the remnant coastal dunes of southern california

Clark: Remnant Coastal Dunes Proceedings of the CNPS Conservation Conference, 17–19 Jan 2009 pp. 20–27 © 2011, California Native Plant Society

THE REMNANT COASTAL DUNES OF SOUTHERN CALIFORNIA KEVIN B. CLARK Clark Biological Services, 7558 Northrup Drive, San Diego, California 92126 ([email protected])

ABSTRACT Coastal dune systems were once extensive in southern California. Pervasive human modification of easily disturbed and highly desirable coastal strand areas have left only small remnants. In order to assess the remaining extent of coastal dunes in the region, I have repeatedly surveyed the remaining coastal dune vegetation from Santa Monica, Los Angeles County, to the U.S.-Mexico border. Species characteristic of California coastal dunes include Abronia maritima, Ambrosia chamissonis, and Camissonia cheiranthifolia subsp. suffruticosa. The introduced Cakile maritima and Carpobrotus edulis are ubiquitous. Less common perennials include Abronia umbellata, Atriplex leucophylla, Calystegia soldanella, and Distichlis spicata. Annuals tend to be more easily extirpated and are found less frequently, including Lotus nuttallianus and Nemacaulis denudata var. denudata. A small dune system in central Orange County contained a population of Cryptantha leiocarpa, previously undocumented south of Point Conception. The principal threats to the remaining dunes include continuing coastal development and especially the extensive beach raking by parks and recreation departments that removes the vegetation from many miles of coastal strand annually. Key words: beach raking, coastal dunes, coastal strand, endangered species, rare plants, restoration.

INTRODUCTION Coastal dune systems were once extensive in southern California. The El Segundo dunes between Venice and the Palos Verdes peninsula once covered nearly 25,000 acres (100 km2) (Cooper 1967). Just to the south, a massive dune and marsh complex connected the mouths of the Los Angeles and San Gabriel Rivers down to present-day Huntington Beach, a distance of over 15 miles (24 km). Most of the shoreline of southern San Diego County from La Jolla to the U.S./Mexico border was also extensive coastal dune and marsh. These coastal areas have nearly all been developed by now, but there are surviving examples of what the coastal flora used to look like. What’s more, there are numerous beaches in public ownership that have the potential to support dune communities with only minimal changes in management and use. Coastal dune systems are typically divided into active foredunes, often thinly vegetated, and subjected to constant wind, sun, and blowing sand; backdunes, which on the west coast are protected from the afternoon sun and generally support higher and denser vegetation; lee or deflation plains, which are the more stabilized sandy flats behind the active systems and often support the highest plant diversity; and dune hollows or pools, which can vary from

relatively mesic to supporting standing water yearround (Cooper 1967). Each of these micro-habitats support their own specialized species (Pickart and Sawyer 1998). In southern California, over ten sensitive plant taxa are primarily restricted to coastal dune habitats (CNPS 2009). With this kind of diversity it is surprising that so little attention is paid to coastal dunes. Part of the reason is that so much has been destroyed that there are few examples of what dune systems used to look like. However, recent surveys have shown that many remnants still remain, and with most of them in public ownership, there is great potential for restoring extensive areas to their former state. An increased awareness among beach managers and the general public about the value of this endangered system is needed to reverse the long-term decline of coastal dunes.

METHODS From 2000 to 2009, coastal strands and dunes containing native vegetation were identified and repeatedly surveyed floristically. Those that supported only exotics, principally Carpobrotus edulis (L.) N.E.Br., were not included. Some of the remnant dune systems were identified during survey work for western snowy plovers (Charadrius


alexandrinus nivosus) while I was Southern California Recovery Coordinator for the species with the U.S. Fish and Wildlife Service (USFWS) in Carlsbad, California. Efforts were made to voucher species where access and permissions were provided, and this work is ongoing. A small number of vouchers are deposited at Rancho Santa Ana Botanic Gardens (RSA-POM). The following results summarize this work and synthesize discoveries by others at coastal dunes within the region.

