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Dr. Randy Keller : Volcanic Rock Formations Here on Mary’s Peak, in the Oregon Coast Range, we find pillow basalts, like the one next to me here.  This one is broken open, so you can see the inside of it, the unique radial fracture pattern that we were able to see very distinctly on the seamounts in the Gulf of Alaska.  And this whole hillside is built out of these pillow basalts.  And if you look up above here, you can actually see one that has not been broken up.  It has that very round, blobby appearance to it that shows you why we call these “Pillows”.  And that’s how they originally look on the sea floor.  Then they break up, and we can see the inside, and this unusual fracture pattern.  This only occurs underwater, and we saw that a lot on the Gulf of Alaska seamounts, and now we can see it on the side of this mountain here, and that tells us that Mary’s Peak used to be a seamount, and was originally formed underwater, and at some point after that, was thrust up onto land and now it is part of the Oregon coastline.

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From http://www.oceanexplorer.noaa.gov/edu/oceanage/04keller/