Masticophis bilineatus. I caught this one by the tail but it was not happy about it, trying to bite me as I tried to get a grip on its head. It got too tangled in a small Palo Verde tree so I decided to let go, after which it proceeded to go up into the branches of a much larger Palo Verde. It settled up in the branches about 12 feet from the ground. Luckily there was a hill with easy access that allowed for a view from above the snake. This is about the cleanest shot I could get. This one was about 4 feet long, and we actually saw another one (much smaller) farther down the canyon, but it was moving too fast to get a photo. These snakes are just about as fast as Coachwhips and Racers.