Orange County, California has two small zoos but could use one major zoo I think. (The current Santa Ana is locked in five acres with no room to expand).
Los Angeles, California has one fairly large zoo but needs a second zoo of at least similar size. Anyone who has been there on a weekend in nice weather knows that it gets crowded beyond carrying capacity (to the point of becoming miserable).
Las Vegas, Nevada desperately needs one as we all agree.
Flagstaff, Arizona could be a candidate for a nice modest zoo focusing on mountain or cold climate animals.
Midland-Odessa, Texas could use one because they are hundreds of miles in either direction from the next major cities with zoos.
Corpus Christi, Texas has a nice aquarium but no zoo.
Spokane, Washington has a cat center (of dubious quality) but no zoo.
Lancaster-Palmdale, California is a large high desert city with a cat center but no real zoo.
Yuma, Arizona has a camel farm but no zoo and is hundreds of miles from the next nearest major cities with zoos.
El Centro, California same situation as Yuma.
I could go on and on...