What was the significance of Promontory Point in Utah?
It was the place where the Transcontinental Railroad met.
The Transcontinental Railroad started in two places in 1863, one in the east, and one in the west. The Central Pacific Railroad began their rails in Sacramento, CA, while the Union Pacific Railroad began their track in Omaha, Nebraska.
On May 10, 1869, the two railroads met each other at Promontory Point in Utah. The east figuratively met the west when the last spike of the Transcontinental Railroad was driven into the ground at Promontory Point.