The United States hasn't always had a great relationship with Mexico, but in 1970 things were pretty congenial. Then, in July, an Athena rocket went off course with vials of radioactive material. Some say the resulting impact created the "Mapimi Silent Zone."
In 1947, a V-2 rocket, launched into the air by the United States, went off course and ended up bombing a patch of ground outside of Juarez. The Mexicans were very good-natured about it, probably because they assumed it wouldn't happen again.
It happened again. Granted it took twenty-three years to happen again, but accidental bombings aren't good, even if they only happen four times a century. In 1970, researchers in Utah testing an Athena rocket were alarmed to see it suddenly go off course and start zooming towards a foreign country. Just to add spice to the potential international incident, the rocket was carrying vials of radioactive cobalt. It took a lot of covert searching but the military eventually found the rocket in the Mapimi Desert, in northern Mexico. It had landed about forty miles outside of the town of San Ignacio. The US military trundled down, built a road out of the desert, and along with the rocket took out tons of contaminated top soil.
Again, the Mexican government was extremely understanding, but locally rumors spread about the area where the rocket crashed down. It's now known as the "Mapimi Silent Zone." Supposedly areas of silence "drift" across the desert, taking out radios and even silencing conversations between two people standing next to each other. Because the zones are mobile, it's impossible to test. This lack of testability may be fortunate for those who claim that the desert has become a hub for UFO activity and other strange phenomena.
[Source: Mapimi Silent Zone]