Where did all this sand come from? To understand the dunes, you must first understand the effects of wind and water. Millions of years ago most of Oregon was under water and had a thick, sandy sea floor. Part of this sea floor was pushed up and became the Coast Mountain Range, which is sedimentary rock that was uplifted 12 million years ago. The heavy rain and wind of the Pacific Northwest eroded the sandstone, then rivers carried it to the ocean where the sand is now at least 150 feet right off shore. As the waves and high tides carry the sand onto shore, it is dried by the sun and blown inland.

The present shoreline stabilized 6,000 years ago. Tides, wave action and strong coastal winds moved sand up to 2.5 miles inland for thousands of years. This area of dune development rests on a gently-sloping terrace of solid marine sandstone called the Coos Bay Dune Sheet. This low rock surface stretches 56 miles from Heceta Head to Cape Arago and contrasts with steep headlands found on most of the Oregon coastline which prevent inland movement of sand.

Introduction of European beach grass disrupted this movement of sand. The grass was first planted to prevent sand from blocking river channels and roads. But has now spread all along the coast and become a barrier to additional sand movement from the beach. When the sand no longer moves, vegetation easily takes hold. Invading an average of 22 feet of sand a year, plants may entirely cover the dunes during the next 150 years. It's a tough management problem, and the park's caretakers are working hard to solve it.

Wind

In winter, winds are generally lighter; however, they can exceed 100 miles per hour during intense winter storms. These winds blow from the south and southwest, moving large amounts of sand. Seasonal changes in wind direction reshape dune sculptures and ridges.

Water

Sand absorbs and stores a large part of the annual rainfall. Where winds have removed sand down to the water table, plants have flourished. In the wet winter, the rising water table creates marshy areas with standing water several feet deep. With the upward pressure of water, the sand grains become saturated and may float, resulting in quicksand. Look for quicksand in low, unvegetated areas between the dunes.

Most waves are created when wind blowing across the ocean pushes against the water at the surface. The water in a wave does not actually move forward. Instead, it moves up and down, while the energy of the wave travels forward. Watch a bird floating on the water beyond the breakers-as the waves roll by, it bobs up and down but doesn't move toward the shore.

Near shore, the wave slows down as it drags on the ocean floor. The water behind the wave begins to pile up, increasing the size of the wave. When the wave top becomes unstable, it topples over into a breaker. The energy of the wave is finally released onto the beach.

Unlike most ocean waves, tides are not caused by winds. They are the regular rise and fall of sea level along the coast produced by the gravitational pull of the moon and sun. Along the Pacific Northwest coast, there are two unequal high tides and two unequal low tides each day.

All tides are measured in relation to their distance above or below sea level, the average height of the sea. In a typical year along our coast, the highest high tides are about +10 feet in December and the lowest low tides are about -2.5 feet in June.

Currents are rivers of water flowing through the ocean. They may be caused by steady winds or by differences in the temperature and salinity of the water. In contrast to waves, which- travel though the open ocean without actually moving the water, currents transport water from one place in the ocean to another.

Along the Pacific Northwest Coast, the California Current carries cold water southward from Alaska during the summer. In winter, powerful southwest winds push the warmer Davidson Current northward, which forces the California current farther from the shore. As a result, the ocean at some places along the coast may actually be warmer during the winter than during the summer.

Estuaries are where fresh river water meets salt water. As ocean tides rise, organic matter and nutrients from both areas pool together, creating one of the most fertile environments in the world. These nutrients stimulate the growth of plankton and other organisms, providing food for many plants, fish, birds and mammals.

Lakes abound on the Oregon Dunes.Some of the 32 lakes were once mountain streams that were dammed by sand. Others were ocean inlets that became cut off. Still others were formed when depressions in the sand filled with water as the water table rose.

Over the years, several lakes have dried up or been buried by sand.

The foredune is a low hill, formed parallel to the ocean edge. Consisting of sand and driftwood, the 20-30 foot high foredune is capped by European beach grass (Ammophila arenaria).

The beach grass was planted along the Siuslaw and other estuaries in the early 1900's to stabilize encroaching sand. Within 40 years, this hardy beach grass which thrives when repeatedly buried by sand, had formed a foredune that effectively cut off the natural sand source for the active dunes.

