This is coprolite--fossilized excrement. It dates back to between the Oligocene and Minocene Epochs, which makes it somewhere around 5.3 to 33.9 million years old. The poop was found in Lewis County, Washington State. The I.M. Chait auction house is selling it, estimating the price at between $8,000-10,000.
According to the auction house, it is a truly outstanding poop. It "boasts a wonderfully even, pale brown-yellow coloring" throughout its full "eye-watering 40 inches." It is a "truly spectacular specimen."
You can see from the picture that this is clearly true. This isn't just an impressive specimen, but a natural work of art.