RANDY PENCH rpench@sacbee.com One of the teams participating in the Amgen Tour of California, Garmin Slipstream, goes for a training ride Thursday along Old River Road in Yolo County. Before today's 2.4-mile prologue stage, riders will warm up for an hour with stationary pedaling.When you arrive downtown today to watch the 2.4-mile prologue stage for the Amgen Tour of California, you may be surprised to see what the cyclists are doing ahead of time. They're riding their bikes.