Dole, not coal

TFSmith is fairly positive about the industrial capacity of San Francisco:

'home of the Benicia Arsenal, Mare Island Navy Yard, and Union Iron Works, among other industrial facilities' (1)
'the most strongly defended and most economically developed bastion on the Pacific Rim in 1861-62, in BROS or outside of it; the realities and resources of the Benicia Arsenal, Mare Island Navy Yard, Union Iron Works, Fort Point, the Presidio, etc. are head and shoulders above the next closest, which is probably Callao' (2)
possessing 'an integrated industrial center (Benicia, Mare Island, Union Ironworks, and the Mint, for example)' (3)
'the Mother Lode and Comstock pretty much forced a level of industrialization - commercial and military - that included what became Union Iron Works in San Francisco proper, and both Mare Island and Benicia Arsenal farther up the east bay, and there was plenty of manpower, horsepower, timber, and livestock in California' (4)

Unfortunately, there is one thing that TFSmith never mentions in the course of these discussions: coal. Of the 99,818 tons of coal brought into San Francisco in 1861, 42,403 tons came from British possessions. A further 16,183 tons came from Oregon, and regrettably (as we have already seen) the Union has no railway to transport the coal and no ships left to escort coal convoys down the coast, even if Britain hadn't been blockading Puget Sound already. The domestic coal supply in California consisted only of 2,662 tons from the Cumberland company, which produces soft low-quality bituminous coal.

This coal is not just needed to forge iron for armour plates or to power the now-mastless ships of the Pacific Fleet. As per Rebels at the Gate, Captain Jeremy Francis Gilmer reported that 'The climate of San Francisco is a peculiar one, the summer months being often quite as cold as the early spring and fall... it is impossible to do business in any office in San Francisco during May June July August and September without fires.' However, we are never given any indication that the interruption of British coal imports has any effect on the industrial capacity of California, let alone that tens of thousands of civilians are burning whatever wood can be found to stay warm, or that large sections of Californian manpower are diverted into the mining industry in order to supply the deficiency.

Why does this matter? Let's compare. In chapter 15, part 1, we are told of the effect that the interruption of American wheat supplies has on Britain:

ending trade with the United States, although it had provided a surfeit of southern cotton to an already saturated market, had substantially reduced the import of wheat and corn to the United Kingdom. Although the supplies could be made up from sources in Europe, including Russia, costs were high and prices had increased in Britain and Ireland, adding yet more stress to the poor and laboring classes, with consequences as yet unknown. Palmerston’s opponents in Parliament, even the Conservatives, were willing to raise the issue, and protests had occurred in the poorest counties in Ireland and Scotland. Irish peers, among others, had raised the issue of the famine, and the possibility of rioting was understood to be very real, especially in the depth of the winter of 1862-63

US wheat amounted to 40% of the British supply at this time: despite finding alternate sources, the British suffer cost increases and is on the verge of famine and riots. British coal amounted to 40% of San Francisco's supply: there are no problems, and indeed California can ramp up its industrial production over OTL. Perhaps the Conestoga wagons being used to carry gold bullion from California to the east are carrying coal on the return journey.