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Haystack Rock, Oregon Coast. Composed of basalt, Haystack Rock was formed by lava flows emanating from the Grand Ronde Mountains 10 to 17 million years ago. The Haystack Rock tide pools are home to many intertidal animals, including starfish, sea anemone, crabs, chitons, limpets, and sea slugs. The rock is also a nesting site for many sea birds, including terns and puffins.