Situated in the middle of the group, Santa Cruz is a shield volcano with an area of 986 km2 (381 sq mi) and a maximum altitude of 864 m (2,835 ft).

The most recent eruptions may have occurred only a few thousand years ago with the effusion of sparsely vegetated lava flows from vents on the north flank and along the summit fissure.

As a testimony to its volcanic history there are two big holes formed by the collapse of a magma chamber known as "The Twins" (Los Gemelos).

[10][11] Tortuga Bay is located on the Santa Cruz Island near Puerto Ayora where fauna such as marine iguanas, birds, Galapagos crabs can be seen.

[12] Santa Cruz hosts the largest human population in the archipelago at the town of Puerto Ayora, with a total of 18,000 residents on the island.