RESULTS AND DISCUSSION Coastal dune vegetation was found to persist at twenty-five separate coastal sites (Table 1). Most sites have some degree of invasion of exotic species, primarily Carpobrotus edulis and Cakile maritima Scop. Many sites also support protected birds or

Table 1. Summary of dunes, acreage, floristics, and notes. Sites arranged from north to south. Plant species richness: 1 = 1–5 species; 2 = 6–10 species; 3 = 10+ species. Exotics: percent cover of exotic species, principally Carpobrotus edulis, over dune remnant. Notes—Notable species Site Acres Plant richness Exotics Venice Beach

7

1

Low

Least tern preserve, Abronia maritima

Ballona dune

10

2

Med

Formerly Potentilla multijuga

LAX-El Segundo

300

3

Med

Dockweiler SB

4

2

Med

Pholisma arenarium, Mucronea californica, Camissonia lewisii, El Segundo blue butterfly Calystegia soldanella

Chevron preserve

1

3

Low

El Segundo blue butterfly

Malaga

57

3

High

Seal Beach

3

2

Med

Pholisma arenarium, Palos Verdes blue butterfly, El Segundo fly, Erysimum insulare subsp. suffrutescens Calystegia soldanella, Abronia umbellata

Surfside/SBNWS

19

2

Low

Calystegia soldanella, Atriplex leucophylla, Abronia maritima

Bolsa Chica

2

2

Low

Nemacaulis denudata var. denudata, Atriplex leucophylla,

Huntington SB

3

1

High

Abronia maritima, Calystegia soldanella

Santa Ana River

12

2

Low

Balboa Pier

20

2

Low

San Onofre SB

8

2

Low

Nemacaulis denudata var. denudata, Abronia maritima, California least terns Calystegia soldanella, Nemacaulis denudata var. denudata, Cryptantha leiocarpa Largest Atriplex leucophylla population, Abronia maritima

Santa Margarita

50

3

Low

Batiquitos

1

1

Low

Lotus nuttallianus, Nemacaulis denudata var. denudata, Phacelia stellaris Nemacaulis denudata var. denudata, Abronia umbellata

San Elijo

2

2

Low

Nemacaulis denudata var. denudata, Abronia umbellata

San Dieguito

8

2

Low

Atriplex leucophylla, Abronia maritima

Penasquitos

1

3

Low

Fiesta Island

3

3

High

San Diego River

12

1

Low

Nemacaulis denudata var. denudata, Heterotheca sessiliflora subsp. sessiliflora, Lotus nuttallianus Nemacaulis denudata var. denudata, Lotus nuttallianus, Abronia maritima, Lotus nuttallianus, Abronia maritima

North Island

31

2

High

Phacelia stellaris, burrowing owls, snowy plovers

Coronado

20

3

High

Nemacaulis denudata var. denudata, Abronia maritima, mesic dune hollows Silver Strand SB 31 3 Low Nemacaulis, Lotus nuttallianus, Phacelia stellaris, Atriplex leucophylla, Heterotheca sessiliflora, dune hollows, snowy plovers NRRF 44 2 High Cordylanthus maritimus var. maritimus, dune hollows, San Diego fairy shrimp Border Field SP 73 2 Low Nemacaulis, Phacelia stellaris, Lotus nuttallianus, Frankenia palmeri, California legless lizard [SB = State Beach, SBNWS = Seal Beach Naval Weapons Station, SP = State Park]

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Because of the increased soil moisture, dune hollows support a variety of taxa more typical of wetland environments such as Antirrhinum nuttallianum Benth., Carex spp., Distichlis spicata, Frankenia salina (Molina) I.M.Johnst., Heliotropium curassavicum, Jaumea carnosa (Less.) A.Gray, Juncus acutus L., and even Salix spp. There are very few remaining dune hollows left in southern California, with Silver Strand State Beach and the Naval Radio Receiving Facility to its south containing the majority of those remaining. Several species once found in dune hollows in the region have been extirpated, including Astragalus tener A.Gray var. titi (Eastw.) Barneby, which is now relegated to one declining population in Monterey (USFWS 2004); Astragalus pycnostachyus A.Gray var. lanosissimus (Rydb.) Munz & McBurney, long thought extinct until rediscovered in Oxnard; and Potentilla multijuga Lehm., which was restricted to the El Segundo dunes near Ballona and hasn’t been observed in over a century (Ertter 1993). Coastal dunes in Southern California have received relatively scant attention by naturalists in recent years as attention has shifted to declining coastal sage scrub and other habitats. The lack of recent survey work in coastal dunes is illustrated by the discovery of a population of Cryptantha leiocarpa (Fisch. & C.A.Mey.) Greene on a small pocket of dunes near the Balboa Pier in central Orange County (Clark 2006). This species had previously not been found south of Point Conception, but is common at this site (Fig. 1).

