I've done a fair bit of hiking/camping/fishing/hunting in the Sierras and I carried several different handguns over the years so I have some opinions based on experience.
My biggest recommendation is to choose the lightest weight gun that you would feel comfortable with. There has been many times when I dreaded the feeling of the heavy revolver on my hip. It gets hot up there and you feel every ounce of gear on your body. So weight is my first consideration.
Chances of having to use the gun are very small.
Defense against snakes is not a consideration IMO. If you have time to draw on a snake you have time to avoid it.
Bears, well you never know but what ever pistol you are carrying is too small anyway so in reality having a gun might make you feel good but hats it. So feel good that you at least have a gun!
Mountain lions, I don't know much as I've never killed one but I feel completely confident that it would approach me from the front, we'd face off like two dueling cowboys and I of course would draw first and nail it between the eyes. Well not exactly but I think you get the picture!
Now that I've owned and carried several types I prefer polymer framed semi autos over revolvers. Mostly due to lighter weight and increased capacity...iow I feel they are more efficient.
The lightest gun I ever carried in the woods was a S&W 642. It wasn't fun to shoot so I sold it. the heaviest gun I ever carried was a 6" 686. Sold it because it was way heavy. I carried it for several trips before realizing it was more of a burden than anything else.
These days I'll carry a Ruger LC9 or the heaviest is a polymer framed SP01 CZ Phantom.
If you are used to revolvers I suggest a pistol without anything extra to think about. Something like a glock is dead simple...squeeze the trigger thats it, no manual safety to fumble with and the trigger pull is the same every time.
Like some others suggested, the compact glocks in 45 acp are real efficient little packages that pack a lot of punch.