ROBERT P. SHARP Division of Geological Sciences, California Institute of Technology, Pasadena, California

Abstract: Kelso Dunes lie in a mountain-rimmed can usually be measured in inches in the crestal zone. basin, 35 miles east of their principal sand source, Lee-slope beds dipping 10-25 degrees pre- where the predominant, sand transporting, westerly dominate within these dunes and are overlain by a wind is locally counterbalanced by strong, orog- thin, well-laminated, windward-slope layer inclined raphically controlled winds from other directions. as much as 16 degrees in the opposite direction. In the sand-mantled source area most grains larger Slip-slope deposits as steep as 30 degrees are only than 1 mm travel principally by creep under salta- scantily preserved. tion impact. The size distribution and sorting The orientation of several hundred lee slopes re- characteristics of eolian sand become well established flects only modestly the influence of prevailing after 10-12 miles of saltation transport. Further western winds. Storm winds from other directions, transport produces greater rounding and more earlier winds with a more southerly component, and mineralogical fractionation but does not greatly local orographic controls complicate the picture. alter other characteristics. This suggests that reliable interpretation of paleo- Fifteen years of measurements along established wind directions from cross-bedding in ancient eolian lines across individual transverse dunes record a sandstones requires a knowledge of the type of high degree of activity but only a hesitating ad- dunes represented and their response to a possibly vance, involving three steps forward and two and a varied wind pattern. half steps back. Opposing winds shift the sand back Observations with smoke pots during high winds and forth from one dune flank to the other, with lead to the conclusion that no strong, fixed eddy frequent reversals in crestal asymmetry. lies to the lee of transverse dunes in the Kelso com- Crestal position is not a reliable index of bulk plex. When strong transverse winds blow, currents movement. Dune crests shifted back and forth on the slip face are for the most part capricious and within a 30-40-foot zone, moving several hundred too gentle to produce significant sand movement. feet in 10-12 years but ending up only a few feet Occasional gusts and traveling eddies traverse the from first-observed positions. Greatest accumulation slip face, usually in a longitudinal or oblique direc- and removal changes lie just to either side of the tion. However, no powerful, fixed, lee-side eddy crest and are associated with reversals in dune form. was found which significantly influences dune be- Although tens to hundreds of feet of sand may be havior and morphology in the manner and to the moved, net surface change in level after 10-12 years degree postulated by Vaughan Cornish.

CONTENTS Introduction 1046 Dune station 5 1057 General statement 1046 Dune station 9 (wood) 1057 Physical setting 1046 Dune station 9 (iron) 1057 Factors bearing on dune development .... 1046 Dune station 10 1059 Localization 1048 Summary of changes measured on transverse Acknowledgments 1048 dunes 1059 Wind regime 1048 Structures within dunes 1060 Current winds 1048 Bedding 1060 Antecedent conditions 1049 Attitude of bedding in dunes 1062 Dune morphology 1050 Scalloped structure 1064 Elongate dune ridges 1050 Lee-slope orientation and the prevailing wind . 1065 Transverse dunes 1050 Some characteristics of the sand 1067 Lee-slope forms 1050 Grain size 1067 Behavior of individual dune ridges 1052 Effects of eolian transport 1067 Introduction 1052 Grain-size distribution on dunes 1068 Procedure 1052 Mineralogy 1070 Dune station 4 1052 The lee-side eddy concept 1070

Geological Society of America Bulletin, v. 77, p. 1045-1074, 19 figs., 5 pis., October 1966 1045

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Introduction 1070 17. Rose diagram of predominant lee-slope Field observations 1071 orientations 1067 References cited 1071 18. Percentage size distribution in sand samples from source to dunes 1069 Figure 19. Grain-size distribution on dunes 1070 1. Location map for Kelso Dunes, Mojave Desert, California 1047 2. Geographic details of Kelso Dunes .... 1048 Plate Following 3. Active and inactive areas and wind directions 1049 1. Kelso Dunes and active slip face, Mojave 4. Cross sections through transverse dune ridges 1051 Desert, California 5. Lee slopes in profile 1052 2. Truncated dune and bedding structure . . . 6. Changes at poles of station 4 in 1953 . . . 1053 3. Bedding in dune sand and cuspate structure . 1048 7. Summation of changes in inches recorded at 4. Rounding of grains by eolian transport . . . poles of station 4 over 9-year period . . 1054 5. Lee-side smoke behavior 8. Contour map of net changes at station 4, 1- year interval 1055 9. Contour map of net changes at station 4, 6- Table year interval 1056 1. Summation of net changes in inches of sand 10. Summary of changes at poles of station 5 . 1057 recorded at poles of station 4 1054 11. Changes at poles of station 9 (iron) .... 1058 2. Summation of net changes in inches of sand 12. Plot of shifts in position of dune crests . . 1061 recorded at poles of station 9 (iron) . . . 1059 13. Bedding attitudes at station 4 1063 3. Greatest changes of accumulation and removal 14. Bedding attitudes in pits across dune at sta- recorded at poles of station 9 (iron) over a tion 5 1064 span of 5.5 years 1059 15. Rose diagram of lee-slope orientations from 4. Summation of net changes in inches of sand air photos 1065 recorded at poles of station 10 1060 16. Rose diagram of lee-slope orientations from 5. Location and shape of dune crest and orienta- transverse dune-crest trends 1066 tion of lee face at station 10 1060

extending north from Granite Mountains (PI. INTRODUCTION 1, fig. 1). Three small rock knobs rise less than 100 feet at the southern edge of the dunes east General Statement of Cottonwood Wash (Fig. 2). The inference The purpose of this paper is to provide field that other bedrock masses, now buried, might data on morphology, structure, and behavior of have initiated sand accumulation receives little some desert dunes observed under a variety of support from the fact that only alluvium is ex- conditions for periods ranging from a few hours posed beneath dune sand in the walls of Cotton- to a few days over an interval of 15 years, begin- wood Wash as it cuts northward through the ning in 1949. dunes (Fig. 2). At present the dune complex is self-sustained and independent of the underly- Physical Setting ing platform. The highest elevation is 3114 feet Kelso Dunes lie in the eastern Mojave Desert (PI. 1, fig. 1), and it must be underlain by fully of Southern California (Fig. 1) 50 miles west of 700 feet of sand, assuming a 2-degree slope on the Nevada border ( lat. 34° 48' N., long. 115° the alluvial floor and no foreign core. The dune 43' W.). They are reached by well-graded desert mass is egg shaped, with the long axis bearing roads from highways to the north and south. N. 55° E., and covers 45 square miles. Its bor- U. S. Geological Survey 15-minute topographic ders are sharp (Fig. 2), because little sand es- quadrangles, Flynn (1956) and Kerens (1957), capes in the prevailing downwind direction. cover the area. Kelso Dunes are part of a large sand sea Factors Bearing on Dune Development (Hume, 1925, p. 36) called Devils Playground. SOURCE OF SAND: Kelso Dunes are at the They lie in a valley rimmed on the south, east, eastern end of a tongue of eolian sand, 35 miles and north by the Granite, Providence, and long by 2-4 miles wide, which bears S. 80° E., Kelso mountains respectively (D. G. Thomp- essentially parallel to the prevailing wind (Fig. son, 1929, p. 551-552). A north-projecting spur 1). The source is a broad alluvial apron formed of Bristol Mountains only partly blocks the by the Mojave River as it debouches from the western side, leaving a gap through which wind- east end of Afton Canyon. Floods renew the blown sand enters from N. 60° W. supply of sand which is derived from the varied The dunes are well out on the alluvial apron sedimentary, igneous, metamorphic, and vol-

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canic rock terranes of the Mojave River drain- and presumably sprouts adventitious roots from age. Earlier variations in dune activity, sug- nodes along its stems when buried. Growths of gested by vegetational and morphological rela- galleta grass create humps on dune flanks. tionships, may to some degree reflect changes in MOISTURE: Annual precipitation, including the amount of sand available in the source area. a little snow, is estimated at 3-4 inches (D. G. The last 23 miles of eolian transport are over a Thompson, 1929, p. 548). As widely recognized gentle uphill grade rising about 1000 feet. (Free, 1911, p. 71; Hume, 1925, p. 78; Bagnold, VEGETATION : Vegetation can play an impor- 1941, p. 245-246; Norris and Norris, 1961, p.

