<P> The mint mark on the coin is located on the reverse beneath the wreath on which the eagle is perched, and will either carry the mint mark "D" for the Denver Mint, "S" for the San Francisco Mint, or be blank if minted at the Philadelphia Mint . </P> <P> The copper - nickel clad Washington Quarter was first issued in 1965 and as part of the switch, the Denver mintmark was added in 1968, which did not reappear on any US coin denomination until 1968 . During the early 1960s, the Federal government had been flooding the market with silver to keep the price down, and therefore keep US coins' intrinsic values from exceeding their face values . This was causing the level of silver in the US Reserves to reach dangerously low levels . Silver was estimated to only last another 3--5 years at the rate the Mint was manufacturing coins, so the US Congress authorized the Mint to research alternative materials for the silver denominations (dime, quarter dollar, half dollar, and dollar). The material chosen was a 75% copper / 25% nickel cupronickel alloy (identical to that in the five - cent coin) clad to a core of "commercially pure" (99.5%) copper . </P> <P> For the first three years of clad production, in lieu of proof sets, specimen sets were specially sold as "Special Mint Sets" minted at the San Francisco mint in 1965, 1966, and 1967 (Deep Cameo versions of these coins are highly valued because of their rarity). </P> <P> Currently, there are few examples in the clad series that are valued as highly as the silver series but there are certain extraordinary dates or variations . The Deep Cameo versions of proofs from 1965 to 1971 and 1981 Type Two are highly valued because of their scarcity, high grade examples of quarters from certain years of the 1980s (such as 1981--1987) because of scarcity in high grades due to high circulation and in 1982 and 1983 no mint sets were produced making it harder to find mint state examples, and any coin from 1981--1994 graded in MS67 is worth upwards of $1000 . </P>

Mint where the washington 25 cent coins were produced