I found two signed sections of the Old Spanish Trail in Utah.
It follows UT 20 west from US 89 and then turns onto
Bear Valley Road, which it follows to
UT 271. It then turns south on UT 271, which it follows to
UT 274. At UT 143, it continues straight onto Old Hwy 91, and then turns left onto
the frontage road on the east side of I-15, which it follows
past the southern end of the pavement (presumably all the way across I-15 back to Old Hwy 91). There are no OS Trail signs at that intersection, but there is another segment nearby which may fork off of the first. The OS Trail is signed
westbound and
northbound at the intersection of Old Hwy 91 and Midvallley Rd, implying that it intersects with the other segment where it left Old Hwy 91 near exit 71 on I-15. This second segment follows Midvalley Road west to
Shooting Range Rd, where it turns north. It follows Shooting Range Rd to its west end, where
it briefly turns northwest onto Iron Springs Rd before turning west onto
Antelope Rd. It then
turns south onto Sand Spring Rd/800 E, which it follows south to
UT 56 (though exactly what path this road follows is unclear; GMSV only goes as far north as
this intersction, where the road is little more than a two-track (but the OS Trail is signed nonetheless), north of which there are at least two plausible routes). UT 56 appears to be the southwestern end of this segment.
