1. On May 12, 1869, the Union Pacific Railroad completed the first transcontinental railway in the United States, connecting the East and West coasts. The final spike was driven in at Promontory Summit, Utah, but this accomplishment had far-reaching effects for Wyoming's growth and economy.

2. In 1891, the town of Casper was incorporated. The town was named after Lieutenant Caspar Collins, a U.S. Army officer who was killed during the Indian Wars in the area. Today, Casper is the second-largest city in Wyoming and a hub for the state's oil and gas industry.

3. On May 12, 1949, the University of Wyoming's Geological Museum was officially opened to the public. The museum is one of the largest natural history museums in the region and boasts an impressive collection of fossil specimens, minerals and rocks, and other artifacts.

4. In 1956, the world's first commercial nuclear power plant went online in Shippingport, Pennsylvania, ushering in a new era of energy production and the beginning of the nuclear age. This had significant implications for Wyoming's uranium mining industry, which became one of the largest in the world in the 1950s and 1960s.

5. In 1972, the catastrophic Wilford Brimley Dam failure occurred near Buffalo, Wyoming. The dam breach resulted in the deaths of three people and caused significant damage downstream, including the flooding of hundreds of homes and businesses. This disaster led to increased scrutiny of dam safety regulations and better public awareness of the potential hazards of dams.