~N II6°I|5' II6°"!00

.#^tfton <^<"^Cru«ro'!v0^r.:^.:::'---\ fy, ~ I •$> V, ^^^^^-.. '.tV ^j on Canyon

Ludlow

Figure 1. Location map for Kelso Dunes, Mojave Desert, California

tant role in dune development and behavior 609) dunes have a remarkable power of water (Olson, 1958). In Kelso Dunes its influence is conservation. They soak up every drop like a minor at present, but was possibly greater in the sponge, and the thin layer of dry surface sand past. Peripheral parts of the complex and small that quickly develops afterwards effectively re- interior areas have a brush cover which largely duces evaporational losses, since intergranular stabilizes dune forms without wholly prevent- openings in well-sorted, wind-blown sand are ing sand movement. Scattered desert willow mostly larger than capillary. Thus even in late (catalpa) trees grow in the southeastern part of summer, months after any rainfall, when the the dunes. Grass and small bushes are not en- rest of the desert is bone dry, wet sand exists at tirely lacking in highly active areas, although depths of only a few inches on recently scoured sparse. They favor prevailing lee slopes and in- dune slopes. terdune hollows. The principal plant in active Moisture influences dune morphology. Moist areas is Hilaria rigida or galleta grass, which ap- sand, exposed at the surface by deflation, re- pears to be a sand lover that thrives under ac- tards erosion although not preventing it entire- tive deposition. It has an extended root system ly. Saltating sand moves more readily across

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firm, moist surfaces than across dry, loose sand. chaudhuri, D. Foster Hewett, J. M. Burgers, Moist sand also stands in steep faces, and the William Otto, Celeste Engel, and Rudolph Von deep scour flutes and channels cut into dune Huene have been especially helpful. Critical crests by strong winds have usually been carved comments by GSA reviewers have improved in wet sand (PI. 2, fig. 1). the manuscript.

Figure 2. Geographic details of Kelso Dunes, location of dune stations, and square-mile sections for lee-slope measurements shown in Figure 16

WIND REGIME Localization The dunes lie in a mountain-rimmed valley, Current Winds but they are not plastered against any topo- The only record of value, supplied by State graphic barrier. As will be shown, they are sub- Climatologist C. Robert Elford, is a 1-year ject to strong winds from several directions. Ob- (1940-1941) hourly observation of wind direc- servations and measurements, to be described, tion and velocity at Silver Lake, 35 miles north- indicate that the dunes are localized at a cross- west of Kelso Dunes. Of winds blowing more roads of winds whose net effect is near zero. than 15 mph at Silver Lake, 37 per cent were from 22.5 degrees on either side of west, and 31 ACKNOWLEDGMENTS and 17 per cent respectively blew, with similar During 53 trips to the dunes I have enjoyed deviations, from north and south. Winds from the company of many geologists, engineers, stu- other directions were less frequent. Silver Lake dents, and visitors whose interest, aid, and com- lies in a north-south valley, and the near-sur- ments are acknowledged with appreciation. face wind patterns must be somewhat different Ronald L. Shreve, W. Barclay Kamb, Bruce R. from that at the dunes, because of orographic Doe, Thomas W. Donnelly, Bimalendu Ray- influences.

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/77/10/1045/3427721/i0016-7606-77-10-1045.pdf by guest on 28 September 2021 Figure 1. Highest (550 feet) peak in Kelso Dunes viewed from south

Figure 2. Slumps on recently active slip face KELSO DUNES AND ACTIVE SLIP FACE, MOJAVE DESERT, CALIFORNIA

SHARP, PLATE 1 Geological Society of America Bulletin, volume 77

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•<.• 2. Complex bedding relationships exposed on eroded dune crest TRUNCATED DUNE AND BEDDING STRUCTURE

SHARP, PLATE 2 Geological Society of America Bulletin, volume 77

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/77/10/1045/3427721/i0016-7606-77-10-1045.pdf by guest on 28 September 2021 Figure 1. Fine layering and black sands in gently dipping beds on frozen, wind-scoured dune surface

Figure 2. Cuspate structure exposed Figure 3. Smoothly truncated cus- on wind-scoured surface, fine beds pate structure exposed on wind- outline form scoured, wet sand surface BEDDING IN DUNE SAND AND CUSPATE STRUCTURE

SHARP, PLATE 3 Geological Society of America Bulletin, volume 77

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------ROUNDING OF GRAINS BY EOLIAN TRANSPORT Sand samples taken over 35-mile path from source to Kelso Dunes. (See Fig. 18 for location of samples by number, + 32-size fraction)

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Figure 1. Lee slope of transverse dune ridge with Figure 2. Same as Figure 1 but with slight back drift of 30 mph wind blowing to right, smoke ascending verti- smoke before caught in wind clearing crest cally until caught in wind current clearing dune crest

Figure 3. Same as Figure 1 but with smoke moving Figure 4. Same as Figure 1 but showing smoke caught slightly away from observer by strong, temporary gust moving obliquely away and somewhat up slip face LEE-SIDE SMOKE BEHAVIOR

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General knowledge of the wind regime at 20,000, they must have experienced secular cli- Kelso Dunes was obtained from direct observa- matic changes capable of affecting sand move- tions and from wind-ripple orientation. On 28 ment and dune behavior. Probably the dunes occasions winds were or recently had been from once were more stable. In an active area of the west or west-northwest, on 21 from east or southeast sector are 22 scattered clumps of des- southeast, on 11 from north or northeast, and ert-willow trees with trunk diameters up to 14 on 6 from south or southwest. inches. Most are still living, but they appear out

Explanation

® Dune Station

Outline of dune area if.*™1* Areas of active sand

Modern Winds

/ Certain, one direction

Alignment certain, direction less certain Certain, both directions

Ancient Winds

Direction certain

/ Alignment certain, ' direction uncertain / Alignment certain, no direction definable

Figure 3. Active and inactive areas and wind directions derived from dune forms

Thus winds from westerly quadrants are the of phase with present conditions. Some are be- most frequent, but sand-moving winds also ing buried, and others appear to have been blow from northerly, easterly, and southerly buried and exhumed. A greater stability of sand quadrants. An impression was gained that non- surface than now exists would seem to be re- westerly winds, although less frequent and of quired to allow such trees to take root and pros- shorter duration, are of higher velocity. Since per. sand transport varies approximately with the Relatively stable dunes with a 25-35-per cent third power of the wind velocity above thresh- vegetative cover, including large creosote old value (Bagnold, 1941, p. 187; Finkel, 1959, bushes, are scattered along the edges of the com- p. 639; Armstrong Price, Nov. 15, 1962, per- plex (Fig. 3). These dunes are more subdued, sonal communication), nonwesterly winds can and their alignment is to a considerable degree produce a significant effect. out of phase with current wind directions. Rem- nants of these ancient trends are also seen in ac- Antecedent Conditions tive areas, suggesting that at some earlier time Since Kelso Dunes have been in existence for much of the complex had a pattern differing several thousand years and possibly 10,000- from that favored by present-day winds.

