Footwear and hiking: What the hell should I be wearing out on the trails?

I've always walked in trail runners but I want to do some hiking in southern AZ soon and we'll be poking around in the desert andchirachuas. I imagine rattlesnakes must be so thick down thee it looks like the road is moving at night as they slither across it. Do people wear some kind of heavy leather boots when hiking or? I'd really like to survive.