The Mint produced Proof Washington Quarters from 1936-1964. Proof Quarters from 1932-1964 did not contain a mint mark. In 1965-1967 the Mint did not produce Proof Washington Quarters. And then in 1968 it began to produce Proof Washington Quarters again, this time the coins had an S mint mark indicating they were struck at the San Francisco Mint.
Proof 1969-S Quarters came in really nice quality overall. Examples in Cameo and Deep Cameo can also be acquired with minimal effort. Only in PR68 Deep Cameo condition or higher do they become really scarce. In PR69 Deep Cameo condition they are even scarcer with less than about 100 examples known and none being graded higher.