I may be having a moment.......I am having yellowing stuff that is either is coming a animal or from the interaction of soil/mulch ?

Last week, i removed a mound that was about 2 feet round....thinking it was animal feces.

I walked by a different area on my way in tonight and I don't ~recall~ seeing it.

I walked by again on my way out and there was the yellow stuff (bright as mustard).......ontop of the mulch . It was approx 6 inches in diameter. I just came back from removing it, and the yellow stuff is not topical on the surface. As I removed the top layer from the mulch - it went deep back to the soil line.

Am I going crazy here. Is it not animal ~stuff~ or is it possible this is some weird interaction happening in the mulch.

I feel like i"m going crazy here...