I am a student of jazz, bluegrass, and American roots music. I play upright bass in the big band and jazz combo of the Mile High Community Band and I also sit in at a few bluegrass/old-time jams from time to time.
I host an outdoor bluegrass jam at Chavez Park (Tennyson St.) in the summertime. For a list of bluegrass jams in Colorado, see the CBMS jams page. It’s a comprehensive list, and they do a good job keeping it up to date.
For a list of jazz jams in the Denver area, see my Denver jazz jams page. (I couldn’t find a comprehensive reference elsewhere on the web, so I created one. I’m cool like that.)