The specific context that transformed the treaty framework of the early 1850s into the catastrophe of the early 1860s was the Colorado gold rush — the discovery of gold near what is now Denver in 1858 and the subsequent flood of American prospectors and settlers into Cheyenne and Arapaho country.

The gold rush was not a slow or gradual process.

Within a year of the discovery, tens of thousands of prospectors and their supporting population had moved into the region.

Denver grew from nothing to a substantial town in a matter of months.

The infrastructure of American settlement — roads, supply depots, newspaper offices — appeared almost overnight.

The people who came with the gold rush did not come to share the country with the Cheyenne and Arapaho.

They came to get gold, and the existing inhabitants were obstacles to that goal, not partners in a shared economy.