PALEODRAINAGE OF PLUVIAL LAKE CLOVER AND THE NEOTECTONIC EVOLUTION OF THE CLOVER VALLEYFAULT, ELKO COUNTY, NEVADA

On the morning of February 21, 2008 a M_W6.0 earthquake sourced at 6.7 km depth and located 18 km northeast of the town of Wells, Nevada destroyed much of the historic downtown and raised questions about the previously unrecognized fault responsible. Subsequent analysis raised the possibility that this fault links southward to the Clover Hill fault, a normal fault bounding a small horst block southwest of Wells that parallels the much larger East Humboldt Range to the west. New mapping, along with the Wells earthquake, indicates that the Clover Hill fault may be much younger and more active than previously thought.

Clover Valley today is filled with alluvial fan sediments derived from the adjacent mountains and lacustrine sediments deposited in Pleistocene pluvial Lake Clover. Previous work by Reheis and others raises the possibility that paleolake Clover may have overtopped a drainage divide during an earlier Pleistocene high stand and spilled northward into the Humboldt River drainage near Wells. A GIS analysis demonstrates the potential extent of paleolake Clover and documents the possible outlet near Wells. Support for this hypothesis may be provided by the discovery at the north end of Clover Hill of flat-lying alluvial boulder conglomerate. This conglomerate contains large clasts of white orthoquartzite and vesicular basalt. The orthoquartzite is most likely sourced from the Wood Hills on the east side of Clover Valley, but the vesicular basalt may originate from a small volcanic hill in the center of Clover Valley known as “the Mound.” The base of the Mound lies approximately 10 m above the highest Late Pleistocene beach ridge, but the crest is very nearly the same elevation as the maximum documented pre-Late Pleistocene high stand. Intriguingly, if the boulder conglomerate deposit did originate from the Mound, subsequent motion on the Clover Valley fault has now uplifted it to a higher elevation than its source. To test this hypothesis geochemical and geochronological comparison of the basalt boulders with the proposed source rock at the Mound is now in process. Here we present petrological comparison of the basalt from the Mound and the boulder conglomerate. In addition, analysis of sands from the slopes of the Mound are consistent with the hypothesis that this feature may once have formed an island in paleolake Clover.