After being stopped by Mexican authorities, the migrants split into groups. On the west side of the crossing, some tried to get through razor-wire fencing in a concrete levee that separates the two countries. On the east side, some pulled back a panel of fencing made of Army surplus steel landing mats to create an opening of about 4 feet, through which a group of more than 30 people crossed, according to a U.S. official who was not authorized to discuss the matter publicly and spoke on condition of anonymity. Others made it over a steel fence farther east.