Alex,
I guess no one can remember how we got there. Brian was leading, and we wandered a tiny bit actually. The trail started behind some new homes in area off to the west of next exit north of the outlet mall. As far as I can remember we met at the outlet mall, then took I-15 north for one exit. Also, once we were on the dirt road it was fairly well maintained, and let to some sort of retreat or maybe religious facility (or, it could have been a nudist camp, I don't remember exactly).
Probably not much help, but maybe with Google maps or something you would work your way backwards from the trails you know down to the street.