Its Spanish name "San Cristóbal" comes from the patron saint of seafarers, St. Christopher. English speakers increasingly use that name in preference to the traditional English name of Chatham Island, derived from William Pitt, 1st Earl of Chatham.
San Cristobal Island is composed of three or four fused volcanoes, all extinct. It is home to the oldest permanent settlement of the islands and is the island where Darwin first went ashore in 1835. A small lake called El Junco is the only source of fresh water in the islands. The availability of fresh water is what led to the early settlement of San Cristobal. A penal colony was built on San Cristóbal Island in 1880 for prisoners from mainland Ecuador. This later turned into a military base for Ecuador and export center for the island's products including sugar, coffee, cassava, cattle, fish and lime.
San Cristóbal has an area of 558 km2 (215 sq mi) and its highest point rises to 730 metres (2,400 ft). The population is approximately 6000. San Cristóbal is the most fertile island of the archipelago and is the second most populated after Santa Cruz. The capital of the archipelago, Puerto Baquerizo Moreno, lies at the south-western tip of the island.
The island is served by San Cristóbal Airport, with daily flights from Quito and Guayaquil.
This island hosts frigatebirds, Galápagos sea lions, Galápagos tortoises, blue and red footed boobies, tropicbirds, marine iguanas, dolphins and swallow-tailed gulls. Its vegetation includes Calandrinia galapagosa, Lecocarpus darwinii, trees such as Lignum vitae, Matazarna. In the waters nearby are sharks, rays, and lobsters.
The largest fresh water lake in the archipelago, Laguna El Junco, is located in a crater in the highlands of San Cristóbal, in the southern half of the island. The lake harbors a large population of birdlife, but reaching the lake requires a short uphill walk. Nearby, La Galapaguera is a breeding station and sanctuary for giant tortoises.
The majority of inhabitants make their living in government, tourism, and artisanal fishing. Also the majority of the residents of San Cristóbal live in the port city of Puerto Baquerizo Moreno, which is the capital of the Galápagos province. Island tourism sites nearer the town of Puerto Baquerizo Moreno include the Cerro Tijeretas, a nesting colony for Frigate birds and a statue of Charles Darwin, marking the original site where he first disembarked in the Galápagos Islands during the voyage of the Beagle, on 16 September 1835. La Loberia, a colony of sea lions, lies about ten minutes by bus from the town.
Local boat tours also take visitors to two popular nearby dive sites. "Kicker Rock" (the Spanish name is "León Dormido") represents the remains of a lava cone, now split in two. "Isla Lobos" (sea lion island) is also a nesting site for blue-footed boobies.