David Akers (1975/88): The 1870-S is a moderately scarce date in the lower grades (EF or less) and very scarce in AU. In strictly uncirculated condition it is rare and choice or gem quality examples, while known, are very rare. Overall, the 1870-S is similar in rarity to the 1869-S, 1871-S, 1872-S and 1873-S as well as such Type I S-Mint issues as the 1858-S, 1859-S and 1863-S. I have seen only a couple of choice uncs of this date and the collector looking for an 1870-S will likely have to settle for something in the VF-AU range.
The Saddle Ridge Hoard of gold coins, discovered in northern California in 2013, contained sixteen 1870-S $20s, many of which were ungradeable. However, of those that were gradeable, three came out at PCGS MS62, representing the finest grade for the date and nearly doubling the population of "Finest Known" 1870-S Double Eagles.
Saddle Ridge Hoard