I ran the numbers. We're living in a scientific impossibility. Element simply couldn't expand fast enough to reach this level of density under natural conditions, even with millennia of uninterrupted growth. That means something accelerated it at an alarming rate, even if this area's readings are an outlier. Well I say "something," but there's an obvious answer here: man.
Any tech that runs on Element emits a few molecules of it back into the atmosphere, which take root in the soil. It's kind of like pollination, but the scale's so small and we consume it so fast that it's practically negligible. To spread it to any significant degree, you'd need a huge spike in Element proliferation.
A spike you'd get from, say, a century of open warfare with Element based weaponry. And the best of that weaponry? That'd be mine.