I just discovered this thread and I'm delighted to find it.
Of course nothing is perfect and our beloved movie Brokeback Mountain has its flaws, some continuity flaws, some verisimilitude flaws, sometimes the films is so faithful to the ss with "set design" that there "appear" to be flaws. Overall though, I think that we all agree, the film works very well.
just off the top of my head without looking at some notes now almost a year old that I made while discussing the film with me sister I noted:
1) the model K-W cattle truck Ennis rode into Signal was not manufactured until the late 1970's
2) the street lights that you see throughout the film were not in use in the 1960's
3) Jack and Ennis needed lanterns if they were camping out, in the ss AP gave them lanterns, they would have had them in real life
4) notice the boys haircuts and beards, they pretty much stay the same all the while on the mountain, that wouldn't have been the case in real life. Also note Jack's hairline around his ear, the hair cut is the same before he married Lureen and after. That would not have been the case in real life. Prosperous men in that time frame in rural Texas towns (Childress) went to the barber once per week, and came away with what was called "white walls", hair clipped closely around ears. Ennis's hair before and after marriage probably is correct, as a poor ranch hand out in the sticks couldn't afford to drive in constantly to get his "ears lowered".
5) note the axe Jack was using in the scene when Aguirre rode up to camp advising Jack of Uncle Harold's condition - a major continuity error on the part of Ang Lee
6) where is the dog food? those sheep dogs have to eat!
7) note the hood on Jack's truck after Ennis helped him start it after shovedown - a major continuity error on the part of Ang Lee
8. in the scene where Jack is in the bar in Electra,TX (1965) : note the "Coors" taps at the bar, Coors was not sold in Texas until after the 1970's, some licensing agreement dispute that was finally resolved well after the setting of the film
9) note the hair length and beard of the bar tender in Electra, unusual to say the least for anyone living in a small rural town in TX in the mid 1960's
10) note the steel sided barns in the scene of the rodeo in Childress - that style of prefab building was not sold until much later in time, barns in that time period would have not been prefab and the look would have been rather different
11) note the pine trees behind the rodeo stands in the Childress scene - Childress is on the edge of the TX Panhandle, there are no groves of Pinetrees in the area, there are hardly any trees at all, except for Mesquite and some planted Cottonwoods and Liveoaks. it was obviously filmed in Canada
12) note the hair styles and beards and the eye glasses frames of some of the men who are watching Jack get his 8 seconds ride, those style would not have been characteristic of rural TX in the mid 1960's
13) when Ennis brings Junior and her baby sister for Alma to baby sit while Ennis goes off to his job, notice how the baby will start crying and a spit second later will be perfectly calm, this is repeated over and over in the scene. baby's moods change rapidly, but their little scrunched up pouting faces don't change that rapidly - this was obviously filmed over and over again and not edited well, perhaps that is why the baby actor gets cross!
14) note the post office in Riverton when Ennis first send Jack a card, no zip code on the building sign, this scene was set in 1967 several years after all US posts office's were mandated to incorporate zip coding and change their signs. the exact year of universal mandatory zip coding was 1964.
15) note the jet airplane apparently taking off crossing the path backscene of Jake in the scene later where he is showing the local yokels how the features and benefits of LD's new combine. Childress did not at that time have an airport designed to accommodate a jet aircraft.
16) the interior of OMT's home has been discussed earlier, and I echo the sentiments of those who also feel that is unrealistic. Mother Twist would have decorated that house with every little religious Jesus object and plaque she could find space for. Mother Twist would have had some plants and a colorful decorative table cloth as well, she had to show here individuality in the face of the tyrant OMT in some way. The white, white everywhere color scheme would drive anyone snow blind by itself. Jack's room is touching but unrealistic, unless mother Twist deliberately redecorated it to resemble the room as Jack would have had in while he was a preteen.
just off the top of my head, I'll review my note from long ago and see if I missed anything.