In May 2000, an error coin bearing the George Washington obverse design of a U.S. state quarter and the eagle reverse of a Sacagawea dollar was discovered in a roll of dollar coins purchased from a bank in Mountain Home, Arkansas. The undated coin, known as a double-denomination mule, was the first of eleven discovered and authenticated. Mint officials estimate that the coins, which bear the 'P' mint mark for Philadelphia, were struck from late April to early May 2000. They were produced on dollar-coin planchets clad with manganese bronze, not quarter planchets with copper-nickel cladding.