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Source: https://outdoors.stackexchange.com/q/13275
License name: CC BY-SA 3.0
License URL: https://creativecommons.org/licenses/by-sa/3.0/

<p>Where I walk weekly (Del Monte Beach in Monterey, California), I beachcomb for shells, glass, and particularly stones. Most of what gets cast up is rather dull and uninteresting - gray and black rocks of no particular noteworthiness.</p>

<p>However, there are always at least some gemlike little rocks of various hues: yellow, green, white, orange, caramel and chocolate brown, reddish-brown, pale blue, etc. These are often well-worn and oval.</p>

<p>Every foray differs from the previous (quantity and "quality" of what gets thrown onto the strand by the relentless waves), yet certain stretches tend to have a consistent concentration of these gemlike stones.</p>

<p>I reckon quantity is determined by the strength of the tide, so full moon and new moon can be expected to produce a good harvest.</p>

<p>Storms would be another factor, obviously.</p>

<p>I assume when certain deposits are washed up, it's because the waves are "digging deep" in certain locations on the ocean floor where these types of stones tend to be concentrated.</p>

<p>So I can predict in a small way what portion of the beach will produce which type of stone; is it possible to predict with a greater certainty which area of the bay is going to get scooped out based on lunar phases and weather patterns?</p>

<p>Basically I'm wondering why certain spots on the ocean floor are "reaped" on one occasion but not on another. Is it such a complicated interplay that it can't possibly be predicted?</p>