It is Interstate highway with enough traffic that if there is any stretch much longer than 50 miles without a place to buy fuel, one of the vendors as you approach will have put up a billboard "Last Services for XX Miles" to make sure you know to stop at his place.
If you do let your fuel supply get down to the under 50 mile range, the places you might get into trouble are the lonely state highways and roads on reservations where the only businesses outside tribal centers might be trading posts. When the road gets that lonely, I top off any place I can if at or below half a tank. Interstates don't get that lonely, though maybe the area looks desolate to an urbanite.
Traveling through rural areas off the Interstate in any part of the country, like Delta Country or forest lands, not just the West, first time through I make notes of the places I may want to stop on the next trip, mostly so I can plan my refreshment and rest stops, as well as gas stops. First time through, though, it is best to stop whenever you can, because you can, rather than trying to push on until you must stop.