March - April
1999
Outdoor California
Algodones
Dunes, Imperial County,
December 1998 Photo © Deborah Sebasta
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By James C. Dice and Deborah Sebasta |
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Extending for approximately 40 miles across eastern Imperial County is California’s largest sand dune system, the Algodones. Their northern most point is just east of the town of Calipatria and their southern termination occurs just across the U.S.-Mexican border, in the Mexican state of Baja California. The Algodones Dunes vary in width from three to six miles across and at various points the crest of the dune system may rise 300 feet or more above the surrounding desert floor. Temperatures in the dunes commonly exceed 110 F in the summer and rarely drop below freezing in the winter. Humidity is low, generally between 10 and 20 percent. Annual rainfall averages around two inches and comes in the form of late summer thunderstorms or light winter rains. The name “Algodones” derives from Spanish and English corruptions of the name of the Yuman tribe that once dwelt on both sides of the Colorado River in the vicinity of the nearby delta and the dunes. The name is not from the Spanish algodon, or “cotton” as some have thought. |
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The Algodones Dunes are an active system composed of a chain of very large barchan dunes. Barchans are crescent-shaped dunes with crests oriented toward the wind and horns oriented away from it. In the Algodones, these horns commonly join together. Some geologists believe the Algodones Dunes originated from sands transported from the shores of ancient Lake Cahuilla, the forerunner of the present day Salton Sea basin. Others disagree, citing evidence to suggest that the sand must have come from beaches and alluvial deposits to the west. In the Lake Cahuilla origination scenario, northwesterly winds are believed to have driven the sand from the beaches of the lake to the southeast. The Algodones are believed to be among the oldest California dunes, possibly dating back to the latter part of the Pleistocene epoch 10 to 20 thousand years ago. Although the Algodones Dunes are thought to be less active today than in the past, they are still observed to be moving southeasterly at a rate of about one foot per year.
Because of their extreme aridity, large area extent, and the challenges associated with their constantly shifting sands, the Algodones Dunes represent a most unique habitat for plants and animals within southeastern California’s Colorado Desert. These natural forces have resulted in the evolution of a number of unique plants and animals found only in the Algodones and nearby dunes in northwestern Mexico. The Algodones Dunes are home to several rare, threatened or endangered plant species. Plant species such as these which are restricted to active dunes are sometimes referred to as psammophites(sand lovers), or psammophytes (sand plants).
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Peirson’s milkvetch (Astragalus magdalenae var. peirsonii) is a silvery, short-lived perennial plant that is somewhat broom-like in appearance. A member of the bean and pea family, it can grow to 2.5 feet tall and is notable among milkvetches for its greatly reduced leaves. Peirson’s Milkvetch produces attractive, small purple flowers, generally in March or April, on stalks with 10 to 17 flowers per stalk. It yields inflated fruit similar to yellow-green pea pods with triangular beaks. Peirson’s milk vetch has the largest seeds of any Milkvetch. Large seeds are an important adaptation in dune plants. |
| Peirson's milkvetch in bloom (above) and in fruit (below) | |
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While small seeds can readily germinate under several inches of moist sand, they may exhaust their stored food before the seeding can emerge from the sand at such depths and begin producing its own food. Large seeds provide a greater reservoir of stored food and enable a seeding to grow a greater distance before emergence and/or depletion of their stored energy. |
| Peirson’s Milkvetch is named for Frank Peirson, an early California plant collector who was the first to prepare a scientific collection of the plant back in 1927. In the United States, the plant is known only from the Algodones Dunes, and in nearby Mexico from a limited area of dunes within the southern Gran Desierto, in the northwestern portion of the state of Sonora. Peirson’s milkvetch is listed as endangered under the California Endangered Species Act (CESA) and threatened under the federal Endangered Species Act (FESA). | |
Algodones Dunes sunflower (Helianthus niveus ssp. tephrodes) is one
of the most attractive plants found in the dune system and is known
in California only from these dunes. This silver-leafed member of the
sunflower, or aster, family inhabits primarily the interior portions
of the dunes at the bases along the sides of large dunes. Extremely
tolerant of moving sand, it grows rapidly to avoid being buried.
The Algodones Dunes sunflower produces clusters of large, bright yellow
daisy-like flower heads from March to May, and again from October to
January. The Algodones Dunes sunflower is recognized as endangered
under CESA and is regarded as a species of concern by the U.S. Fish
and Wildlife Service (USFWS).
Wiggins’ croton (Croton wigginsii) is a shrubby,
silver-leaved member of the spurge family, a relative of the familiar
Christmas poinsettia. Wiggins’
croton plans are dioecious, meaning that individual plants have either
staminate (male) or carpellate (female) flowers. In Wiggins’ croton individual plants are either male or female.
The flowers that are produced by Wiggin’s croton are small, yellow
and generally inconspicuous. Individual plants are frequently found with extremely long
surface roots exposed by the wind. Wiggins’
croton is recognized as a rare species under the California Native Plant
Protection Act and is considered a species of concern by USFWS.
