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There are a couple of plutons in Southern Indiana ~ the ones we know about the most are on a line with Martinsville, Crothersville and Cincinatti. Martinsville used to have a lot of hotsprings. That one is big enough it reaches as far South as Paoli, Indiana and may even be the source of heat for a couple of others just East of Bloomington.

The pluton at Crothersville actually makes its presence known with a CIRCLE that shows in the soil type at the surface. The down wind area in Jennings County Indiana has a feldspar based soil ~ fairly typical of a sort of ancient volcano.

So this sucker has been toking off and on for probably a couple of hundred million years spewing stuff on Jennings County. That suggests there's an even deeper heat source closer to the mantle ~ maybe a plume like the one under under Oregon, Idaho and Wyoming (Yellowstone).

The only advantage to these hot spots is they weld the cracks overhead. Obviously it's not doing a good job gluing the Mississippi faults back together, but maybe this is their cause!

We have an ancient volcanic vent in Fairfax county just like the one at Crothersville. It's been covered over for tens of millions of years, but it is detectable at the surface. The headquarters for the Coast and Geodetic Survey is there ~ and the main driveway out front CIRCLES THE TOP! Very cute way to tell us about it.

The pluton at Crothersville actually makes its presence known with a CIRCLE that shows in the soil type at the surface.

Very interesting! I'm trying to find what you're referring to. What series (or complex/association) are you talking about, the Peoga? Forgive me, but I'm not at all familiar with that area.

The down wind area in Jennings County Indiana has a feldspar based soil ~ fairly typical of a sort of ancient volcano.

Typical for plutonic source, too. Is there other evidence of this being volcanic along with the plutonic?

Suggests to me that someone's timeline is off. Gondwanaland was still together back then, and Jennings County was on Laurasia. I doubt a plume was following Jennings County around the globe. :-)

Are these hypotheses of yours or are they someone else's work? This whole topic will have absolutely no useful or positive impact on my life, so it's just the type of thing that catches my attention!

I'm confused by your description. I'm guessing you're referring to the USGS in Fairfax County, Virginia, not Indiana or the NGS...? If so, I think it's near some diabase with surrounding hornfels, but I don't think it's on any sort of volcanic vent, per se. It's just the typical Triassic rifting, and the USGS driveway doesn't circle any of the ones nearby. Or are you referring to a historical location (Coast and Geodetic Survey was absorbed by NOAA decades ago)?

I came across this, which describes Indiana tectonic features.