Antioch Dunes National Wildlife Refuge is unique within the National Wildlife Refuge system: it is the only wildlife refuge that was established specifically to protect endangered plants and insects. The special species protected here are the Antioch Dunes evening primrose, the Contra Costa wallflower, and the Lange’s metalmark butterfly. The refuge is accessible for the public to visit only on a docent-led tour one day per month. When I learned that a good, if not the best, time to see the evening primrose was around May, I immediately put the associated docent-led tour date on my calendar. The tour is not long – mine was just over 1 mile and lasted nearly 2 hours – but it was a unique opportunity to visit an otherwise inaccessible wildlife refuge and see special sights.
The star of the tour, in my view, was the Antioch Dunes evening primrose (Oenothera deltoides ssp. howellii), listed on the California Native Plant Society (CNPS) Inventory of Rare and Endangered Plants. Although I could see a few plants within the refuge even before the docents arrived to open the gate, of course the best close-up views came later in the tour.
The GPS track shows the relatively short loop that we hiked: only a bit over 1 mile long. Although we did climb up the dune, here the dunes are small, and the total elevation change was only about 20 feet. On the GPS track image, the orange dot shows where the visitors gathered for initial orientation before we started the walking part of the tour.
Near the entrance there was a bushy plant with several showy yellow flowers. I think it is telegraph weed (Heterotheca grandiflora), one of the common native plants that grow in the dunes. It is in the same family as daisies, asters, and sunflowers.
There is an interesting story behind the sand dunes. Historically they were larger than the present dunes. Following the 1906 great earthquake and fire in San Francisco, the sand was harvested for making bricks for rebuilding the city and the dunes were nearly destroyed. Before that the dunes had accumulated over millennia from silt deposited in the area as the Sacramento and San Joaquin Rivers converged and their flow to San Pablo and San Francisco Bays was constricted by the narrow Carquinez Strait. Prevailing winds blew deposited sand eastward (upstream) and created a localized area of sand dunes, perhaps a few square miles. Wildlife such as plants and insects that thrived in the ecosystem were isolated from others and evolved to be unique and endemic to the area. The use of sand for industrial purposes nearly eliminated the local species. After creation of the wildlife refuge the sand dunes are gradually being rebuilt, in part using sand that is dredged from the San Joaquin River channel to preserve a shipping channel to Stockton. So today the dunes themselves are gradually being restored. This view is along the side of one of the sand dunes. Non-native plants growing nearby are not able to thrive on the dune, where native plants will grow naturally.
Modern evidence of the reliable winds in the area was in the form of a large windmill farm visible not far away in southern Solano County. Although the refuge is in Contra Costa County, there is a narrow slice of Sacramento County between the San Joaquin and Sacramento Rivers, and on the north side of the Sacramento River is Solano County.
There were Antioch Dunes evening primrose plants thriving in the sand where other, non-native, plants were not growing. This picture shows several blooms as well as a couple that had turned pink after the blooming cycle was complete. This color change is characteristic of other large/showy evening primroses; I have seen examples both in the Sierras and in the Southern California desert.
The area known as the Delta is very flat, and it was easy to see Mt Diablo rising abruptly to over 3800 feet elevation, only about 12 miles away. On the day of my visit it seemed that Mt Diablo was capturing some of the passing clouds and even training them into a plume extending down-wind. The lower, brown hills in the right foreground are in Black Diamond Mines Regional Preserve.
Among the non-native grasses growing near the dunes there were several other colorful plants. Deerweed (Acmispon glaber) is considered by some to be a weed, but it is actually considered by biologists to be beneficial to the ecosystem since it provides food for hummingbirds, bees, butterfly larvae, and deer.
On the other hand, this has been a banner year for vetch, probably winter vetch (Vicia villosa ssp. villosa), which seems to be considered to be more of a nuisance (although it’s rather pretty). We noticed a bee busy feeding on some vetch, with fat orange pollen pouches.
Occasionally a few boats powered past in the San Joaquin River. The Delta is very popular with boaters, especially during the summer.
Near the far end of our loop walk – while a walkway had been mown, there are no established trails – we came to a small stand of Contra Costa wallflower (Erysimum capitatum ssp. angustatum). The wallflower flowers are much bigger than the flowers of the wild mustard grass that also was present in the refuge. The four-petal pattern is characteristic of the mustard family of plants.
We did not see Lange’s metalmark butterfly, the insect protected by this wildlife refuge. This butterfly has only one reproductive cycle per year, and the butterflies do not emerge until August and September. We did not go to a location where the larvae are known to be present. An important food supply for the butterflies is the California poppy (Eschscholzia californica), which blooms throughout the spring and summer. The poppies in the refuge are not the most typical poppy color, but rather are bright yellow with a bit of the poppy color near the base of the petals. I am trying to learn whether this coloration difference is due to genetic differences (e.g. color mutation variant), nutrients, or some other factor(s).
Along the river side of the dune we passed several clusters of elegant clarkia (Clarkia unguiculata), whose blossoms are indeed elegant, as well as complex. It is another of the common native plants that grow in the dunes area.
Eventually we completed the loop and arrived back at the entrance gate. A visit to Antioch Dunes is a little different each month, as the docents focus on what is happening / blooming at the time, as well as the general history and ecology. It was a very enjoyable visit – and I just might come back to try to see the butterflies during their short season in the fall.