Pasadena Humane said the animals were living in cramped and unsanitary conditions inside a trailer with no air conditioning.
The cats were sent back to the shelter where they received medical exams, officials said. They're now under the supervision of a veterinarian.
Some of the cats were showing symptoms of upper respiratory but are overall in stable condition. The healthy cats are all now up for adoption.
The cats will be spayed/neutered, vaccinated and microchipped before they're released to their new home, Pasadena Humane said.
Adoptions are available by appointment and can be made on the shelter's website.