The precious metals from California gold fields and Nevada silver deposits were a major part of the financing fo the Union during the war. Gold from the California deposits discovered in 1848 was refined and smelted and shipped through the Golden Gate as was the silver from the Comstock Lode discovery of 1858.
So concerned about this precious resource was the Federal Government that they fortified San Francisco harbor with numerous defensive works. The largest was Fort Winfield Scott, later called Fort Point, at the entrance of the harbor. It was the only masonry fortification constructed west of the Mississippi River. It was armed in 1861 and designed too mount 127 of the 8″ and 10″ Columbiads, some of which were replaced with large caliber Parrots. Fort Alcatraz on Acatraz Island had been in place to a limited extent since the early 1850’s. When complete it mounted 95 smoothbore guns, 8″ and 10″ Columbiads.
Additionally earthen forts were placed around the entrance. Forts Barry, Cronkite, McDowell and Baker were in Marin County. Earthen forts were located on Angel Island. Point Stuart mounted 4 smoothbores, Point Knox mounted 10 smothbores, Point Blunt was incomplete but mounted 7 smoothbores and Blckpoint at Point San Jose mounted 12 smoothbores. All these were installed in 1863-64 to counter the concern over the CSS Shenandoah which had been prowling the Pacific as far north as the Bering Sea. Camp Reynolds with 4 temporary batteries was located at Fort McDowell.
Ft Alcatraz was used a prison for special catagories of Union soldiers such as deserters and malcontents.
It is intersting that this area, part of the Department of the Pacific, was under the pre-war command of Brigadier General Albert Sidney Johnston. One of his last official acts was to transfer batteries from Ft Vancouver to strengthen the defenses. He also arranged the transfer of small arms and accoutraments to the area for defense of the harbor.
Why all the fuss? During the three and one half years of the war $173,083,098 in gold and silver bullion passed through the Golden Gate.