Pillow basalt forms when lava erupts underwater and cools into rounded, pillow-shaped lobes. Outcrops of it along Hurricane Ridge originated on the deep ocean floor, more than a mile beneath the surface, and were later uplifted to roughly a mile above sea level as the Olympic Mountains rose, a vertical journey of over two miles.
Study the rock cuts as the road carves through them. You're looking at stone that began its life more than a mile underwater. Some of it is what geologists call pillow basalt, lava that oozed out on the deep seafloor and cooled into rounded blobs, like a stack of dark pillows, far below the surface. Today that same rock rides about a mile above the sea. Up and down, more than two miles of travel for a stone, and you're driving right past it without a second glance. Now you know to look.
Photo: Dllu · CC BY-SA 4.0
