Welcome new rider - join the local Meetup group plenty of people on there to ride with. (y)
also a bunch of us will be doing a 10 mile Sprint on Tuesday the 30Th at late-night parking lot, food and such 6:30pm.. ALL is invited
In addition to Rob's suggestion, the local chapter of IMBA... Southern Nevada Mountain Biking Association can be found here: www.facebook.com/SNMBA
SNMBA does regular trail maintenance/building, group rides, and has a bunch of cool dudes and one or two losers. If you're not familiar with Vegas MTBing, you might be pleasantly surprised with the quantity and diversity of trails. You'll learn the goods in due time.