In the 1950's, the racks were full of cowboy comics; Will Eisner's Western Picture Stories was tied for the first, along with a book called Star Ranger, in 1937. Television and the movies had a cowboy "hay day." By the mid-70's, they were mostly being reprinted rather than produced in first runs; Marvel's Westerns usually carried great covers!
Steve Englehart, while writing the Avengers superhero comic in 1975, decided to visit those thrilling days of yesteryear, with a time travel story featuring Thor, Hawkeye, and Moondragon on the trail of Kang the Conqueror. As Hawkeye had discovered, Kang figured taking the 20th century would be much easier if he started in the 19th century.
This story, in AVENGERS #142 and 143, had an old-fashioned train robbery. Thor and Moondragon disguised as passengers, anticipating the attack, mostly fended off by Two Gun Kid, the original Ghost Rider (or Night Rider), Kid Colt and a very Indian-costumed Hawkeye. The next half of the story involved an assault on Kang's fortress---a bit far out for a cowpoke. Fortunately, one hero goes in disguise, with a mind to give Kang one final, all-out battle. Kang had been popping in and out of the Avengers' lives throughout Englehart's run, so it was something of a climax.
The cowboy heroes were not quite sure what to make of their 20th century counterparts. Add to this the very non-traditional, unearthly nature of Moondragon.
Despite this, Two Gun makes a surprising announcement: he wants to go back with the Avengers, particularly his buddy Hawkeye, and see life in the future. It was a good set-up for a new "man out of time" story line, but writers following Englehart decided not to touch it, and Jim Shooter sent him back on his way in Avengers #175.
Stainless Steve may have been testing the waters, or he may have made a sentimental choice, a tip of the hat to the gun hawks and owl hoots before the end of his run.
On the newsstands, the day of the Western had ridden into the sunset. Not long after Kane left Marvel, the reprint lines were cancelled. Over at DC, Jonah Hex and his weird Western tales were still going strong; but with the exception of occasional revival efforts, they were put to pasture.
Superheroes and cowboys wouldn't mix again until 1987, when Englehart came back to West Coast Avengers.