We live north of Tucson but the snake of concern, you are most likely to encounter is the western Diamondback and they are found throughout the southwest. While most of them are denned up for the winter the Official Snake season here is January first through December 31st. Any sunny day can bring them out.
We see the most activity in the spring following the first week or so of 80 degree days. At this point they emerge, hungry and horny seeking meals and mates and can be very aggressive. In the spring if you see one chances are there is another close by. The best advice year round, is simply to never put your hands or feet where you cannot see. Don't step over a log, low wall or reach where up to or into any area that is not clearly visible. Avoid tall grass and heavy brush as that is where they will often be found. Sticking to the trails and paying attention are your best defense.
If someone is bitten transport them immediately to a the nearest medical facility while treating for shock as necessary. Do not use a tourniquet, make cuts to the wound, apply ice etc..
:C