Depends on where you include upper middle class. If upper middle class is within the middle class, than surely 300,000+
If upper middle class is not included in middle class, than 70,000+
^^^^^^^^^^^^^
I picked 70,000
Even in Georgia, with a low cost of living, a family of two parents with two kids making 70k could hardly be called rich. Hell, an individual living on their own making that shouldn't be considered rich. It's really not that much money - it would give some disposable income for sure, but you wouldn't be rich.
I voted 300k, though 200k would also be a reasonable cutoff.