Hydrography.— The general drainage in the eastern two-thirds of the State is from south to north; in the west from north to south. The State is included within four dis tinct drainage areas. The major portion lies within the Missouri Basin, comprising the val leys of the North Platte. Sweetwater, Wind, Big Horn, Powder. Belle Fourche and Cheyenne rivers. The western part of the State is cut by Green River, an affluent of the Colorado, and hence within the Gulf of California drainage system. North and west of Green River rises Snake River, a tributary of the Columbia and hence within the Pacific drainage area, while through the extreme southwestern part of the State flows Bear River. the principal affluent of the Great Salt Lake, and, accordingly, a water of the Interior Basin. The water surface of the State totals only 320 square miles. The largest lakes are Yellowstone, Jackson and Shoshone, all in the northwest. There are many small lakes•amid the mountains, small bodes of dear water surrounded by wooded mountains.
Wyoming lies partly in the Great Plains and partly in the Rocky Mountain provinces, thus presenting the three chief divi sions of land forms, namely, plains, plateaus and mountains. The salient structural features of the region are great anticlinal folds separated by deep synclinal basins, some of which are 1(0 miles long and 20 to 50 miles wide. Forma tions of pre-Cambrian age are exposed along the crests of the major mountain ranges, namely, the Laramie, Medicine Bow, Wind River, Big Horn and Black Hills. The rocks which com pose these formations constitute a complex group of metamorphosed sediments and associ ated igneous intrusives. The Paleozoic is but slightly developed. Formations of Cambrian. Ordovician, Mississippian. Pennsylvanian and Permian age are found over the northern and western portions of the State. The Meso ink is represented by slight developments of the Triassic. Jurassic and Lower Cretaceous, while the Upper Cretaceous attains a thickness of several thousand feet The Cenoroic is char acterized by a great thickness of continental Tertiary formations rich in mammalian fossils. Volcanic eruptive. of Tertiary age cover large areas in and adjacent to the Yellowstone Na tional Park Wyoming's chief contributions to geoare found in the rich reptilian fauna from1e Cretaceous and the mammalian fauna from the Tertiary and in the unsurpassed gey sers of the Yellowstone. The chief resources thus far developed are oil from the Pennsyl vanian and Cretaceous, and coal from the Cre taceous and Tertiary.
Minerals and Mining.— The mineral re sources of the State are annually attracting greater notice. Fourteen out of the 22 coun ties are producers of metallic minerals. The relatively small quantities of gold, silver and copper, the metals for which the State has been prospected, have led to an underestimation of the State's resources. Placer gold was found at Atlantic City in west central Wyo ming in 1842 and subsequently in small quanti ties in the Grand Canyon of the Snake. Lode
deposits have been worked in the north Lara mie Mountains and elsewhere intermittently since 1871. The veins are not phenomenally rich but are believed to persist in depth. The future of gold mining here depends on increased capital investment, modern methods of ore treatment and improved transportation and power facilities. In 1915 Wyoming ranked 15th aming the States in gold production. To 1911 the total placer yield was estimated at $1,725, 000; the lode yield at $4,137,000. The following table shows the oroduction in recent rears: Silver is usually found in conjunction with gold especially in the western part of the State. The following table shows the value of the silver mined in the State during the past few years: A considerable portion of Wyoming is under laid with bituminous coal of excellent quality. The best fields are those near Newcastle and at Hanna, Rock Springs, Kemmerer and Dieu. Other rich deposits exist in the north and north west but have not been developed to any ex tent. In 1914 the State produced 6,475,293 tons; in 1915. 6,554,028 tons; and in 1916, 7,500,000 tons. In 1915 Wyoming ranked sixth among the States in the production of iron ore, yield ing in that year 908,845 gross tons. Copper is found in central Wyoming and in the Medicine Bow Mountains in the south. The production in recent years has been as follows: 1914, 165, 1123 pounds; 1915, 1,020,9a5 pounds; 1916, MO pounds Petroleum is already one of the most important mineral products and the State Fives every promise of becoming a leader both in production and in quality of output, some geologists even having gone so far as to say that Wy,,ming is !thralls- underlaid with a sea of oiL The exigence of petroleum has been known for ?cars, hut among the first to call attention to its ommercial possibilities was the late Prof Wilbur l hnicht of the State Lin vergty. The slialei that have been drilled contiun oils atilt tuah a an asphalt base. Many of the former are of surpassed quality. The principal fields dos IN developed are the Salt Creelc. Powder River. Big Muddy, Basin. Lost Soldier, Pilot Bane. Crow Creek, Torchlight, Lovell. Little Buf falo and Rock Creek The largest prodneig fields are the Salt Creek and Big 'kiddy in 1918 the bringing in of a well on Rock 50 miles north of Laramie. gave great prowler of large quantities of rich oil with 'a parafase base in a hitherto little exploited field. la nearly all the fields the oil lies at a depth of 1,500 to 4,000 feet. The difficulties now en countered include lack of transportation fedi ties and detailed geologic studies of the State and the danger of litigation. The following table shows the production since 1912: Natural gas has been encountered in eat oil fields and is used locally. In the Salt field the conservation of the natural gas has be come a model for the country.