LPRV Aquifer Management: Physical Hydrology

This figure reveals that the lower Portneuf Valley aquifer is actually a system of several aquifers: unconfined in the southern valley, and a series of confined sedimentary and basalt lava aquifers in the northern valley (transitioning into the basalt lava aquifer of the eastern Snake Plain).
Note the principal directions of ground water flow - through the Portneuf Gap and from the southern Bannock Range - and across the bedrock lip which separates the southern and northern valley.

One of the most important features of this aquifer system is the presence of coarse gravels at and near the surface (the portion shown in yellow). These gravels were deposited by a catastrophic flood some 14,000 years ago, when glacial Lake Bonneville (located in the Great Salt Lake basin) broke through its natural dam at Red Rock Pass and emptied in the space of a few months.

Because the deepening of the water table, most of the Bonneville gravel is not part of the aquifer in the northern valley. However, it is the single-most important feature in the southern valley.

Visit the Hydrology section of the Digital Atlas of Idaho to learn more about the Lake Bonneville Flood.