Alligators are no big deal along the coastal counties of Texas, and even in the Rio Grande.
If I had to guess, there are probably 40 or 50 of them living within a mile of where I live.
Hudspeth County is half way to Los Angeles.
Fort Hancock is about 75 miles southeast of El Paso. That is not quite half way to LA, but it is an awfully long distance upriver from the coast.
It will be interesting to see whether they can survive. As one poster said, some stretches of the Rio Grande are nearly dry for much of the year. I am not acquainted with that particular stretch of the river, so I do not know how much water is to be found there. For that matter, I am not sure how much water alligators need.