Geology of East-Central Idaho: Geologic Roadlogs for the Big and Little Lost River, Lemhi, and Salmon River Valleys
Link and Janecke -- Geology of East-Central Idaho: Roadlogs 295 Geology of East-Central Idaho: Geologic Roadlogs for the Big and Little Lost River, Lemhi, and Salmon River Valleys Paul Karl Link Department of Geology, Idaho State University, Pocatello ID 83209 Susanne U. Janecke Department of Geology, Utah State University, Logan UT 84322 INTRODUCTION As part of this introduction we present several summary fig- This article contains a discussion of the regional geology and ures. First is a regional geographic map (Fig. 1), and a simplified historical geography of east-central Idaho, north of the Snake River geologic map on the same base (Fig. 2). The Proterozoic and Plain and southeast of the Salmon River, and four roadlogs for Paleozoic stratigraphic correlation diagram (Fig. 3) also shows the main highways in this huge (15,000-km2) area. The roadlogs thrust fault relations. Figure 4 shows major structures and basins progress from south to north and west to east. They include: of the Trans-Challis fault zone and Figure 5 shows the Challis 1) Big Lost River Valley, Volcanic field. Photographs in the road log section illustrate many 2) Little Lost River-Pahsimeroi Valley, of the field localities. In the introductory summary we cite (out- 3) Birch Creek-Lemhi Valley, and of-sequence with their position in the text) several photographs 4) Stanley to Salmon along the Salmon River. in which specific stratigraphic features are present. This article covers much of the same country described by East-central Idaho contains diverse and economically impor- Ross (1963) in the first geologic roadlog of east-central Idaho, tant, mineral deposits.
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