A unique Bay Area wildlife refuge is beginning to thrive again — but its most fascinating endangered species is still in peril

Looking out at the wildflower-laden landscape of the national wildlife refuge along Antioch’s waterfront, it’s hard to imagine it was once part of a massive sand dune system that stretched more than two miles along the San Joaquin River’s southern banks.

Ancient deposits of glacial sands carried downstream from the Sierra Nevada formed the dunes, shaped by the winds and tides, once reaching almost 120 feet tall and stretching some 800 feet inland. Up until the early-to-mid-1900s, the 400-acre...