Q. David Bowers (derived from the PCGS Coin Guide): In 1866 the motto IN GOD WE TRUST was added to the reverse of the eagle and appears on a ribbon or scroll from that time through 1907. Otherwise the Liberty Head obverse and perched eagle reverse are the same as employed earlier.
Production was continuous at the Philadelphia Mint during this span and nearly continuous at San Francisco. Beginning in 1870, examples were struck at the Carson City Mint. New Orleans coins were produced from 1879 through 1883 and again in several later years. Coins were struck at the new Denver Mint in 1906 and 1907.
In grades from Very Fine to AU the type set collector will have a wide choice of specimens. Examples are not rare. Uncirculated pieces are readily encountered of certain dates toward the end of the type. Superb Uncirculated-pieces are very elusive. A possible exception to the rare-if-superb-Uncirculated rule is the 1901-S, of which quite a few exist.
Proofs were minted and are occasionally available; all are rare.
Among varieties of this type, several Carson City coins are quite rare, with laurels going to 1870-CC, the first year of issue, for being the very rarest. The 1879-0, of which just 1,500 were minted, is rare, as are several other O-Mint coins. Several San Francisco Mint issues of the early years of this type are scarce to rare.
In Mint State, eagles of the 1866-1880 span are nearly all major rarities to an extent not fully appreciated by the marketplace. There has never been a full Mint State set formed, nor, probably, will there ever be.