Backpacking overnight in Mount San Jacinto State Park is my favorite place to take first-timers. You take the Palm Springs Aerial Tram up the mountain, and when you get off the tram you are already in an entirely different world.
Lots of options, including summiting Mount San Jacinto if you’re so inclined.
I’ve taken at least five people for their first backpacking trip there, including my own daughter (when she was still in diapers).
Here’s a guide to the trek: https://socalhiker.net//hiking-mt-san-jacinto-via-the-palm-springs-aerial-tram/