Hummocks are immediately inland from the foredune. These knob-like mounds are created by sand accumulating around vegetation. When the water table rises in the winter, puddles may surround the hummocks and they appear to be floating islands.

The foredune now blocks the supply of new sand. Winds strip away the sand east of the foredune, deflating the area down to permanently wet sand. This creates a deflation plain where water-loving vegetation thrives. As the dunes move eastward, the plants of the deflation plain also spread eastward.

The northwesterly winds of summer create wave-like patterns called transverse dunes. The crests of these 5-20 foot high dunes are perpendicular to the wind direction. Changes in wind direction create the interesting and unusual ridges; although strong winter winds from the southwest tend to smooth out these dunes. As the deflation plain expands eastward, so do the transverse dunes.

Tree islands, floating in sand, are small isolated versions of earlier coastal forests that were almost completely buried by sand. The islands are proof that moving sand is capable of burying whatever is in its way. Steep slopes make the tree islands unstable and susceptible to erosion.

Oblique Dunes are the largest and most impressive dunes. Occurring in parallel series, these dunes can rise to heights of 180 feet with lengths up to a mile. Some oblique dunes are nearly 500 feet above sea level. "Oblique" refers to the slanted angle at which both summer and winter winds hit these dunes.

Oblique dunes move constantly making it impossible for vegetation to grow on them. The west side of an oblique dune consists of a long, sloping ridge. The east side is usually higher and steeper, forming a precipitation ridge. In winter, the southwesterly winds create free-standing sculptures called yardangs. These unusual carvings can reach 15 feet high.

Winds create "blowouts" in some unstable areas of the coastal forest. Strong winds erode the vegetation-covered surface to bare sand. Once a section has eroded, wind carries the sand downwind, creating the characteristic U-shaped ridges called parabola dunes.

Changing Plant Communities

Beach grass spread quickly, stabilizing the sand and forming a"foredune" along the beach . The foredune grew taller and eventually cut off the inland supply of sand. The sand immediately behind the foredune was blown away, by the continual coastal winds, revealing the wet sand of the water table.

The stage was set for the plant communities that you now see. Plant communities naturally mature from pioneer species to climax plants. The invading beach grass altered this natural process of succession. Creating its own succession story, beach grass is changing the dunes to a more vegetated environment.

The flat, wet area of the deflation plain was quickly invaded by plants tolerating moisture and low nutrient levels. Plants such as red fescue, seaside tansy, false dandelion, coast strawberry, pearly everlasting, and salt rush yarrow thrived in the deflation plain.

Drier parts of the deflation plain were quickly covered with seashore lupine, European beach grass, seashore bluegrass, gray beach pea, beach knotweed and beach silvertop.

Even areas with standing water for six months or more prove popular with slough sedge, creeping buttercup, king's gentian and coast willow.

As these plants continue growing, they are gradually replaced by a community of scattered shrubs and tree seedlings up to six feet tall. Willow is the most common shrub with salal, evergreen huckleberry, waxmyrtle and shore pine close contenders.

The forested stage of deflation plain plant communities feature shore pine as the dominant tree species with scattered spruce sharing the overstory.

Managing Resources

The Waxmyrtle Trail follows Siltcoos creek as it flows toward the estuary and eventually out to sea. Hikers who walk the 3/4 miles to the beach experience many wonders of nature-from magnificent views of the river estuary to close up encounters with wildlife. River otters, herons, bald eagles and ospreys are just a sampling of wildlife viewing that you can experience.

Western snowy plovers are small, well-camouflaged birds who also live along the beach surrounding Siltcoos estuary. The U.S. Fish and Wildlife Service listed the coastal population of this species as"Threatened" in 1993 due to population and habitat declines.

How do we help the western snowy plover recover while allowing people to experience the Siltcoos river estuary?

Important pieces of the answer include creating additional nesting habitat, protecting existing nesting areas, and reducing our human impact. Many local trail users helped us decide how to allow limited access along the river and estuary while moving the trail away from the plover's nesting habitat. A trail junction sign will direct you along the main trail to the beach or to the unmaintained spur trail that follows the river and ends at the estuary. Please take the main trail if you have your dog along. When on the beach, please keep all activities away from the roped and signed snowy plover nesting areas.

Please follow all regulations. It is through your cooperation that we can successfully manage both sensitive habitats and provide public access for all who wish to experience the wonders of nature.