Soon after Ben, Pardner, and Mad Jack open their secret "gold mine" underneath No Name City, a young farmer is recruited to help dig. To emphasize the need for secrecy, Mad Jack threatens to shove a stick of dynamite in the farmer's mouth if he blabs. The film is set in 1849 or 1850, before California becomes a state. Dynamite wasn't yet invented (it was patented by Alfred Nobel in 1867).
At the end of the movie, the tunnel system collapses and the buildings start to topple over. In several shots the cables used to pull over various buildings are clearly apparent, even though it appears that attempts were made to camouflage them with pennants. What gives it away is that the 'pennants' (until the buildings they are attached to topple over) are clearly under far too much strain to be merely hung as decorations.
During "The Best Things In Life Are Dirty", Ben Rumson rides up on a cart full of sloppy mud. The three Irishmen, led by Mad Jack, are pulling the cart up on a block and tackle, with a heave-ho motion. The cart should rise a few inches at a time, to synch up with their motions. Instead, while they pull and rest, pull and rest, the cart rises out of the pit at a constant speed.