Blue clay?

[Skyco]

A quick google revealed that lots of places have naturally occuring blue clay...
In fact a 7" layer underlies Lake Mendota in Wisconsin...the OP is in Wisconsin...so......

 

[davitk]

A quick google revealed that lots of places have naturally occuring blue clay...
In fact a 7" layer underlies Lake Mendota in Wisconsin...the OP is in Wisconsin...so......

25 miles SE of Lake Mendota, in fact.

I knew it!! I'm rich

 

[MicroPilot]

All the dirt/clay around here is blue. They say it's from the limestone or something. Even the rocks have a blueish cast when you bust them open.

 

[DocHeb]

You can make a lot of horseshoe pits.

 

[pedalstomper78]

There's a ton of that stuff in my yard. Where it's at the surface, grass doesn't even seem to grow in it. I've been building my compost piles to hopefully amend the soil where I'll be planting. We'll see what happens next spring.