Welcome to the forum. Your first few posts are moderated, so they will take time to appear, especially over a weekend. But stick around and that passes quickly.
Unfortunately, there’s not a lot of American-outline Z scale, especially for that early era. (Not that much in the larger N- or HO scales, either). There weren’t a lot of railroads operating in California in the true Gold Rush period, although they followed in the late 1850s and into the 1860s.
If you have some model-building experience, you might be able to start with a European-outline steam engine chassis and build up from there for a locomotive, but it’s probably not a beginner’s project. And any loco that small will have challenges in terms of fitting a motor, as has been noted.
Good luck with your layout.
Byron
Layout Design GalleryLayout Design Special Interest Group
There may be difficulty in finding older, smaller prototypes in Z that can actually pull trains. You might have to go to 'reskinning' a locomotive as a passenger car, changing the sideframes, and making both engine and tender as 'dummies' to be pushed. You could start with this
https://www.shapeways.com/product/M9LNU2XAU/grant-4-4-0-metal-zscale
and adapt it with a free-rolling chassis. Inside valve gear greatly simplifies making rods that work effectively and look right.
Looking at eBay locomotive listings, you might be able to kitbash a more American superstructure on something like a German-style 2-6-0; I notice there is a NYC&HR locomotive that is too late for your period but perhaps a starting point for detailing.
I would consider joining something like the Civil War modeler's group on the groups.io platform. I am not sure they have taken up designing for Z in detail, but I suspect some of them would take interest in the idea.
Hi-
I'm trying to build a small z-scale layout for my 13 yo grandson and me to work on together. Our cabin (where we spend 2-weeks together each summer) is located 30 miles from Jamestown, CA. I'm interested in the early steam era. Has anyone done anything in Z scale for this era or geography that they can share?