Haystack Rock and other "seastacks" dot the Oregon coast. The stacks are extrusions of lava from eruptions that occurred 7 to 17 million years ago. Originally buried beneath the sea, the basalt rocks gradually uplifted with the earth's movement and then eroded from marine sediment when the Ice Age lowered the level of the ancient sea by several hundred feet. Igneous and sedimentary features are present in the rocks.