What were the weather conditions? I have driven that road and many like it numerous times. In fair weather you can often see a long way ahead but if it starts raining hard in that climate visibility can be very reduced.
Not sure if the northbound vehicle was actually passing or in the wrong lane for other reasons, but as you know, passing trucks can be a real challenge on those roads, if they are at near maximum speed, or slowly picking up speed on an incline.
There are also deer and antelope running around in those regions which can create problems if they come out of nowhere. We were in an antelope reserve one time in that general area, never saw one antelope, then a mile outside the fenced boundary, three of them ran across the road just ahead of me. I wasn’t going fast enough for it to be a big problem but I never saw them coming out of the bushes.
Saw half a deer carcass on the I-84 in southern Idaho on another trip, obviously hit numerous times.
You couldn’t have asked for better weather. Completely dry and unlimited visibility.
There weren’t many trucks since it was early Sunday morning.
Didn’t see any animals or carcasses. We did see some pronghorn in Idaho the next day.
Traffic was moderate. Other drivers were driving reasonably and I didn’t see any idiotic maneuvers.
There are a couple of strange no-passing zones, though, where the road is straight and road visibility ahead is clear for miles, but you have maybe five to ten miles od double-yellow no-passing zone. No construction. No hills. I could see somebody getting impatient with an interminable no-passing zone put there for no apparent reason. I don’t think the accident area had one of those extended no-passing zones, though.