What is the last year they made silver quarters?

The U.S Mint discontinued the use of silver in quarters after the 1964 series. U.S quarters minted in 1964 or before contain 90 percent silver and are now worth significantly more than their face value.

All U.S coins that were produced before 1964 that were not pennies or gold dollars contained 90 percent silver. Until the 1960s silver was economical to use for common coinage, however in post-1960 markets the value of silver has become high enough that pre-1964 quarters are highly sought after as scrap silver. These coins may fetch as much as 14 times their original value when sold in bulk.