There was also The Wild Bunch (1969), which was set in 1913.
And 1970's more light-hearted Ballad of Cable Hogue
, also from Sam Peckinpah and set around the same time. I would guess those two would be the primary inspirations, like Butch Cassidy and the Sundance Kid
for Alias Smith and Jones
and Coogan's Bluff
. A template like "Cable" would seem almost perfect for Garner's Maverick
and Support Your Local Sheriff
characters. Just a guess, though.
Makes me wonder what inspired 'Hec Ramsey.' A Columbo style police detective circa 1900 (starring Richard Boone).