1. Pioneer Day: September 15 marks the iconic Pioneer Day, which is celebrated every year in Utah to commemorate the arrival of the Mormon pioneers into the Salt Lake Valley in 1847. Pioneer Day is a nationally recognized holiday in Utah, and is marked by parades, fireworks, and other festivities throughout the state.

2. Statehood Day: September 15 also commemorates the day that Utah officially became a state of the United States, in 1896. This event is celebrated annually as Statehood Day, and is an important part of the state's history and culture.

3. Natural Disasters: September 15 has seen its share of natural disasters in Utah, including a number of devastating floods and wildfires. In 1909, the Great Flood swept through Salt Lake City, killing several people and causing extensive damage to homes and businesses. In more recent years, Utah has also been plagued by severe wildfires during the late summer and early fall months.

4. Record-Breaking Weather: Utah's weather can be unpredictable, but on September 15, 1936, the state set a record for the highest temperature ever recorded in the United States outside of Death Valley, California. The town of St. George, located in southern Utah, recorded a temperature of 118 degrees Fahrenheit, which remains a record to this day.

5. Historic Conferences: September 15 has also been the site of several historic conferences and meetings throughout Utah's history. In 1856, Brigham Young called a meeting of Mormon leaders to discuss the impending arrival of the U.S. Army, which set the stage for the infamous Utah War. More recently, the annual Salt Lake City International Tattoo Convention has been held on September 15, drawing tattoo artists and enthusiasts from around the world to the state.