There were a number of events that increased interest in a route to California. Probably the most important was the acquisition of California in the Mexican-American War, and the immediately following California Gold Rush. The Civil War added urgency to the transcontinental Railroad, and was very important as well.
building of the transcontinental railroad - disappearance of the frontier
The California Gold rush of 1849.
The Union Pacific and Central Pacific built the transcontinental railroad and when it was finished, a golden spike was nailed when it was finished to celebrate the event.
The Mexican War and the debate over the new territories such as California.
The driving event was the westward expansion of U.S. territory, esp. in connection with the Mexican War (the product of the annexation of Texas). How the territories were to be organized - whether open to slavery or not - became a burning issue. The territorial issue was intensified at the end of the decade, by California's growth (aided immensely by the Gold Rush) and the issue of building a transcontinental railroad through the territories to link east & west.
The California gold rush in the early to mid 1800's
building of the transcontinental railroad - disappearance of the frontier
The California Gold Rush was a major factor in expansion west of the Mississippi. That westward expansion was greatly aided by the completion of the Transcontinental Railroad in 1869, and passage of the Homestead Act in 1862.
the gold rush
It brought 30000 people to California
Yes, they have been increased by 16.7% They are increased by that much in my location since the 26th.
The railroad system
It's a formal event.
The Omaha area is where the first tracks of the Transcontinental Railroad were placed in 1863.
building of the transcontinental railroad - disappearance of the frontier
The event that officially marked the end of World War I was the Treaty of Versailles. It was signed in a railroad car on June 28, 1919.
It is an outcome of a trial in which the event of interest does not occur.