The 1951 Proof Washington Quarter has the second lowest mintage from the 1950-1964 Proof Washington Quarter series.
Proof: In proof non cameo or deep cameo it is not difficult to find up to PR67 grade. In PR68 it becomes much more difficult to find.
Proof Cameo: Most examples displaying Cameo surfaces are scarce. The majority of Cameo examples fall in the PR65-PR67 range. Anything grading higher than PR67 Cameo is considered rare.
Proof Deep Cameo: Examples displaying Deep Cameo surfaces are almost unheard of. Although, there are a few examples known but they are considered extremely scarce in any condition.