Greetings.
Location: Southern Washington State, in the Cascade Range, by a river.
Geologic studies of the area suggest there was a massive landslide at this location over 1 million years ago.
Present day it is a very wet area with lots of fungi.
Material density and hardness appear identical to the petrified wood found at the same spot (highest concentration of petrified wood I've come across in the Cascade Range.
I first thought it was wood until I noticed the direction of the lines seem to be perpendicular to how I'd expect tree rings to be.
Reminds me of some sort of shelf mushroom, though I do understand any sort of petrified/fossilized fungus is extremely rare and unlikely.
I look forward to your input.