invertebrates, which was often the primary reason that the dune sites are still extant (Table 1). Several sites are extremely limited in area, with one acre or less of the site supporting native vegetation (Table 1). Nineteen sites were surveyed for floristics (Table 2). The most frequently encountered native species include Camissonia cheiranthifolia (Hornem. ex Spreng.) Raim subsp. suffruticosa (S.Watson) P.H.Raven, Ambrosia chamissonis (Less.) Greene, and Abronia maritima S.Watson. Several species show distinct distributions within the study area. Calystegia soldanella (L.) R.Br. is frequently encountered in the northern dune systems in Los Angeles and Orange counties, while it is rarely found in San Diego County. Both Lotus nuttallianus Greene and Nemacaulis denudata Nutt. var. denudata show a southerly distribution, with Lotus not being found north of San Diego County, while the distribution of Nemacaulis ends in central Orange County. Rare species found at few sites include Atriplex leucophylla (Moq.) D.Dietr., Phacelia stellaris Brand, and Heterotheca sessiliflora (Nutt.) Shinners subsp. sessiliflora. At the high tide line, the first terrestrial plant to make an appearance is Atriplex leucophylla. This species is extremely salt tolerant, being regularly overwashed by the highest tides. It is also one of the rarest dune species in the region, being one of the first to succumb to the beach-raking activities. Because it does not occur much beyond the beginning of the foredune, it is typically completely extirpated from beaches that are mechanically groomed. Recent surveys have located only five occurrences in the study area, each with fewer than 100 individuals (Table 2). Farther up the beach, Abronia maritima appears, and the beginning of dune topography begins to be noticed. Abronia maritima accretes blowing sand, and as a mound of sand begins to form over this perennial, the plant continually grows out of the top. Ambrosia chamissonis is another mat-forming perennial that occurs in the foredune. Other typical foredune species include Calystegia soldanella, Camissonia cheiranthifolia subsp. suffruticosa, and the introduced Cakile maritima. The backdunes typically support many of the preceding species, as well as Nemacaulis denudata var. denudata, Distichlis spicata (L.) Greene, Abronia umbellata Lam., and Heliotropium curassavicum L. The flatter deflation plain behind the dunes proper is where the floristic diversity is at its peak. Species found here include many of the preceding species plus specialists such as Camissonia lewisii Raven, Phacelia stellaris, and Heterotheca sessiliflora subsp. sessiliflora.

Fig. 1. Cryptantha leiocarpa from Balboa Pier dunes. Photo by Kevin B. Clark. Besides the diversity of flora that exists in coastal dunes, there is a wealth of specialized animals that have adapted to the unique hardships posed in the dune community. Birds such as horned larks

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Venice Beach

X

X

X

Dockweiler SB

X

X

X

X

Seal Beach

X

X

X

X

Surfside/SBNWS

X

X

X

X

Bolsa Chica

X

X

X

X

Huntington SB

X

X

X

X

Santa Ana River

X

X

X

Balboa Pier

X

X

X

X

X

San Onofre SB

X

X

X

X

X

X

Santa Margarita

X

X

X

X

X

X

Batiquitos

X

X

X

X

X

San Elijo

X

X

X

X

San Dieguito

X

X

X

X

X

X

X

Penasquitos

X

X

X

X

X

X

X

X

X

X

Fiesta Island

X

X

X

X

X

X

X

X

X

San Diego River

X

X

X

Coronado

X

X

X

Silver Strand SB

X

X

X

Cryptantha leiocarpa

Heterotheca sessiliflora

Phacelia stellaris

Lotus nuttallianus

Atriplex leucophylla

Cynodon dactylon (L.) Pers.

Calystegia soldanella

Heterotheca grandiflora Nutt.

Carpobrotus edulis

Nemacaulis denudata var. denudata

Heliotropium curassavicum

Abronia maritima

Distichlis spicata

Abronia umbellata

Ambrosia chamissonis

Cakile maritima

Camissonia cheiranthifolia subsp. suffruticosa

Table 2. Selected species distributions.

