Hey, RM. I tried to PM you, but couldn't.
I recently did a tri at Oquirrh Lake, just south of the BMX park. You could ride from the Daybreak neighborhood, south and west. There is some mild climbing, but then you get a great speedy return trip. Daybreak has a paved trail all the way around the lake and it is a fun little run. If you are interested in company, let me know. There is a little reservoir for swimming a bit further south, if you want to swim, too. Oquirrh Lake is closed for swimming except on race day.
The flat ride out by the airport is okay. Part of the pavement is pretty chopped up. I was recently out there because it is lightly traveled and provided a good place for me to experiment with aero position on my new bike. I wouldn't ride out there by yourself, as it is relatively isolated, but parallels the interstate. If you want to do that ride other than the time the group is doing it, I could meet you there, depending on when you want to go.
There are some pretty places to ride up in Park City, and it will be cooler there, but would take about 40 minutes to drive there from where the BMX park is.