This is a very unusual saguaro cactus. It has at least 44 visible arms on this side. A saguaro has to be at least 50 to 75 years old before it sprouts any arms at all. According to the Arizona-Desert Museum, these cacti can have as many as fifty arms but that is not very common. I sent this image to Judy Hedding of about.com and she posted these comments:

http://phoenix.about.com/od/desertplantsandflowers/ss/how-many-arms-on-a-saguaro.htm