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Current and ancient wind directions as de- smooth windward slope rising to a sharp junc- termined from dune forms have been mapped tion with a steeper lee slope (Fig. 4, profile A) largely from air photographs, checked by field is more the exception than the rule here. Many observations. Determination of wind alignment transverse dunes with steep slip faces have broad is easy, but a decision on predominating direc- rounded crests curving downward to lee before tion is difficult in stabilized areas because dune- breaking off sharply (Fig. 4, profile B). Con- asymmetry is softened. The contrast in align- trary to Smith's (1940, p. 157) impression, this ment, and in some instances of direction, be- form shows no obvious relation to dune size. tween adjacent areas of old and modern dunes Bagnold's (1941, p. 209) distinction between is apparent (Fig. 3). the brink, that is the sharp break to the slip Making allowances for the strong influence face, and the crest or summit, is useful. On most exerted on surface winds by the dune form it- Kelso dunes the slip face does not exceed a self, the pattern of arrows within active areas height of 25 feet and usually constitutes only suggests a predominant northwesterly wind. the upper part of the lee slope. The remainder Other orientations are also discernible reflect- consists of a gentler surface with an inclination ing short-lived but powerful winds from other ranging downward from about 20 degrees (Fig. directions, patterns inherited from earlier 4). At times longitudinal winds smooth the slip stages, and the influence of large topographic face and destroy the brink (Fig. 4, profile C). features such as the high southern dune ridge Residual forms related to reversals in orienta- and gaps therein. In places three intersecting tion of the slip face are also seen (Fig. 4, profile linear dune-ridge patterns are recognized. With- D). Scouring and truncation of dune crests oc- in some stabilized areas, rhombic waffle patterns cur when a sharp crest is subjected to a power- are created by intersection of two sets of linear ful reverse wind (PI. 2, fig. 1). transverse ridges shaped by winds from the southwest and southeast. Lee-Slope Forms Lee slopes exist here in three states: (1) fresh- DUNE MORPHOLOGY ly shaped by the deposition of sand swept over the crest from the windward side, (2) modified Elongate Dune Ridges by slumping to form a slip face, (3) modified by The largest dunes are four nearly parallel lin- later winds of a longitudinal, oblique, or reverse ear ridges trending roughly N. 65° E. (Fig. 2). direction. In some ways they resemble Cooper's (1958, p. Maximum deposition occurs at the top of a 49-54) oblique ridges with transverse dunes lee slope receiving sand from windward because superimposed upon their flanks. The southern- transport is by saltation and surface creep. Thus, most and largest ridge (Fig. 2, loc. A) has the the slope gets ever steeper up to the angle of re- following characteristics. It is fully 4 miles long pose. In Kelso Dunes angles up to 34.5 degrees and 550 feet high. The crest is irregular in plan have been measured at the top of fresh lee and profile (PL 1, fig. 1). Short reaches diverge slopes, and Poole (1962, p. D148) has recorded by as much as 35 degrees from the prevailing angles up to 34 degrees. Van Burkalow's (1945, trend, and crestal peaks and saddles differ in p. 684-692) data suggest this is a permissible elevation by as much as 350 feet. In places the angle for eolian sand. Not all newly deposited crest line bifurcates and reunites, inclosing a lee slopes or all of their parts are this steep. crestal hollow. In cross section, the upper part Angles on one new lee slope about 6 feet high of an elongate ridge is essentially symmetrical, ranged from 34.5 degrees at the top to 31.5 de- with slopes of 20-25 degrees, except for the up- grees at the bottom (Fig. 5, slope A). permost part, which has a 30-33 degree lee Lee slopes modified by subsequent winds are slope that shifts from one side to the other. less steep and have rounded junctions, top and These ridges are not longitudinal to any well bottom. Longitudinal winds smooth and pack defined prevailing wind. They may have been the lee slopes and sometimes form spectacular established under earlier, different conditions, ripples orthogonal to slope contours. Longi- but at present, transverse winds play a major tudinal winds may not greatly gentle lee slopes, role in shaping, and possibly in building, these but oblique and directly opposed winds do, pro- elongate ridges. ducing angles between 20 degrees and 30 degrees (Fig. 5, slope C). Transverse Dunes Lee slopes approaching 34 degrees are meta- The classical transverse-dune shape of a stable, and slumps are easily initiated on them

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naturally or artificially. The movement starts show fresh evidence of slumping even though as a slide which changes shortly to a flowing all parts have been repeatedly affected. sand tongue usually several feet wide. A small Flow tongues initiated by slumps display break-away scar at 34.5 degrees is left at the top transverse surface ridges and marginal embank- of the 30-31-degree flow tongue. The intersec- ments, and they are affected by progressive and tion at both top and bottom of fresh, slump- regressive kinematic waves. As the flow passes,

Crest •Brink Slip face Lower lee slope

Truncated top 12° Old lee slope Fresh slip face 29 33°

Figure 4. Cross sections through transverse dune ridges

shaped lee slopes is usually sharp (Fig. 5, slope the sand surface rises an inch or so, but it settles B)' . . back except in the terminal part, which remains Slumping is so common on active lee slopes higher. The deep-pitched sound heard in these (PI. 1, fig. 2) that it must be a principal factor and other dunes during and immediately follow- in shaping them (Bagnold, 1941, p. 201-204; ing strong winds is made by sand avalanches McKee, 1945, p. 315-317; 1957, p. 1719). (Hume, 1925, p. 60; Bagnold, 1941, p. 250-256; Slumps occur individually at different times Logan, 1960, p. 136). It can be produced arti- and places, so only a fraction of the slope need ficially on steep lee slopes.

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moval on the southwest flank and net accumu- BEHAVIOR OF INDIVIDUAL lation on the northeast flank, as expected from DUNE RIDGES the dune form. The body of the dune moved northeasterly, but at the surprisingly slow rate Introduction of 12 feet in 12 years, as calculated from accu- Accumulation and removal of sand and mulation at various poles. The crest shifted back changes in form and facing direction of dunes have been measured at 10 stations in the Kelso complex at intervals over 15 years. The longest single continuous record approaches 12 years. Fresh All stations were on individual transverse dunes Wind-Deposited selected for differences in orientation, setting, Lee Slope and other characteristics. All except one lay south of the principal elongate ridge (Fig. 2). Data obtained are so voluminous and detailed that only summaries can be presented here. At- tention is confined to stations 4, 5, 9, and 10. Procedure Each station consisted of 8-12 poles equally spaced in a straight line across a dune. The half- inch 3-foot wooden dowels used at first were too easily buried or unseated, so 1-inch, 10-foot dowels, dug in 4 to 5 feet, were employed. These Slump-Shaped 34° proved satisfactory except as subject to break- Lee Slope age. Eventually 6- and 8-foot rods of half-inch structural steel that could be driven into the -3 sand were substituted. Changes were recorded by measuring the projection of each pole and surface slope at the pole base. 30° B Dune Station 4 Twelve poles were set 20 feet apart on a bearing N. 35° E. across a transverse dune ridge striking N. 55° W. Although this station twice suffered heavy damage from vandals, it none- theless provides one of the more interesting Wind-Modified records covering nearly 12 years. A tabulation Lee Slope of all measurements has been prepared, and a copy will be sent to anyone interested; only -3 summarizations are presented here. Measurements were made on 45 occasions between January 16, 1953 and November 28, C 1 1964. Intervals between measurements were 19 hours to 318 days. Changes during 1953 are shown graphically in Figure 6. During this year, crestal asymmetry reversed and net crestal Figure 5. Lee slopes in profile movement was 22 feet southwestward, contrary to expectations from over-all dune form, which suggested movement to the northeast. Gross and forth within a zone about 30 feet wide and changes during a 19-hour interval (May 23-24) is not a good index of bulk movement. are of the same magnitude as net changes for The sums of net changes recorded on 41 oc- longer intervals. casions at station 4 over 9 years from January The inadequacy of a 1-year observation is 16, 1953 to January 6, 1962 are interesting (Fig. shown by Table 1, summing changes recorded 7). They show that the crest and upper reaches over nearly 12 years. These data show net re- of the adjoining slopes were the most active in

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jt—i^^^

23 May I953J24 May !953-l9hrs) - 23'/2(-2) ,,. \ I '. —. 8(—I) '»

28Npv_1953-188days _ JT I I] ... '2

Summation of changes-16 Jan. to 28 Dec. 1953 7'/4 !33/4 20 48'/4 8'/2 4'/2 5'/4

0 20 40 60 80 100 120 FEET + Accumulation Horizontal and Vertical Scale — Removals in inches Figure 6. Changes at poles of station 4 in 1953. Plus and minus figures above each profile show changes in inches since preceding measurement. Dune crest bears N. 55° W.

terms of sand movement. Furthermore, the have been several times larger than shown. The greatest activity was just off the crest (see Fig. total of 813 inches recorded at pole 6 for 12 7, poles 6 and 8) rather than on it (pole 7). This years can be but a fraction of the true total, occurs because of the building and destruction which probably approached 200-250 feet of of steep slip faces on opposite sides. Table 1 con- sand. In spite of all this activity, net lowering firms the relationships. Because any observation of the surface at pole 6 was only 18 inches in 12 interval exceeding a few hours or days records years. only net changes, the total shifting of sand must Information on areal relationships was ob-

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TABLE 1. SUMMATION OF NET CHANGES IN INCHES OF SAND RECORDED AT POLES OF STATION 4, KELSO DUNES, MOJAVE DESERT, CALIFORNIA, AT INTERVALS FROM JANUARY 16, 1953 TO NOVEMBER 28, 1964 (See Figure 6 for pole locations.)

