While in Salt Lake City itself, try doing some urban hiking. https://www.slc.gov/transportation/urban-trails/

A very popular hike goes from downtown Salt Lake City into near wilderness in just a few miles. I know of no other major city where such a hike is possible.
https://www.visitutah.com/places-to-...y-creek-canyon

I personally like to hike along the Jordan River Parkway Trail. https://en.wikipedia.org/wiki/Jordan_River_Parkway The trail is much too long to hike all in one day, but the stage of it that I do the most is the segment that runs between two light rail stations, River Trail Station and Fairpark Station. There is lots of free parking at the River Trail Station, so one option would be to park your rental car there and hike to the other station and then ride the train back. One caveat, you will likely encounter homeless people camping out along the river. But I have never had a problem with them and it would be educational for your son.