BENTONVILLE (AP).- A visitor arriving at Crystal Bridges Museum of American Art sees a curved concrete facade with the museum’s name and, behind it, a stand of trees on a hillside. Where’s the museum? Get closer, then look down. A series of connected pavilions under curved copper roofs stretch through a tree-lined ravine. Two of the buildings serve as bridges over ponds filled from a spring-fed stream that flows through the site. To get in, just follow the wave of people going downstairs. Crystal Bridges is regarded as the most important museum to open in the U.S. in decades, and it has done so in a city of 35,000 in the Ozark Mountains that’s served by a single interstate highway that terminates in the middle of town, not far from the headquarters of Wal-Mart Stores Inc. More than 175,000 people have