Southwest Crestal poles Northeast Pole number 1 2 3 4 5 6 7 8 9 10 11 12 Accumulation +35 +63 +104 +98 +113 +398 +219 +419 +257 +152 +88 +46 Removal -68 -86 -111 -120 -121 -415 -253 -372 -207 -119 -48 -12 Total sand moved 103 149 215 218 234 813 472 791 464 271 136 58 Bala —33 -23 -7 -22 -8 -17 -34 +47 +50 +33 +40 +34

tained from 1-foot contour maps made on 3 oc- greater activity there related to slip-face re- casions at station 4, recording changes over 1- versals. Maximum prevailing lee-side accumu- and 6-year intervals. From these surveys, maps lation is well down the slope near pole 10. The of net accumulation and net removal were con- contour maps confirm that only modest net structed (Figs. 8 and 9) which confirm the pole change in form and position of this dune oc- observations of net removal from the southwest curred over a 6-year interval in spite of much flank and net accumulation on the northeast sand movement. Planimetric measurements of flank. However, neither has occurred uniformly areas between contours on Figure 9 provide in terms of area. volumetric comparisons. In the 6 years of rec- The zero contour (Fig. 9) defines the result- ord, a net of 327 cubic feet was removed from ant crest of the dune, and its location near pole the southwest flank and 187 cubic feet were de- 7 is consistent with the pole data of Figure 7. posited on the northeast flank, for a net loss of Bunching of contours in the crestal area reflects 140 cubic feet within the map area. The map

SW Pole number NE 16 Jan. 1953

120 Feet + Accumulatiori\ 'Jan. 1962 Horizontal and Vertical Scale -Removal /Inches Figure 7. Summation of changes in inches recorded at poles of dune station 4 over a 9-year period. Because of intervals between measurements, gross changes recorded are probably only one-third to one-fourth of the absolute changes.

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EXPLANATION — +2— Accumulation -2 Removal Contour Interval in Feet • WT Dune Station Pole 0 10 20 30 4O Scale in Feet

Figure 8. Contour map of net changes at station 4, 1-year interval

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— + 3— Accumulation ; -3 Removal Contour Interval in Feet « VTTT Dune Station Pole'•• -I"'' 0 10 20 30 40 5O 60 Scale in Feet

Figure 9. Contour map of net changes at station 4, 6-year interval

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does not cover the entire dune, so the material may simply have been shifted longitudinally Dune Station 9 (Wood) and not necessarily lost from the dune. This station was in the southern part of the complex not far from stations 4 and 10 (Fig. 2). Dune Station 5 The line of poles bore N. 24° W. across a trans- This station lies just north of the principal verse dune striking N. 75° E. Changes in orien- elongate ridge (Fig. 2) where transverse dunes tation of the slip face were frequent, but a of unusually regular trend, spacing, and shape, northward orientation predominated. The sta- and with a consistently steeper flank to the east tion was established December 29, 1953 and prevail. Twelve poles were set 25 feet apart abandoned February 4, 1961. The total record

+ Accumulation in inches — Removal in inches Horizontal and Vertical Scale I I I Figure 10. Summary of changes at poles of station 5 from January 17, 1953 to February 15, 1964

along a line bearing N. 82° W. across a dune is unsatisfactory because of unseated poles and bearing N. 2° E. The record spans nearly 12 human vandalism. years and is a good one, as remoteness afforded In 1954 and 1957, years of nearly complete protection from vandalism. A summation from record, the dune experienced net accumulation January 17, 1953 to November 28, 1964 is pre- on its north side and removal on its south side. sented graphically in Figure 10. Net accumulation of 40 to 60 inches was meas- Net removal occurred at all poles on the ured at several poles over intervals of 3-4 western flank and accumulation at all poles on months. An annual net removal of 85 inches the eastern flank. The magnitude of change in- was recorded at another pole. However, net creases toward the crest; departures presumably change at the crest in 1957 was only -(-0.75 represent temporary perturbations resulting inch, even though changes as great as 29 inches from recent episodes of slip-slope reversal. Bulk had been measured over shorter intervals at the movement of the dune has been about 18 feet crest during the year. eastward in 12 years. As observed on 38 occasions over 12 years, the slip face was to the east Dune Station 9 (Iron) 23 times, to the west 13 times, and twice the A new line of 8 iron poles was established on crestal profile was essentially symmetrical. Slip June 20, 1959, 75 feet east of station 9 (wood). faces to the east were also higher and more en- The poles extend N. 10° W. across the dune, during than to the west. During this time the which strikes N. 75° E. Changes measured on crest shifted back and forth over a distance of 10 occasions during the first 1.5 years are shown 33 feet. It once shifted 28 feet in 2 months. in Figure 11.

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10 Oct. 59 T 6° 112 days

Summation of changes - 20 June 1959 to 28 Dec. I960 \

\ 93/4 2 1/4 !73/4 >96'/4 61'/z 283/4 2l'/4 0 20 40 60 80 IOO 120 FEET Horizontal and Vertical Scale

Figure 11. Changes at poles of station 9 (iron) for 1.5 years. Plus and minus figures above each profile indicate change in inches since preceding observation.

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TABLE 2. SUMMATION OF NET CHANGES IN INCHES OF SAND RECORDED AT POLES OF STATION 9 (IRON), KELSO DUNES, MOJAVE DESERT, CALIFORNIA, AT INTERVALS FROM JUNE 20, 1959 TO NOVEMBER 28, 1964 (See Figure 11 for pole locations.)

North Crestal poles South Pole number 1 2 3 4 5 6 7 8 9* Accumulation +55 +55 +55 +151 +222 +177 +153 +8 + 11 Removal -30 -24 -30 -76 -138 -101 -96 -97 -78 Total sand moved 85 79 85 227 369 278 249 105 89 Balance +25 +31 +25 +75 +84 +76 +57 -89 -67

' Pole 9 set February 4, 1961, so time interval represented is 70 per cent that of other poles.

Changes in crestal shape have been many and probably exceeded by a factor of 3 or 4 the 163 impressive. They were produced by shifts of feet measured, as observations were too widely sand, first to one side and then to the other separated to record all changes. The crest once (Fig. 11). Heavy deposition on one flank was moved 7.5 feet in 18 hours. Reversals in slip- usually accompanied by removal, less heavy and face orientation were frequent. On 5 out of 20 over a larger area, on the opposite flank. Longi- occasions it faced north, 12 south, with 3 in- tudinal winds produced scour not necessarily determinate. accompanied by deposition elsewhere along the Table 3 provides further evidence of major pole line. The magnitude of changes within an movement of sand on the upper slopes of a dune. 18-hour interval (December 27-28, 1960, Fig. Considering all occasions of measurement, the 11) confirm that measurements covering longer greatest changes on the upper part of the dune exceed the greatest changes at the foot by a factor of 8 for accumulation and of 3 for re- TABLE 3. GREATEST CHANGES OF ACCUMULATION AND moval. The greatest accumulation exceeds the REMOVAL RECORDED AT POLES OF STATION 9 (IRON), greatest removal on the upper part of the dune, KELSO DUNES, MOJAVE DESERT, CALIFORNIA, DURING ANY ONE OF 20 OBSERVATION PERIODS OVER A SPAN but relationships are reversed on lower slopes. OF 5.5 YEARS Dune Station 10 Accumulation Removal This station consisted of 8 iron poles set 20 Pole number (inches) (inches) feet apart in a line N, 20° E. across a transverse dune bearing N. 70° W. Dune shape suggested 1 (north toe) +8 -13.25 a dominant influence of westerly winds. Table 2 +10,5 -12.25 4 provides a summary of changes recorded in 3 +15 - 8.75 +44 -23.75 5.5 years. 1 +65.75 >-33.5 Rapid shifts in crestal position and frequent , > (crestal area) +42.25 -24.5 change in slip-face orientation have occurred 7J +59 >-40 (Table 5). The crest shifted a total distance of 8 +7.25 >-18.5 9 (south toe) +7.25 -16.75 194 feet in 5.5 years but was then only 4 feet south of its first-observed location (Fig. 12). The slip slope faced south on 10 occasions, north on 8, with 2 indeterminate. intervals record net rather than absolute The orientation of this dune diverges by 35 changes. degrees from that at station 9, and it responds A summation of net changes on 20 occasions differently to the same winds as shown by the over 5.5 years is given in Table 2. Accumulation crestal movements plotted in Figure 12. at all poles except the two lowermost on the south flank suggests that longitudinal winds Summary of Changes Measured on Transverse from the west or northwest are bringing sand Dunes to this dune. (1) Despite great activity, the net change in The dune crest shifted back and forth at least form and position of transverse dunes was small. 163 feet in a little less than 5.5 years, but within The figures for total turnover of sand given in a zone only 40 feet wide. Total crest movement Tables 1, 2, and 4 are almost certainly 3 to 4

