This is a rather large and lovely fruiting body of a fungus.
Although I was happy to find it, it is a bad sign for the oak on which it resides.
It is also referred to as root rot or butt rot.
This part of the fungi is called a basidocarp. These can get several feet wide and over half a foot tall.
The top is a mixture of oranges, browns and whites. The top is hard and leathery or rubbery. The underside is white with tiny pores.
These two were found around the base of my neighbors’ oak. This is twice as bad as finding one because it means the decay is more severe. (Sorry M & N.)
I also spotted the one below downtown, which I plan to report to our local arborist.
The Conk is lovely but a deadly delight.