DEPARTMENT OF THE INTERIOR FRANKLIN K. LANE, Secretary UNITED STATES GEOLOGICAL SURVEY GEORGE OTIS SMITH, Director Bulletin 655 THE LAKE CLARK-CENTRIL KUSKOKWIM REGION ALASKA BY PHILIP S. SMITH WASHINGTON GOVERNMENT FEINTING OFFICE 1917 CONTENTS. Page. Preface, by Alfred H. Brooks....................... ........................ 9 Introduction.............................................................. 11 Scope of report....................................................... 11 Sources of information................................................ 12 Early explorations................................................ 12 The Lake Clark-Iditarocl expedition of 1914......................... 17 Narrative of the expedition.^................................... 17 Methods of work............................................... 19 Topographic survey, by R. H. Sargent..................... 19 Geologic survey.......................................... 21 Miscellaneous observations................................. 22 Acknowledgments.................................................... 22 Geography. .............................................................. 23 Major features......................................................... 23 Drainage and relief......_.............................................. 24 Kvichak basin .................................................... 24 Mulchatna basin ................................................. 26 Kuskokwim basin ................................................. 27 Main stream.................................................. 27 Holitna River basin........................................... 29 Stony River basin............................................ 31 George River basin ........................................... 32 Climate.............................................................. 33 Temperature..................................................... 33 - Precipitation ........T............................................ 35 Population and settlements............................................. 35 Animals.............................................................. 38 Vegetation........................................................... 41 Geology.................................................................. 45 Major geologic features................................................. 45 Paleozoic sedimentary rocks............................................ 48 Subdivisions...................................................... 48 Gneiss, quartzitic schist, and slate .................................. 48 Distribution .................................................. 48 Lithologic character .......................................... 48 Age and interrelation ......................................... 49 Limestone. ........................................................ 50 Distribution and topographic expression........................ 50 Lithologic character .......................................... 51 Structure.................................................... 53 Age and interrelation ......................................... 54 Mesozoic sedimentary rocks........................................... 57 Subdivisions...................................................... 57 3 4 CONTENTS. Geology Continued. Mesozoic sedimentary rocks Continued. Pago. Conglomerate of Cairn Mountain and vicinity..................'...... 58 Distribution and topographic expression........................ 58 Lithologic character........................................... 59 Structure.................................................... 60 Age and interrelation ......................................... 61 Mesozoic shales south of the Kuskokwim............................ 63 Distribution and topographic expression........................ 63 Lithologic character .......................................... 64 Structure.................................................... 66 Age and interrelation ......................................... 68 Mesozoic sandstones south of the Kuskokwim....................... 72 Distribution and topographic expression........................ 72 Lithologic character .......................................... 73 Structure................../................................. 74 Age and interrelation ......................................... 76 Mesozoic sedimentary rocks north and west of the Holitna............ 77 Distribution and topographic expression........................ 77 Lithologic character .......................................... 79 Structure..................................................... 80 Age and interrelation ......................................... 82 Unconsolidated deposits................................................ 84 Subdivisions...................................................... 84 Glacial deposits.................................................... 85 Iliamna Lake region.......................................... 86 Lake Clark basin.............................................. 87 Mulchatna and Hoholitna basins ............................... 90 Stony -River basin............................................ 92 Other parts of the Kuskokwim basin............................ 94 Fluviatile deposits................................................ 96 Lacustrine deposits............................................... 97 Marine deposits.................................................... 98 Volcanic-ash deposits.............................................. 100 Organic deposits................................................... 100 Mud springs and earth runs......................................... 102 Igneous rocks......................................................... 103 x Subdivisions...................................................... 103 Older lavas........................................................ 104 Distribution and field occurrence. ............................ 104 Lithologic character........................................... 106 Structure...................................................... 109 Age and interrelation.......................................... 110 Granitic rocks .................................................... 112 Distribution and field occurrence................................ 112 Lithologic character........................................... 114 Age and interrelation.......................................... 116 Dikes cutting Mesozoic sediments.................................. 118 Distribution and field occurrence................................ 118 Lithologic character........................................... 119 Age and interrelation.......................................... 121 Younger lavas...................................................... 122 Distribution and general features................................ 122 Lithologic character.....................................°...... 124 Age and interrelation.......................................... 125 CONTENTS. 5 Page. Mineral resources.......................................................... 127 General economic conditions............................................ 127 Wages and supplies................................................ 127 Transportation .................................................... 128 Power.......................-..............."...................... 130 Kinds and distribution................................................ 131 Gold deposits.......................................................... 132 Iditarod region..................................................... 132 Kuskokwim basin.................. '. ............................... 134 Mulchatna basin.................................................. 136 Lake Clark and Iliamna Lake basins................................. 137 Possible future areas............................................... 137 Quicksilver deposits................................................... 339 Parks prospect.................................................... 139 Location and developments........'............................. 139 Geologic occurrence............................................ 140 Character and relation of mineralization.......................... ' 143 Miscellaneous localities............................................ 144 Origin and probable extent........................................ 146 Possible future area................................................ 147 Economic conditions affecting the production of quicksilver......... 148 Miscellaneous metalliferous deposits..................................... 150 Copper............................................................ 150 Antimony........................................................ 152 Silver-lead deposits ............................................... 153 Molybdenum...................................................... 153 Manganese...................................................'...... 154 Coal resources.......................................................... 154 Water resources........................................................ 156 ILLUSTRATIONS. Pago. PLATE I. Topographic map of the Lake dark-Central Kuskokwim region. In pocket. II. A, View southward across the Mulchatna Valley showing terraces B> and distant hills; B, Transverse gap through hills at head of Port­ age Lake drainage; C, View westward down the Kuskokwim from the vicinity of camp of August 17.............................. 26 III. A, The Hoholitna near camp of July 23; B, Stony River and dis­ tant limestone hills from near camp