Much of Iceland sits on active volcanic zones. In fact, that is why the country is known as the land of fire and ice. In those volcanic areas, when ground water flows down into the cracks of the Earth's surface and encounters hot or molten rock, it either turns into hot water that can be harvested to heat buildings, or steam that can be used to generate electricity in a fairly cheap and clean manner. This is so successful that Icelanders consider geothermal energy and fish to be their two largest natural resources.
From what we can gather, California's Paleo-Indians were using the steam and hot water of the geysers in the Mayacamas Mountains in Sonoma County more than 10,000 years ago to keep warm, and geothermal pools have been a part of Icelandic culture from the time of their first settlers.
The first prototype of a geothermal power plant was built in Tuscany, Italy, in 1905, and that plant went into full production in 1911. Tuscany's facility continued to be the only geothermal power plant in the world until New Zealand built another one in 1958. Since that time, geothermal plants were brought on line in Mexico in 1959, the United States in 1960, Japan in 1966, Siberia in 1967, and Iceland in 1969.