Well Noel, it looks like you've started a mystery!! I grew up in New
Mexico a lot, went rock hounding and fossil hunting since I could
walk, and I've never seen anything like that. To me it looks
opalized - my first impression, too. There's a telltale thing,
though, at least in the photo: Around the edge where it's flaked,
there are some broken circles. If it were petrified wood, and solid
wood to start, those circles would go down into the rock, just like
the original - that's how it works. Since they don't, then they are a
surface thing of some sort. If it were fish eggs, and a layer of silt
layed on top of them, that could opalize, and you could have what you
have, for example. Opalization is similar to petrification, but
petrification gives you a stone version of the original, even inside.
If those were stalks or wood grain they would go all the way through,
or at least inside. It appears to me that it's a fossil - beyond just
petrified wood fossil.
P.S. Crinoids are a common fossil in the area, and almost look like
that, but they have a serrated edge and a hole in the center - was my
first thought when I saw it, but it's not.