1. On September 20, 1909, the Boise River was diverted for the first time to irrigate farmland. The diversion, known as the New York Canal, was a major milestone in the development of Idaho's agriculture industry.

2. On September 20, 1870, the first train arrived in Boise, marking the beginning of the city's growth as a major transportation hub. The arrival of the train also spurred development of new businesses and industries in the area.

3. On September 20, 1899, Idaho's state flag was officially adopted. The flag features a blue field with the state seal in the center, and was designed by a committee of Idaho women.

4. On September 20, 1935, the Idaho State Police was established by the state legislature. Today, the agency is responsible for enforcing state laws and providing support to local law enforcement agencies.

5. On September 20, 1977, the Teton Dam in eastern Idaho failed, unleashing a catastrophic flood that caused extensive damage and loss of life. The disaster led to major changes in dam safety regulations and design standards.