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TABLE 4. SUMMATION OF NET CHANGES IN INCHES OF SAND RECORDED AT POLES OF STATION 10, KELSO DUNES, MOJAVE DESERT, CALIFORNIA, AT INTERVALS FROM JUNE 20, 1959 TO NOVEMBER 28, 1964 South Crestal poles North Pole number 1 2 3 4 5 6 7 8 Accumulation + 12 +27 +52 +102 +191 +74 +27 +27 Removal -31 -22 -39 -168 -208 -77 -44 -12 Total sand moved 43 49 91 270 399 151 71 39 Balance -19 +5 +13 -66 -17 -3 -17 +15

times smaller than they should be, because of of activity, and it has been a hesitant advance, compensating effects that occurred during three steps forward and two and a half steps periods shorter than the intervals between ob- back. servations. Total sand moved at near-crestal poles probably amounted to 200-250 feet in 12 STRUCTURES WITHIN DUNES years, with a net change in surface level of only 1-2 feet. The net change in 9 years on the crest Bedding of one dune was only 0.25 inch (Fig. 7). Bedding is obscure in dry dune sand but (2) Deposition on one flank is nearly always clearly apparent in moist sand subject to dif- accompanied by removal from the other (Figs. ferential drying, grain fallout, or wind erosion. 6 and 9). The greatest changes in level occur Specimens can be collected by permeating the just to one or the other side of the crest, not on sand with a plastic such as glyptol, and with it (Figs. 7 and 10; Tables 1, 2, and 4). Indi- further treatment they can be thin-sectioned vidual episodes of accumulation and removal for microscopic study. lower on a dune are smaller but more consistent. Bedding differs considerably in Bagnold's (3) In any single episode, accumulation is (1941, p. 127, 236-241) "accretion sand" and heavier and more restricted in area than is re- "avalanche sand." The windward surface layer moval. For example, in less than 18 hours on December 28-29, 1960, a strong wind deposited nearly 22 inches of sand at one lee pole while TABLE 5. LOCATION AND SHAPE OF DUNE CREST AND ORIENTATION OF LEE FACE AT STATION 10, KELSO removing not more than 8 inches at any wind- DUNES, MOJAVE DESERT, CALIFORNIA ward pole of one station. Differences in mech- anisms of accumulation and removal explain Direction this behavior. Location in which (4) The largest movements of sand are as- Date of crest Shape lee slope sociated with reversals in the slip slope. These in feet of crest faced occur many times a year on all dunes but more June 20, 1959 at pole 5 sharp north frequently on some (stations 4, 9, and 10) than Oct. 10, 1959 2 ft S. of 5 sharp south others (station 5). Strong storm winds, although Jan. 16, 1960 15 ft S. of 5 rounded south seldom prevailing for more than 12-24 hours, March 20, 1960 15 ft S. of 5 sharp south play a significant role in these reversals and in May 15, 1960 5 ft S. of 5 sharp north July 10, 1960 0.5 ft N. of 5 sharp north dune morphology. Oct. 16, 1960 13 ft S. of 5 sharp south (5) Dune crests moved back and forth within Nov. 19, 1960 8 ft S. of 5 moderately no marked zones 30-40 feet wide, with the cumulative sharp lee face distance covered probably attaining several Dec. 27, 1960 21.5 ft S. of 5 sharp south Dec. 29, 1960 24 ft S. of 5 sharp south hundred feet in 5-12 years but with a net Feb. 4, 1961 25 ft S. of 5 rounded south change ranging from virtually zero to a few April 4, 1961 11 ft S. of 5 rounded north and feet (Fig. 12). Movements of 7.5 feet in 18 south hours and of 28 feet in 2 months have been May 13, 1961 2 ft S. of 5 rounded north Jan. 6, 1962 27 ft S. of 5 sharp south measured. April 29, 1962 5 ft S. of 5 rounded north (6) Over the years some transverse dunes Oct. 14, 1962 at pole 5 sharp north have experienced net removal on one flank and Dec. 29, 1962 10 ft S. of 5 sharp south net accumulation on the other. This produced April 11, 1963 1.5 ft N. of 5 rounded north Feb. 15, 1964 18.5ft S. of 5 rounded south bulk dune movements of 12-18 feet in 12 Nov. 28, 1964 4 ft S. of 5 sharp north years. This is small, considering the high degree

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Crest Bearing N 75°E 4—South ' ' III 40 30 20 10 0 10 30 20 10 0 10 Crest Movement in Feet Figure 12. Plot of shifts in position of dune crests at stations 9 (iron) and 10

of a dune consists of accretion sand with well man and others, 1966, p. 787). Some well defined laminae a fraction to 3 mm thick. The laminated layers are intercalated within the layers of finest grains are thinnest and dark avalanche materials. Lee-slope deposits accum- colored, because black minerals occur in small ulating beyond the base of the slip face have grains (PI. 3, fig. 1). Occasional layers of coarser bedding similar to but not as good as accretion sand, 1-5 cm thick, are intercalated within sand. No buried sand ripples or related struc- these thin beds. Beds of avalanche sand in slip- tures have been seen. face deposits are coarser, 2-5 cm thick, more Deposition of the well-laminated fine sand of irregular, and less sharply defined (see also In- accretion deposits is a problem. Bagnold (1941,

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p. 237-238) suggests that fine materials are laid most preserved lee-slope material has an in- down first during a depositional episode and clination considerably lower than 30 degrees then mantled by coarser grains. The fine grains (see also Smith, 1949, p. 1489). need protection if they are to survive, but in Many pits 4-5 feet deep were made in the Kelso sands one fine layer succeeds another Kelso Dunes at miscellaneous locations, but without intervening coarser material. Perhaps more useful information was obtained from 3- the fines accumulate by sifting down through a foot pits at the poles of dune stations 4, 5, 9, mantle of coarser sand that creeps across the and 10. The results from stations 4 and 5 are surface in the form of sand ripples (Sharp, 1963, shown graphically (Figs. 13 and 14). The data P. 622). are biased by the fact that pits could not be Impregnated samples of avalanche tongues dug on the steepest part of the lee slopes be- display relatively homogeneous, coarse-sand cause of dry sand, and the depth of one or two layers up to 5 cm thick without discernible in- pits was limited by the thinness of the wetted ternal structure. McKee (1945, p. 321) men- layer. tions sorting during avalanching, but this pre- At station 4 a well-laminated sand layer, sumably occurs in the downslope direction as several inches to 3 feet or more thick, with earlier described by Bagnold (1941, p. 240). bedding conformable to the surface, mantles Superimposition of successive avalanche tongues the windward slope. Dips are as great as 16 would presumably produce layering. However, degrees, and in places the layer consists of more avalanche tongues are relatively long and nar- than one set of beds separated by angular un- row (PI. 1, fig. 2), and it seems unlikely that conformity (see Fig. 13, pit 2). Relationships they alone produce the great sweeping lee-side may actually be more complex than shown, as bedding surfaces seen in some ancient eolian slight differences in attitude are not easily dis- sandstones. Such surfaces are probably formed cerned in small pits. These beds dipping upwind through the reworking of lee slopes by oblique rest with angular unconformity upon lee-side or longitudinal winds. There is ample field evi- deposits dipping downwind, for the most part dence in present-day dunes that this occurs. at angles less than 30 degrees. Only in pit 1 (Fig. 13) were true slip-face deposits (31-degree Attitude of Bedding in Dunes dip) exposed. The more gentle downwind dips Interest in the cross lamination of ancient in all other pits, even on the lee flank, presum- eolian sandstones (McKee, 1933; Shotton, ably reflect accumulation on the lower part of 1937; Reiche, 1938; Opdyke and Runcorn, the lee slope (Fig. 4). 1960; Poole, 1962; among others) has stimulated Similar relationships are exposed in pits at investigation of bedding within modern dunes station 5 (Fig. 14) on a dune of more consistent (McKee and Tibbitts, 1964). McKee's (1957, form and behavior. Again slip-face bedding was p. 1721-1723) informative study of a barchan exposed only in one pit, number 5, and the lee- is not strictly applicable to a transverse dune side bedding underlying the veneer of wind- complex with more varied and complex rela- ward deposits in other pits dipped even more tionships (W. O. Thompson, 1937, p. 748; gently leeward—10-15 degrees—than at sta- Cooper, 1958, p. 29). McKee found that simple tion 4. Slip-face deposits were not found even barchan geometry and unidirectional wind on the lee slope, but dry sand prevented dig- produced predominantly slip-face beds dipping ging in the most likely spots. The beds dipping 31-32 degrees, mantled by a windward veneer upwind at the toe of the lee slope (Fig. 14, pit dipping 5-7 degrees in the opposite direction. 11) are probably a remnant of the next dune Poole (1962, p. D148) feels that modern dune downwind. At both stations bedding relation- deposits consist almost exclusively of steeply ships are more complex and thicknesses of units dipping lee-slope beds, and this may be true in greater in the crestal area, presumably because the upper part of a seif dune (McKee and of frequent reversals in asymmetry and back- Tibbitts, 1964, p. 11). The windward beds of a and-forth movement of the crest. transverse dune, called topset by Shotton The data suggest that steeply dipping (>30 (1937, p. 544) and backset by Smith (1940, p. degree) slip-face deposits are rarely preserved 161), are said in most instances to dip no more within these dunes. This could be because the steeply than 12 degrees (McKee, 1945, p. 315; slip face composes only part of the lee slope and 1957, p. 1720; Cooper, 1958, p. 29; Laming, is subject to severe erosion (PI. 2, fig. 1) during 1958, p. 180). However, in Kelso Dunes wind- reversals. Perhaps slip-face bedding is exten- ward bedding dips as much as 16 degrees, and sively preserved only in barchan or barchanoid

