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| Geology
of the Portneuf River Ecosystem |
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The Portneuf River
ecosystem lies at the northern edge of the Basin
and Range
province. This geologic province is
characterized by fingers of steep mountain ranges alternating with
wide, flat desert valleys. It extends from eastern
California to central Utah, and from
southern Idaho into Sonora, Mexico. The entire region has been
subjected to extension which thinned and cracked the crust, creating
large faults. Along these roughly
north-south-trending faults mountains were uplifted and valleys
lowered, producing the distinctive alternating pattern of linear
mountain ranges and valleys. The relief created by these faults
can
result in a vertical difference between basin and ranges that
approaches 3,000 meters. |
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The
direction the
Portneuf River flows is determined by topography, which is in turn
influnced by geology. And although rivers and streams tend to
follow geologic structure, they
also carve out the landscape as they descend. Over the last twenty
million years, this river has flowed across a changing geologic
landscape and has, in turn, changed that landscape. The Portneuf
initially flows south, then turns west, and finally flows northwest to
the Snake River. Water flows downhill, not north to south.
The river simply finds its way dowhill across areas of recent volcanic
activity and uplifted mountain ranges. For a more extensive look at the geology of this region, visit the Geology Section of the Digital Atlas of Idaho. |
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| Ground Water
and Hot Springs Ground water returns to the surface in springs. In most cases these springs contain water that fell upslope, was absorbed into the ground. Water may remain in these systems for long periods - as long as 25,000 years in some places. Most springs return cool water to the surface, but hot springs are also present within the geologically active Portneuf River Ecosystem. The most well-known of these is located in Lava Hot Springs. These springs are produced by the very slow circulation of water to depths of 3,000 meters, where it is heated. These waters then recirculate to the surface as hot springs. |
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| The Lower
Portneuf River Aquifer The cities of Pocatello and Chubbuck, in the Northwest corner of the Portneuf Ecosystem, sit on top of a shallow aquifer. This aquifer is actually a system of aquifers - a series of confined basalt and sedimentary aquifers, and an unconfined aquifer in the southern end of the valley. Because these two cities are completely dependant on this aquifer for all domestic, commercial and irrigation needs, and because it is a shallow aquifer, protection of this resource is an important concern. It is currently threatened by pollution in many forms. Trichloroethylene (TCE), perchloroethylene (PCE), and chloride from stormwater runoff and from septic tanks are the major threats to this aquifer. Learn More |
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| Location
of the Lower Portneuf River aquifer (left) and location and extent of
TCE
contamination within the aquifer (right). Click for larger
images. Images courtesy of J. Welhan. |