All in all, folks don't generally throw away guns...
Back then, there was no reliable way to trace the bullet to the piece that fired it - matter of fact, that hadn't really been thought of.
Plus, in the Gold Rush Era, guns were relatively expensive and hard to find, so they had a greater value there, because of the shipping difficulties it took just to get them there than they did 'Back East' where there were well-established rail lines.
If they 'owned' a gun - they 'kept' the gun - or they sold it for a profit and went home to the farm when they found that their claim didn't pan out.
No - those guns were merely lost - dropped out of pockets, or from waistbands while crossing a stream, most likely - or left forgotten in an old cabin site and found much later when the owner had gotten something better.
Not much by way of a thrilling story - but the truth seldom is...
Incidentally, those old Pepperbox pistols were exceptionally popular out there - probably because they were cheap, more than anything, I suppose - but they seem to be found more often in Old California than anyplace else - I've got one myself, and it came out of a streambed - no wood left, but after soaking in penetrating oil in the hot summer sun, it cycled - but it sits in a shadowbox, now.
Scouts Out!