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a -o3

Q. C

-O 3

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dunes in which the entire lee slope is a slip face. Much of the bedding in ancient eolian sand- Scalloped Structure stones dips more gently than 30 degrees, so On occasions an unusual structure was seen deposits of the lower part of the lee face may on wet, wind-scoured sand surfaces truncating be principal materials represented. Because beds that dipped about 30 degrees. On near- internal structures of transverse, barchan, and horizontal surfaces the structure appeared as a seif dunes differ, careful study of cross-bedding repetitive scalloping (PL 3, figs. 2 and 3) with in ancient eolian sands may reveal the type of wave lengths of 7-25 cm and amplitudes of

-12

Pole number and Dune Station 5 Surface slope -24 December 27, I960

0 10 20 30 Horizontal Scale (Feet) West ^ (? East

Figure 14. Bedding attitudes in pits across dune at station 5

dune involved (McKee and Tibbitts, 1964, p. 2-5 cm. Each scallop consists of coarse, homo- 13). This information is needed for proper de- geneous sand without discernible structure, termination of paleowind directions from eolian outlined by a thin layer of fine dark grains. cross-bedding because of the complex relation- Beds containing scallops are interlayered with ships between dune form, dune behavior, and unscalloped sequences as much as 3 feet thick. wind patterns (Jordan, 1965). This scalloping is attributed to lee-side ava- Exposures on smooth, gently inclined sur- lanching. As noted by Bagnold (1941, p. 239) faces cut by the wind in wet sand reveal many and Inman and others (1966), a layer of fine angular unconformities among groups of beds of dark material collects along the slip surface of different attitude (PL 2, fig. 2) and suggest that the open U-shaped chute formed at the head relationships appear overly simple in cross of a sand avalanche. The coarse material, con- sections. The geometrical complexity of a dune stituting the bulk of the structure, probably mass and the changes in form that occur with represents a filling of this chute by the wind- time make this planimetric irregularity under- blown sand that accumulates on the upper part standable. of the slip face. Eventually a new avalanche

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creates another U-shaped chute in the newly Salamuni, 1961, p. 1103-1104; Irving, 1964, p. accumulated material and the filling process is 233-240). Thus, investigations of relationships repeated. Scallops are rarely seen, because they between lee-slope orientation and existing wind are localized on the uppermost part of the slip patterns in modern dunes are pertinent. face and requirements for exposure are unusual. Because of complex morphology and local If the origin proposed is correct, the structure orographic factors, Kelso Dunes may not be may be unique to dunes and could be used to ideal for such a study, but the testimony they confirm the eolian origin of ancient sandstones. offer is worth reporting. Local meteorological

320° 330° 340° 350° 0 10° 20° 30° 40°

310'

230 Measurements\ 130° \ \ 220° 210° 200° 190° 180° 170° 160° 150° 140° Figure 15. Rose diagram of lee-slope orientations from air photos of September 15, 1950, for entire Kelso Dune complex

data, first-hand observations, and geographic- LEE-SLOPE ORIENTATION AND geological features indicate that the prevailing THE PREVAILING WIND wind direction over much of the eastern Mojave Lee-slope bedding in eolian sandstones has Desert is westerly. The question asked of the been used to determine paleowind directions by dunes was ' 'how well is this prevailing westerly Shotton (1937), Reiche (1938), McKee (1940, wind recorded in the orientation of your lee p. 823), Wright (1956, p. 416-419), Poole slopes?" (1957; 1962), Opdyke and Runcorn (1960), Two approaches were used. First, orienta- Bigarella and Salamuni (1961), and McBride tions of 344 prominent lee slopes scattered and Hayes (1962) among others. Interest in throughout the entire complex were deter- this procedure has been heightened by paleo- mined from vertical air photos taken Septem- magnetic location of ancient earth poles and by ber 15, 1950. These data are plotted in a rose interpretations of cross-bedding in old sand- diagram (Fig. 15) which gives the impression stones as compatible with wind patterns related that winds from about S. 60° W., S. 30° E., and to these former polar positions (Laming, 1958, N. 30-60° W. have been the most effective. p. 183; Opdyke and Runcorn, 1960, p. 968- (This procedure involved a subjective judg- 969; Runcorn, 1961, p. 298-308; Bigarella and ment in the choice of lee slopes plotted.)

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The second approach was to measure, within At the time these 617 dune crests were several selected square-mile areas, the orienta- measured, an estimate was made of a possibly tion of all transverse dune crests more than 50 predominant lee-slope direction for 384 of feet long. From 15 years of observation it is them. A rose diagram (Fig. 17) of these data known that the lee slopes of such dunes can, at certainly suggests a westerly wind pattern, al- different times, face in opposite directions, although one must recognize the subjective judg- though at the time of measurement, January ment involved in selection of data plotted. The 6-8, 1962, many slopes faced westward because difference between the two rose diagrams (Figs.

320° 330° 340° 350° 0 10° 20° 30°

310

230 6/7^Mepsurements 130° \ 220' 200° 190° 180° 170° 160° 150° 140° Figure 16. Rose diagram of lee-slope orientations from transverse dune- crest trends in south part of Kelso Dunes. Lee face to both sides of crest is assumed possible, hence symmetry of diagram.

of a recent strong easterly wind. Orientations of 16 and 17) may be due to an inheritance of 617 dune crests were measured in sections 3, 4, former dune patterns established by ancient 5, 8, and 9, T. 9 N., R. 12 E. (Fig. 2). A plot of wind regimes. The possibility of inheritance is the two possible lee-slope directions for each of supported by the orientation of stabilized dunes these dunes yields a rose diagram (Fig. 16) on the margins and at spots within the Kelso which certainly does not reflect a dominant in- complex (Fig. 3). Dunes built by an ancient fluence of westerly winds. wind may retain the original linear trend with The pits dug at dune stations 4 and 5 (Figs. good lee-slope relationships even though re- 13 and 14) suggest that lee-slope bedding may activated by current winds striking them be dominantly in one direction even though obliquely. From Figures 15 and 17 one could the dune undergoes frequent reversals, so the make a case for the predominance of westerly procedure used in plotting Figure 16 may not winds, but certainly not from Figure 16, which be reasonable. However, elimination of the is the only plot based on unselected data. western half of the diagram would still not yield If earlier wind directions influence the orien- a strong indication of predominantly westerly tation of lee slopes in the Kelso Dunes, the ef- wind. fects of inheritance should be even more strong-

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ly expressed in ancient eolian sandstones hun- these ancient lee-slope beds noted by Poole dreds of feet thick, that involved longer time (1962, p. D148). Before going too far in using periods and hence greater possibilities of mete- lee-slope bedding for determining ancient pole orological change. It appears that the Kelso locations, more studies should be made of rela- Dunes may be modestly aware of the predom- tionships between prevailing winds and lee- inance of westerly winds in the current regime, slope orientation in modern dunes, a point em- but a house-to-house canvass of individual dunes phasized by Eaton (1964, p. 1).

