THE OUTLAW TRAIL: A Journey Through Time, by Robert Redford. Photography by Jonathan Blair (Grosset & Dunlap, $22.50). There is nothing profound in this expansion of the piece Redford wrote for National Geographic about his retracing of the Outlaw Trail, but it is nevertheless a quiet and pleasant book, filled with pretty and sometimes breathtaking photographs. The Outlaw Trail, which winds down from the Canadian border to Mexico through Montana, Wyoming, Utah and New Mexico, was the center of a no man's land where any outlaw could roam freely, provided he kept his head down and his gun up. Redford and eight companions spent three weeks, on horse and on foot, working their way back into those powerful legends. Wisely, Redford has chosen to let the oldtimers and "characters" he met speak for themselves. Much of the time is spent chewing over the legends of Butch Cassidy and the Sundance Kid -- not surprisingly -- and there is a jolting reminder that the Old West is a relatively young ghost in the fact that the cabin at Hole-in-the-Wall, where the Cassidy gang lived, is still standing. There are perhaps a few too many color photographs of Redford looking handsome and in his element, but on the other hand, he is.