It is an interesting question that most visitors in the tide pools ask. I was also puzzled by the shape of these rocks and intrigued by the idea of how they got here. I was sure those rocks weren’t man made even though they have shapes and structures very similar to those of gravel. Interestingly, Yaquina Head Outstanding Natural Area sits on site of a former quarry — an industry that provided the city of Newport with important revenue for several years.
The critical question to ask here is: how do all those cliffs form? Researching the answer to that question led me to fascinating discoveries about the geology of this site. It turns out all those rocks, cliffs, and even the cobbles by the tide pools are made of volcanic magma. The same lava reservoir that is responsible for the geysers and boiling waters in Yellowstone National park is responsible for the formation of these cliffs. Literature mentions that about 15 million years ago the volcano that now resides underneath Yellowstone erupted and the magma that emerged was of such large proportions that it made it all the way to the coast of Oregon were it met the ocean and cooled down until it solidified into the cliffs and rocks that we now see.
That is a brief story of how those rock formed, but how did the cobbles by the tide pools take that shape? All those gray and almost perfectly round rocks have formed over the course of hundreds of years. The west tides, controlled chiefly by the gravitational forces of the moon and Earth, are responsible for shaping the rocks in this particular way. Two times per day we have high tides and low tides. These movements combined with the chemical composition of sea water, are responsible for the existence of Cobble Beach.