That white line is from an ancient snow fall many centuries ago, that got trapped within sediment before it had a chance to melt, and thus fossilized. It’s pretty rare.
Okay, remember what I said before? Yeah. I have no idea what created this geology, but it could be a cool story. Not as cool as mine, though…
Snow melts, but volcanic eruptions are forever, being eroded. And I liked the erosion made the formation of teeth eating an Oreo cookie.