September 24 (1850) incoming to San Francisco - CDS with matching "Ship 6" red clamshell handstamp on folded cover from Valparaiso, Chile.  Manuscript "pr Str New Orleans" endorsement.  The New Orleans was the third of three Empire City Line (ECL) steamers to arrive in SF as competition to the PMSC.  The steamer arrived in SF on September 24, 1850, 210 days out from New York, the CDS showing the inaugural arrival date.  Clamshell "Ship 6" marking indicates 6 cents due for the incoming non-contract steamship rate. This is scarce struck in red.
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A new CDS with "Cal." at the bottom emerged in mid-1850.  It is similar to the 1849 CDS except there is a smaller gap between "S" of SAN and "C" of Cal. and is 1 mm larger in diameter.  This CDS had a much longer lifespan (at 3 years) than all the prior CDS versions (which were in use 2 years or less at this time depending upon style).  This CDS is often found with a separate rate handstamp.

Some of the unique identifying characteristics of this CDS are;
3.5 mm gap between "S" of SAN and "C" of Cal.
34 mm diameter
Serif font
"Cal." with lower case "al" and period, at bottom (period is raised compared to 1849 CDS)
Day/Month only, no year


Examples of this CDS are shown below.


Side-by-side comparison of similar 1849 CDS (left) and this CDS (right).  Note the gap size differences between "S" of SAN and "C" of Cal (5.0 mm gap on left and 3.5 mm on right).



Postmarked April 29 (1852), incoming to San Francisco - CDS with matching "Ship 6" black clamshell handstamp on folded cover from Valparaiso, Chile (datelined March 20 1852).  Endorsed "via Panama pr Vapor Winfield Scott" with red purser marking "STEAMER WINFIELD SCOTT."  Unpaid 6¢ non-contract incoming steamship rate (Ship-6 due marking) delivered to port of entry.  This was the maiden voyage of NY & SF Steamship Co. Winfield Scott to San Francisco.  The company changed name in May of 1853 to the NY and CA Steamship Co.  After the demise of this line, ownership was transferred to the PMSC in July 1853.  Letter carried under cover by private ship to Panama where it was transferred to the Winfield Scott.  The ship was wrecked/lost in the Santa Barbara Channel on December 2, 1853.
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August 21 (1852) local San Francisco use - Separate "1" handstamp used to indicate the unpaid local drop rate.  This rate marking is not commonly found on SF mail.
 Addressed to J. L. Folsom for whom the town of Folsom, CA (near Sacramento) is named after.



Earliest/Latest Found Dates (Bookends) For This CDS
Ref # Rate Date Destination Image
SF CalCDS-1  Earliest 40 June 11, 1850 New York
SF CalCDS-2
Latest
42 (incl ship fee) April 30, 1853 Connecticut (from Hawaii)