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).

Census of San Francisco Straightline Covers (1849)
Ref # Rate Date Destination Image
SF SL1 80 June 20 Massachusetts
SF SL2 80 June 20  New York
SF SL3 40 June 20  New Jersey
SF SL4 40 June 20  New York
SF SL5 40 June 20 New York
SF SL6 40 June 20  Georgia
SF SL7 40 June 20  Pennsylvania
SF SL8 40 June 20  Connecticut
SF SL9 40 June 20  Connectict
SF SL10 40 (45 with 5c fwd fee) June 20  Missouri

This is the only known forwarded straightline cover
SF SL11 80 July 2  New Jersey
SF SL12 40 July 2  Connectict
SF SL13 40 July 2 Connectict
SF SL14 40 July 2 Massachusetts
SF SL15 40 July 2 New Jersey
SF SL16 40 July 2  New Jersey
SF SL17 40 July 2 Maine
SF SL18 40 July 2 New York
SF SL19 40 July 2 New York
SF SL20 40 July 2 Vermont
SF SL21 40 July 2 Iowa
SF SL22 40 July 2 Rhode Island
SF SL23 40 August 1  Maine
SF SL24 40 August 1  New York
SF SL25 40 August 1  New York
SF SL26 40 August 1  New York
SF SL27 40 August 1 Massachusetts
SF SL28 40 August 1 Massachusetts
SF SL29 80 (Uprated from 40) August 1 Massachusetts
SF SL30 40 August 1 Connectict
SF SL3140June 20Wash. DC
Best image available, last found in Siegel Auction 375 (Lot 903) in May of 1970.
SF SL32 40 June 20 New Jersey
SF SL3380June 20Maryland