If you do not put in intermediate stops, Google Maps recommends this direct route between St George and Ruby Valley.
365 mile route via US-93
If you use only the freeways (I-15 and I-80), which means you go through Salt Lake City, it's 551 miles:
551 mile route via freeways.
Not only is the direct route almost 200 miles shorter, it's quicker. US-93's speed limit is 65mph in most areas.
We can safely assume that Steven returned from Ruby Valley via the I-80/I-15 route (due to the presence of a receipt from a Taco Time, of all things).
Yes, had looked at those routes but gas is the issue. Even if he left St George with both tanks full, if he went to Ruby Valley first then he was sliding into Pilot/WWendover on fumes. Steven does appear to have been very conscientious about gas and didn't seem to try and hide any records of his travel.
While there are not specific dates on the bank receipts (we call them receipts here which might clear the confusion) the locations of the purchases and date of bank posts tend to make them a logical part of his travels.
http://maps.google.com/maps?f=d&sou...118.059082&sspn=4.221512,9.876709&ie=UTF8&z=9