically changed the way the landscape sounds over about half of the 48 contiguous states. Eastward of the Plains states, it's hard to find large areas where the average ambient noise level is below 40 decibels (dB).
That's about the background noise level of a quiet neighborhood with lots of trees. That sounds pretty good, until you remember that it's the background noise level, the combined low roar of all the noisy human activities within a few miles, and that individual annoying sources of noise are added to that. A loud whisper can reach about 40 dB. Imagine someone loudly whispering next to you 24 hours a day. With background noise levels of 40dB, you're getting into the range that's been established to interfere with sleep in some people. And that's an average: half the time, the background noise will be louder. It doesn't need to get a whole lot louder before stress, depression, and long-term cardiovascular complaints can result. Studies indicate that a sixth of Americans 20 and under may have permanent hearing damage from exposure to artificial noise.
Those ailments don't just affect people. Wildlife suffers from human noise as well, whether its due to stresses similar to those humans experience, or inability to be heard over the din when making sounds used for mating or territorial display, or even abandoning otherwise suitable habitat because human noises are just too prevalent.
Average noise levels in the contiguous United States. Dark blue is quiet, yellow is noisy. | Map: National Park Service
Wildlife can also suffer hearing loss from loud noises, even if those noises don't go on for long. The desert kangaroo rat provides a good example. The rat's hearing is so sensitive it can detect a sidewinder - a main kangaroo rat predator - slithering quietly on sand 15 inches away, which is well out of striking distance for most sidewinders. After being exposed to engine noise at 90 dB about 14 feet away on and off for eight minutes, roughly equivalent to what a rat might experience if an off-road vehicle idled nearby, the rats had trouble hearing sidewinders less than an inch away. The rats in this experiment recovered their hearing, and they weren't actually in danger of being eaten by the snake, but rats in the wild generally don't get the opportunity to recover from temporary hearing loss.
And animals that rely on hearing for navigation, like bats, can fare even worse when noise levels get too high.
In the West, fortunately, we're blessed with a relative absence of noise over much of the landscape. There are noisy areas in urban areas and along the highways that connect them. But across the intermountain West, there are plenty of places where you could walk for miles with a background noise level of 26 dB or less - about a third as loud as the quietest places in Ohio.
Along the Hana Highway, Maui | Photo: Brodie Guy, some rights reserved
It's not that those places are silent. Far from it. Wind and bird song and the crunching of your feet on the gravel, rainfall and thunder and coyote song are all found in quiet places, and some of them can be pretty loud. But for the most part, aside from those gravelly footfalls, the sounds there aren't made by humans.
That may seem to be a literally artificial distinction, but it's important. Noise is defined as unwanted sounds. That's a very subjective metric. Your dog's barking may be music to your ears. It ain't necessarily so for the hundred other households within earshot. Music is a perennially popular example of how one person's pleasant sounds are another person's noise.
Across the United States, the majority of noise doesn't come from barking dogs or Justin Bieber. It's made by cars, trucks, and other road vehicles. Aircraft also make a significant contribution. Though the actual sound level of a jet cruising 35,000 feet above your ears may be small, it may well be audible over hundreds of square miles at a time. Industrial machinery adds to the urban roar, as do appliances from air conditioning units to leaf-blowers and chainsaws.
Detail of the NPS noise map. California state line added in red. Los Angeles and San Diego are on the right. | Map: National Park Service
Fortunately for Californians, noise pollution isn't nearly as pervasive here as it is back East. Our cities are as noisy as any others in the country, and in some spots, like Central LA and Long Beach, ambient noise levels can reach someone's vacuuming the room while you're trying to sleep levels. But even after a century of sprawl, California's noisy cities are still mainly limited to the coast and the Interstate 5 corridor through the Central Valley. East of the mountains, California has a lot of a
