The Marieta Islands were originally formed many thousands of years ago by volcanic activity, and are completely uninhabited. The islands are about an hour long boat ride west-northwest from the coast of Puerto Vallarta and are visited daily by hundreds of tourists, yet no one can legally set foot on the islands. In the early 1900s the Mexican government began conducting military testing on the islands because no one lived there.
Many bombings and large explosions took place on the islands causing amazing caves and rock formations to be created. After a massive international outcry, started by scientist Jacques Cousteau in the late 1960s, the government eventually decided to label the islands a national park and therefore protected against any fishing, hunting or human activity.