CENTRAL OREGON  -- 13 Search and Rescue Volunteers and two Deschutes County Deputies and 2 off-duty nurses who happened to be on scene assisted in the rescue of an injured mountain biker yesterday.  About 11 a.m. a call was placed to 9-1-1 for help for 40-year-old Corina Davis of Seattle.  She had been on the Tiddlywinks Trail west of Bend. Davis was carried by wheeled litter, then transferred to a Sheriff's Office 4-wheel drive pickup and driven to a waiting ambulance and taken to St. Charles. The rescue took over 2 and a half hours.