Fossilized Wood?

[Ago13]

I found this in Mokelumne River in California. I’m not sure whether it is fossilized wood or just a river-worn rock? I was hoping someone could tell me which one it is and maybe let me know what parts of it are key to identifying whether it’s fossilized wood or a rock, so I can learn how to identify further specimens. 

[Tidgy's Dad]

I can't see the details in those photos very well and there's no scale, but I would guess at water-worn shale.  

[Rockwood]

7 hours ago, Ago13 said:

let me know what parts of it are key to identifying whether it’s fossilized wood or a rock

Fossilized wood looks like wood. Some that is less well preserved can be difficult for even the experts to identify in a photo. Often the context in which it was found is the best clue. It is rarely found in isolation.

I agree that as best I can tell from the photos this appears to be a layered sedimentary rock.