U.S. Department of the Interior

U.S. Geological Survey

Professional Paper 1756

The Role of Eolian Sediment in the Preservation of 

Archeologic Sites Along the Colorado River Corridor 

in Grand Canyon National Park, Arizona
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The Role of Eolian Sediment in the Preservation of 

Archeologic Sites Along the Colorado River Corridor 

in Grand Canyon National Park, Arizona

By Amy E. Draut and David M. Rubin

Professional Paper 1756

U.S. Department of the Interior

U.S. Geological Survey 
U.S. Department of the Interior

DIRK KEMPTHORNE, Secretary

U.S. Geological Survey

Mark D. Myers, Director

U.S. Geological Survey, Reston, Virginia: 2008

This report and any updates to it are available online at:

http://pubs.usgs.gov/pp/1756/

For additional information write to:

U.S. Geological Survey

Box 25046, Mail Stop 421, Denver Federal Center

Denver, CO 80225-0046

Additional USGS publications can be found at:

http://geology.usgs.gov/index.htm

For more information about the USGS and its products:

Telephone: 1–888–ASK–USGS (1-888-275-8747)

World Wide Web: http://www.usgs.gov/

Any use of trade, product, or firm names in this publication is for descriptive purposes only and does not imply 

endorsement by the U.S. Government.

Although this report is in the public domain, it may contain copyrighted materials that are noted in the text. Permission

to reproduce those items must be secured from the individual copyright owners.

Cataloging-in-Publication data are on file with the Library of Congress

Produced in the Western Region, Menlo Park, California

Manuscript approved for publication, August 13, 2008

Text edited by George A. Havach

Layout and design by Stephen L. Scott

COVER—Photograph taken in 2007 of eolian sedimentary deposits in the Palisades area of the Colorado River corridor, 

Grand Canyon, Ariz.
Contents

Executive Summary.......................................................................................................................................1

Introduction.....................................................................................................................................................3

Overview of Wind, Precipitation, and Eolian-Sediment-Transport Measurements ...........................4

Overview of Sedimentologic and Geomorphologic Investigations .......................................................6

Identifying Fluvial and Eolian Deposits by Using Sediment Grain Size........................................7

Two Types of Eolian Deposit Defined for the Colorado River Corridor ........................................7

Sedimentary Environments—Implications for the Preservation of Archeologic Sites ..........14

Criteria for Identifying Site Sensitivity to Dam Operations ...................................................................15

Three Case Studies.............................................................................................................................17

Effects of the November 2004 Controlled-Flood Experiment on Eolian Sediment Transport ..........19

Recommended Future Research...............................................................................................................21

Conclusions...................................................................................................................................................22

Acknowledgments.......................................................................................................................................23

References Cited..........................................................................................................................................24

Appendix 1. Site-Specific Observations ..................................................................................................29

24.5 Mile................................................................................................................................................29

Malgosa................................................................................................................................................34

Palisades..............................................................................................................................................39

Comanche ............................................................................................................................................44

Forster ..................................................................................................................................................46

202.9 Mile..............................................................................................................................................49

Arroyo Grande.....................................................................................................................................51

Appendix 2. Evaluating the Predictive Power of Eolian-Sediment-Transport Models—

 Can Sediment-Supply Limitation Be Discerned?...........................................................................55

Introduction..........................................................................................................................................55

Eolian-Sediment-Transport Models.................................................................................................55

Sediment-Supply Limitation ..............................................................................................................56

Model Testing ......................................................................................................................................56

Experimental Methods.......................................................................................................................56

Results ..................................................................................................................................................58

Discussion............................................................................................................................................61

Potential Sources of Error........................................................................................................61

Performance of Tested Models ...............................................................................................62

Relevance for Investigation of Sediment-Supply-Limited Systems ..................................64

Conclusions..........................................................................................................................................64

Appendix 3. Estimation of Historical Changes in Eolian Sand Sources..............................................65

Introduction..........................................................................................................................................65

Aerial Photographs Incorporated into a GIS Database Compiled by the Utah State 

University..............................................................................................................................................65

