On the south shore of the San Joaquin River in Antioch, there is a small patch of sand that matters far more than its size. The U.S. Fish and Wildlife Service says Antioch Dunes National Wildlife Refuge is the only known place in the world where the Lange's metalmark butterfly lives.
What it protects
The refuge was set up in 1980 to protect three federally endangered species:
- Lange's metalmark butterfly
- Contra Costa wallflower
- Antioch Dunes evening primrose
These dunes were once part of a larger river sand dune system full of plants and insects found nowhere else. Over the past 150 years it was badly damaged by sand mining, invasive plants and other threats, according to the Fish and Wildlife Service. Today it is one of the last river sand dune habitats left in the Sacramento-San Joaquin Delta.
A butterfly on the brink
Wikipedia, citing the East County Times, says the metalmark count fell from 2,342 in 1999 to 45 in 2006, then rose to 78 in 2013. That year a restoration project began. It was sponsored by the Port of Stockton and carried out by the U.S. Army Corps of Engineers. Sand dredged from the river was pumped onto the dunes and then replanted with buckwheat, the butterfly's host plant, and the two endangered plants. The refuge's library lists a San Joaquin River dredging project from November 2023 and a 2023 vegetation inventory that compares changes since 2017.
Can you visit?
Not on your own. The habitat is fragile, so the refuge is closed to the public, the Fish and Wildlife Service says. It used to offer free docent-led tours, but the agency says those tours were paused for the rest of 2025 because of limited resources and safety issues. The refuge's listed office is in Sonoma.