Later geological investigations showed them to be a local rock known as Monterey shale, and they are thought to have been used by Chinese settlers fishing off the coast in the nineteenth century.
之后的地质学调查显示，它们是当地的一种叫作“蒙特雷页岩”的岩石，并且它们被认为曾在十九世纪被中国定居者使用来在该海岸捕鱼。