Jaime Hernandez: 1921 is the last year in which the Mint struck Morgan Silver Dollars. The coins were struck from the large and famous Nevada Silver discovery, the Comstock Lode.
The 1921-D Morgan Dollar is also the only Morgan Silver Dollar that was struck at the Denver Mint. Despite being the last year of the Morgan Dollar it is also the only year in which you can obtain an example from each three different Mints. Which are the 1921 Philadephia, Denver and San Francisco Morgan Dollars.
According to a notice in the June 1934 issue of The Numismatist (p. 416), collectors could still purchase Uncirculated 1921-D Morgan Dollars for "the face value of the coins and an amount sufficient to cover the mail charrges by first-class mail."
Heritage 4/2013:4382, $44,062.50
Mike Gilley - Arno Collection - Heritage 1/2009:5073 - Gold River Collection (PCGS Set Registry)