According to The Devil’s Highway, what factors pushed Wellton 26 into the most inhospitable parts of the US-Mexico border (the harsh Sonoran Desert)? Please think about border control policies and physical geography.

According to the book The Devil’s Highway, the desert’s geography is inhospitable. The sun is scathing hot, and the main cause of human deaths is hyperthermia. The wildlife is mainly nocturnal and consists of all kinds of poisonous things, such as rattlesnakes, scorpions, tarantulas, and coral snakes. There are also few watering holes for travelers, who resort to drinking their own urine for survival.
People brave the difficulties in the desert in order to avoid arrests by the Border Patrol. The San Diego Border Patrol has big floodlights with surveillance trucks at half-mile checkpoints along the border fence. Other entry points into the United States have been closed off. For example, the western barrier is cordoned off by armed feds who work in the state park. Thus, walkers and coyotes prefer to cross into the United States by walking through the desert instead of jumping over the border fences. The Wellton 26 walked the desert as they fled their Mexican homes. There were economic hardships back home, which were brought about by the falling prices of income-generating commodities (like coffee) and rising living costs. This and other sociopolitical problems encouraged more immigration into the United States. According to Don Moi, a recruiter for the coyotes, it was less expensive to get into the United States by walking the desert rather than driving into it. The coyotes that handled the Wellton 26 walked them into the desert and abandoned them there.

The Devil's Highway is a journalistic account of illegal immigration from Mexico into the United States. It focuses on the Wellton 26, a group that was attempting to cross the border in May 2001, led by Jesus Antonio Lopez Ramos, an inexperienced young coyote who seemed either ignorant of desert survival techniques or not particularly concerned about the safety of his clients. 
They had planned to cross the border and arrive at the town of Ajo, Arizona. Ramos's plan had them walking at night to avoid the heat, something that made it difficult to navigate, especially without appropriate navigational tools such as a contour map, altimeter, and compass. Their route was planned to follow the foothills of the Growler Mountains, as temperatures are lower at high elevations. 
The first problem with their plan was that it is very difficult to navigate or walk in the desert at night. Not only are you likely to brush against chollas (a type of cactus with long and very unpleasant spines), but navigation is also quite difficult. You cannot walk in a straight line across the desert, but instead must follow paths along washes or animal trails to avoid the vegetation (most of which has sharp spines); this means following a very indirect course. To avoid getting hopelessly lost, you need good navigational tools. A better choice would be walking in early evening (5 - 8 pm) and the morning (about 4 - 11 am), where you have milder temperatures than midday but still good light. Thus, the first problem they had in navigating was their choice to walk in the dark; they also had to stay off established roads and trails to avoid being caught.
The next problem was that at 11:30 pm they saw lights in the pass which would have led them in the right direction, but, afraid that the lights belonged to the border control, decided to seek another route. They headed northwest, leading them to lower elevations. The next morning, Ramos, probably suffering from heat exhaustion, led them far off course, heading south rather than north.