I'm new to the Mando world and live in Eugene. I'm familiar with the Bluegrass and Irish jams at Sam Bond's. What else is happening in Oregon?
If you like Irish sessions you can go here to find them: http://thesession.org/. Last time I looked there were a number of them in Oregon. But it's a big state so that's no guarantee that there is one near you.
There is also the Oregon Mandolin Orchestra if you like larger, orchestral groups, though they play all kinds of music.
A quick Google search shows up a regular blues jam, but in the Portland area: http://www.meetup.com/Portland-Blues/events/206451192/
A small group of us have started a jam session in McMinnville. We are meeting at McMinnamins on Third street the second and fourth Mondays at 7:00. I'm the only mandolin player so far, lots of guitars and a fiddle player.
Thursdays, weekly .. Astoria Senior Center , 11th and Exchange St ukes mandolins guitars, just singing .. do what you do . no pressure.. Wednesday Port of Call Bar & grill 9th and commercial Electric .. open mike 1st then a Jam Bar Band Veterans .. And Moose Lodge (up hill from Maritime Museum) quiet Very few people , Private Club , but players welcome Its a open Night on the week 2 of my friends pay Lodge member dues , i don't.
