It is a rock on a beach. Impossible to say just how the business of the Pilgrims landed on or near it ever started. I learned that story in Elementary School. I grew up not far from the site.
At some point, the rock was split, and later patched together, which I have always thought to be an odd fact.
Of course the Liberty Bell is also cracked. They fixed that long ago and it simply split again, so I read.
Peculiar symbolism exists in American History.