The Rock the Road Is Cut Into — a stop on Chuckanut Drive.
The rock in the cuts beside you is Chuckanut sandstone, and it has an unexpected story — it is the remains of a subtropical river delta.
Around fifty million years ago, this region sat in a warm, wet, near-tropical climate, and enormous rivers were dumping sand and mud across a lowland here. Those layers hardened into the sandstone you are looking at, and they carry the evidence: fossil palm fronds, ferns, and the tracks of animals that walked across that mud.
It is a genuinely strange thing to hold in your head on a grey Pacific Northwest afternoon — that this hillside was once a swampy delta with palms growing on it.
The sandstone is also good building stone: fine-grained, easy to cut, and it weathers well. And that is why there was a quarry here from the eighteen fifties — Boone has that story shortly.
Look for the LAYERS in the roadcuts as you pass. You can pick out individual beds laid down by individual floods, tilted now from later mountain building. And where the rock is fresh you will see it is quite pale and warm-coloured, which is exactly why Victorian architects liked it.