Part 1

Sand Dunes Story

DONNA P. BESSKEN

To Scotty’s Castle Grapevine Mts. To Beatty Death Valley Buttes Funeral Mts. Cottonwood Mts. Kit Fox Hills “Old” Stove Pipe Wells Picnic Area Tall Dunes Stove Pipe Wells Devil’s Cornfield Mosaic Canyon Salt Creek To Furnace Creek Tucki Mt. To Lone Pine

WELCOME!

What do YOU see as YOU look across the dunes? Piles of lifeless sand? A giant sandbox? Each of us sees the dunes differently. We would like to share the story of the Death Valley Sand Dunes with you. This booklet provides answers to some of your questions about the origin, composition and formation of the dunes. We will also look at the plants, and for evidence of animals that make their home here.

The features discussed are near the edge of the dunes and all you need is your curiosity to explore this fascinating place. A magnifying glass or magnet may add to your enjoyment. Remember—the dunes can be hot in spring and fall as well as in summer months. Be sure to carry water, distance is deceiving, and a short stroll may become an extended walk. Do you want to walk barefoot? Be careful around the bushes; thorns and plant debris are hidden in the sand. Carry your shoes, your feet may get tired, or the sand may become too hot. When you are in the shade, look around to see if other creatures are sharing the same cool place. This is home for such desert dwellers as lizards, kangaroo rats and sidewinders.

There is no guided trail since wind can soon cover a trail with sand. It’s easy to find your way around and can be fun to choose your own route. Look behind you to get firmly in your mind which mountain feature will be your landmark to guide you back to your vehicle.

To make the best use of this booklet, flip through it to locate topics of interest. Read in sequence, or follow the order of your discoveries. Use your senses to appreciate and explore the sand dunes more fully. Pick up some sand occasionally and compare the texture, temperature and other qualities to that found in other locations. Be alert for little things—notice plants, sand ripples, animal burrows and tracks.

Let’s walk into the dunes a short distance and learn their secrets. To form sand dunes, three things are needed: wind, sand, and a place for the sand to collect. The story of the dunes involves interaction among these factors and the plants and animals that make their homes in this sea of sand.

WHY ARE THE DUNES HERE?

Are they limited to this section of the valley? Do they migrate? Answers to these questions are in the winds.

Winter and summer bring winds from different directions; northerly in winter and southerly in summer. Landforms influence crosswinds and swirling wind currents (eddies). These crosswind and eddy patterns result in decreased wind speed and cause the sand to drop out in the same general area time after time. Seasonal variations in wind direction help keep the sand in one area.

Between individual dunes, white salt deposits are often seen on the surface of an old clay lakebed (playa). Here too, we see how tall the dunes are because the sand is piled entirely on top of this playa. Infrequent rains produce changes in the playa surface, and occasionally gravel is washed into the area from nearby mountains. Because of the clay content of the soil, rain water does not soak in quickly, but lies in pools. As the pools evaporate, fresh deposits of salts and minerals remain on the surface. Similar salt deposits throughout the valley to the south minimize the amount of available blowing sand by cementing it together.

Dunes in Death Valley consist of sand from local materials found in nearby mountains. The primary source of this sand is believed to be the Cottonwood Mountains to the west and northwest. Although the shapes and patterns of individual dunes may vary daily or seasonally, the dune field itself is relatively stable.

Pick up some sand! Is it fine or coarse? Wet or dry? Warm or cold? Notice the different colors. A magnet may help you separate particles, and a magnifying glass will allow you to examine them more closely. Most black particles are magnetite—most white ones are quartz. Other minerals provide still different colors. The sand here is a product of weathering by wind, rain and chemical changes—breaking blocks of rock (primarily granite) from nearby mountains into particles small and light enough to be carried by run-off and tossed around in the frequent desert winds.

HOW ARE DUNES AND RIPPLES FORMED?

Each wind produces changes to the surface of the sand. It takes a 10 mph (16 kph) wind to move fine, dry sand. During a sandstorm, it may seem as if the sand is blowing thousands of feet into the air. Your view of the distant mountains may be obscured. Don’t be fooled! The dunes are not entirely airborne! What you see are dust particles being carried aloft because they are smaller and lighter than sand grains. Seldom does dune-sized sand itself rise more than 6 ft. (2 m) above the ground, it is too heavy.

Actually, most sand travels within about 18 in. (46 cm) of the ground in a jumping movement called saltation. A windborne grain bounces a short distance before crashing into the sandy surface sending other grains into flight. The process continues as the wind carries the new grains a little farther, crashing them, in turn, into the surface and other grains along the way. Sand grains too heavy to blow in the wind creep along the surface of the sand, while smaller ones are truly airborne above the dunes. As a consequence, the entire sand surface flows or creeps along.

Have you been comparing the texture, size and color of sand in various sections of the dunes? Some differences will be more obvious if you have the chance to visit both the tall dunes by Highway 190 and the low ones by the picnic area. The soft, fine sand by the picnic area is carried farther by the wind than the coarser material found in the taller dunes.

Smaller grains move farther than large ones. As a result of this sorting of sand grains by variable winds, the larger grains accumulate in small ridges forming ripples. Size and shape of these formations are related to specific interactions between sand and wind. The windward side of a dune generally has more dramatic sculpturing. Examine an area with interesting ripples. Wind speed, direction, duration, and the amount of sand are important factors that have been measured and used to determine the size and spacing of dune ripples. Just as these ripples form, the dunes themselves respond to changes in each of these factors.

{ Speed { Size WIND { Duration + SAND { Uniformity = RIPPLE FORMATION { Direction { Amount

SUMMIT ANGLE OF REPOSE SLIPFACE WINDWARD ANGLE OF REPOSE FOC 34°

All dunes may be described by the above traits. Variations in shape and size of individual dunes are determined by the mathematical values applied to each of the traits mentioned in the discussion of ripple formation. Another feature of interest is the dune shape. Among these dunes you may find examples of this classic textbook model and its variations.

Note that the downwind side of the dune, the slipface, is the steeper one. Fine dry sand can only pile up so high before it breaks away and slides down the slipface as an avalanche to rest at the more stable angle of repose, about 34 degrees. We create miniature avalanches as we walk along the crest of a steep dune.

WHAT PLANTS LIVE HERE?

Each area within the dunes has something different to offer. Low dunes near the picnic area have more vegetation than the tall dunes near Highway 190.

Plants, visible from the top of many dunes, help the dunes remain here by stabilizing the sand with their branches and roots. You will see different plants, depending on whether you are in the tall or low dunes. You may find them in a different sequence from that used in this booklet. By looking for different shades of green, you should find each of the major shrubs and trees that live in the dunes. Use the diagrams and photos to help identify those you see. Let’s take a closer look to learn how they survive and how they relate to the story of the dunes.

Can you find a low bush which appears to have no leaves? The stems are jointed and succulent (juicy) and vary in color from yellowish to bright green, depending on the season. Pickleweed (Allenrolfea occidentalis), is often found on top of low mounds of sand. Do the stems look like tiny pickles joined end-to-end? During summer months, tiny, inconspicuous, yellow flowers may be seen at the joints. With a magnifying glass, you may see the miniature leaves.