Mining the Bonanza Bar

For many years, what we call Idaho was the place no emigrant wanted to stop. As the wagon trains rolled over the hills toward Fort Hall, the travelers were confronted with a view of the high desert Snake River Plain. Usually arriving in July or August the vista was dispiriting, even the three buttes were ominous far away in the distance. Ahead lay nothing but sand, sagebrush, bunchgrass and the chasm of the mighty Snake River. One night at Fort Hall was more than enough with massive swarms of mosquitoes flocking toward anything with red blood. The emigrants could not get out of Idaho fast enough. A few took the Goodale cutoff around Craters of the Moon, but most followed the more established southern trail where they found better water. Their only remaining decision was whether to turn left at Raft River and go to California through the Nevada desert, or go straight on toward Oregon through the Idaho desert.

What none of them thought to do was stop at the confluence of the Snake and Raft rivers and build a mining community.

All of that would change when gold was discovered in Boise Basin. The rush was on and thousands sprinted to the Idaho mountains in 1862 and 1863 to stake a claim. As time wore on, though, the claims were all taken and prospectors focused more on the Snake River that so many migrants had followed to Oregon. They reasoned the Snake must have gold in it, too; they just had to get at it. Small mining camps sprouted up along the river and in the canyon to work the placer deposits around Twin Falls and further downstream, but an often forgotten mining area was near the parting of the ways at Raft River. Numerous prospectors had recognized the presence of gold in the sand bars and benches in the area, but all the color was ”flour” or “float” gold — so fine it was nearly impossible to isolate and would float if the water was contaminated with oil or was too turbulent. Everyone knew there was gold there, but it was useless trying to sluice it because the water would just carry the microscopic flakes away.

However, where there’s enough gold, and a little gold fever, there is a way. Around 1879, miners from Salt Lake hit upon a new idea for capturing flour gold. Using copper plates amalgamated with mercury, the gold would adhere to the plate as the silt flowed over the end of the sluice. Armed with the new technique a new mining claim was situated about 5 miles above Raft River at a place the miners named Bonanza Bar.

Soon more claims were staked on both the south and north side of the river near Fall Creek. Cabins went up, flumes were built, and copper plates were treated. Ditches were dug diverting Fall Creek to provide water for sluicing. Closer to Raft River, other claims were staked at Badger Bar, Warm Springs Bar, Sagebrush Bar, Bed Rock Bar and Boyd Claim Bar. The entire area, though, was collectively known as Bonanza Bar.

The mines paid reasonably well, albeit nothing like those in Boise Basin. Some claims at Bonanza Bar could pay up to $114 (in 1914 dollars) to the ton of processed gravel. In 1881 one mine was reportedly making $800 a month and was sold for $60,000 to a New York company. Still, it was backbreaking work. Some of the paystreaks were ten to twelve feet down and the material had to be moved up to the sluices for separation. Many of the miners were Chinese who were willing to work harder for the lower paying gold flour. However, if times were tough, or someone had a new idea, whites and Chinese worked claims next to each other.

While some miners used extensive burlap flumes to capture the fine flakes of yellow metal, the majority used the new copper plate process because it captured more of the gold. The 1/16-inch plates were 6 feet or more long and were first treated with a nitric acid wash. Then mercury, also treated with nitric acid, was rubbed onto the plates causing it to adhere to the copper. The treated plates were put into service at the end of the flume. The mercury coating captured the gold as the silt-laden water flowed over the plates. To free the precious metal, the plates would be heated over a fire to evaporate the mercury. Once cooled, they were rubbed with a diluted muriatic acid and left under wet cloths for the night. The next day they were rubbed with a solution of salt peter and salammoniac and heated over a fire again. As the plate went through this final heating process, the gold blistered on the surface and could be scraped off. Base metals were then dissolved with nitric acid and the gold could then be smelted. How many miners were poisoned over the years by this process is unknown, but inhaling mercury vapor results in neurological problems as mercury builds up in the system. Acids also have well-known dangers.

Still, gold was gold and people needed to make a living. A small community developed around the mines with cabins and a recorder’s office. Situated along the stagecoach road the mining village was a short ride to American Falls for supplies. As the years wore on, more sophisticated methods of mining were used including dredges that worked the bottom of the river. The mines went in and out of service as new techniques evolved and economic conditions changed. During the Great Depression, some of the old mines were opened again and provided enough gold for people to live on.

Eventually commercial mining ceased entirely as the pay dirt disappeared. By the 1960s, Bonaza Bar had become a ghost town of old dilapidated cabins and broken sluice boxes occasionally visited by history wonks and school children. The small community, long disappeared, had been replaced by a ranch and a few farms. Hobby miners occasionally continue to work some claims in the area. In the back of their minds is the knowledge that around a million dollars a day worth of gold floats in the Snake River, they just have to find a way to get at it.

Today the cabins are gone, most lost through wildfires, but some of the workings are still visible on satellite images of the private land where the mine used to be. Nearly no one traveling the interstate today would ever guess that they are passing through what was once a thriving mining district. Like the emigrants of the 1850s, they are focused on making it over the big hill and on down the freeway. However, as you pass Register Rock and head toward the Coldwater exit, look to the right near mile marker 22 for a small unnamed island in the river. Just beyond is Bonanza Bar.