I also ride trail these days... I competed in Arab and jumping circles earlier, and now I just like the quiet of trail, and sometimes a respectful imitation of a little dressage.
It's cool that you have access to horses to ride while you get yourself ready to get back into it.
I can't believe you can be that active outside in Phoenix... I am up in Washington State, and not very heat tolerant. I spent a few summers in Phoenix as a teenager... working for my Grandpa... and it's so hot there I thought I'd die just trying to move from the shade to the swimming pool. ;~D I can't imagine riding a sweaty animal in that kind of heat.
I don't ride in the heat, Hair. It's just miserable and I'm not heat tolerant, either. If I just have to work outside on a hot day I keep hosing myself down every few minutes. That's the only possible way I can do it. My barn is ok as long as I'm just sitting in a chair drinking a cold coke and have a fan on me.
It's only hot here in Phoenix three months out of the year, the rest of the time it is wonderful. Special care to keep the horses cool during the summer months though.