DEPARTMENT OF THE INTERIOR UNITED STATES GEOLOGICAL SURVEY GEORGE OTIS SMITH, DIRECTOR BULLETIN 485 A GEOLOGIC RECONNAISSANCE OF THE ILIAMNA REGION, ALASKA BY G. C. MARTIN AND F. J. KATZ WASHINGTON GOVERNMENT PRINTING OFFICE 1912 CONTENTS. Tage. Preface, by Alfred H. Brooks________________.._________ 9 Introduction_____________________________________ 11 Location ____________________________________ 11 Geographic features____..________________________ 11 Topography ___________________,______________ 11 Lakes.__________________________________ 13 Rivers___________________________.._____ 13 Glaciers______.._________________________ 14 Climate____________________________.. 15 Vegetation __________..____________:____________ 16 General features____________________________ 10 Forests _________________________________ 1C Treeless areas _____________________________ IS Cause of limits of forests_______________________ 19 Settlements__________________________________ 20 Transportation routes____________________________ 21 Account of investigations___________________________ 23 Geology______________________________________ 25 General features of the region______________________ 25 Geologic subproviuces ____________________________ 26 Cook Inlet basin_____________________________-- 26 Chigmit Mountains____________________________ 27 Alaska Peninsula ____________ ____________ 28 Ilianma Basin__________.._______________..___ 28 Bering Sea coastal plaiu______ _ _ __ 29 Stratigraphic geology _____ ___ _________________ 30 General features____________________________ 30 Paleozoic rocks _____________________________ 30 Gneisses and quartzite schists___________________ 30 Areal distribution _ ____________________ 30 Lithologic character_______________________ 31 Age_______________________________ 32 Crystalline limestone and calcareous schist__________ 32 Areal distribution______________________ 32 Lithologic character ..____________________ 33 Age_________________________________ 34 Paleozoic or early Mesozoic rocks________________ 35 Slate and chert___ _ _ ____________ S5 Areal distribution________________________ 35 Lithologic character____________________ 36 Age_______________________________ 37 Greenstones ______ _ _ __________ 38 Areal distribution. ______________________ 38 Petrographic description__________________ 39 Age _ _ _ ____________ 40 3 4 CONTENTS. G eology Continued. Stratigraphic geology Continued. Page. Mesozoic rocks_____________________________ 41 Upper Triassic rocks______ ___ ________ 41 Limestone___________________________ 41 Areal distribution._ _ _ _ ___ 41 Lithologic character and stratigraphic relation­ ships____________________________ 42 Fauna __________ ______ 44 Age and correlation___________________ 46 Kamishak chert________________ _ 47 Areal distribution____________________ 47 Lithologic character________________..__ 47 Fauna-____________________________ 48 Age and correlation_______ _ ___ 48 Lower Jurassic ( ?) rocks_________ _________ 50 Porphyries and tuffs_________ ___ __ _ 50 Areal distribution____________.____..__ 50 Lithologic character in Cook Inlet district_____ 51 Lithologic character in Lake Clark district____ 53 Lithologic character in Iliamna Lake district-.___ 56 Age and correlation_________^__ ____ 58 Middle Jurassic rocks________________ 59 Tuxedui sandstone __________________ 59 Areal distribution____________________ 59 Lithologic character and sections___________ 59 Fauna and flora_____________________ 62 Age and correlation_________L__ __ 63 Chinitna shale_________________________ 65 Areal distribution____________________ 65 Lithologic character and sections __________ 65 Fauna and flora______________________ 66 Age and correlation ___________________ 68 Upper Jurassic rocks________________ ______ 68 Cliisik conglomerate_________________ 68 Areal distribution_____________________ 68 Lithologic character_______________..__ 68 Age and correlation__________________ 68 Naknek formation________________________ 69 Areal distribution____.______________ 69 Lithologic character and sections___________ 69 Fauna____________________________ 73 Age and correlation____________________ 73 Granitic rocks _________________________ 74 Areal distribution_________ ____________ 74 Petrographic description________ ;___________ 74 Age_______________________________ 76 Tertiary rocks__ ________________ __.. 77 Sedimentary beds.______________ _^________ 77 Areal distribution_______________________ 77 Lithologic character ____________.________ 77 Flora and age____________________ ______ ^ 78 CONTENTS. 5 Geology Continued. Stratigrapliic geology Continued. Tertiary rocks Continued. Page. Basaltic flows and tuft's______________________ 78 Areal distribution____________________ 78 Petrographic character ___________ ____ 79 ' Stratigrapliic relations_____________.._______ 81 Flora___________________.