Ogallala Aquifer - General Characteristics

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. In that respect, the process is little different from that currently prevailing in other modern rivers of the area, such as the Kansas River and its tributaries. The major differences are time and depth.

The depth of the Ogallala varies with the shape of then-prevailing surface, being deepest where it fills ancient valleys and channels. The Ogallala Formation consists mostly of coarse sedimentary rocks in its deeper sections, which transition upward into finer-grained material.

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. 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 an exceedingly slow rate, suggesting that much of the water in its pore spaces is paleowater, dating back to the last ice age and probably earlier.