Composed of basalt, Haystack Rock was formed by lava flows emanating from the Blue Mountains and Columbia basin about 15-16 million years ago. The lava flows created many of the Oregon coast's natural features, including Tillamook Head, Arch Cape, and Saddle Mountain. Haystack Rock was once joined to the coastline but years of erosion have since separated the monolith from the coast. Three smaller, adjacent rock formations to the south of Haystack Rock are collectively called The Needles.