From events that take place in this episode, it can be dated historically it as June 1876.
The last few lines of poetry that Paladin recites, "...And when they fell before the thunder, It was as when the lordly redwood, green with boughs, Goes down with a great shout upon the hills, And leaves a lonesome place against the sky." is from "Lincoln, Man of the People" by Edwin Markham. The poem was written in 1901.