A sea stack is a geological landform consisting of a steep vertical column of rock in the sea near a coast, isolated by erosion. There are quite a few different types, but the ones along the California coast are most often formed by the dynamic tectonic activity associated with the earthquake faults. The picture below was taken near Bodega Bay, California. If you are interested in the geology specific to this area, but typical of much of northern California coast, there is some interesting reading on Bodega Head.
This shot was part of a panorama series. PS CS5 chocked on the full series. Gonna have to test out some other software to get the panorama working. That is probably the topic of my next post.