X X

X X

X

X

X

X

X

X

X

X

X X

X X

X

X

X

X

X

X

X

X

X

X X

X X

X X

X X

X

X

X

X

X

X

X

X

X

X

X

X X

X

X

X

X X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

Border Field SP X X X X X X X X Count 19 19 18 15 15 14 12 11 11 10 [SB = State Beach, SP = State Park, SBNWS = Seal Beach Naval Weapons Station]

(Eremophila alpestris), burrowing owls (Athene cunicularia), and the threatened western snowy plover (Charadrius alexandrinus nivosus) use dune systems for foraging and nesting. The endangered California least tern (Sterna antillarum browni) nests in significant colonies in some dune systems, which is often the only reason that these dunes haven’t been cleared. Mammals such as the San Diego black-tailed jackrabbit (Lepus californicus bennettii) and reptiles such as the California legless lizard (Anniella pulchra) and coast horned lizard (Phrynosoma coronatum blainvillei) spend their entire lives in the dunes. Rare and little-known insects such as the globose dune beetle (Coelus globosus) and sandy beach tiger beetle (Cicindela hirticollis gravida) are entirely restricted to these dune systems.

X X

X X

X X

X

X

X

X

X

9

6

5

4

2

2

1

KEY REMNANT DUNE SITES A small number of coastal dunes survive in southern California that still harbor populations of rare and endangered species. The El Segundo dune system is a well known pocket of endemism that has almost been lost several times in recent history, with houses built and torn down, and golf course plans proposed and rescinded (Mattoni 1990). Some of the earliest ecological studies were performed within this dune system, with Couch (1914) noting the predominance of Erysimum insulare Greene subsp. suffrutescens (Abrams) R.A.Price on the top of the dunes. This species has long been in decline and is on the CNPS list (CNPS 2009). Pierce and Pool (1938) noted the presence of Dithyrea maritima (Davidson ex 23


California. These dunes contain one of a few known populations of Phacelia stellaris and healthy populations of the rare Lotus nuttallianus, here at its northern distributional limit. The dunes show a natural gradation between sparse foredunes to saltmarsh vegetation at the estuary to dense vegetated backdunes at the base of the low bluffs. Portions of this dune system also support one of the largest California least tern colonies with over 1000 pairs nesting there. At the southwest corner of San Diego Bay lies the U.S. Naval Radio Receiving Facility. This site is the last southern California site with vernal swales and pools backing the dune system. Comparisons of historic maps with current aerial photography (Fig. 2–3) show the persistence of the dune swales over extended periods. These vernal pools are occupied by the San Diego fairy shrimp (Branchinecta sandiegonensis), an endangered species. Here the endangered saltmarsh bird’s beak (Cordylanthus maritimus Nutt. ex Benth. subsp. maritimus) occurs in brackish pools behind the dunes, the only known site that this plant occurs outside of tidal salt marsh. Unfortunately, the majority of the dunes themselves have been taken over by Carpobrotus mats that have swamped most native taxa. These dunes continue for about 1.5 miles of coastline before they meet up with the south end of Silver Strand State Beach, now restored and managed for endangered species. Together, these two sites represent one of the largest intact dune systems left in southern California. Border Field State Park and the adjacent Tijuana Slough National Wildlife Refuge at the southwestern corner of the U.S. support a dune system similar to the Santa Margarita dunes in that it occurs on a natural barrier beach in front of a dynamically changing estuary and river outlet. Here, the rare Frankenia palmeri S.Watson creeps up the back of the dune swales from its comfort zone in the adjacent saltmarsh and California legless lizards swim through the sand under mats of Abronia maritima.

