Rattlesnakes are the only type of venomous snake found in the Santa Clara Valley. You are most likely to spot one on a hot day when they may be sunbathing on a trail or exposed rock. They have triangular heads and chunky olive or tan striped bodies. Their tails have a set of rattles at the end, made of keratin, the same material found in your fingernails. Snakes vibrate the rattles when alarmed and may also hiss. Be warned: Rattlesnake venom is highly toxic. Rattlesnakes eat a variety of small mammals, lizards, and birds. They hibernate during the winter.