Vertical cracks running up and down between the ribs of a saguaro cactus, such as is seen in this photo, are sure signs of over watering. The central spongy core is the location within the plant where water is stored for future use. The hard wooden ribs that give strength to the plant are just under the spine covered ridges. The soft tissue in the "valley" between the ribs allows the plant to expand and contract as stored water levels increase or decrease depending upon plant water use and drought conditions. It is possible for the plant to absorb more water than it can hold. When this happens, the tissue in the valley can crack and pop open like an over ripe watermelon. In southern Arizona, rainfall alone rarely will cause this problem. If you have a saguaro with this kind of damage, look around and see if you can find the source where the saguaro is getting water. Then, you will need to help it get back on a proper water budget. Keep in mind that the saguaro can send out roots for some distance. The actual source of water may be several yards away. In this case, the definition of yard means your yard, your neighbor's yard, and maybe even the neighbor's yard beyond that.