You might say that landscape moulds character - this difficult land with its rocky mountains where even the lower slopes were harsh places much of the time and its constant wind and extreme winters might produce people who need to be self-sufficient and unemotional in order to survive.
Lureen and even her family are more open and less inward than the people from Wyoming. (Maybe why Jack manages to make a life there for something like eighteen years - Ennis would never have fitted in there.) The difference between Lureen and Alma in the early sixties isn;t just a question of how much money each has - Alma, like Ennis, has grown up in a harsh landscape with limited expectations not only of material things but also of emotional relationships. It's ironic that Lureen turns into somethingmuch harder as the story progresses - the effect of Jack's directing all his emotional intensity at Ennis in a futile attempt to change him from what life has made him.
The ruggedness of the landscape certainly made a mark on the protagonists. This is true with any Proulx characters. The state of mind seemed to have had a more physical manifestation -- in the land itself. It shaped the people, and it certainly resisted change.