(Multnomah County, OR)  --  Authorities say a woman was killed and her son was injured after both fell off a trail at Horse Tail Falls.  Multnomah County sheriff's deputies say the 37-year-old woman and her three-year-old son fell yesterday afternoon off a 50- to 60-foot cliff, then continued another 20 to 30 feet down a slope.  Authorities say the three-year-old is being treated for serious injuries.  No names have been released.