The Lakeside Trail is another excellent trail; 3 miles of curving singletrack beginning at the camping area at Bridger Bay on the far northern end of the island. The middle mile of the ride is insanely rocky and rates an "expert" in technical difficulty, but you can easily hike through the areas that make you nervous. You can ride the trail back, or head overland by dirt road. (Or, you can zip 1/2 mile down to the White Rock Bay Trail!)
One of Antelope Island's permanent residents eyeballs a biker. Among the wildlife in this nature preserve are 900 bison. The big guys aren't usually aggressive, but they are wild. And they're definitely BIG. Don't get close during the calving or breeding seasons.