None of the dead kittens appeared to be more than two months old, they said.
Seaside police and the Society for the Prevention of Cruelty to Animals for Monterey County discovered the animals on Tuesday, SPCA Sgt. Stacy Sanders said.
Officers were alerted by a property manager who discovered dead kittens during an inspection. They received another tip that more cats were moved to a nearby house.
There, another group of investigators found 51 adult cats that were alive but sick and neglected.
"The cats were living in extremely horrible conditions," Sanders said. "They were separated into two groups and locked into rooms with little to no ventilation. The floors were saturated in urine and feces."
Officers stayed about six hours to recover all the cats because an occupant in the house had lost count of how many were there.
"We had to go through every nook and cranny, pull apart every bed and chair," Sanders said.
SPCA staff members treated the surviving cats, which were in stable condition. SPCA spokeswoman Beth Brookhouser said most of those animals had respiratory infections, parasites and broken teeth. Two underwent emergency surgery for potentially life-threatening uterus infections. At least five were pregnant.
"It definitely makes you go home and kind of hug your animals a little tighter at night," said Sanders, who has a dog and a cat.
No arrests were made or citations issued, but the SPCA has referred the case to the Monterey County district attorney's office to consider criminal animal abuse charges. They declined to identify the suspected hoarder while the investigation is ongoing.
Sanders said authorities received tips the cats may have taken from the street. The officers are asking community members to send in photos of their missing cats.
"I hate to see any of these hoarding cases," Brookhouser said. "They are all tragic in their own ways, but for me personally, this is the first time with so many deceased cats."