B.L.Rob.) Davidson on the active portion of the dune, though this rare mustard now appears to be extirpated from southern California. Currently the 300-acre dune remnant at the west end of the LAX airport is in a tenuous stasis with a still uncertain future. The 300-foot-tall dunes support rare taxa such as Mucronea californica Benth., Camissonia lewisii, and Pholisma arenarium Nutt. ex Hook., while Isocoma menziesii (Hook. & Arn.) G.L.Nesom, Eriogonum parvifolium Sm., and Lupinus albifrons Benth. form a dune scrub community on protected lee slopes (Mattoni 1990). Just east of the main dune ridge the topography flattens to a sandy plain supporting one of the last examples of the coastal prairie community that once covered much of what is now western Los Angeles (Longcore and Mattoni 1997). The formerly extensive vernal pools and dune hollows east of the dunes are now only a remnant, with a few shallow pools persisting on the LAX airfield, with the endangered Riverside fairy shrimp (Streptocephalus woottoni) and western spadefoot toads (Spea hammondii) hanging on as well. A few miles to the south, Malaga dune represents a completely unique dune system located on the bluffs of the Palos Verdes peninsula over 300 feet above the ocean. These dunes are likely of Pleistocene origin and represent the southern extension of the previously more extensive El Segundo dunes (Cooper 1967). This dune contains many rare taxa that have persisted amongst the surrounding housing developments, roadways, and golf course. Among the taxa recorded from this site are Pholisma arenarium, a root parasite found on perennial shrubs such as Ericameria and Eriogonum spp., and Erysimum insulare subsp. suffrutescens. Other notable species include the endangered Palos Verdes blue butterfly (Glaucopsyche lygdamus palosverdensis) and the El Segundo flower-loving fly (Raphiomidas terminatus terminatus), until recently thought to be extinct and a close relative of the endangered Delhi Sands flowerloving fly (Raphiomidas terminatus abdominalis) (George and Mattoni 2006). Unfortunately, this 57acre site is overrun with exotic plants such as Eucalyptus, Acacia, Bromus diandrus Roth, and many others. However, as it is owned by the city of Palos Verdes Estates adjacent to the Palos Verdes Golf Club, a restoration project could bring this dune system back. The Santa Margarita dunes, located on the Camp Pendleton Marine Corps Base in northern San Diego County, are perhaps less well known because of the limited access. However, these dunes represent a diverse flora that is located on a natural estuary at the mouth of the largest undammed river in southern

CONSERVATION AND RESTORATION Southern California coastal dunes have been in decline since the construction of Highway 1 in the early part of the twentieth century. This not only directly modified and fragmented the dune structure by generally splitting the foredunes from the backdunes, but it contributed to coastal access by vacationers and developers that would create further changes. As these coastal areas were developed, increasing public use of beaches led local cities to begin mechanized beach cleanup operations. These

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Fig. 2. Detail of 1857 map of San Diego Bay by the U.S. Navy (U.S. Navy 1857). Note the two mesic areas in the sandy flats to the southwest of the bay. Also note the three pools just behind the dunes. Photo by Kevin B. Clark.

Fig. 3. Current aerial photo of Naval Radio Receiving Facility site. The two mesic areas from the 1857 map (Fig. 2) are clearly visible east of the circular fenced radio facility. The three pools are also still present east of the dunes south of the radio. One of these pools supports Cordylanthus maritimus var. maritimus. Image courtesy of Google Earth.

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rakes and groomers not only pick up the trash, but scrape away all vegetation, while also flattening the natural dune topography (Fig. 4). The vast majority of public beaches in Los Angeles and Orange counties are now raked on a daily or weekly basis year round, prohibiting any dune formation or vegetation to occur. Dunes in northern Baja California have been degraded through the years as well, though not to the extent of those north of the border. The dune system at El Descanso has been persistently degraded for years by off-road vehicle traffic. Farther south, the dunes around La Salina have been lost to marina and home development. The dunes at El Estero de Punta Banda are partially protected and a nice example of coastal dune flora, yet this area is also under threat from home development and human disturbance. The dunes near Colonet are under threat from a proposed port development (Clark et al. 2008) while those at San Quintín have no permanent protection (S. Vanderplank, pers. comm.).

this project has created a thriving native plant community on over one mile of bluff (Urban Wildlands Group 2009). Numerous signs educate the public to the value of native species (Fig. 5). A few years after the plantings, the project area was naturally colonized by the endangered El Segundo blue butterfly (Euphilotes battoides allyni), adding a new population to the few that remain. The mouth of the San Diego River has likewise been adopted by an active group called the Friends of the San Diego River. A multi-year effort initiated by the non-profit group Ocean Discovery Institute has succeeded in removing Carpobrotus and other invasives and planting native plants (Ocean Discovery Institute 2009). A few years back over 20 pairs of California least terns colonized the dune system, some successfully raising a brood of young despite the presence of an unleashed dog park adjacent to the area. Silver Strand State Beach represents a great example of what coastal beach management could look like. A heavily used public recreational beach with RV parking is located on one portion, while to the south over a mile of natural and restored dune systems supports numerous rare species. This area has also been colonized by the threatened western snowy plover that nests in the dunes. If only the California Department of Parks and Recreation, that deserves great credit for their management of Silver Strand, would apply their management skills to the many miles of state beaches in Orange and Los Angeles counties that are raked on a regular basis to remove any shred of native flora and fauna.

