Yucca brevifolia--commonly known as a Joshua Tree--is one of the more recognizable of the Mojave Desert plant species. The Joshua Tree is "endemic" to the Mojave Desert, meaning it is a unique species found only in this geographic region.

Gopherus agassizii, or the desert tortoise, is an endangered species found in southeastern desert regions of the United States and down into Mexico.

Transmitters affixed to a tortoise's carapace (top portion of the shell) allow biologists to locate the animal using a receiver tuned in to the transmitter's radio frequency. The transmitter is glued onto the carapace in such a way that it does not interfere with growth and expansion of the shell, so it does not hurt the animal.

Males like this one have what is called a "gular horn," a projection on the plastron (the bottom of the shell) that is usually enlarged and used when competing with other males for a mate.

When desert tortoises are translocated from one area to another, they are placed inside plastic containers not only for the safety of the animal but also for ease of the handler. The notable size difference between the two sexes can be seen with the larger male on the left and the smaller female on the right.

Because rain is such a rare commodity in desert climates, animals that live in these environments have various physiological and behavioral adaptations to conserve water and utilize water when it becomes available. Tortoises excavate depressions in the ground for the purpose of collecting water during a rain event so that they can later gather at their impromptu watering hole.

The moon rising over the desert in the late afternoon.

While all the plants in the desert are beautifully adapted to survive in a seemingly harsh environment, they can be problematic to a person not paying attention to their own footsteps. A lesson quickly learned! This is Echinocactus polycephalus, a cottontop cacus.

View from atop a hill of bubbly rocks.

Two males gathered on the ridge, although it is hard to say what, if any, interaction they had before or after I left. Transmitters are placed on the back of the carapace (posterior) of males so as not to interfere should two males engage in aggressive behavior. With females, the transmitter is placed towards the front of the carapace (anterior), near the head.

Face to face with a large male.

Tortoises can raise their internal body temperatures by basking in the sun, stretching their neck and limbs so that the maximum surface area of their skin is exposed to the sun. This tortoise was basking when I approached it, but he became more alert as I got closer.

One of the many beautiful Mojave sunsets we were able to enjoy while camping in the desert.

Although it is always unfortunate to come across a tortoise carcass, it is interesting to see the internal structure of these amazing animals. A tortoise's shell is made up of both bone (the white) and overlying scutes that contain keratin, the same material found in our fingernails. The scutes overlap the bony elements underneath to provide strong support for the shell. Only a few scutes are left on this carcass.

The hollowed out shell of a tortoise carcass. Tortoises generally don't have to worry about predators, but both ravens and coyotes will prey on them when food is scarce. It does not take long for a carcass to be cleaned out like this one.

Desert tortoises can retract their heads and limbs completely into their shells when they feel threatened.

A male tortoise at the mouth of his burrow. Underground burrows can be as long as 30 feet and can even have multiple openings to house more than one animal.

Stopping for tarantula crossings while driving through the desert was a pretty common occurrence.

Surveying for tortoises basically involves systematically hiking through the desert looking for animals that have not been tagged and transmitted. Sometimes the tortoises are out in the open and easy to spot, but other times they are inside burrows and can only be detected and coaxed out with a long probe. I found this tortoise a few yards away from its burrow, and a permitted handler began the process of affixing the temporary transmitter.

The temporary transmitter is simply taped to the animal until someone can come back the next day and attach a permanent one.

Another beautiful desert view seen while surveying for tortoises.

Although people may have a difficult time finding relief in the desert sun, tortoises find adequate cover under bushes, inside burrows, or in this case, in the shade of a Joshua tree.

Tortoises are curious animals and can often be coaxed out of their burrows simply by scratching in the dirt or rubbing two rocks together near the burrow entrance. This tortoise, an older female, almost always rushed out to greet me when I came near her burrow.

A very young tortoise tucked away in a burrow with an entrance only as wide as the front of my hiking boot.

This little animal with a big attitude is a type of darkling beetle. It is sometimes called a desert skunk beetle because it will raise its rear abdomen into the air when it feels threatened and can even emit a foul odor if so inclined.