The 1850 double eagle (20 dollar coin) is the first year of the regular issue for the type and denomination.
It is extremely popular as such and is one of the more available dates of the type. A surprising number of coins have been auctioned in the last 15 years; most, however, grade VF (very fine) to AU (almost uncirculated.) Fully Mint State examples of this issue are rare, with fewer than a dozen choice pieces.
The treasure of the S.S. Central America contained 26 coins, but all were circulated.