Any ideas what this may be? It just showed up. I suspect water is the culprit we just had some hard rains, but I've never seen this before

Is it soft/mushy at all?

Eh... I might lean toward water, too, knowing the pressure of groundwater can be incredibly intense, but if it is water, then my guess is that it's groundwater pressure pushing a boulder up.

... just a guess.

Yes it is soft/mushy like a big bowl of jello. I'm located in Southern WV

Do you know the geography of your area? My 2nd guess is that your in an area of bedrock, clay or other very firm ground and the groundwater has found an opening to push up through.

If you do end up doing a little digging, please post to let us know.

... and hang tight. I see folks online right now checking this out. One of them might have seen this before.

Our whole yard is a dense clay. It's not the red clay you find in Georgia or other parts of the south. It's a fine dense clay, that's grey in color.

Ok here's the explanation. I talked to my father and he said there is and old terracotta drain system through the yard. A newer section of corrugated pipe had been added some years back and it had filled up with grass roots and sediment over the 30 years or so it had been in the ground. All of the water that was draining through the pipe and terracotta ahead of the obstruction had built up pressure under the sod and pushed it up. Guess I'm in for some heavy digging in the coming weeks! We're going to dig up all the old pipe and replace it with new and do the job right. Thanks for the post's.