Laws' guide to the Sierra Nevada starts with fungi, goes through plants, all kinds of animals, and ends with the starry sky. The Sierras start down near Mexico in California and run about 500 miles up to Lassen, with peaks reaching the 14,500 feet of Mt. Whitney, the highest mountain in the US south of Alaska. Though they are so far south, there was lots of snow in the upper regions, and enough at 6,000 feet that I could keep my food cool using snow.
I am a snake phobic, sorry to report, so the fact that everyone said there were rattlesnakes on all the trails kept me very alert! I never did see one and was disappointed in the end, but I did see plenty of other reptiles-mostly western fence lizards but also the Sierra Alligator Lizard, Rubber Boa (an odd duck of a snake) and two big Pacific Gopher Snakes. Of course every one of these had to be checked for rattlesnake-ness! People say that they are very laid back, rattle if you get too close and really don't want to have to bite you, but they wouldn't like being stepped on.
I was impressed with how the National Park Service managed people, and there were probably thousands of them every night in the Yosemite Valley, in many kinds of lodging as well as campgrounds. By providing big steel bear-proof boxes at every campsite, and constantly nagging people to use them, the Service has about defeated the all too intelligent bears. As the bears had learned to jump on car roofs to pop open the windows, people are forbidden from leaving even toothpaste in cars. Mother bears have been known to send their cubs into the cars to retrieve food when they themselves were too fat to fit. They still do occasionally go from box to box slapping at the doors to find ones that bounce open because they are not locked properly! But I saw only two bears, moving peacefully through the forest.