Animal control officers discovered the dead animals Wednesday at the Lake Elsinore reptile-breeding business Global Captive Breeders, the Los Angeles Times reported.
"Our primary focus at this point is to ensure the health and well-being of the animals on the site," said Willa Bagwell, executive director of Animal Friends of the Valley, which volunteered to remove the carcasses from the business.
Global Captive Breeders, which has been in operation since 2009, came under investigation after the animal rights group People for the Ethical Treatment of Animals made a complaint against the company on Dec. 7, the Riverside (Calif.) Press Enterprise reported.
City officials inspected the business and found more than 700 dead rodents and reptiles, as well as filth and other problems.
Animal control officials estimated there are 6,000 to 10,000 living rats inside.
No arrests have been reported.