At the end of the movie when they are all sitting on horseback with Lake Tahoe in the background, the glare off a moving car windshield in the background can be seen across the lake.
Near the end of the movie Augustus Brandenburg is shooting at the Cartwrights from the back car of his train. The gun he is using is a Browning M1911 .45ACP Designed in 1911 by John Browning. However the date for the events in the movie is clearly given as 1905