Back in the mid-1970s, there was a "huge" black cat reported on the Concord Naval Weapons Depot in Concord, CA. A Marine guard reportedly shot a couple of rounds at it but it ran off.
Then more reports. I tracked one sighting down to a house in Pine Canyon, behind Walnut Creek at the base of Mount Diablo, a few miles south of the Weapons Depot. The guy said about midnight his 2 shepherds started barking after they heard a loud THUMP on the patio roof. He let them out and they immediately came ki-yiing back into the house with their tails between their legs. He went outside and shined his flashlight onto a big black cat standing by his barn. "It was bigger than my shepherds."
When the light hit the cat at an angle, he said he could see spots in the black fur. Also a big long fat tail that curved down to the ground, huge head, yellow eyes … a fine description of a black (melanistic) African leopard.
This was also back in the days when it was legal to have exotic cats in Calif., and I knew people who had tigers, leopards, African lions, etc. for pets. I’d previously known of an African lion and an ocelot that had escaped from their cages.
I went out to the house in Pine Canyon and found tracks and made plaster casts of a large cat paw print about 7-8 inches across.
Eventually started getting reports from ranchers in Bollinger Canyon behind Danville (5-6 miles further south from Pine Canyon) about a big black cat. I had a friend who lived out there with some cattle, who saw the black cat regularly. They all thought it was neat and it never seemed to bother their horses or cattle, so they didn’t care. A park ranger found a deer carcass stuffed in the crotch of a tree. Mountain lions don’t do that. Leopards do.
For the next 5-6 years I’d get regular reports from Rossmoor residents who saw a black cat while on their early morning walks. (The Rossmoor retirement community in south Walnut Creek backs up to one end of Bollinger Canyon.)
The black cat sighting reports stopped around 1981-82 and I figured the animal had died.
I also did considerable research during that period and found no one had ever found a melanistic mountain lion in North or South America.