YELLOWSTONE NATIONAL PARK, Wyo. — Rangers are navigating a dangerous landscape where boiling water flows beneath a fragile rock crust as they search for a man who reportedly fell into a hot spring at Yellowstone National Park. Officials said Wednesday that the safety of park personnel was a top concern during the search in the popular Norris Geyser Basin. Spokeswoman Morgan Warthin says authorities consider the witness who reported the man’s fall Tuesday to be credible.