Gold was discovered in Idaho just before the Civil War and the territory was admitted as the Civil War began. During the gold rush era, from around 1862 until about 1870, there were probably equal numbers of Southerners and Northerners. The impact of the South in my part of the state is pretty clear - towns like Atlanta and Dixie, the Secesh (as in secession) River and such.
Even after the war, right up until statehood in 1890, there were hard feelings. The territorial officials were appointed by the Republican administration in Washington, DC, but the Democrats maintained a pretty good hold on elected offices due to the support of the Southern contingent. It led to a virtual gridlock in the courts and more than a few "bushwhackings". Of course, there was the general chaos that came with gold fever, but it's pretty safe to say that there was a great deal of pride reserved by both sides of the Mason-Dixon line and plenty of fellows willing to back up that pride with a revolver.
I doubt that the Boise Basin in Idaho is unique in that aspect - I'm sure that other areas in the West had their own North-South "interactions" as well.
Interestingly, my family managed to combine both sides. My great grandfather was a died in the wool abolitionist, Protestant, Catholic-hating Northerner, while my great grandmother came from a line of devout Catholic, slave-renting Southerners. Thankfully for all, he worshiped the very ground she walked on and love overcame all, although I believe that Lent, Easter and Christmas caused a little prickliness with the family.
They were married by the justice of the peace. A fitting compromise, I think.
Well we don't rent pigs and I figure it's better to say it right out front because a man that does like to rent pigs is... he's hard to stop - Gus McCrae