We do 1st Saturday of every month M&Gs (some are charity events) Here is the M&G for March
Phoenix M&G March 2nd!
Even if you don't have a Facebook, you should still be able to see the posts and things like that. I post up M&G locations the beginning of each month on a hand full of forums. As for trail runs, people will post those up or they will be by word of mouth. That way there is some control to how many show up at trail.