Christopher Keller, a reader of Botany Photo of the Day, asked me if we could honour this particular saguaro cactus, “The Grand One” with an entry (for an idea of its height, note the person standing near the trunk). “The Grand One”, sad to say, may not survive recent fires north of Phoenix, Arizona.
Seekers of champion saguaro cacti, including Joe Pleggenkuhle, believe that the combination of height (46 feet / 14m), girth (94 inches / 2.4m) and crown width (12 feet x 12 feet / 3.7m x 3.7m) make this the largest saguaro in Arizona, if not the world.
To read more about Carnegiea gigantea, see: the life cycle of the saguaro cactus or a guide to the saguaro (PDF), both from the US National Park Service. The Wikipedia entry on saguaro also features a decent set of images.