About 4 million years ago
the hot spot was located in eastern Idaho, near Rexburg. Lake Idaho, in the subsiding
central and western Snake River Plain, was at its maximum extent. The Centennial
and Teton Ranges were uplifted, with normal faults on their northern and eastern
margins. Teewinot Lake occupied present-day Jackson Hole, and the headwaters of
the Snake River drained eastward up the Hoback River Canyon to the Green River.
In general, drainage was centripetal, away from the hot spot, south to the Bonneville
Basin and north to Montana. Near Hagerman, at the southeast corner of Lake Idaho,
streams and marshes were home to a diverse set of Pliocene animals, including
the Hagerman horse (the Idaho state fossil). We show Lake Idaho as draining to
the south through northern Nevada to the Sacramento River, as suggested by ages
of distinctive sedimentary minerals (zircons) and the distribution of giant beaver
and pygmy muskrat fossils.
Heise Eruptive Center
Cross-section of the
Images courtesy of the U.S.
Forest Service, Department of Agriculture.