I see only the full field photo is linked. How can I attach / send the closeup of the nasty plant? Sorry this is my first time putting up images on to the forums.

I can't answer your photo question, but I'll take a wild stab at the yellow flower ID and guess lesser celandine (ficaria verna)?

Here is a link that might be useful: lesser celandine

You can upload your images to any free web-storage (Photobucket, Picassa,etc.) and give a link to them here in your post.
Do not ferget to make the pictures "public" so everyone could see them.

Ranunculus ficaria -- it definitely is the culprit -- and it looks horrible. I can vouch that it's nearly impossible to dig up all the underground parts of a single plant, much less an infestation. I am now going to have to deliberate: Use Roundup / glyphosate even though I have avoided chemicals for years, or spend an eternity digging and probably not succeed.

This link sent by kalmia10 says lesser celandine spreads mostly by the underground tubers, but here at my house it seems to pop up FAR from existing colonies, meaning 15 feet from nearest plant, as if it spread by airborne seeds. Is it just inadvertant movement of tuber segments??? or could it also spread by seed?