Heino, here is much of the yellow stuff as I could find. This is from a couple of different but very close by specimens. They were all very dark/rotting unknown Fungi that when disturbed or lifted up, had lots of the rich yellow stuff underneath.
Species of Sepedonium are generally parasites of boletes (or bolete relatives) and commonly you see evidence of the genus as a bright yellow powdery mass on a smelly, decaying bolete. That powdery mass is composed of thick-walled asexual spores and it is common to see them on the ground or underlying, leaves, litter, etc, as noted by Aaron.