Bannack: Discovery launches Montana gold rush

Fur trappers following in the Corps of Discovery’s footsteps left no settlements in their wake. But a mere 50 years after Lewis and Clark, prospectors were combing the West for gold.

One man was instrumental in adding Montana to the gold-seekers’ travel itinerary, inadvertently setting events in motion that would lead to the settlement of Bannack and, eventually, Montana.

A twist of fate led Granville Stuart to the gold deposits in the country that was to become Montana. In 1857, Granville, his brother James and cousin Reece Anderson were mining in Yreka, Calif., when they decided to return to Iowa to visit family. The trio commenced their eastward trek on July 14, 1857.

When the group arrived at Malad Creek (south of today’s Pocatello, Idaho), Granville became gravely ill and spent nearly two months recovering. Here he overheard rumors of possible placer gold near the Deer Lodge Valley in what was then Dakota Territory (seven years later to become Montana Territory).

On April 4, 1858, they moved to the Deer Lodge Valley and eventually joined up with Thomas Adams. On May 2, 1858, the Stuarts, Anderson and Adams set out for Benetsee. Being unprepared to work the area, they left the country and didn’t return until the warm months of 1860, when they founded a small camp near Gold Creek, calling it American Fork (nothing is left of it today).

Granville wrote to his other brother Thomas in Colorado, urging him to join them. Through that bit of correspondence, word got out to the “Pike’s Peakers,” as the Colorado prospectors were called, that this northern territory held gold.

Two years later, while aiming for Idaho, a Colorado party led by John White was prospecting its way through southwest Montana. Coming to Lewis and Clark’s Willard Creek, they headed up its gulch to try their luck.

On July 28, 1862, while panning the gravels of what they called Grasshopper Creek — owing to the dense population of “hoppers” on its banks — the prospectors hit upon a bonanza. The place of discovery came to be called White’s Bar and the Grasshopper Diggings.

Shortly, the sound of “Eureka!” echoed through area mining camps, setting off a genuine gold rush to Montana and bringing a dramatic change throughout the southwest part of Big Sky Country.

The strike was about three miles downstream from where the gold camp eventually sprouted, and early miners named their camp after a local tribe, the Bannock Indians. The spelling was inadvertently changed when the town’s name was submitted to Washington, D.C., for the post office in 1862.

By the fall of 1862, up to 500 people had moved into Grasshopper Creek. It is estimated that by the time winter halted work, $700,000 worth of gold had been collected along the creek.

At first glance, Bannack must have seemed an unlikely place to look for an ore body. The pebbles and boulders along the creek are limestone, a specimen that rarely contains gold. And since there is no gold upstream from Bannack and very little downstream, the source of the bedrock gold must be within the cliffs above the area.

Geologists surmise that during a period of widespread volcanic activity in southwestern Montana, the limestone canyon walls on each side of Grasshopper Creek and a few hundred feet above its level were intruded by large masses of molten magma. The rock formed by the hardened magma was the most common igneous intrusion — granite.

When molten granite magma comes in contact with limestone, it reacts to create a wide variety of minerals. As the magma hardens, it forms an outside layer over the granite intrusion, separating it from the limestone. This mineral-filled contact zone may be anywhere from a few feet to a few hundred feet thick.

Prospectors have long known that contact zones around granite intrusions, especially those in limestone, are likely to contain deposits of gold. The early miners at Bannack must have learned that lesson well. Before the summer of 1862 ended, they had found the gold in the contact zone and staked claims around its margins on both sides of Grasshopper Creek.

Rick and Susie Graetz teach at the University of Montana’s Department of Geography.