1. On August 20, 1805, the Lewis and Clark expedition encountered the Shoshone tribe near present-day Salmon, Idaho. The Shoshone provided the expedition with horses to help them cross the Rocky Mountains.

2. August 20, 1861, marked the beginning of the Confederate invasion of New Mexico Territory through the Battle of Mesilla. Confederate forces led by Brig. Gen. Henry H. Sibley were ultimately defeated by Union troops in the area.

3. In 1894, Helena, Montana experienced a massive fire on August 20 that destroyed over 30 buildings in the downtown area. The fire was started in a Chinese laundry and swept through the wooden structures.

4. The Great Falls Proving Ground, now known as the Malmstrom Air Force Base, was established on August 20, 1942, during World War II. The base played a significant role in testing and developing various military weapons and equipment over the years.

5. On August 20, 2005, hundreds of firefighters battled a wildfire that spread across over 70,000 acres in eastern Montana. The fire, known as the Longfellow Fire, destroyed several buildings and resulted in one injury. It took nearly a week for firefighters to fully contain the blaze.