I picked up a couple of tossed out hay bales a few weeks ago. I wet them down pretty good a couple of times to speed up the decay process. I have picked up discarded bales before and I liked how they decomposed and the worms seemed to like them also. Sometimes I get straw, but this appears to be some type of grass hay. I walked past this bale a few times this morning , just assumed it was ice or snow remaining, then it hit me that all that was melted and gone. It looks like some type of fungi maybe, don't know but it is strange looking. Just don't want it to be dangerous, I know sometimes spores in the garden can be bad.