The Hawthorne Army Depot is a military installation in the heart of the Nevada Desert. Located more than 100 miles from Sonora, it was the last location many would have thought to be connected to strange, rumbling booms that are reported constantly throughout California’s Gold Country.

And yet, that seems to be precisely what has been happening for some time now.

“I can’t explain all the physics involved, but the atmosphere is bouncing in response to the energy and it’s reflecting and bouncing (sounds) back down,” said Columbia College instructor Glen White, in an interview with Sonora ABC affiliate News 10.

“The really odd part is people fairly close to the source of the energy, the explosions, aren’t hearing it,” White said. “The sound goes over them.”

For some time now, loud “mystery booms” have been reported in the area, which become particularly prevalent during the summer months. In the summer of 2014, a group of scientists at Southern Methodist University began investigating their possible cause, instituting four monitoring stations in locations aimed at detecting explosions occurring throughout the region.

At the Hawthorne facility, the US Army detonates obsolete munitions between 11 AM and 2 PM local time on various days of the week. It was found that the blasts at the facility coincided with the times mystery booms were being reported in the vicinity of Mother Lode, as indicated with a 2300-strong Facebook group called “Mother Lode Mystery Booms”.

However, not all are satisfied with the idea that the Hawthorne explosions explain the booms. Competing theories among group members have suggested seismic activity, mining operations, and military aircraft producing sonic booms could also be contributing to the sounds.

In the 1990s, at Cal Tech found that sonic booms were consistent with a number of the reports, but they were unsuccessful in linking any known USAF flight operations with the booms.

In an interview, Hawthorne Army Depot commander Lt. Col. Greg Gibbons noted that he was surprised that the sounds could be heard so far away, noting that he rarely heard the explosions from his office, located within 23 miles of the blast site.

Similar circumstances involving refractions of sound like those reported around Mother Lode have been recorded elsewhere, with some reports dating as far back as the nineteenth century. In 1874, English researcher John Tyndall documented a letter from R.G.H. Kean, who had observed the Battle of Gaines’s Mill during the American Civil War. Kean wrote:

“I distinctly saw the musket-fire of both lines… I saw batteries of artillery on both sides come into action and fire rapidly. Yet looking for near two hours, from about 5 to 7 P.M. on a midsummer afternoon, at a battle in which at least 50,000 men were actually engaged, and doubtless at least 100 pieces of field-artillery… not a single sound of the battle was audible to General Randolph and myself. [However, the] cannonade of that very battle was distinctly heard at Amherst Court-house, 100 miles west of Richmond, as I have been most credibly informed.”

The report is remarkably similar, even in Kean’s recollection of the distance of 100 miles across which the artillery had traveled. Thomas B. Gabrielson of Pennsylvania State University’s Applied Research Laboratory discussed this incident in his paper, “Refraction of Sound in the Atmosphere,” in which the history of the phenomenon, as well as the science behind it, are explored in depth.

With the “mystery booms” reported at various locales, it might stand to reason that a number of factors, ranging from explosives tests to sonic booms, do contribute. However, it is the knowledge of the way that sound travels, and often over great distances, that becomes key in understanding the frequent misperception that the noises, as loud as they appear to be, must have originated much closer than they actually do.