Abstract

The Warner Range of northeastern California is a north-trending horst at the northwest margin of the Great Basin. The 3,000-m-thick bedrock section exposed in the southern part of the range is Tertiary in age, and it dips homoclinally 20° to 25° west-southwest. Much of the section consists of volcanic rocks whose K-Ar ages range from about 32 m.y. near the base of the section to about 14 m.y. at the top. Rocks older than about 26 m.y. are principally andesitic lahars, those between 26 and 17 m.y. are andesitic lava flows and rhyolitic, welded, ash-flow tuffs, and those younger than about 17 m.y. are principally basaltic and andesitic lava flows.

The homoclinal character of the Warner section indicates that block faulting responsible for uplift and tilting of the range began after emplacement of the youngest exposed rocks. Drilling in the deeply alluviated graben adjacent to the eastern face of the range indicates that aggregate vertical offset across the range-front fault is at least 3,600 m—the difference in elevation between alluvium in the bottom of the deepest bore hole and the crest of the nearby part of the range. Thus, vertical displacement has occurred at a minimum average rate of 26 cm/1,000 yr during the past 14 m.y. Offset of alluvium along the eastern base of the range records the continuation of block faulting into Holocene time.

The onset of block faulting, somewhat less than 14 m.y. ago, and the change in character of volcanic rocks from principally andesitic to principally basaltic in mid-Miocene time are similar to volcano-tectonic events of a much broader region proposed by previous workers. The Warner Range is remarkable for the nearly complete record of regional late Cenozoic, volcanic and tectonic events found within a single horst.

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