What was previously thought to be an impossible error in U.S. coinage, proved to be possible in May 2000. Frank Wallis of Arkansas was looking through a roll of Sacagawea Dollars when he found what is refered to as a "mule". A "mule" in numismatic terms is defined as a coin that is struck with a pair of dies that weren't intended to be paired together. In this case, a States Quarter Dollar obverse and a Sacagawea Dollar reverse were used together. It was struck on a golden dollar planchet. Although mules are found on coinage throughout the world, this is the first time one was found on a U.S. coin. When first discovered, the Sacagawea Dollar/Quarter Dollar mule was widely publicized in newspapers, magazines, and on television shows such as Good Morning America and CNN Headline News. To date, only ten confirmed Sacagawea Dollar/Quarter Dollar mules have been found and authenticated. The date does not appear on either the obverse or reverse of these pieces, but they are determined to have been produced in 2000 since they were all found in the calendar year 2000 and that was the first year of issue for the Sacagawea Dollar. Had they been found in 2001 or later, the date would not have been discernable.

Many novelty pieces have been manufactured outside the Mint by hollowing out a Sacagawea Dollar and inserting a Washington Quarter. The pieces are then plated a golden color to closely match the dollar. They should be easily distinguishable from genuine pieces due to improper weight, a seam where the two coins meet, and noticeable "golden" plating. Authentication of genuine pieces is mandatory.

To read more about the ten confirmed pieces, visit Fred Weinberg's "Error News" Page.