Both circular and rectangular fields follow the path of the Snake River on the Snake River Plain, in southern Idaho, USA. The large lake is the American Falls Reservoir, created by the dam of the same name.
The dam and reservoir are a part of the Minidoka Irrigation Project on the Snake River Plain and are used primarily for flood control, irrigation, and recreation.
The darker brown areas that differ from the otherwise tan terrain of the uncultivated parts of the plain are lava fields. The largest of these is Craters of the Moon National Monument and Preserve, which encompasses three major lava fields and about 400 square miles (1,036 km2) of sagebrush steppe grasslands to cover a total area of 1,117 square miles (2,893 km2).
All three lava fields of Carters of the Moon lie along the Great Rift of Idaho, with some of the best examples of open rift cracks in the world, including the deepest known on Earth at 800 feet (240 m). There are excellent examples of almost every variety of basaltic lava as well as tree molds (cavities left by lava-incinerated trees), lava tubes (a type of cave), and many other volcanic features
The second largest lava field on the Snake River Plain, in the upper right quadrant, is Hell’s Half Acre lava field. It is the youngest of the eastern basaltic lava fields of the plain, and covers an area of about 400 km2.
The lava is basaltic in nature which formed a broad, low shield volcano with dominantly pahoehoe flows that were erupted from a 3 km long, north-west to south-east trending vent system at the north-west part of the field during a brief eruptive episode about 5,200 years ago.