The number of roundabouts controlling traffic at intersections is growing, in California and in the entire US.  Roundabouts have a long track record of safety improvement at intersections, greatly reducing the number of fatalities and serious injuries when they are deployed.  Roundabouts can be recognized because there are Yield signs on all approaches to roundabouts (no Stop signs), and there is usually a raised island to the left of each driver approaching the intersections that guides them into the ideal approach angle so they will reduce their speed while also being positioned at the ideal angle to see traffic in the roundabout.
  
For a database of the entire US see Roundabouts Database Home Page (kittelson.com)