However, get medical help right away if you notice any symptoms of a serious allergic reaction, including: rash, itching/swelling (especially of the face/tongue/throat), severe dizziness, trouble breathing, kidney problems (such as change in the amount of urine). This is not a complete list of possible side effects.
They are more active when it is cooler, but they can and do come out of hiding at any time of the day. Here in the desert, Arizona Rattlesnakes can easily overheat and die if they cannot find a cool place to keep themselves cool.
April 10 2015 RPM Reports: Found this on a sunset jeep ride in the canyons of Sedona AZ on April 9. As the sun started setting more and more of them became visible in the desert terrain, but don't know what they are.