Later California gunsmiths built muzzleloaders through the 1870's and maybe beyond. The lack of a cheekpiece, and the style of the hardware, suggest this time period. It has features very reminiscent of late California guns. And just to add another ingredient to the mix, it might have been built special for someone living far enough from civilization, that a flintlock made more sense.
As for using it as a shooter, I wouldn't recommend that. This gun is quite restorable, and if the maker can be identified, maybe quite valuable. Other than it getting possibly more regular cleanings, shooting an antique will take its toll. I have two "shooters" on my bench right now that the hundred plus year old wood just snapped, ruining a fine antique. New steel, new wood, and new metallurgy are always better, build or buy a shooter.
Hungry Horse