March 25, 2010
Impressive Rainbow Rock is located at the southern end of the Samuel H Boardman State Scenic Corridor, on Oregon’s southern coast. This geological marvel displays radiolarian and diatom compaction in chert and in other rock types as well. Radiolarians are amoeba-like protozoa with mineral skeletons which cover large portions of the sea floor. Diatoms are a form of algae encased in a unique form of silica. Both radiolarians and diatoms date back to the Cambrian Period (about 542-488 million years ago). If you look closely, you can see that the rock layers have several small anticlines (upward curved folds) and synclines (downward u-shaped folds). There’s also evidence of faulting within the rock. Faulting likely caused the rock to be exposed as it is today. It’s indeed unusual to have so many different geological features contained in a single rock. Note also the sea stacks just offshore. Photo taken on March 18, 2010.