Looks like you are having fun. Remember to always ride with somebody.
If you haven't, check out RMDRA. Bunch of local guys and girls who maintain those very trails you are on. They host group rides Wednesday nights during the summer. Great way to meet riding buddies and shoot the *crap*.
A free tip. Yours to decide if you want it. But learn to stand. Youll be a much faster and confident rider in the future. That being said there are fast riders who sit a lot, but most don't. RMDRA guys would be also willing to provide lots of tips on guided rides night.