A, Economic Geology, 48 Series Professional Paper NO. 41 B, Descriptive Geology, 60 DEPARTMENT OF THE INTERIOR UNITED STATES GEOLOGICAL SURVEY CHARLES D. WALCOTT, DIRECTOR GEOLOGY OF THE CENTRAL COPPER RIVER REGION, ALASKA WALTER C. XENDENHALL GOVERNMENT PRINTIKG OFFICE 1905 CONTENTS. Page. Letter of transmittal ...................................................................... 9 Introduction .............................................................................. 11 Organization and itinerary ................................................................. 13 Geography ............................................................................... 16 Chugach Mountains ............................................................... 17 Wrangell hlou~itains............................................................. 17 Alaska Range .................................................................... 19 Interior valley .................................................................... 19 Copper River and its tributaries ................................................... 20 Relations of geography to settlement ...................................................... 22 Geology .................................................................................. Geologic summary .................................................................... Description of formations ............................................................. Dadina schists .................................................................... Occurrence and character ...................................................... Diorite intrusives ............................................................. Correlation and age of the schists ............................................. Age of the diorite intrnsives ............................................. -:... Tanana schists ................................................................... Occurrence and character .................................................... Age and no~nenclature........................................................ Valdez formation ................................................................. Chisna formation ................................................................. Occurrence and character ...................................................... Age anti relations ............................................................. Intrusive~and eff usives ....................................................... Tetelna volcanics .......................................................... ,...... Occurrsnce and character ...................................................... Correlation and age ........................................................... Ahtell diorite ..................................................................... Nikolai greenstone ................................................................ Jlankomen formation ............................................................. Occurrence and character ...................................................... Age .......................................................................... 42 Correlation ............................................................... 42 Faunal comparison with other Alaskan Permian areas ................... .. 43 General faunal comparisons ............................................... & 4 CONTENTS . Geology--Continued . Description of formations-Continued . Mankomen formation-Continued . Structure ..................................................................... Intrusives .................................................................... Correlation and physical conditions ........................................... Triassic shales and limestones ..................................................... Kennicott formation .............................................................. Gakona formation ................................................................ Occurrence and character at type locality ....................................... Occurrence and character at other localities. .................................... Wrangell lavas ................................................................... Occurrence ................................................................... General aspect ................................................................ Period of eruption ...................... - ..................................... Petrologic character ........................................................... Copper Valley Pleistocene ........................................................ Occurrence ................................................................... Character .................................................................... Pleistocene surface ............................................................ Sources of the n~aterial....................................................... Conditions of deposition ...................................................... Summary ..................................................................... Sand dunes, land slides, and terraces .............................................. Outline of geologic history.-. ............................................................. Physiographic development ............................................................... Physiographic divisions ............................................................... Chugach Mountains .............................................................. Interior valley ................................................................... Wrangell Mountains .............................................................. Alaska Range .................................................................... Origin of the interior valley ........................................................ Character of the defonned surface .................................................. Summary ........................................................................ Glaciation ...-............................................................................ Economicgeology ........................................................................ Introduction .......................................................................... Copper ............................................................................... Location ......................................................................... Routes and trails ................................................................. Character and relations of the ores ............................................... Description of properties .......................................................... Cheshnina River ............................................................. Kotsina River ................................................................ Keystone claim ....................................................... Copper King claim ................................................... CONTENTS. 5 Economic geology-Continued . Page . Copper-Continued . Description of properties-Cor~tinued . Kotsina River-Continued . Eleanor, Davy, and associated claims ................................. Skyscraper claim ..................................................... Warner prospect ...................................................... G . & B . and United Verde claims ..................................... Kluvesna Creek .............................................................. Copper Creek ................................................................ Elliott Creek ................................................................. Location and accessibility ................................................. Geology .................................................................. Relation of ore deposits to geologic structure .............................. Description of prospects ................................................... Mineral King ........................................................ Copper King ......................................................... Copper Queen ........................................................ Mamot .............................................................. Louise ............................................................... Goody ear ............................................................ Henry Prather ....................................................... Elizabeth .............................................................. Fog .................................................................. Albert Johnson ....................................................... Chitina drainage basin ........................................................ Strelna Creek deposits ................................................ Kuskulana River occurrences .......................................... Bonanza mine ........................................................ Old Independent vein ................................................ Nikolai mine ......................................................... Other occurrences ............................. 1...................... Economic considerations .......................................................... Gold ................................................................................. Chistochina gold field ........................................................... Location ..................................................................... Cieography and drainage ......................................................