OF THE FOUR CIVIL WAR PATRIOTICS USED FROM HAWAII THAT WE RECORD, ONLY THIS COVER IS A MIXED FRANKING
Assuming that the San Francisco datestamp reads August 15, 1861 (only the day and year are clear), this cover was probably carried on the Speedwell, which cleared Honolulu on July 22 and arrived in San Francisco on August 14.
Our records contain just three examples of Civil War patriotic stationery used from Hawaii. This is the earliest usage, the only mixed franking, and the only U.S. 1857 Issue franking. The others are: a 12c 1861 on Standing Liberty red and blue patriotic cover postmarked at Honolulu on April 18, 1863; and two small red-and-blue patriotic emblem covers used between islands, each with a 2c Kamehameha IV stamp. Other examples, if any, must be extremely rare.
Ex Matthies, with 1971 P.F. certificate