June 20 (1849) to New York, First-day use of the SF straightline marking with associated manuscript date and rate, an unpaid transcontinental 40 cent single rate letter. Cover endorsement via Panama p California with letter datelined April 30, 1849. The PMSS California actually departed May 1 (see this cover). The steamer which actually left on June 20 was the PMSS Panama. The sender intended to catch the departure of the California but the letter was apparently too late (and because of this the cover received the straightline marking instead of the manuscript marking). The next opportunity for contract mail sailing was seven weeks later on June 20. This is the earliest found cover from the SFPO with a specific steamer name on it.
Beginning June 20, 1849 and for only three sailing dates, June 20, July 2 and August 1, the San Francisco Straightline postmark was used. This marking is 30 x 2.5 mm and is known in black ink only. These straightline covers also include a manuscript date (June 20, July 2 or Aug 1) and associated rate (40 or 80 cents) known both in black and red/magenta ink. Thus far 33 straightline covers have been identified all shown in the census table below. While not a large number these markings are certainly more plentiful than the manuscript markings.
The last use of the straightline postmark was August 1, see SF SL25 below as an example. This was also the inaugural date for the first CDS device used at the SFPO (and the only CDS used in 1849, which continued into 1850).