The Snake River Plain aquifer is a huge underground body of water covering 10,000 square miles, stretching from the town of Hagerman upstream to near St. Anthony. The aquifer is made up of water which is stored in a series of lava flows erupted over the past 15 million years. The lava flows are separated by layers of broken rock and cinders as well as sand, gravel, and clay which mark the location of ancient lakes and rivers. In addition, the lava is cracked, leaving large spaces through which water can flow. Farmers depend on the aquifer to irrigate over one million acres annually.
Most farms also depend on wells for domestic and stock water.
In addition, over 41 communities serving 127,000 people utilize the aquifer for municipal water supplies, either from wells or springs. The aquifer lies approximately 1,000 feet below the surface and flows slowly, following the gradual slope of the Snake River Plain. Streams entering the lava plain, rain, and snow melt all disappear into the porous rock. The water then makes its slow journey southwestward, eventually cascading from the canyon walls into the Snake River at Thousand Springs. In 1992, researchers began an Aquatic Resources Assessment at Craters of the Moon.