Every once in a while unicycles can be seen out and about in Davis. There isn't an organized group, but many unicyclists attend the Damento Juggling Club. One can buy unicycles at Ken's Bike & Ski. If I remember correctly they offer Torker 20", 24", and even a giraffe unicycle. During Picnic Day unicyclists appear with Whymcycles, a group that rides creatively built bikes and other moving contraptions.
There are many styles and skill levels when it comes to unicycling. Styles of riding include mountain unicycling (MUni-ing), Trials, Freestyle, and road unicycling. Each style requires a different kind of unicycle.
Giving a comprehensive view of the different styles of unicycling, the following video is from a documentary covering the 2012 Unicycling World Championships and Convention : http://www.youtube.com/watch?v=-kDPOwMwQHo