This movie was suppose to be sometime at the end, or just after the California Gold Rush (1848–1855). Perhaps that can help pin down the date better. At one time the drug store title was more of a general store title. The apothecary did not only supply drugs & medical supplies but the owner may have been a dentist or pseudo-doctor.
The guns in the film say something about the date too. If you watch close, during the raid of the tin-panner's camp at the beginning of the film, 1 member of the gang is shown shooting a 1872 Colt SA Army revolver at a steer. The film is set prior to that gun's availability & all other revolvers shown throughout the film are Colt cartridge conversions of the 1860 Army model, or Eastwood's cartridge converted Remington.
FWIW...
...bug
