Pigeon with broken leg, what should I do?

I live in vegas, where the average heat right now is 108. There is a bird with a broken leg/foot behind a bush, making a high pitched crying noise. He can't walk or fly, and has been there for like 3 days. I've given it bread and a dish of water, but it won't move. What should I do? What are it's chances of survival? What should I do? I have nosey dogs, and put one of those baby fences to protect it, but other than that, what should I do? I haven't touched it and won't touch it unless I absolutely have to. Help this poor bird!!!!