[4] Isabela and nearby Fernandina Island—honoring Isabella's husband Ferdinand II of Aragon—also preserve the names bestowed on the third and fourth islands encountered by Columbus during his voyage.

At approximately 1 million years old, the seahorse-shaped island was formed by the merger of six shield volcanoes; Alcedo, Cerro Azul, Darwin,[11] Ecuador, Sierra Negra, and Wolf.

The island is primarily noted for its geology, providing excellent examples of a geologic occurrence that created the Galápagos Islands including uplifts at Urbina Bay[12] and the Bolivar Channel,[13] tuff cones at Tagus Cove, and Pulmace on Alcedo and Sierra Negra, one of the most active volcanoes in the world.

The relatively new lava fields and surrounding soils have not developed the sufficient nutrients required to support the varied life zones found on other islands.

Another obvious difference occurs on Volcan Wolf and Cerro Azul; these volcanoes loft above the cloud cover and are arid on top.

Today, tortoises roam free in the calderas of Alcedo, Wolf, Cerro Azul, Darwin,[11] and Sierra Negra.