Strange sounds heard in a town in California left some residents wondering about an imminent alien invasion.

Some are convinced the booming noise, heard every day between 11AM and 2PM, are caused by mining operations while others cite alien theories.

But a local geologist believes he has solved the mystery, and the answer comes from 100 miles (160km) away.

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Strange sounds heard Sonora, California (pictured) left some residents wondering about an imminent alien invasion. Some are convinced the booming noise, heard every day between 11AM and 2PM, is caused by mining operations while others cite alien theories

THE CONSPIRACY THEORIES Some locals say the booms were from nearby mines. Others say they come from Area 51, a remote detachment of Edwards Air Force Base, within the Nevada Test and Training Range. Its secretive nature and connection to classified aircraft research, together with reports of unusual phenomena, have led Area 51 to become a focus of modern UFO and conspiracy theories. Advertisement

Residents in Sonora, California, have been hearing the noises for at least a year, according to a report by ABC News.

Some locals said on the report the booms were from nearby mines, while others said it came from Area 51, a remote detachment of Edwards Air Force Base, within the Nevada Test and Training Range.

Its secretive nature and connection to classified aircraft research, together with reports of unusual phenomena, have led Area 51 to become a focus of modern UFO and conspiracy theories.

Local geologist Glen White told ABC affiliate KXTV-TV he believes the explosions come from an army depot outside of Hawthorne, Nevada, where a private company disposes of old ammunition.

Residents in Sonora, California, have been hearing the noises for at least a year. Local geologist Glen White told ABC affiliate KXTV-TV he believes the explosions come from an army depot outside of Hawthorne, Nevada, where a private company disposes of old ammunition

This base is about a hundred miles away from Sonora.

He says they explode old bombs and grenades to get rid of them once they have exceeded their shelf-life.

The sound waves generated from the explosion bounce of the stratosphere, the second major layer in the Earth's atmosphere, Mr White said.

They then come back towards the ground where they can be heard up to 100 miles away.

Solving the Mother Lode Mystery Booms. This is the source.https://t.co/IWteFAIJLw — Glen White (@GeologistGlen) July 17, 2016

'Solving the Mother Lode Mystery Booms,' Mr White said on Twitter. 'This is the source.'

He captured video footage of the explosions at the site, to back up his claim.

'They go through old munitions bombs, grenades, then they destroy them,' Mr White said.

Ken Thomas, who works at the Hawthorne Army Depot, told ABC News hey do detonate munitions regularly at the depot.

But he is not convinced these noises can be heard as far away as Sonora.

'It doesn't feel right that what we're doing here would be heard 200 miles away when there's a mountain range in between us,' Mr Thomas said.