1. On May 21, 1888, the first train arrived in Ogden, Utah, marking the completion of the transcontinental railroad. This event played a significant role in the development and growth of Utah's economy, allowing for easier transportation of goods and people across the country.

2. May 21, 1958, marked a tragic event in Utah history when a United Airlines flight crashed into a mountain near Bryce Canyon, killing all 52 people on board. The cause of the crash was attributed to the pilot's failure to properly navigate the mountainous terrain.

3. On May 21, 1960, a magnitude 5.3 earthquake struck Salt Lake City, causing significant damage to buildings and infrastructure. Despite the destruction, only two fatalities were reported, and the city was able to quickly recover from the disaster.

4. May 21, 1983, saw the opening of the LDS Conference Center in Salt Lake City, Utah. The massive building, which seats over 21,000 people, serves as the primary meeting place for the semi-annual general conference of The Church of Jesus Christ of Latter-day Saints.

5. In 2014, Utah became the first state in the United States to recognize same-sex marriage after a federal judge ruled that the state's ban on such marriage was unconstitutional. The ruling was issued on May 21, and though it was later stayed and reversed, it played a significant role in the ongoing national debate surrounding same-sex marriage.