well when i lived in california i was in the antelope valley in los angeles county. i grew up in leona valley and we had more rattlers (western diamondbacks i believe) then anything else really but i did get 1 opportunity to rescue/re-release a common kingsnake from our dog.
ya gotta look up the specific snake/animal you want to see and try to find out it's natural habitat and go there.
for example the mojave desert should have a ton of mojave rattlers, just DO NOT let one bite youcuz they're supposed to be the deadliest of the rattlers.
typically early evening when it's cool is a good time to go herping for reptiles like snakes cuz that's when they'll be out when the sun is not beating down.
also snakes such as rattlers like to hole up underneath things like piles of wood, large rocks, large, very thick bushes, etc.