1. On September 15, 1855, Isaac Stevens negotiated a treaty with the Walla Walla, Cayuse, and Umatilla tribes, known as the Treaty of Walla Walla, which ceded a large portion of Oregon's tribal land to the United States government. This treaty was a significant step in the federal government's efforts to expand westward and establish control over Native American lands.

2. In 1902, a fire broke out in downtown Portland, destroying more than 20 buildings and causing an estimated $1 million in damages. The fire started on a Saturday afternoon and was so intense that it required multiple fire departments to respond. The blaze was eventually contained after more than 10 hours of firefighting efforts.

3. On September 15, 1938, the Oregon State Police was formed, replacing the Oregon State Traffic Division. The new agency was tasked with enforcing all state laws and providing assistance to local law enforcement agencies. Today, the Oregon State Police is responsible for a wide range of public safety initiatives, including highway safety, criminal investigations, and emergency response.

4. In 1946, a commercial airplane crashed near Kelso, Washington, killing all 19 passengers and crew members onboard. The United Airlines Flight 624 was traveling from Los Angeles to Seattle when it collided with a military aircraft in mid-air. The crash was one of the deadliest aviation accidents in the Pacific Northwest at the time.

5. On September 15, 1952, the Oregon State Fairgrounds in Salem hosted a concert featuring country music legend Hank Williams. The concert was one of the first major events held at the fairgrounds following its renovation in the early 1950s. Williams played a set of his greatest hits, including "I'm So Lonesome I Could Cry" and "Your Cheatin' Heart," to a packed crowd of more than 9,000 fans.