The islands were formed during the Cretaceous era by volcanic activity that created ragged formations, ideal places to shelter life.
The Marietas are an important area for nesting, refuge, reproduction and migration of at least 92 species of aquatic and sub-aquatic birds, native and migratory. This beautiful place shelters the biggest colony and breeding ground in Mexico for the white-capped marine swallow (Anöus stolidus) and the band-tailed swallow (Sterna anaethetus).