The ‘experts’ don’t know exactly how many mountain lions are in California but they can make a decent guesstimate. That is the truth of it and I don’t like to see websites, sometimes ostensibly authoritative websites, simply copying what other websites state and presenting it as the gospel truth. The numbers in the spreadsheet below are the best estimates and perhaps the most accurate number is 3,145 by a website – Mountainlion.org – which calculates the population size of the mountain lion in California by referring to the density of mountain lions per 100 km² and dividing that into the number of square kilometres of the state. They state that there is a general consensus that there are 1.7 pumas per 100 square kilometers in California.
The important point to note is that you cannot wholly rely on the numbers because they are estimates and it is difficult to count wild cat numbers of any species. The same problem exists with tigers in India. They are always estimates. The way you count pumas and other wild cat species is to analyse scats and camera trap captured images. As you can imagine this is not going to be super accurate.
It is notable as you can see in the spreadsheet that Wikipedia and IUCN Red List don’t have the confidence to provide a number which they think is the population size of the mountain lion in California or anywhere else for that matter.
One of the big problems with conservation of the puma in California is that their habitat is broken up by human constructions, usually roads. A fragmented distribution causes inbreeding as the smaller parcels of land cannot sustain decent-sized population numbers. This leads to smaller groups and as a consequence inbreeding leading to health issues including sterile males. This leads to a declining population. It is self-serving. One example of a way to ease this problem in California is a green bridge for pumas traversing California’s Freeway 101 which will be world’s biggest.
Below are some more articles on the mountain lion.