Unknown Fossil Plant/tree

[fossiljim]

More than 40 years ago I met a California desert rat who was nearing the end of his life. He took me to his storage shed and showed me an amazing collection of fossils and minerals he had found over the years. He offered me fantastic fossils at incredible prices, but I was a poor student living on macaroni and cheese. The one thing I bought was a doorstop that he said was some sort of petrified palm. It doesn't look anything like the petrified palm we find here in Texas, but I wondered if anyone had an idea of what this is:

[Plax]

could be a stromatolite or stromatoporoid, have seen them cut and polished like that, could also be wood of some sort I suppose but not likely palm, their wood is differently structured