Most of the snakes my BIL kills are babies that he runs into at night that are catching the last bit of warmth on the road (no rattling). He lives in the foothills in Tucson and sees quite a few of them - like several a week. He worries about his dogs and kids getting bitten although the kids are old enough now and the dogs get rattlesnake training every year.
I've also seen a few in the Tucson area when mountain biking. They like to sun themselves in the middle of the paths in the mornings. I just bunnyhop over them most of the time. In general, they can only strike up to 1/3 of their body length when coiled and if the are not coiled they can only strike a very short area.
I live up in Sedona and have only seen one or two in 5 years. When it's cool (< 80 deg) they like the sun and are easy to spot. When it's warmer, they like the shade and hide out in rock piles or at the base of shrubs. As was said, they are lazy in the mornings until things warm up.
Tim, Tara and Canyon - 'TnT' (& C now...)
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