1. The Lewis and Clark Expedition reached Oregon on May 20, 1805. This day marked the first time that explorers from the Eastern United States had set foot in what is now Oregon.

2. On May 20, 1911, the first rail connection was made between Portland and the Willamette Valley. The connection was made possible by the completion of the Springwater Line, which ran from Portland to Boring.

3. Oregon State University was founded on May 20, 1868, as the Corvallis College. The college was initially established as a community school and later evolved into one of the state's leading research universities.

4. On May 20, 1859, Oregon became the 33rd state to enter the United States. This event marked the end of Oregon's territorial status and the beginning of statehood.

5. May 20, 2004, saw the official opening of the Oregon Historical Society's new museum in Portland. The museum houses a collection of more than 85,000 artifacts and documents that are related to Oregon's history. The opening of the museum marked a significant milestone in the state's preservation of its history.