One of the planet's largest calderas — a huge, cauldron-like hollow that forms after an eruption — it measures a staggering 20 miles long and 11 miles wide, and is up to 3,000 feet deep.
Despite the absolute chaos that Long Valley could cause if it were to erupt, little is said of it.
Yet, according to the Science Channel, Long Valley could well be on its way to erupting.
"And there are clues pointing towards an imminent eruption scattered throughout this valley — the site of the second largest explosive volcanic eruption in North America.".
Even if a modern-day eruption from Long Valley was not on the same scale as previous events, it still poses an "existential threat" to the millions who live around it.
An investigation carried out by the Science Channel in a part of the valley found several instances of smoke billowing out from beneath the ground.
Pointing to a map created from the data, Mr Peacock said: "Right here in the middle, you see there's a resurgent dome.".
A baking-hot red point is pictured located directly beneath the ground, where magma likely resides.
In order to determine whether the Long Valley Caldera was truly coming back to life, Mr Peacock and Mr Nelson set up a pair of sensor pipes directly above the point that the InSAR data identified the resurgent dome, and scanned for signs of trouble deep underground.
The scientists estimated the Long Valley Caldera reservoir contains “considerable qualities of melt”, likely greater than 240 cubic miles (1,000 cubic kilometres)