Saguaro National Park has been described as a "Wilderness with a City at its Center."
So, our search for color shifted from vistas to small areas of interest. The Rincon Mountains provided the background for this prickly pear cactus and
"On cholla cacti (left and below), which are often called jumping cactus, the spines also play a major role in reproduction. Cholla are segmented cacti. The plants are made up of many segments, which are loosely attached to the preceding segment. Additionally, each spine is covered with a thin sheath, which separates from the spine quite easily. When an animal accidentally brushes against the cactus, the sharp spines stick into its skin and the segment breaks off the parent plant. Eventually, the spines slip from their sheaths and the segment falls to the ground. If soil conditions are right, the segment may take root and grow into a new plant (nps.gov/sagu/planyourvisit/upload/Cacti%20of%20Saguaro%20National%20Park).
The relationship between the saguaro and "nurse plants" was very interesting. Seeds of the saguaro are eaten by a rodent under a palo verde or mesquite tree (for protection from predators). The seeds of the saguaro fruit must go through the digestive tract of an animal to break down the outer coating of the seed in order for germination to be possible. When the rodent later expels the seed, usually in the same area, and conditions such as temperature and rainfall are right, the seed can then begin the process of forming a living plant.
Unfortunately for the nurse plant, as the saguaro grows larger, it needs more and more water and nutrients, and over the decades the nurse plant does not get enough water to live.