Obverse missing clad layer with the obverse side copper and the reverse side nickel. The error was caused by the clad layer missing before strike, leaving the copper core exposed. The coin is underweight as a result, and has a slightly weak strike. A popular error type die to its visibility, being copper instead of nickel, and also because the state quarter series is very popular.
Very scarce state for missing clad layers.
PCGS MS-64 blazing red luster!