Practical Mining in Eastern Oregon
The following data is extracted from Baker County, Oregon, Gold Mining History.
In the topographical survey of the United States, all that portion laying between the Rocky Mountains and the Sierra Nevada, up into the southeastern portion of Washington, is known as the Great Basin. This basin was once an extensive lake bottom, and now, for the most part, filled with alkaline plains of the quaternary age. The surface Is diversified by subordinate ranges of mountains, formed of tilted paleozole rocks and extensive overflows of igneous eruptions. These ranges are barren and shattered, and the stratafied rocks are often found in confusing and irregular positions.
The chief characteristics of the Great Basin, alkaline deserts and subordinate north and south ranges of mountains, are carried into Eastern Oregon, Washington and Idaho.
Along the coast we find a prolongation of the Coast Range with its fertile valleys of the cretaceous and tertiary. East of the Coast Range we have the quarternary valleys, covered more or less thoroughly with immense outpourings of igneous rocks. These extend into Idaho. On the north we have the characteristic carboniferous rocks extending into Northern Montana interspersed with quarternary and tertiary lake deposits.
The mountains of Eastern Oregon present strong evidence as belonging to the Sierra Nevada Range.
The Northeastern portion of Oregon is formed by the prolongation of the igneous plateaus of Washington, while the southeastern portion belongs to the Great Basin which comes up from Nevada. It is traversed by the same block-tilted ranges peculiar to the basin region farther south. The general surface is covered by quaternary lake deposits, and outflows of igneous rocks. The basin ranges of mountains are all of the block-tiling sort, and, where exposed show paleozoic rocks of great thickness. In these ranges is where mining is almost exclusively confined while between them lay great alkaline plains.
The characteristic rocks are of the igneous type-granite, seyenite, diorite, gabbo, and diabose in the holocrystallime varieties, and phorphyries, trachytes, and basalts in the porphyritic sorts, with some pitchstone and obsidian. In Baker County we find slates and granites predominating, although, for the most part, covered by igneous overflows.
As a producer of gold and silver, Oregon is taking a prominent place, and Baker County is the seat of the chief mining districts of the state, and presents the characteristic placers and quartz ledges of the Sierra Nevada region of California, Grant and Union Counties are also important gold producing localities.
Outside the counties forming Southeastern Oregon, the gold and silver production is very limited. Some auriferous beach sands are encountered at Port Orford, where the ocean has access to cliffs of gravel, which is broken down by the waves. A sorting action occurs and the gold is accumulated and can be gathered up at low tide. The quantity, however, is small, and the deposit is of interest chiefly as to its scientific aspects. The placer mining of Eastern Oregon is of considerable importance. Our placers have produced many millions and they are extensively worked to-day.
Quartz mining is in its Infancy yet. Probably not more than 800 stamps, or their equivalent, are cropping in Baker and Grant Counties. It is safe to conclude, however, that this number will be doubled in the near future Whether our ores are workable at the highest saving by the stamp mill will be subsequently considered. Where we find the Great Basin tilted sort of mountain ranges we can reasonably expect to find sufficiently rich quartz ledges to work into mines.
Source: Baker County, Oregon, Gold Mining History