| Abstract |
As part of a U.S. Navy Geothermal Program Office research project at the Hawthorne Army Weapons Depot (HAWD), we investigated the occurrence, distribution, and age of late Quaternary faults in order to better understand the structural relations that may control geothermal potential in the southern Walker basin near Hawthorne, Nevada. We utilized specialized 1:12,000- and 1:18,000-scale low-sun-angle aerial photography together with existing 2.4-m-resolution LiDAR to detect and map late Quaternary fault scarps. Although the location and Holocene age of the Wassuk range-front fault system was previously known, we have now also identified a new zone of Holocene faulting that splays northeastward from the Wassuk range front, extending through the HAWD and the town of Hawthorne. Near Cottonwood Canyon at the southwestern edge of the HAWD, late Holocene fault scarps comprise the range-front fault system which here has probable dextral slip occurring on northwest-striking faults. These faults extend northwest to Lucky Boy Pass where slip is apparently transferred to a series of north-northeast-striking, normal-slip faults that comprise the principal range-front faults of the Wassuk Range. The largest normal scarps along the Wassuk Range occur at the structural range-front bend at Cat Canyon where Holocene scarps as large as 10 m occur. These scarps continue to the north where exploratory trenching of the range-front fault at Rose Creek indicates that at least two Holocene faulting events have occurred. The newly recognized Holocene faults splay from the Wassuk range front at a point mid-way between Lucky Boy Pass and Cat Canyon as a series of northeast-trending scarps cutting post-Lahontan lake and alluvial-fan deposits. Multiple sets of down-to-the-east and -west scarps form a nested graben as much as 20 km in width. Field investigations show that these scarps are of mid-Holocene age. A comparison of the mapped faults with detailed gravity data indicates that the graben overlies a structural trough in the basement. The structure may continue to the north-northeast and connect with the west-dipping Holocene range-front fault of the Gillis Range. These newly recognized fault traces demonstrate which fault orientations are active in the present stress field, and strain modeling can show which of the faults have dilational or shear tendencies. |