340° 350" 0 10° 20° 30° 40°

384 Observations\ s \ s ,\ 200° 190° 180°-170°-(60° -150° 140° 130 Figure 17. Rose diagram of predominant lee-slope orientations of 384 of the 617 dunes plotted in Figure 16 as judged from over-all dune form

produces a confused picture; selective poling is SOME CHARACTERISTICS required. OF THE SAND These studies suggest that lee-slope bedding in some ancient eolian sandstones may possibly Grain Size be the product of occasional strong winds (Bag- Insofar as grain size, sorting, and rounding nold, 1951, p. 80) from other than the prevail- are concerned Kelso Dune material is typical ing direction. This is important because a com- wind-blown sand with about 90 per cent of the mon paleoclimatological assumption is that lee- grain diameters between 0.25 and 0.50 mm. slope bedding is created by a prevailing wind Coarse grains, up to 4 mm, are sparse, but local which is related to major wind belts and geo- concentrations exert a considerable influence on graphic pole positions. On the Colorado Plateau minor morphological features, especially rip- lee-slope bedding in late Paleozoic and early ples. Mesozoic eolian sandstones indicates wind from predominantly northerly directions (Reiche, Effects of Eolian Transport 1938, p. 907; Poole, 1957; 1962). These could Eighteen samples were collected along the have been storm winds, and the lee slopes could umbilical cord of wind-blown sand extending subsequently have been smoothed, gentled, and eastward from the mouth of Afton Canyon to good layering established thereon by prevailing Kelso Dunes (Fig. 1). Consideration is given to winds of some other orientation. This could ac- changes in sorting, size, and rounding that oc- count for the 5-10 degree subnormal dip of curred during a wind-driven transport of 35

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miles. Data on a selected 13 samples, summar- tinues progressively to the dunes, where most ized in graphic form in Figure 18, lead to the of the grains are in this category. A qualitative following conclusions. inspection of the +60 fraction suggests a de- (1) Specimens of Mojave River sand (Fig. crease in the number of ferromagnesian particles 18, points 1 and 2) contain significant quanti- with increasing distance of transport. ties of +9 (<11.8 per cent) and +16 (<16.9 per cent) size fractions, but these grades are in- Grain-Size Distribution on Dunes significant in wind-blown samples. This sug- Grain-size distribution on and within dunes gests that grains larger than 1 mm do not travel has been much discussed but with inconsistent much if at all by saltation but move principally conclusions. Sand is said to be finer at the crest by creep under saltation impact. They are thus than at the base of some dunes (Bagnold, 1935, winnowed out and lag behind the saltating p. 360; 1941, p. 145, 205; McKee, 1957, p. grains. Small concentrations of -f-9 and +16 1720; Simonett, 1960, p. 234), and histograms grains within the Kelso Dunes are probably by Amstutz and Chico (1958) modestly support local in origin, as angularity suggests limited this. However, Simonett (1960, p. 233-234) transport. cites some instances in which crestal grains are (2) Wind-blown samples (Fig. 18, points 3, coarser and others in which differences are min- 4, and 5) from the vicinity of Crucero reflect imal. proximity to the source, only 6 miles upwind, Samples for investigation of this relationship in their abundance of +32-size particles and were taken from piles of sand made by scraping lesser dominance of +60- or +115-sized grains, to a depth of 1-2 inches over an area of about compared to samples farther downwind. 4 square feet at the poles of stations 4 and 5. (3) Most of the size-distribution plots (Fig. Results are presented graphically in Figure 19. 18) of wind-blown sand are highly asymmetri- Data from station 4 do not support the proposi- cal, rising steeply on the coarse side to high tion that crestal sand is finer in terms either of peaks in the +60 and +115 sizes and tapering size distribution or of arithmetic mean diam- offgradually into finer sizes. This characteristic, eter (Fig. 19). However, crestal sand at station in which the +60 and +115 sizes together com- 5 is finer than at either the windward or lee- pose 80-97 per cent of the total sample, devel- ward base, even though it is not the finest sand ops after more than 6 but less than 15 miles of on the dune surface. Considering only grains eolian transport. It appears that once debris has larger than 0.5 mm, relationships are clearer. traveled perhaps 10-12 miles by eolian saltation At station 4 such grains constitute only a trace and creep, its characteristics of sorting are well of the crestal sample but make up 1.7 per cent established and change little on further trans- of the windward-base and 1.1 per cent of the port except through contributions from local leeward-base samples. At station 5, grains of sources. this size compose 0.8 per cent of the sand at the (4) Introduction of local material is sug- crest, 4.8 per cent at the windward base, and gested by samples (Fig. 18, points 8, 9, and 11) 25.8 per cent at the leeward base. from the lobe of sand extending north-north- Among the processes concentrating coarser westerly between Soda Playa and Old Dad grains at the foot of a dune is lee-slope avalanch- Mountain. These samples and those from point ing which, as McKee (1945, p. 321; 1957, p. 12 (Fig. 18) north of the highest Kelso Dune 1720) notes, causes larger grains to gather at ridge contain unusual amounts of +32 grains. the base of the slip face because they roll or slide Their geographic setting is favorable to the in- the farthest. Deflation also plays a part, as wind troduction of such material for the north-north- currents at either base are usually underloaded, west. having just dropped much sand on a lee slope. Rounding and mineralogical fractionation are These currents not only pick up sand, princi- two other characteristics presumably affected pally in the finer sizes, but, being lightly loaded, by transportation. They have been investigated are not well equipped to move larger grains by in the +60 and +32 fractions. The river sands saltation impact. The result is a lag concentra- (PI. 4, sample 2) consist predominantly of sub- tion of larger grains. angular particles with only a few rounded and In the Kelso Dunes there are fewer coarse well-rounded grains. At Crucero (PI. 4, sample grains at the crest of a dune than at its base. 3), after 6 miles of saltation transport, there is a However, the finest sand, as measured by arith- noticeable increase in the number of rounded metic mean diameter, is more often on the and well-rounded grains, and this increase con- flanks than the crest. If a dune has a lee slope

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facing fairly consistently in one direction, the sphene, garnet, rutile, tourmaline, monazite, il- concentration of coarser grains is likely to be menite, magnetite, cassiterite, and topaz (?). greater at the lee base than at the windward This assemblage is about what might be ex- base, as shown at station 5 (Fig. 19) and as pected from the Mojave River drainage, which noted by W. O. Thompson (1937, p. 748-750) traverses a complex rock terrane. The relatively and McKee (1957, p. 1720). large proportion of black minerals, primarily

Horizontal and Vertical Scale of Profile

0.31 mm 0.34mm 0.27mm 0.29mm 0.30mm 0.30mm 028mm 0.26mm 0.30mm 0.37mm

(TrPole Number

Figure 19. Grain-size distribution on dunes at stations 4 and 5

magnetite but including some amphibole and Mineralogy ilmenite, is striking. The magnetite probably Mineralogically, the Kelso sands are com- comes from exposures of magnetite iron ore for- plex. In thin sections the following minerals merly mined at the mouth of Afton Canyon have been identified: quartz, potassic feldspar, (Lamey, 1945). plagioclase, hornblende, sphene, tremolite, epidote, biotite, composites of more than one min- THE LEE-SIDE EDDY CONCEPT eral, and small fragments of fine volcanic rock. In sieved samples, treated by heavy-liquid and Introduction magnetic separation, the following minerals Since 1884, it has been recognized that a fixed were identified: quartz, feldspar, amphibole, eddy lies at the lee of current ripples in water pyroxene, zircon, biotite, epidote, apatite, (Darwin, 1884, p. 22-23). Cornish (1897, p.

