Yosemite has over a dozen species of slithering snakes, but don't worry. Only the western (diamondback) rattlesnake is venomous. The park's other snakes are harmless, although some visitors mistake the orange, black and white stripes of the mountain king snake for a venomous coral snake, which it is not. Garter snakes and rubber boas are also common in the park.
Park visitors may stumble upon rattlers curled up alongside hiking trails or moving through the forest's dry underbrush. Always be careful where you step and look before your put your hands or feet anywhere that you can't see (e.g., inside your hiking boots at night in your campsite). If you encounter a rattler, give it a wide berth and it should leave you alone. Most bites occur when visitors tease the snakes or attempt to pick them up.
Also hanging out alongside Yosemite's hiking trails are eight different kinds of lizards. The most commonly seen is the western fence lizard. It often basks in the sun atop granite rocks and does little "push-ups" with its front legs, displaying the strikingly bright blue markings on its belly and underneath its throat (if the lizard is male, that is).
Yosemite is home to only one species of turtle, the western pond turtle. These slow-moving reptiles inhabit calm ponds, lakes and streams at lower elevations, mostly on the park's west side. Your best chance of spying one is when the turtle basks in the sun atop a river rock or a fallen tree snag.