The 1999 US Mint 50 State Quarters Proof Set includes coins in denomination of 25 cents, all composed of copper and nickel. Minted in San Francisco, these uncirculated coins bear the proof strike type and come with a Certificate of Authenticity from the U.S. Mint. This set is a valuable addition to any coin collection, showcasing the unique designs representing each of the 50 states in the United States.