The four postal markings illustrated here were used by the San Francisco,
California Post Office as steamship markings on mail received from
contract steamers of the Pacific Mail Steamship Company during the
period between 1863 and 1873.
Steamship letters were defined by the Post Office as letters which
entered the United States on Steamers under contract to carry mail
for the United States. The steamship rates in effect when these
markings were introduced in 1863 were 10 cents if the distance carried
from the mailing office was less than 2,500 miles and 20 cents if
over that distance.
On July 1, 1864 the blanket steamship rate of 10 cents
went into effect. This rate was applied regardless of distance carried
from entry port. All mail arriving from non-contract vessels was
to be treated as ship letter mail and subject to different rates.
These four markings were used on mail that arrived in San Francisco
from steamships of the Pacific Mail Steamship Company. This company
had a contract with the United States Post Office to carry mail
and all such letters received should have been treated as steamship
letters and subject to steamship rates. From the known usage's it
appears that markings were applied specifically to mail bagged at
each of the various ports of call of the Pacific Mail Steamers.
Separate bags of mail were delivered to the steamer at Panama, and
the Mexican ports of Acapulco, Manzanillo and Mazatlan (see map
on following page). Mail from all of these locations was subject
to the same steamship rates, regardless of origin. However, the
frequent errors of rating, especially in 1863 and 1864, are evidence
that the Postmaster at San Francisco did not understand the somewhat
confusing postal regulations.
The quantity of mail picked up at Panama, and hence receiving the
Steam Panama handstamp, was far larger than that picked
up at the Mexican ports. Panama served as the transfer point for
mails from a wide variety of Central and South American countries.
Mail arrangements for getting mail to Panama varied.