'nineties; it fell thereafter, averaging
about 493,269 barrels from 1899 to 1903; in 1905 the yield was 376,238
barrels; and in 1907, 331,851 barrels. In 1905 the state ranked
eleventh, in 1907 twelfth, in production of petroleum. It is mostly
refined at Florence, the centre of the older field. The Boulder district
developed very rapidly after 1902; its product is a high-grade
illuminant with paraffin base. Asphalt occurs in the high north rim of
Middle Park (c. 10,000 ft.). Tungsten is found in wolframite in Boulder
county. In 1903 about 37,000 men were employed in the mines of Colorado.
Labour troubles have been notable in state history since 1890.

Mineral springs have already been mentioned. They are numerous and occur
in various parts of the state. The most important are at Buena Vista,
Ouray, Wagon Wheel Gap, Poncha or Poncho Springs (90 deg.-185 deg. F.),
Canyon City, Manitou, Idaho Springs and Glenwood Springs (120 deg.-140
deg. F., highly mineralized). The last three places, all beautifully
situated--the first at the base of Pike's Peak, the second in the Clear
Creek Canyon, and the third at the junction of the Roaring Fork with the
Grand river--have an especially high repute. In 1904 it was competently
estimated that the mineral yield and agricultural yield of the state
were almost equal--somewhat above $47,000,000 each.[2]

In 1900 only 4.6% of the population were engaged in manufactures. They
are mainly dependent on the mining industry. There are many large
smelters and reduction plants in the state, most of them at Denver,
Leadville, Durango and Pueblo; at the latter place there are also
blast-furnaces, a steel plant and rolling mills. Use is made of the most
improved methods of treating the ore. The cyanide process, introduced
about 1890, is now one of the most important factors in the utilization
of low-grade and refractory gold and silver ores. The improved dioxide
cyanide process was adopted about 1895. The iron and steel
product--mainly at Pueblo--is of great importance, though relatively
small as compared with that of some other states. Nevertheless, the very
high rank in coal and iron interests of the state among the states west
of the Mississippi, the presence of excellent manganiferous ores, a
central position for distribution, and much the best railway system of
any mountain state, indicate that Colorado will almost certainly
eventually entirely or at least largely control the trans-Mississippi