The Gold Rush
We considered going with the more general period of westward expansion in North America, but we realized The Oregon Trail has that covered, and then some. And Red Dead did the whole cowboy thing, although granted Mr. Marston was a little old-fashioned for a gentleman in 1910.
But the mid-19th century was an exciting and dangerous time for lunatics looking to seek their fortunes and likely ruin their lives by heading to Cal-ee-forn-aye-ay the second some sap discovered gold at Sutter's Mill.
Few of them came back with much more than they started with, but playing as a lawless forty-niner staking claims and doing anything he can to survive the wild west would be a fantastic premise for a game.