The Silvery coloration of the stems and leaves in many dune plants is an adaptation to the excessive heat and light of this very arid region. The leaves of some plants, like the Algodones Dunes sunflower, have a dense covering of fine hairs that give them their silvery appearance as well as a velvet-like softness. Other plants, like Wiggins’ croton, have tiny plate-like overlapping scales that cover the leaves. Leaf hairs or scales help the plant to control evaporation from the leave surface, and thus slow water loss. They also help to regulate the temperature of the leaf by blocking out some of the light and heat within the environment. This helps the plant to keep leave temperatures low enough for the process of photosynthesis to continue, allowing the plant to maintain the production of sugars for growth even in the face of high air temperatures.
Giant Spanish needle (Palafoxia arida var. gigantea) is an attractive pink-flowered member of the sunflower, or aster family. It is an annual or short-lived perennial species with dark green, linear shaped leaves. Heads of pink disk flowers appear in both the spring and fall, with sufficient rainfall. As its name implies, the giant Spanish needle is larger than its more common relative, Spanish needle (Palafoxia arida var. arida). Giant Spanish needle grows to be three to six feet tall and is found only within the Algodones Dunes system. The common Spanish needle generally grows to be only two feet tall, or less, and is found throughout much of the Sonoran and Mojave deserts. Like many psammophilic species, the seeds of the giant Spanish needle will germinate and emerge as greater depths than the non-psammophilic Spanish needle. Studies of seed germination and emergence in the two varieties of Spanish needle have shown that in dune sand greater than one inch deep, twice as many seedlings of giant Spanish needle will emerge when compared to the more common Spanish needle. At depths of three inches or greater, only seedlings of giant Spanish needle emerged. Giant Spanish needle is listed on the Department of Fish and Game’s (DFG) Special Plants list and is regarded as a species of concern by the USFWS.
Sand food (pholiuma sonoras) may be the most
unusual plant of this (and possible any) dune system. A member of the lennoa family, sand food is a flowering plant that is
parasitic on the roots of a few perennial plans found in the Algodones Dunes,
most notably dune buckwheat (Eriogonium deserticola, and plicata coldenia (Tiqulia
plicata). Most of
the year the sand food plant remains unseen, buried deep in the sand, but
attached to the root of its host plant. In
late winter or early spring, particularly after an unusually wet fall or
winter, sand food produces a flowering stalk that passes through several feet
of sand to reach the dune surface. At
the surface, the head—a flattened, tan-colored, fuzzy disk up to five inches
in diameter—resembles the head of a mushroom. Clusters of small, lavender to purple heliotrope-like flowers usually
appear in the woolly disks during the months of April. Comparatively few host plants are actually parasitzed by sand food.
When they do occur, flowering heads of sand food may be observed in
clusters of a few (one to three) to many (20 to 30). After flowering, the flower heads dry and turn brown, remaining visible
on the sand for many months. Sand
food was an important food source for the indigenous peoples of the Colorado
River delta area, particularly the Sand Papago and the Cocopa. It is said to taste something like a sweet potato.
Sand food is listed on the DFG Special Plants list and is regarded as a
species of concern by the USFWS.
TheAlgodones Dunes are managed by the U.S. Department of
the Interior’s Bureau of Land Management (BLM) as part of the 184,000 acre
Imperial Sand Dunes Recreation Area. The
dune system itself comprises approximately 140,000 acres of the recreation
area, including popular off-highway vehicle (OHV) recreation spots such as
Mammoth Wash, Glamis, and Buttercup Valley. An estimated 500,000 OHV enthusiasts visited the dunes with their
vehicles in 1998. Approximately
118,000 acres of dunes (77 percent of the dune system) are open to OHV use.
The remaining 32,000 acres (approximately 23 percent of the dunes
system) are protected within the North Algodones Dunes Wilderness, established
by the 1994 California Desert Protection Act. Motorized vehicles are prohibited in the wilderness area and access is
by hiking or horseback only.
In the spring of 1998, the BLM with the help of the DFG,
the California Native Plant Society, and the USFWS, began a long-term
monitoring program to review the distribution and health of rare plant
population within the Algodones Dunes. A
total of 34 transects across the entire length of the California portion of
the dunes, including the wilderness and OHV open area were examined. Data collected from these transects will be compared with data to be
collected in coming years and with a 1977 study of the Algodones Dune rare and
endangered plant populations to evaluate the effects of OHV recreation on
these unique dune plants. The
ongoing challenge for the BLM, USWS and DFG is to ensure that the management
of the Algodones Dunes provides for reasonable recreational access for the
public while preserving the rare, threatened and endangered plants and animals
of this unique system for future generations.
James Dice is a plant ecologist with the California Department of Fish and Game’s region 6. Debra Sebasta is a botanist with the Bureau of Land management California Desert District El Centro Field Office.