This provides some early information on the location of San Francisco Station D (a/k/a post office located at the Ferry Building):
Quote:
In the early 1890s, the U.S. Post Office Department began nationwide studies to facilitate city mail delivery and processing using local rail transit systems. At the time, private wagons moved mail between San Francisco post offices. In June, 1894, former San Francisco mayor and state senator Frank McCoppin was appointed Postmaster of San Francisco and came up with a plan to transport mail between post offices in sealed pouches carried on street railway vehicles.
McCoppin felt that Railway Post Office (RPO) service -- whereby mail was sorted, distributed, and picked up by onboard clerks -- was inappropriate for San Francisco; the distance between post offices seemed too short to make it practical. However, the U.S. Post Office Department desired mail cars that provided a combination of closed pouch and RPO services, giving San Francisco a predominantly RPO operation.
The proposed service was primarily designed to provide rapid mail movement between the Ferry building and outlying post offices. The then-main post office at Battery & Washington Streets (site of today's U.S. Custom House) was hopelessly inadequate and outdated. To solve this problem, Station D -- the postal facility located at the Ferry Building -- was emphasized. Almost all of San Francisco's incoming and outgoing mail passed through the Ferry Building because of its links to the national rail network that terminated in Oakland.
An interesting story about the early RPOs at San Francisco at this link:
http://www.streetcar.org/blog/2006/...he-mail.html