1. Mount St. Helens eruption: On May 20, 1980, one of the most significant volcanic events in American history occurred with the eruption of Mount St. Helens. The eruption caused widespread devastation throughout the region and led to over 50 deaths.

2. Seattle World's Fair: On May 20, 1962, the Seattle World's Fair opened its doors, welcoming millions of visitors from around the world. The fair showcased a wide range of exhibits, including the world-famous Space Needle and the futuristic monorail.

3. Washington Statehood: May 20, 1889, marks the day Washington was granted statehood by the United States government, becoming the 42nd state in the union.

4. First Boeing 747 flight: On May 20, 1970, the first Boeing 747 took its inaugural flight from Everett, Washington. The jumbo jet would go on to revolutionize commercial air travel and become one of the most iconic aircraft in history.

5. Branches of Government Building: On May 20, 1929, the Washington State Capitol Campus in Olympia, Washington, broke ground on the construction of the iconic Branches of Government Building. The building is home to the offices of the governor, lieutenant governor, and other high-ranking officials in the state government.