Ogallala Aquifer

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The Ogallala Aquifer, also known as the High Plains Aquifer, is a vast yet shallow underground water table aquifer located beneath the Great Plains in the United States. One of the world's largest aquifers, it covers an area of approximately 174,000 mi² (450,000 km²) in portions of the eight states of South Dakota, Nebraska, Wyoming, Colorado, Kansas, Oklahoma, New Mexico, and Texas. It was named in 1898 by N.H. Darton from its type locality near the town of Ogallala, Nebraska.[1]

About 27 percent of the irrigated land in the United States overlies this aquifer system, which yields about 30 percent of the nation's ground water used for irrigation. In addition, the aquifer system provides drinking water to 82 percent of the people who live within the aquifer boundary.[2]


General characteristics

The deposition of the aquifer material dates back 2 to 6 million years to late Miocene to early Pliocene age when the southern Rocky Mountains were still tectonically active. From the uplands to the west, rivers and streams cut channels in a generally west to east or southeast direction. Erosion of the Rockies provided alluvial and aeolian sediment that filled the ancient channels and eventually covered the entire area of the present-day aquifer, forming the water-bearing Ogallala Formation. The depth of the formation varies with the shape of the pre-Ogallala surface, being deepest where it fills ancient valleys and channels. The Ogallala Formation consists mostly of coarse sedimentary rocks in its lower sections, which grade upward into finer-grained lithologies.[3]

The water-permeated thickness of the Ogallala Formation ranges from a few feet to more than 1000 feet (300 m) and is generally greater in the northern plains.[4] The depth of the water below the surface of the land ranges from almost 400 feet (122 m) in parts of the north to between 100 to 200 feet (30 to 61 m) throughout much of the south. Present-day recharge of the aquifer with fresh water occurs at a slow rate; this implies that much of the water in its pore spaces is paleowater, dating back to the last ice age.

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