A single golden spike, hammered in Utah, joined the US by rail coast to coast

On 10 May 1869, officials from the Central Pacific and Union Pacific railroads met at Promontory Summit, Utah, and drove a ceremonial golden spike to complete the First Transcontinental Railroad. A trip that once took months by wagon could now be made in about a week. Much of the track on the Central Pacific side was laid by Chinese immigrant laborers, work later commemorated but for decades left out of the official story.

— Wikipedia contributors, First Transcontinental Railroad — Promontory Summit, Utah, 10 May 1869