Corvallis' tourism site mentions hiking, biking, wine tasting, theater, bird watching, craft beer, and public art. I'm sure omitting geocaching was just an oversight.
The details about the daylong sunrise-to-sunset cache machine (start time 6:45 a.m. on September 19) are in this forum discussion, but the official event is this after-machine dinner.
Dinner will be at Woodstock's Pizza Parlor, 1045 NW Kings Blvd, N 44° 34.632 W 123° 16.488. Be there at 7:30 p.m. on Saturday, September 19, 2020. It should run about two hours.
Be sure to put this on your watch list now, so you'll be the first to know about changes and updates as the big day approaches!
A "will attend" note here will be greatly appreciated in order to help plan dinner arrangements.