Northwest Caving Association Regional
http://www.caves.org/grotto/wvg/regional/
Over Memorial Day weekend there is going to be a caving convention just outside of Portland OR (trout lake, WA). I expect some great caving going on there.
Right now southwest is selling round trip tickets to Portland for $152 and some people in the local grotto will be able to pick you up from the airport and take you to the camping site; so you wont even need to rent a car. If you are interested I would suggest getting the tickets now.
Tony