After our visit to Casa Grande Ruins National Monument, we headed a bit further south to Tucson. Our goal here was to visit the Saguaro National Park. While here, we started learning a lot about the Sonoran Desert. It was pretty interesting to discover. Some of what we learned related to the places we visited earlier in the year. And we found that the next stop, Organ Pipe Cactus National Monument was also in the Sonoran Desert.
This post will be divided into 3 parts, first the dirt on deserts (Sonoran included), then the Saguaro National Park and finally, the Organ Pipe Cactus National Monument.
First, some background on deserts in general on the North American continent. There are four distinct desert biomes on the North American continent. The furthest north is the Great Basin Desert. This is a cold desert and covers parts of Utah, Idaho, Oregon, Nevada, California, Colorado, and Arizona. By that list of states, you can see that it is a large area of about 158,000 square miles. The precipitation mainly comes in the form of snow in the winter. The amount of water from the snow averages 7-12 inches a year. Temperatures can be hot in summer, and very cold in winter. It is a rain-shadow desert, meaning that the mountains block the moisture. The plant community is dominated by sagebrush with some prickly pear braving the cold. Mule deer and pronghorn antelopes are represented along with mountain lions, coyotes, foxes, desert bighorn sheep, ringtail cats, beavers, and porcupines.
The Mojave Desert is the smallest and is found in eastern California, southern Nevada, and western Arizona. It only covers 25,000 square miles and includes Death Valley. The desert has a wide variety of elevations which brings a certain level of plant/animal diversity. The northern parts are more like the Great Basin with sagebrush. The southern areas have lots of creosote bushes and cholla cacti. There are several varieties of yucca growing here, the most unique being the Joshua Tree. A beautiful feature is the explosion of spring annuals. This desert has the highest amount of flowering annuals and the least amount of moisture with only 2-6 inches a year.
The Chihuahuan Desert is the largest North American desert at 175,000 square miles, but most of it is in Mexico. The northern edges hit western Texas, southern New Mexico and south-eastern Arizona. It, too, has several varieties of yucca, but no Joshua Trees. The rainfall comes from the Gulf of Mexico, and since there are no mountains to block it, there is more water than in the Great Basin Desert, about 8-15 inches. Most of the Chihuahuan Desert sits at 4,000 feet above sea level. Temps are cooler with freezing nights in the winter which limits the type of cacti growing here. The extra water allows for more grasses and agaves. Small cacti are here, but not the larger ones found in the Sonoran.
The Sonoran Desert
Finally, the Sonoran Desert covers most of Arizona, a part of south-eastern California, Nevada, Baja California, and the Sonoran state of Mexico. The size is about 120,000 square miles. It is considered a “wet” desert because it has two rainy seasons. Rains in the summer are brief, violent storms while the winter rains are long, gentle showers. This extra bit of moisture allows for an extreme amount of diversity for a desert. In fact, it is one of the most diverse deserts in the world with about 560 plant species, 261 bird species, 58 species of reptiles, 12 species of amphibians, and 60 species of mammals.
A small population of jaguars, the only ones in the United States, are located here. An endangered sub-species of pronghorn, the Sonoran Pronghorn is holding on here as well. Other mammals include the desert bighorn sheep, kangaroo rat, nine species of bats, javelinas, cottontail rabbits, jackrabbits, mountain lions, wolves, foxes, coyotes, and mule deer.
Plants include creosote bushes, mesquite, palo verde, pinion pine, ponderosa pine, ironwood trees, desert willow, ocotillo, acacia, jojoba, and, of course, cacti. The iconic Saguaro and Organ Pipe cactus are well known, but also several types of cholla, hedgehog, fishhook, prickly pear, and night blooming cereus grow abundantly here.
We found Ocotillo bushes to be very interesting. They look like a bunch of sticks until rain comes. Then they suddenly sprout thousands of tiny leaves which only hang around for a few weeks then they appear to go dormant and back to looking like sticks. They can actually leaf out two or three times a year.
Cholla cacti are extremely unfriendly. Definitely watch yourself around them. They are opportunists and will detach sections way too easily in order to catch a ride. The thorns are barbed, so they go in easily, but coming out is another matter. The Smithsonian was doing some research on the structure of the cholla needle, and a single needle could hold onto a half pound weight without pulling out. Here is a link to that research report: Researchers Stabbed Slabs of Meat With Cacti Spines to Learn About Puncture Strength
Arizona is pretty special in that it is the only state with a little bit of all four deserts in its boundaries. We think that the Sonoran is the prettiest of the deserts.
Saguaro National Park
The Saguaro is a very slow growing cactus. Incredibly, they only grow an inch or two their first 6 years. It will take 50 years before the arms start to grow. You would think as big as they are, they are tops in the plant chain. But we found out while visiting the park, the first 50 years or so is a vulnerable time for the cactus. Not many make it to that age. In order to make it to old age, they have to start growing in the shade of a nurse tree like palo verde, mesquite, or creosote. The nurse tree provides shade and protection from wind. But these saguaros do not treat their nurses kindly as they age. Oh, no, once they get big enough, they steal all the water and end up killing the nurse tree.
We also found it interesting that the cacti have wood ribs supporting their form. The Saguaro needs this framework as the oldest ones can weigh a ton or more. Most of the large cacti have some form of a wooden framework hidden inside their fleshy, prickly outside. Now when we see something called a “cactus forest,” we know why.
The fruit of cacti are very important to a multitude of critters, people included. They are rich in vitamin c and contain thousands of tiny seeds. They supposedly taste very good. We were tempted to try some, but refrained.
While reading about the park and its cacti, we learned about a deformation called crestate, or crested, that happens to several types of cacti. No one exactly knows why it happens, but it creates a fan shape instead of the usual columnar form. The cactus has growth cells at the tip of the column which normally grow in a circle to create the columnar form. The crested version happens because the growth cells form a straight line instead of a circle. We were able to find one which was pretty cool.
This was a wonderful place to take in the variety of plants and animals. Here are some more images of the Saguaro NP.
Organ Pipe Cactus National Monument
This park is on the border of Mexico so it was a little daunting to go there with all the warnings about illegal activity. But really, it was no big deal other than the border patrol check points you have to go through.
The namesake cactus here is the Organ Pipe cactus. The native O’Odham people called the cactus chuhuis. It, too, is slow growing and takes about 20 years to reach 3 feet tall. They are similar to the Saguaro in their life cycle except not needing nurse trees. They crave warmth and sun, so they tough it out a bit more.
The Organ Pipe only grows in this area of the Sonoran Desert in the U.S. because it is very vulnerable to freezing. This part of the desert generally stays above freezing during the winter. Climate change is beginning to threaten this cactus. Drought is happening more often and the temps are dropping below freezing more in the winter. Time will tell if the Organ Pipe can adapt.
We were lucky to find another crestate Saguaro on our trip to this park. It was exciting to find it ourselves without being told by a ranger to go look there.
It was an interesting, informative month. It was really inspiring to see the beauty here. We will definitely be coming back some day to explore these parks further.