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280-281; 1900, p. 7; 1914, p. 39-41; 1934, p. these scraps moved, it was in an aimless pattern 54) applied this concept to wind ripples and of short spurts down, up, laterally, or obliquely sand dunes, maintaining that both features have across the slip face, interrupted by frequent and a fixed lee-side eddy which exerts a major in- extended periods of rest. They remained well up fluence on their shape and development. In on the slip face for a significant time but even- spite of objections by experienced field men tually worked their way to the base, where they (Beadnell, 1910, p. 387; King, 1918, p. 21-23; remained more or less inactive except for oc- Hume, 1925, p. 48), this concept became deeply casional lateral movements. The wind velocity entrenched in the literature. Its history is re- required to move such materials is far less than viewed by Cooper (1958, p. 41-44), who con- that needed for sand grains. cludes that no permanent lee-side eddy exists (2) Repeatedly, during and immediately strong enough to affect the morphology and after windy intervals, a considerable body of evolution of sand dunes in the ways argued by dry grass has been observed at the base of fresh Cornish. Bagnold seems inconsistent in his han- slip faces. dling of the lee-side eddy; he (1937a, p. 431) (3) The only sand grains seen ascending the discounts it entirely with respect to wind rip- slip face of a dune while transverse winds were ples and describes (1941, p. 209) the almost per- blowing were those caught up by a temporary fect wind shadow to the lee of a barchan dune. traveling eddy or vortex sweeping obliquely On the other hand he mentions (1937b, p. 264; across the face. Evidence of erosion or under- 1941, p. 140) the "elutriating" effect of "the cutting of the slip face by a fixed eddy has permanent wind eddy to the lee of a dune never been observed. crest." (4) Smoke from pots placed in different posi- Proponents of the eddy concept will point to tions on slip faces during high-velocity trans- observations of wind currents over Lake Michi- verse winds fails to give any indication of an gan dunes (Landsberg, 1942, p. 237; Rossby, established eddy. For the most part the move- 1943, p. 5; Landsberg and Riley, 1943) as con- ment of smoke is leisurely and follows no set firming its existence. However, the lee-side re- pattern. It may ascend slowly (PI. 5, fig. 1) un- verse movement of air had a velocity only one- til caught by the transverse current, which dis- tenth that across the dune crest and was much perses the smoke rapidly downwind, or it may too small to move sand or affect dune shape, as drift lazily in any direction (PI. 5, figs. 2 and noted by Olson (1958, p. 261). Inman and 3), up the slip face, outward from it, or (most others (1966, p. 787) made measurements sug- commonly) obliquely along the face (PL 5, fig. gesting an eddy to the lee of well-shaped bar- 4). Now and then the smoke is suddenly and chanoid dunes under near-unidirectional winds. violently displaced by a strong gust or eddy, Velocity of the eddy currents was too low to but only momentarily. move sand, but it was said to divert grains fly- With oblique winds or in special topographic ing over the crest from windward, concentrat- situations—close to a narrow saddle in a dune ing them on the upper part of the lee slope and crest, for instance—a variety of wind currents thus promoting oversteepening and avalanch- may affect the lee slope. Such currents may in- ing. deed contain traveling eddies or vortices, dis- tributing sand in all directions across the lee Field Observations slope and smoothing the slip face. However, (1) Many times during strong winds (30-40 even under these conditions nothing like a fixed mph) small scraps of paper or cellophane were eddy of the Cornish type appears to exist. dropped onto the slip face of a dune. When

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Beadnell, H. J. H., 1910, The sand dunes of the Libyan Desert: Geog. Jour., v. 35, p. 379-392 Bigarella, J. J., and Salamuni, I., 1961, Early Mesozoic wind patterns as suggested by dune bedding in the Botucats Sandstone of Brazil and Uruguay: Geol. Soc. America Bull, v. 72, p. 1089-1105 Cooper, W. S., 1958, Coastal sand dunes of Oregon and Washington: Geol. Soc. America Memoir 72, 169 p. Cornish, Vaughan, 1897, On the formation of sand-dunes: Geog. Jour., v. 9, p. 278-302 1900, On desert sand-dunes bordering the Nile Delta: Geog. Jour., v. 15, p. 1-30 1914, Waves of sand and snow: London, T. F. Unwin, 383 p. • 1934, Ocean waves and kindred geophysical phenomena: Cambridge Univ. Press, 164 p. Darwin, G. H., 1884, On the formation of ripple-marks in sand: Royal Soc. London Proc., v. 36, p. 18-43 Eaton, G. P., 1964, Windborne volcanic ash: A possible index to polar wandering: Jour. Geology, v. 72, p. 1-35 Free, E. E., 1911, The movement of soil material by the wind: U. S. Dept. Agriculture, Bur. Soils Bull. 68, 272 p. Finkle, H. J., 1959, The barchans of southern Peru: Jour. Geology, v. 67, p. 614-647 Hume, W. F., 1925, Geology of Egypt, v. 1, Cairo, Govt. Press, 408 p. Inman, D. L., Ewing, G. C., and Corliss, J. B., 1966, Coastal sand dunes of Guerrero Negro, Baja Cali- fornia, Mexico: Geol. Soc. America Bull., v. 77, p. 787-802 Irving, E., 1964, Paleomagnetism and its application to geological and geophysical problems: New York, John Wiley and Sons, 399 p. Jordan, W. M., 1965, Prevalence of sand-dune types in the Sahara Desert, p. 104-105 in The Geological Society of America Abstracts for 1964: Geol. Soc. America Special Paper 82, 400 p. King, W. J. H., 1918, Study of a dune belt: Geog. Jour., v. 51, p. 16-33 Lamey, C. A., 1945, Cave Canyon iron-ore deposits, San Bernardino County, California: Calif. Div. Mines Bull. 129, p. 71-83 Laming, D. J. C., 1958, Fossil winds: Jour. Alberta Soc. Petroleum Geologists, v. 5, p. 179-183 Landsberg, Helmut, 1942, The structure of the wind over a sand-dune: Am. Geophys. Union Trans., v. 23, p. 237-239 Landsberg, Helmut, and Riley, N. A., 1943, Wind influences on the transportation of sand over a Michi- gan sand dune: Univ. Iowa, Studies in Eng. Bull. 27, p. 342-352 Logan, R. F., 1960, The central Namib Desert, South West Africa: Natl. Res. Council, Pub. 758, 162 p. McBride, E. F., and Hayes, M. O., 1962, Dune cross-bedding on Mustard Island, Texas: Am. Assoc. Petroleum Geologists Bull., v. 46, p. 546-551 McKee, E. D., 1933, The Coconino sandstone—its history and origin: Carnegie Inst. Washington, Pub. 440, p. 78-115 1940, Three types of cross-lamination in Paleozoic rocks of Northern Arizona: Am. Jour. Sci., v. 238, p. 811-824 1945, Small-scale structures in the Coconino sandstone of northern Arizona: Jour. Geology, v. 53, p. 313-325 1957, Primary structures in some recent sediments: Am. Assoc. Petroleum Geologists, v. 41, p. 1704- 1747 McKee, E. D., and Tibbitts, G. C., 1964, Primary structures of a seif dune and associated deposits in Libya: Jour. Sed. Petrology, v. 34, p. 5-17 Norris, R. M., and Norris, K. S., 1961, Algodones Dunes of southeastern California: Geol. Soc. America Bull., v. 72, p. 605-620 Olson, J. S., 1958, Lake Michigan dune development: 1. Wind-velocity profiles; 2. Plants as agents and tools in geomorphology: Jour. Geology, v. 66, p. 254-263, 345-351 Opdyke, N. D., and Runcorn, S. K., 1960, Wind direction in the western United States in the late Paleozoic: Geol. Soc. America Bull., v. 71, p. 959-972 Poole, F. G., 1957, Paleo-wind directions in late Paleozoic and early Mesozoic time on the Colorado Plateau as determined by cross strata: Geol. Soc. America Bull., v. 68, p. 1870 1962, Wind direction in late Paleozoic to middle Mesozoic time on the Colorado Plateau: U. S. Geol. Survey Prof. Paper 450-D, p. D147-D151 Reiche, Parry, 1938, An analysis of cross-lamination in the Coconino sandstone: Jour. Geology, v. 46, p. 905-932

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Rossby, C. G., 1943, Introduction to the conference and some applications of boundary-layer theory to the physical geography of the Middle West: N. Y. Acad. Sci. Annals, v. 44, p. 3-12 Runcorn, S.K., 1961, Climatic change through geological time in the light of the paleomagnetic evidence for polar wandering and continental drift: Quart. Jour. Royal Meteorol. Soc., v. 87, p. 282-313 Sharp, R. P., 1963, Wind ripples: Jour. Geology, v. 71, p. 617-636 Shotton, F. W., 1937, The lower Bunter sandstones of north Worcestshire and east Shropshire: Geol. Mag., v. 74, p. 534-553 Simonett, D. S., 1960, Development and grading of dunes in western Kansas: Assoc. Am. Geographers Annals, v. 50, p. 216-241 Smith, H. T. U., 1940, Geological studies in southwestern Kansas: Kans. Geol. Survey Bull. 34, 212 p. 1949, Physical effects of Pleistocene climatic changes in nonglaciated areas: Eolian phenomena, frost action, and stream terracing: Geol. Soc. America Bull., v. 60, p. 1485-1516 Thompson, D. G., 1929, The Mojave Desert region, California: U. S. Geol. Survey Water Supply Paper 578, 759 p. Thompson, W. O., 1937, Original structures of beaches, bars, and dunes: Geol. Soc. America Bull., v. 48, p. 723-752 Van Burkalow, Anastasia, 1945, Angle of repose and angle of sliding friction: An experimental study: Geol. Soc. America Bull., v. 56, p. 669-708 Wright, H. E., 1956, Origin of the Chuska sandstone, Arizona-New Mexico: A structural and petro- graphic study of a Tertiary eolian sediment: Geol. Soc. America Bull., v. 67, p. 413-434

MANUSCRIPT RECEIVED BY THE SOCIETY JUNE 14, 1965 CALIFORNIA INSTITUTE OF TECHNOLOGY, DIVISION GEOLOGICAL SCIENCES, PUB. No. 1349

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