The guys in the picture were all volunteering for the Union army, fighting for the North, because the miners were afraid that if the Confederacy won it would make California a slave state and import their slaves to mine for gold. They didn't want to compete with slaves who work for nothing. The entire mother lode gold rush area was predominantly pro-Union. There were enclaves of Confederate sympathizers here and there, but the pro-Union people pretty much kept them in check.