__________ 81 Age and correlation_____________ ___ 82 Quaternary deposits___________________________ 82 Glacial deposits_________________________ 82 Areal extent__________________________ 82 Character of the deposits__________________ 82 Conditions of deposition__________________ S3 Existing glaciers______________________ S3 Former glaciation____________________ 85 Terrace gravels__________________________ 88 Areal extent________________________ 88 Character of the deposits__________________ 90 Conditions of deposition_.________________ 92 Beach and flood-plain deposits_________________ 93 Recent volcanic deposits____________________ 94 Structure__________________________________^_ 94 Introduction_________________________________ 94 Cook Inlet forelands______________.._________ 95 General features__________________________ 95 'Local observations________________________ 95 Tuxedni Bay___________________________ 95 Coast between Tuxedni and Chinitna bays _______ 96 Chinitna Bay___________________________ 97 Coast between Chinitna and Iniskin bays_________ 98 Iniskin Bay______________________._____ 98 Ursus Cove__________________________ 99 Coast between Ursus Cove and Bruin Bay_________ 100 Bruin Bay____________________________ 100 Coast of Kanrishak Bay, south of Bruin Bay_______ 100 Chigruit Mountains____________________________ 100 General features__________________________ 100 Local observations_________________________ 101 Iliamna Bay_\__________________________________ 101 Mountains between Iliamna and Pile Bays________ 102 Pile Bay___________________________.___ 104 Chekok and Tazimiua valleys and neighboring districts. 104 Kontrashibuna Valley____________________ 105 Upper end of Lake Clark_________________ 105 Iliamua Basin________________________________ 108 General features__________________________ 108 Local observations__________________________ 108 Bering Sea coastal plain______________________ 109 Historical geology___________^____________________ 110 Mineral resources ____ _ ___ ____ _______ 113 General statement______________._________________ 113 Geographic distribution___________________________ 113 6 CONTENTS. Mineral resources Continued. ( Page. Geologic occurrence_____^_______________________ 114 Description of mineral deposits_______________________ 116 Copper __________________________________ 116 Occurrence of the ores______________________ 116 Copper minerals__________________________ 117 Descriptions of claims_________________._____ 117 Dutton prospects_________________ _____ 117 Copper King group______________ ________ 121 Kasna Creek claims________________ _____ .121 Millet claims_________________________ 122 Durand prospect_______________________ 123 Knutson prospect_________________:____ 123 Silver___________________________________ 124 Occurrence of the ores_________________:____ 124 Silver-bearing minerals_______________________ 124 Descriptions of claims__________T________..___ 124 Duryea claims__.._______________ _...____ 124 Gold______________________________________ 125 Lodes________________________________ 125 Claims on Iliamna Bay______________._____ 125 Aukney claim__________________________ 125 Placers___________________________.. __..__ 12G Petroleum______________,___________________ 126 Surface indications________________________ 126 Developments____________________________ 127 Character o'f the petroleum___________________ 129 Notes on the Mulchatna region_________________________ 131 Introductory statement___________________________ 131 Routes and supply points__________________________ 131 Prospects_._________________________________. 132 Index ________-_____________________________ 135 ILLUSTRATIONS. Page. PLATE I. Topographic map of the Iliamua regio_ ________ In pocket. II. Geologic map of the Iliamua region_____________ In pocket. III. A, Iliamua village and river, showing character of lowlands in valleys tributary to Iliamna Lake; B, Tanalian Falls, show­ ing water power and character of timber on Lake Clark___ 14 IV. Map showing distribution of forests_____ _______ 16 V. A, Closely folded Kamishak chert on south shore of Bruin Bay; B, Kamishak chert with intrusive sheet or flow of basic igneous rock on north shore of Ursus Cove__________ 40 VI. A, Banded rhyolite from south shore of Iliamna Lake; B, Chisik conglomerate on east shore of Iniskin Bay _______ 56 VII. A, Naknek formation and underlying Chinitna shale on east shore of Oil Bay; B, Horizontal sandstone beds of Naknek formation on west shore of Kamishak Bay__________ 66 VIII. A, Accordant mountain summits, showing Mount Iliamna rising above them and smooth, glaciated slopes below; B, Mount Augustine from the