1. Battle of the Snake River Canyon: On October 21, 1855, a battle took place in the Snake River Canyon between the Cayuse Indians and the U.S. Army. This battle was a part of the Yakima War, which was fought in Washington and Oregon territories. The Cayuse Indians were eventually defeated, and their leaders surrendered. This marked the end of the Yakama War.

2. Statehood: Idaho became a state on July 3, 1890, but it wasn't until October 21, 1890 that President Benjamin Harrison signed the proclamation officially declaring Idaho a state. This event was celebrated as a major milestone in Idaho's history and marked the beginning of Idaho's growth and development as a state.

3. First Woman Elected to Congress: On October 21, 1932, Idaho elected the first woman to Congress, Margaret Chase Smith. She was elected to the House of Representatives, where she served until being elected to the Senate in 1948. She was a trailblazer for women in politics and a champion for issues such as civil rights, labor rights, and environmental protection.

4. Evel Knievel's Snake River Canyon Jump: On October 21, 1974, legendary daredevil Evel Knievel attempted to jump the Snake River Canyon near Twin Falls, Idaho. He used a specially designed rocket-powered motorcycle, but the jump didn't go as planned, and Knievel landed in the river. He survived the jump but suffered a few injuries.

5. Boise River Flood: On October 21, 1983, a major flood hit the Boise River, causing widespread damage and forcing thousands of residents to evacuate. The flood was caused by a combination of heavy rain and snowmelt and was one of the worst natural disasters in Idaho's history. The flood caused millions of dollars in damages, but also brought the community together as people worked to help those affected by the disaster.