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 site was Antioch’s sandy gateway to the river — a place to picnic, play and bask in the sun.

But over many years, natural processes and human intervention — starting from the late 1800s with large-scale sand mining — isolated the Antioch Dunes into a much smaller footprint: 55 acres, plus another 12 with the recent addition of nearby unused PG&E land. Sandwiched between a gypsum processing plant and the former Fulton Shipyard where WWII vessels were once built, the now-isolated landscape contains certain plants and a butterfly species that are entirely unique to the dunes.

“I have a lot of eco-pride for the fact that Antioch is home to the only national wildlife refuge to protect plants and an invertebrate,” Julie Haas-Wajdowicz, Antioch’s environmental resource coordinator, said. “Because this one (the Lange’s metalmark butterfly) is very much a species in peril.”

Created in 1980, the Antioch Dunes National Wildlife Refuge — the first of its kind dedicated to plants and insects — is the only home to the endangered Lange’s metalmark butterfly, which has been scarce in the last few years, and the main home for the Antioch Dunes evening primrose and the Contra Costa wallflower.

The refuge is managed as part of the San Francisco Bay National Wildlife Refuge Complex, an organization under the National Fish and Wildlife Services.

Haas-Wajdowicz returned to the refuge last week, along with some 30 public employees from various agencies, to talk about sustainability and pull weeds such as winter vetch, yellow star thistle, mustard and brome grasses to improve the habitat for the endangered plants in the western dunes known as the Stamm Unit.

“In springtime, there’s a lot of invasive plant control,” wildlife refuge specialist and tour guide Louis Terrazas told the volunteers. “We’re doing it manually today, but we’ve also had spraying out here, a lot of mowing and weed wacking.”

“More rain means more plants. The endangered plants like it, but so do these non-native species.”

Terrazas has worked at the refuge for nearly 20 years, and he’s seen many of the changes, including decades of conservation work to help to restore the land, making it a better habitat for the endangered plants and butterflies. In recent years, though, he said there’s been an even more concerted effort to bring back the lost sand to the refuge.

The late 1800s saw two brick companies open near the site, and after the 1906 San Francisco Earthquake, the freshwater sand was sought out for high-quality bricks to rebuild the city with materials that would withstand fire.

“It was a good location in the Bay Area where you can get sand material in order to quickly create bricks, and it was freshwater sand; it is easier to make freshwater sand into bricks,” Terrezas said.

Sand mining continued through 1980 when the U.S Fish and Wildlife Service negotiated a deal for the property, which was almost sold to a developer to build condominiums. The Lange’s metalmark butterfly and Antioch Dunes evening primrose were listed as endangered species shortly before that.

Over the years, little of the endangered species’ critical habitat was left; it was further damaged by removing the sand and by visitors’ trampling and accidental fires, so officials closed it to the public in 1986.

Realizing the dunes desperately needed restoring, the U.S. Fish and Wildlife Service began looking for sand in the years that followed. The answer came from the Port of Stockton, which regularly dredges the nearby deepwater channel and was looking for a place to dump sand.

The river has been dredged about every other year since 2012 from a location in the main channel about 600 yards away from the refuge, Terrazas said.

“It was a win-win situation where they needed a place to put it — and it saves them money,” he said. “They don’t have to pay a tipping fee and they don’t have to barge it somewhere farther away or pump it somewhere farther away.”

Last October, the Port of Stockton dumped nearly 8,000 cubic yards of sand at the refuge and over the years Terrazas estimates it has added about 109,000 cubic yards of sand material on two different sites: the large Stamm Unit to the west and the smaller Sardis Unit to the east.

“This area was mined down to the hard pan, and so a lot of that sand has gone,” Terrazas said. “An estimated 3.2 million cubic yards of sand was taken out of the upper dune system and an estimated 1.7 million of that was on the refuge footprint that was removed from the sand dunes. We’re putting a little bit of that back.”

Refuge workers have also placed bricks along the property line to keep the sand from blowing away.

“It makes it easier for us to collect it and put it back somewhere else,” Terrazas said.

One inhabitant of the refuge thriving loving the new sand is the endangered Antioch Dunes evening primrose, according to wildlife biologist Susan Euing, who keeps track of the plants.

“They really have started taking off in numbers,” she said.

Euing said from 2006 to 2016, the refuge averaged 602 mature primroses, but by 2017, that number had climbed to 1,735 and then to 8,506 in 2021 – a 390% increase.

Counts are done every three years, she said, adding that the next one will be done in May. The new sand “has been a godsend,” she said.

Terrazas agreed.

“Their numbers have skyrocketed out here in this area where we brought in new sand material, because there’s less competition for them,” he explained.

Not faring quite as well are the endangered Contra Costa Wallflower, which is primarily found along the river, underneath oak trees and in shady areas.

“Their numbers have not responded like the primrose numbers,” Terrazas said. “Their numbers dipped a little bit so we’re focusing on them now.”

This spring staff is conducting pollination experiments on the Contra Costa Wallflower to understand how this endangered species reproduces and to estimate its genetic diversity. Results will help refuge workers learn how to better conserve and recover the endangered species, according to the Wildlife Services.

The tiny Lange metalmark butterfly has also seen better days, at its height in 2000 with a population of 2,300. The butterfly is only seen in the Sardis Unit ever since a fire engulfed the Stamm Unit of the refuge in 2007. Even so, refuge workers continue to plant Antioch Dunes buckwheat, the insect’s host plant, in hopes they will return.

Wildlife Service biologist Wayne Hayes said the Lange’s metalmark butterfly has been declining for the past two decades but it’s not clear why.

“It is most likely the result of a combination of stressors, including habitat loss and degradation, low population size, environmental pollutants, pesticides, wildfires, and changing climatic conditions,” Hayes said.

The biologist noted that the U.S. Fish and Wildlife Service is working with UCLA’s California Conservation Genomics Project to study the metalmark butterfly’s DNA. They want to see how the Dunes metalmark is related to other nearby butterfly populations, which could help them in captive propagation efforts, he said.

Euing, too, has not lost hope.

“Their numbers have been depleting, and we did not see any last year, but we’re not counting them out yet,” she said. “We are still going to be looking for them.”

Due to the sensitivity of the habitats at the Dunes, the refuge is not open to the public except during regular monthly guided tours on second Saturdays and during other special events. The next tour is at 10 a.m. May 11. See www.fws.gov/refuge/antioch-dunes.