Before Rio Grande joined Amtrak, 5 and 6 did indeed go straight across Wyoming, through Ogden, and then out over the causeway. But Amtrak never really liked the causeway because it was so danged rough. For a time in the 80's 5 & 6 were rerouted through Salt Lake, using the UP station. Back in those days there was a three way split in Salt Lake. Westbound 5 was broken up into the Zephyr to Oakland, the Pioneer to Seattle, and the Desert Wind on to Vegas and LA. Of course 6 reversed that process in Salt Lake going eastbound. The story actually is a little more complex than that, but my chronology is a little rusty. I remember that for a time the Pioneer originated in Salt Lake by itself, with the Zephyr coming south from Ogden to Salt Lake. During that period when the Promontory Chapter NRHS held its meetings in the station (above the waiting room) we would sometimes catch the Pioneer, ride it to Ogden and then catcth the Zephyr back to Salt Lake, all in one evening. There have been many changes through the years.
Utah's interurban network is being rebuilt-who'd a thunked it?!