Let's get some organized rides going!

Hello!

I'm looking to do some mountain biking towards the end of august,
sadly my friends are all pretty sedate compared to me, so that's shot
down. Does anyone know of any groups, clubs, or companies that
organize multiday mountain biking rides? I'm dreaming of biking around
in Colorado for a week and seeing some really nice peaks... but biking
alone is out of the question.

I started thinking about this after I was in Germany for a year. There
was a local biking club that organized rides almost every weekend. The
coolest was a two day ride along the Limes near Frankfurt in Hessen.
It's so much fun when you're with some other people! Any ideas?

Kai.