Which two railroad companies met at Promontory Summit, Utah in 1869 to complete the first transcontinental railroad in the United States?

In the early days of American railroads, companies fiercely competed to create the first transcontinental railway system. This monumental achievement would forever change transportation in North America, connecting the East and West coasts and enabling unprecedented movement of goods and people across the continent. The race to complete this engineering marvel involved corporate maneuvering, government incentives, and remarkable construction feats under harsh conditions.

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Union Pacific Railroad and Central Pacific Railroad
Baltimore & Ohio Railroad and Santa Fe Railroad
Pennsylvania Railroad and Southern Pacific Railroad
Northern Pacific Railroad and Great Northern Railway