This is a sterile mycelium (i.e. the vegetative, feeding part of a fungus - with no spore producing organs/structures present). This sort of fanned out growth is common in leaf litter, in mulch, under wood lying on the ground, etc etc. The mycelium is expanding and exploring. A photo at this stage doesn't give any clues as to what sort of sporing structure the mycelium would eventually produce.
