IMPERIAL SAND DUNES, Calif. – Every weekend he can, Gene Elwell heads to the desert and races his buggy over the largest sand dunes in the U.S. Nearly 200 miles west, on California’s Pacific shores, the Rev. John Fanestil spends every Sunday at Friendship Park, where people on both sides of the U.S.-Mexico border touch hands and talk through holes in a chain-link fence. For decades, the dunes and Friendship Park were virtually unchanged. But in its final months, as the Bush administration raced to fulfill a pledge to erect 670 miles of fencing and vehicle barriers on the border, they were transformed almost overnight.