Erratic in Washington State

Reader Melissa S. writes:
Thought you may enjoy Nat'l Geographic's picture of the day today [click here]. Below is the caption to the picture:

Looking as if it fell from the sky, a 40-ton erratic stands on the Colville Indian Reservation in Washington State. Such boulders are sometimes called rubbing stones because bison scratched up against them. See more pictures from the March 2012 feature story "Rock … And Roll."