Cacti are a non-issue, unless you are planning on riding through one. Here in NM the big problem is goatheads. You will need some sort of extra-thick tire or slime or some such. I have had good luck with both, and currently use both. Heavy, but I only get one or two flats a year. As to the temps, right now we are running 50's at night at 70's during the day. You shouldn't find freezing temps until you are above 6000 feet or so, at least until the end of the month. Below 5000 feet it won't freeze much at all, at least until after the new year. Unfortunately there isn't much of a way to cross the state without crossing some mts. I don't know much about any other states, but if you want some specific info about NM let me know.