It may look like a vaguely impressionist painting, or a crackle-style ceramic glaze, but it’s actually the remnants of a barnacle colony. The rock that the colony is attached to had recently been exposed by an exceptionally low tide, and the waves and sea debris had made short work of most of the colony members. You can see a few intact fellows in the lower left.
The largest base is around three quarters of an inch in diameter.
March 11, 2006. Kala Point, Pete Townsend, Washington.