Fig. 4. Beach raking in Los Angeles County. Most of the beaches in Los Angeles and Orange counties are raked on a weekly basis throughout the year. All vegetation and dune topography is cleared in these operations. Photo by Kevin B. Clark.

In some areas of Southern California, local efforts are succeeding in restoring the native flora and fauna back to coastal dunes. In between Malaga dune at Palos Verdes and the El Segundo dunes at LAX lie several miles of sandy bluffs and slopes that back the public beaches of southwestern Los Angeles. In the city of Redondo Beach, a restoration project has begun on one of these bluffs that was formerly covered with extensive mats of Carpobrotus. Undertaken by the Los Angeles Conservation Corps' SEA Laboratory and The Urban Wildlands Group,

Fig. 5. Sign at Redondo Beach bluff restoration area. This is one of six signs educating the public about the value of native plants and dunes. Photo by Kevin B. Clark

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ERTTER, B. 1993. The puzzling potentillas. Fremontia 21(1): 25–29. GEORGE, J. N. AND R. MATTONI. 2006. Rhaphiomidas terminatus terminatus Cazier, 1985 (Diptera: Mydidae): notes on the rediscovery and conservation biology of a presumed extinct species. Pan Pacific Entomol. 82: 30– 35. LONGCORE, T. AND R. MATTONI. 1997. The Los Angeles coastal prairie, a vanished community. Crossosoma 23(2): 71–102. MATTONI, R. 1990. Species diversity and habitat evaluation on the El Segundo sand dunes at LAX. Administrative Draft, 1 Feb 1990. Prepared for The Board of Airport Commissioners by Agresearch, Inc. 74 p. + app. OCEAN DISCOVERY INSTITUTE. 2009. http://www. oceandiscoveryinstitute.org/ (31 Oct 2009). PICKART, A. J. AND J. O. SAWYER. 1998. Ecology and restoration of Northern California coastal dunes. California Native Plant Society, Sacramento. PIERCE, W. D. AND D. POOL. 1938. The fauna and flora of the El Segundo sand dunes. Bull. S. Calif. Acad. Sci. 37: 93–97. URBAN WILDLANDS GROUP. 2009. Beach bluffs restoration project. http://www.urbanwildlands.org/bbrp.html (9 Oct 2009). U.S. FISH AND WILDLIFE SERVICE [USFWS]. 2004. Recovery plan for five plants from Monterey County, California. U.S. Fish and Wildlife Service, Portland, Oregon. xii + 159 p. U.S. NAVY. 1857. San Diego Bay, California. From a trigonometrical survey under the direction of A. D. Bache, Superintendent of the Survey of the Coast of the United States. Triangulation. Triangulation by R. D. Cutts, Assistant, Topography by A. M. Harrison, SubAssistant, Hydrography by the party under the command of Comdr. James Alden U.S.N. Asst. Scale 1/40,000.

CONCLUSION Coastal dunes in southern California represent a paradox. They are one of the most heavily impacted native communities and support some of the rarest and most endangered plant and animal species, yet much of their historic extent is publicly owned and potentially restorable. While this means that buying up large acreages for conservation is not necessary, it also means that the solution lies in changing agency management practices that are designed for the recreational interests of millions of residents and tourists. Beach raking represents the most pervasive and continuing threat to these beaches, especially in Los Angeles and Orange counties where dozens of miles of beach are raked weekly.

LITERATURE CITED CALIFORNIA NATIVE PLANT SOCIETY [CNPS]. 2009. Inventory of rare and endangered plants. v7-09, b 4-1009. http://cnps.web.aplus.net/cgi-bin/inv/inventory.cgi (9 Oct 2009). CLARK, K. B. 2006. Noteworthy collections—California (Cryptantha leiocarpa [Boraginaceae]). Madroño 53(1): 85–86. ———, M. DODERO, A. CHAVEZ, AND J. SNAPP-COOK. 2008. The threatened biological riches of Baja California’s Colonet Mesa. Fremontia 36(4): 3–10. COOPER, W. S. 1967. Coastal dunes of California. The Geological Society of America, Memoir 104. Boulder, Colorado, USA. COUCH, E. B. 1914. Notes on the ecology of dune plants. Plant World 17(7): 204–208.

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