Flying Dog Trails
The Flying Dog trail is an immaculate trail system that's great for most skill levels--this probably shouldn't be your very first mountain biking trail experience, but if you've been out a few times you will find this to be a great way to take your abilities to the next level. Intermediate and expert riders will love this trail system as well.
Utah Mountain Biking maps out three different trail options here. They suggest the Lapdog Loop (10 miles/Easy), Big Dog Loop (16 miles/moderate), or The Big Pretzel (23 miles/tough).