Both are a bit of a drive, but:
In SLC, I enjoyed going to Timpanogos Cave
and canyon hike.
In LA, Mt Wilson Observatory
is fun and hey, you get up above
the smog layer. Last time, I stopped at the La Brea Tar Pits
which was interesting, if a bit kitschy, but do not step off the path
anywhere in the park or oil seeping up out of the ground will ruin your shoes. Even though the grass looks nice and green. And then they won't let you in to the art museum next door...