Of the three mints, San Francisco is the rarest for the 1888 Morgan. During the previous 10 years of production, most mints involved in producing these coins struck them in the millions. For some reason, which is not documented, the San Francisco Mint produced only 657,000 examples of the 1888 Morgan silver dollar.
Morgan dollars were all of the same basic design - and the 1886 Morgan dollars were no different. The original casting, designed by George Morgan, who was recruited from the Royal Mint in London, England, was used to make the dies, with only the date being changed.
The 1880 Morgan silver dollar benefited from two years of experience in minting these "new" silver dollars at the US Mints in Carson City, San Francisco, New Orleans, and Philadelphia. The 90% silver and 10% copper composition of the piece made this silver dollar coin very difficult to forge.
One of the other major factors which skews the price of the 1878 Morgan silver are the "tailfeathers" of the eagle. There are three known combinations of tail feather varieties. The coin can have either eight tailfeathers, 7 over 8 tail feathers, or seven tailfeathers.