Not sure where they came from or what they've been feeding off. The previous owners of my property built some raised beds along a slope with a boardwalk in between. At the edge of the boardwalk, a couple mushrooms that I'm pretty sure are morels (unless there are other mushrooms that look similar?) just popped up.
I know they like growing on dying root systems. There's tarp under the boardwalk, and tarp on the section of slope beside it, and the morels just came through in the little gap between the two sheets of tarp. I haven't cut any trees nearby, and the plants in my raised beds that died in the winter like tomatillos and eggplants shouldn't have such big root systems that they'd reach as far as where the morels popped up (the trunks of those plants were probably 4-6 ft away).
Maybe it was from a bed of reeds I was trying to smother? I put tarp over them last spring to try to get rid of them since their root system is so dense I can't dig them out. Their root system was about 3ft from where the fruiting bodies popped up. I don't see any others near the edge of the tarped over reeds though (that reed bed was about 8x30ft).