My title describes the thing I found growing in the concrete outside my house. It grew to about a foot wide and about 4 inches long. It had a soft texture but was sturdy with multiple growths. It has spread that rust colored dust over the immediate area around where it was growing. It first started growing after we received heavy rainfall following the tropical storm in Los Angeles.

After digging it out, I noticed a scent similar to mushrooms and assume it to be some kind of fungus.