I'm in the midst of a month-long road trip, and I'll have soon visited every single half-decent California zoo and aquarium. The fact that California is leading this poll is a joke, unless one includes aquariums. Simply looking at zoos then San Diego Zoo and San Diego Zoo Safari Park are brilliant, and then there is a very long list of average to mediocre zoos. Of the major cities Oakland, Santa Barbara and Los Angeles are all average, and San Francisco is borderline terrible. There is an enormously steep decline after the two big San Diego parks. However, California's aquariums are fantastic! Monterey Bay Aquarium, Aquarium of the Pacific, Steinhart Aquarium and Birch Aquarium are all terrific, San Diego SeaWorld is massive and even Aquarium of the Bay is worth a visit. California must clearly be the #1 state for aquariums, but for zoos there isn't much to write home about after the pair of San Diego behemoths.
Texas has one great zoo in Dallas, and then many average to excellent ones in Fort Worth, Cameron Park, Caldwell, Houston, Gladys Porter and El Paso. Overall, looking only at zoos, then Texas is the clear winner. If one were to include aquariums then things get quite tricky.