(Bloomberg) — Here’s something you probably didn’t know you needed to worry about: There’s a layer of 300 million-year-old rock under Interstate 95 that’s capable of killing the lights from Washington to Boston and beyond the next time the sun erupts in all its fury.

Sound far-fetched? Perhaps. But not to scientists. A solar storm is now viewed as enough of a risk in fact that grid operators across North America are working on plans to respond to just such a disturbance. And a draft of a soon-to-be-published U.S. Geological Survey report pinpoints the Eastern Seaboard as one of the areas most in danger.

That’s because this Paleozoic-era rock doesn’t let the energy from a major geomagnetic storm — a once-in-a-100-years kind of event — pass through it but instead acts as a backstop that sends the surge back up above the ground for a second shot at causing mayhem.

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