Early prospectors found portions of the ancient rivers and worked them for their rich gold content. Later, mining companies used hydraulic mining or drift mining techniques to recover the gold. In hydraulic mining, water under pressure is directed to, for example, the side of a ravine to dislodge the gravels and send the material to the sluices where the gold is recovered.
The equipment that was used (called a "monitor" or "giant") was similar to a very large hose nozzle.
Geologic reports speak of gravel deposits up to 250 feet deep with gold deposits interspersed at various levels within the gravels. Some of the gravels of the ancient rivers of gold have been cemented together over time. Smaller materials between the larger gravels have bound the larger gravels together. Drift mining is used in those instances to follow the channel underneath the volcanic covering.
In drift mining, tunnels are driven in bedrock underneath the channels and when the channels are reached, the richest stratum, resting immediately on the bedrock, is extracted by underground mining methods and then washed at the mouth of the tunnel.
Many miles of the ancient rivers are still un-worked and may be very rich in gold.
SOME OTHER MINERALS OF THE ANCIENT RIVERS OF GOLD
Platinum
Platinum is widely distributed in the gravels of the Tertiary rivers of the Sierra Nevada. The platinum is always associated with the gold. Some of the counties where platinum has been proven to be present in the sands are: Butte, Calaveras, Nevada, Placer, Plumas, Sacramento and Yuba.
Garnet
Garnet is widely distributed especially in the vicinity of granitic contacts. It is usually found in small rounded grains of red to purplish color. The largest quantity recorded was from the black sands at Rough and Ready, Nevada County at 446 pounds to the ton.
Zircon
Zircon is universally present. In some local areas it has been found in considerable quantities, such as at Placerville and at the North Fork of the American River in Placer County. The greatest relative quantity was found in black sand from a channel at Nevada City. It yielded 928 pounds to the ton.
Copper
Small flakes of metallic copper are occasionally observed.
Pyrite
Pyrite is of common occurrence in the gravels.
Diamonds
Diamonds have been found to occur with the gold, mainly at Cherokee Flat in Butte County and in the gravels at Placerville, El Dorado County. The diamonds that have been found were generally of small size and yellowish color. As is the case of diamonds in North Carolina and South Carolina, the diamonds in the California Mother Lode region are mostly scattered. Diamonds come up through the rock through a "pipe" of relatively small diameter, such as the diamond pipes in South Africa. (The state of Arkansas has acquired a diamond property at Murfreesboro where the public is permitted to search for diamonds. The diamonds are of good size and high quality. The Arkansas property is Crater of Diamonds State Park.)
Minerals in the Ancient Rivers of Gold
Ancient American River
The Ancient American River, Ancient Yuba River, Ancient Calaveras River, Ancient Mokelumne River, Ancient Tuolumne River, Ancient Magalia Channel, Ancient Intervolcanic Cateract Channel, Ancient Intervolcanic American River and the Ancient Jura River (from the Jurassic Period), are are plotted in detail on Big Ten’s California Gold Map 5 .
The Ancient Rivers of Gold in northern California are from the Tertiary Period. The Tertiary rivers existed millions of years ago and many of them had large quantities of gold within their gravels. Because of that, they are known as the "Ancient Rivers of Gold." Each ancient river is discussed below.
Information on this page is based on the classic work of Waldemar Lindgren of the United States Geological Survey and by study of Big Ten’s California Gold Map 5, which shows the relationship of the ancient rivers to landmarks, such as roads, creeks and towns in the region.
These now-dry Tertiary rivers are thought to be a prime source of the gold found in many of the rivers and streams of the Mother Lode region of northern California. The ancient rivers are discontinuous and sometimes follow tortuous routes.
They have been altered by volcanic activity, erosion, and in some instances portions of the rivers have been covered by lava. Much of the region underwent extreme volcanic eruptions. Volcanic flows have been found up to 4,000 feet deep. Volcanic flows were up to 60 miles in length. Portions of an ancient river may be found at ground level or near the top of a mountain, or on the side of a mountain, or buried.
