When you say "true ghost town", I assume you are envisioning a scene from straight out of spaghetti western movie? (ie.: like Bodie, etc...) eh? No, I'm afraid you're not going to find those towns at the end of 4x4 roads, sitting their virgin and ready to detect. And as far as all the ones along the Rte. 49 itself, they're pretty much all tourist traps now, or simply modern towns (where the board-&-batton era of the gold rush era is under asphalt, etc...). And any random ruins you'll see along the road (chimneys or foundation pads along the roadsides there) have no doubt been detected oodles of times (d/t their plain visibility from the well-traveled road). And they're pretty junky with iron!
So rather than looking for ghost towns per se, you want to look for the old tent-city towns, where a hundred or so miners would live in temporary tent cities, while going from strike to strike. A lot of those never turned into actual towns, but were more like the camp zone for whatever mine was being worked at the time (which could be just a few months or whatever, before moving to the next canyons, etc...). Those worker-camp zones would be somewhere fairly close to the industrial workings, tailings, etc.... ('cuz figure, they didn't want to walk far each morning and night). So check any flats, meadows, etc... that border such historic mining areas. The thing about these zones, is unlike towns, and industrial zones, there will be NOTHING left to indicate where they were. Because, of course, tents were just disassembled, and never permanent.
There's a fellow on the kinzli CA forum who has done well at finding some of these type sites. Seateds, cache coins, and even a few gold coins by doing this.
