A> Econoraic Geology, 82 Bulletin No. 295 B, Descriptive Geology.101 DEPARTMENT OF THE INTERIOR UNITED STATES GEOLOGICAL SURVEY CHARLES D. .WALCOTT, DIRECTOR THE YUKON-TANANA REGION, ALASKA DESCRIPTION OF CIRCLE QUADRANGLE L. M. PRIISTDLE WASI-IINGTO^7 GOVERNMENT PRINTING OFFICE 1906 CONTENTS. Page. Preface, by Alfred H. Brooks............................................. 5 Description of Circle quadrangle .......................................... 7 . Introduction......................................................... 7 Geography .:..........................---.................-.......-.. 9 Belief............................................................ 9 Drainage ...:....... '......'....................................... 9 General statement............................................ .9 Birch Creek system .......................................... 9 Charley River system ........................ ................ 10 Seventymile Creek system .................................... 10 Fortymile Creek system ...................................... 10 Volkmar River system ....................................... 10 Goodpaster River system ..................................... 10 Shaw, Tenderfoot, and Banner creeks.......................... 11 Salcha and Chena drainage ................................... 11 Relations of relief and drainage ................................... 11 Climate and vegetation .......................L................... 12 Transportation................................................... 14 Geology............................................................. 15 Statigraphy....................................................... 15 Sedimentary rocks ............................................... 16 Metamorphic rocks........................................... 16 Pre-Devonian................. ........................... 16 Devonian................................................ 17 Nonmetamorphic rocks.............;......................... 17 Cretaceous............................................... 17 Tertiary.................................................. 17 Quaternary .............................................. 17 Igneous rocks.................................................... 18 Distribution....................... .......................... 18 Intrusives.-._........-....................................... 18 Volcanics.................................................... 19 Summary........................................................ 19 Gold placers ................................. ...^.................... 20 Distribution and character ......................................... -20 Birch Creek region ............................................... 20 General conditions ........................................... 20 Deadwood Creek ............................................. 21 . Mammoth Creek ............................................. 21 Mastodon Creek.............................................. 22 Independence Creek.......................................... 22 3 4 CONTENTS AND ILLUSTEATIONS. Description.of Circle quadrangle Continued. Gold placers Continued. Birch Creek region Continued. Page. Miller Creek ............................................J.... 22 Eagle Creek and tributaries ............. 4'..................... 23 Summary ...........^...................................^.... 23 Yukon region .................................................... 23 Seventymile region............................................... 24 General conditions ............................................. 24 Nugget Creek .................................................. 24 Flume Creek.................................................. 24 Seventymile Creek ...............................1............ 24 Fortymile region................................................. 24 General conditions ............................................ 24 North Fork of Fortymile ..................................... 25 Montana Creek .............................................. 25 Gold Run.................................................... 25 Salcha region .................................................... 25 General conditions .....................................:..... 25 Butte Creek....... ............;............................ 26 Caribou Creek ............................................... 26 Coal resources......................................................... 27 Washington Creek................................................ 27 Bonanza Creek................................................... 27 Coal.Creek......._..........................................;... 27 Index .................................................................... 29 ILLUSTRATIONS. Pajre. PLATE I. Reconnaissance map of Circle quadrangle....................... Pocket. FIG. 1. Index map, showing location of Circle quadrangle................... 8 2. Map showing distribution of timber.......................... 1..... 13 3. .Geologic sketch map ......-...........-...-....---.-..-.....--.-.. 15 PREFACE. By ALFRED H. BROOKS. In planning the surveys ana investigations of Alaska, the attempt was made to 'cover first those regions which were of the greatest economic importance. As a result of this, many of the mapped areas are very irregular in outline, and it now seems desirable to introduce greater uniformity into the published maps as rapidly as the data available for their preparation will permit. With this end in view a system of maps has been projected covering quadrangular areas outlined by parallels of latitude and meridians of longitude, this being in conformity with practice in surveys made within the United States proper. But the Alaska surveys being for the most part of a reconnaissance character and the region being very thinly popu­ lated, it has seemed best to adopt a map unit larger than that used in the States. This unit will include 4 degrees of longitude and 2 degrees of latitude, making a map about as large as can be conveniently handled. It is hoped eventually, that these published reconnaissance topographic maps can be accompanied by sheets showing the geology and the economic resources, but in view of the great demand for the topographic maps it has been^deemed advisable to give them immediate publication, with such accounts of the geolog"yxand mineral resources as may be available. Nor is it deemed desirable to delay the issuing of the maps until the complete areas have been covered. The following report and the accompanying map (PI. I) is the first of this series to be issued, and it will be followed by others as fast as the accumulation of the field notes will permit. The topographic surveys upon which the map is based were made under direction of Mr. T. G. Gerdine in 1903 and Mr. D. 0. Witherspoon in 1904 and 1905; the geology is by Mr. L. M. Prindle, who has worked in this gen­ eral field in 1903, 1904, and 1905. Mr. Prindle has presented the salient features of the geology so far as known in simple language devoid of technicalities. A more elaborate discussion of the scientific results is.in preparation. 5 THE YUKON-TANANA REGION, ALASKA. DESCRIPTION OF CIRCLE QUADRANGLE. By L. M. PRINDLE. INTRODUCTION. The Yukon-Tanana region includes that part of the interior of Alaska delimited by Yukon and Tanana rivers and the international boundary. It is 300 miles west from the boundary to the junction of the two rivers, and the greatest distance in a north-south direction between them is about 175 miles. The area is approximately 40,000 square miles, or more than half that of the State of Washington. Some of the earliest prospecting in the interior was done in this area. The dis- coveryof placer gold on Fortymile Creek in 1886, and later discoveries in the Birch Creek and Rampart regions, in 1893, led to a rapid development of mining on streams tributary to the Yukon. The gold discoveries in 1902, about 260 miles above the mouth of the Tanana, have resulted in the development of the Fairbanks region, one of the most important gold placer camps in Alaska. Besides these four widely separated regions producing placer gold the Fortymile, Birch Creek, Ram­ part, and Fairbanks regions there are in this area several others, of less present importance, which illustrate the wide distribution of gold through the area. Gold has been, found at a few localities in the bed rock, but as yet in insufficient quantities to afford a basis for the development of quart/ mining. Coal occurs at several points along the Yukon and on small tributaries of the Yukon from the south, and has been mined to a small extent. The Yukon and Tanana are the main routes of travel, and from these rivers the productive areas are reached either by overland trails, by tributaries navigable for small boats, or, in the case of the Fairbanks region, by railroad and wagon road. Governmental investigation by the Geological Survey has, so far as possible, kept pace with the rapid development of the area and responded to the increasing demand for information by the publication of topographic and geologic maps and reports on conditions in the gold-producing regions. The accompanying map (PI. I) is framed by the one hundred and forty-second and one hundred and forty-sixth meridians and the sixty-fourth and sixty-sixth parallels, and includes about 17,000 square miles. Its relation to the larger area is shown in fig. 1. The part of this area mapped by the topographic parties extends west from the limits of the Fortymile quadrangle a as far as the headwaters of Birch Creek,