What appears on maps and on the ground to be the west side of a wye was the SP&S overpass that crossed over I-90. I believe a color photo of SP&S Alcos crossing this bridge appears in the Walt Grande SP&S book. I'll doublecheck after I get home.

Remember, before the BN merger and subsequent construction of Latah Creek Bridge, SP&S trains crossed Hangman Valley to the north on GN's large bridge between Spokane and Fort Wright Jct. SP&S then tunneled south from Ft. Wright Jct. under the cemetery and, after the construction of I-90, had to cross that bridge on the west leg of your wye.

After Latah Creek Bridge replaced both the GN/SP&S and UP bridges to the north, there was no longer need for the short SP&S bridge over I-90. Not everyone realizes that from Latah Junction up to Lyons, the present BNSF alignment is mostly of BN construction, situated higher on the side of the bluff than the original GN alignment. However, some of the BN/BNSF alignment does rest loosely on a bit of the SP&S grade from the northwest end of Latah Creek Bridge about halfway up to Indian Canyon Bridge. And of course BNSF still uses the SP&S from the southwest end of Latah Creek Bridge south through Marshall Canyon to UP Junction. (BNSF owns the last bit of SP&S from UP Junction south to Fish Lake, but only UP trains operate there.)