It's a 1967 silver quarter

The U.S. Mint stopped making circulating quarters out of silver in 1964. The only silver quarters after that are found in special sets - the bicentennial proof sets and starting in 1992, special silver proof sets. These quarters all are minted in San Francisco and have an S mint mark. Your quarter is a regular circulating quarter. While it is almost 60 years old, it has not special value and can be spent.