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SAN DIEGO — It’s the story that shook up San Diego County this week: a mystery “boom” that rattled windows, startled pets and sent flocks of people to social media asking, “What was that?”

And now, after several days of speculation and with an earthquake ruled out, the Tuesday night phenomenon has an explanation.

“So, about the other night…” Marine Corps Air Station Miramar wrote on Twitter Saturday morning, following the coy message with a more straightforward news release that said the “boom” was “possibly due” to two aircraft that had been engaged in combat training off the coast of San Diego.

“While MCAS Miramar cannot account for every sound event that occurs within the area, in this case the cause is possibly due to aircraft training occuring in the W-291 range, approximately 30 miles southwest of San Diego over the Pacific Ocean,” the base statement reads. “Two units departed from MCAS Miramar and were conducting simulated air-to-air combat training.”

While officials went on to say there are “many different factors that could cause a sonic boom” to be heard so widely, “variations in temperature and humidity can create atmospheric conditions that can cause sound waves to travel further than at other times.”

Supersonic flight is largely restricted by the Federal Aviation Administration over land, but the base statement says speeds that could break the sound barrier are permitted over the Pacific Ocean in the range where training was taking place.

“Ranges like W-291 are vitally important to the training of our combat aviators,” the statement continues. “This practice has been occurring for well over 24 years that the Marine Corps has operated from Miramar and continues to enhance the aerial combat skills of our pilots.”

On Saturday, FOX 5 spoke to the President and CEO of the San Diego Air And Space Museum, Jim Kidrick, who has flown thousands of hours in the W-291 range. He says, “it’s a training area, designated for the military aircraft to fly in, and the FAA knows where it is; it has boundaries, like being in a sand box.”

Kidrick noted that while the ‘boom’ may have been concerning, it was all part of the training. “The pilots were not in danger, nor were any civilians in danger – here in the immediate San Diego area it is something fully in the capability of the airplanes.”

And as for San Diego native and golf great Phil Mickelson’s claim that he had been “testing a few drivers” at the time of the boom?

“Not sure why (Mickelson) tried to steal the thunder,” the base wrote on Twitter. “He can come play on our course whenever he’d like.”

Strategically located near the ships of San Diego naval bases, the site of MCAS Miramar has served as some form of U.S. military base since 1917. It’s existed in its current form since 1997, and it’s home to more than 11,000 active duty service members, including Marine Corps aviators.

The base houses the 3rd Marine Aircraft Wing, including MAG-11’s fixed-wing F/A-18 and KC-130 Hercules squadrons and MAG-16’s, MV-22 Osprey tiltrotors and CH-53E Super Stallion helicopters.

“The support command Marine Air Control Group 38 and the 3rd MAW Band are also located here,” a base website explains. “The 4th Marine Air Wing, an MV-22 Osprey squadron and H&HS Marine Flight Division’s UC-12 and UC-38 squadrons are here at MCAS Miramar as well.”