Results and Interpretation.................................................................................................................65

Figures

1. Colorado River corridor in Grand Canyon National Park, Ariz., showing 

locations of study sites....................................................................................................................5

III
 2. Aerial photographs of study area sites along the Colorado River corridor in 

Grand Canyon National Park, Ariz., with geomorphology shown in colored 

overlay................................................................................................................................................8

 3. Grain-size distributions, obtained by using laser particle-size analysis, in 

fluvial and eolian deposits along the Colorado River corridor in Grand Canyon 

National Park, Ariz..........................................................................................................................11

 4. Aerial photographs showing two types of eolian deposit defined for the 

Colorado River corridor in Grand Canyon National Park, Ariz................................................12

 5. Sedimentary profiles at Palisades, Lower Comanche, and Arroyo Grande 

study sites in Grand Canyon National Park, Ariz. .....................................................................13

 6. Sedimentary material in area where a tributary channel erodes an eolian 

deposit containing cultural material (site 2) along Colorado River corridor 

in Grand Canyon National Park, Ariz...........................................................................................18

 7. Study site at Malgosa (river mile 57.9) along the Colorado River corridor 

in Grand Canyon National Park, Ariz., showing effects of November 2004 

flood and subsequent fluctuating flows. ....................................................................................20

 8. Aerial photographs taken in May 1965 and May 2004 of 24.5 Mile, Colorado 

River corridor in Grand Canyon National Park, Ariz.................................................................30

 9. Rose diagrams of sand-transport potential calculated from 2 years of wind

data collected at weather station 24.5 L along the Colorado River corridor 

in Grand Canyon National Park, Ariz...........................................................................................31

10. Rose diagram of sand-transport potential calculated from 2 years of wind 

data collected at weather station 24.5 U along the Colorado River corridor 

in Grand Canyon National Park, Ariz...........................................................................................31

11. Rainfall, wind, and sand-transport data collected at weather station 24.5 L 

along the Colorado River corridor in Grand Canyon National Park, Ariz., 

from November 2003 to January 2006.........................................................................................32

12. Rainfall, wind, and sand-transport data collected at weather station 24.5 U 

along the Colorado River corridor in Grand Canyon National Park, Ariz., from 

November 2003 to January 2006. ................................................................................................33

13. Aerial photographs taken in May 1965 and May 2004 of 23.5 Mile area along 

the Colorado River corridor, Grand Canyon National Park, Ariz.............................................34

14. Aerial photographs taken in May 1965 and May 2004 of Malgosa area along 

the Colorado River corridor in Grand Canyon National Park, Ariz.........................................35

15. Rose diagrams of sand-transport potential calculated from 2 years of wind 

data collected at weather station Mal L along the Colorado River corridor 

in Grand Canyon National Park, Ariz...........................................................................................36

16. Rose diagrams of sand-transport potential calculated from 2 years of 

wind data collected at weather station Mal U along the Colorado River 

corridor in Grand Canyon National Park, Ariz. ..........................................................................36

17. Rainfall, wind, and sand-transport data collected at weather station 

Mal L along the Colorado River corridor in Grand Canyon National Park, 

Ariz., from November 2003 to January 2006...............................................................................37

18. Rainfall, wind, and sand-transport data collected at weather station 

Mal U along the Colorado River corridor in Grand Canyon National Park, 

Ariz., from November 2003 to January 2006...............................................................................38

IV
V

19. Zones within dune field at Malgosa along the Colorado River corridor 

in Grand Canyon National Park, Ariz...........................................................................................39

20. Aerial photographs taken in May 1965 and May 2004 of Palisades area 

along the Colorado River corridor in Grand Canyon National Park, Ariz..............................40

21. Rose diagrams of sand-transport potential calculated from 2 years of 

wind data collected at weather station Pal L along the Colorado River 

corridor in Grand Canyon National Park, Ariz. ..........................................................................41

22. Rose diagrams of sand-transport potential calculated from 2 years of 

wind data collected at weather station Pal U along the Colorado River 

corridor in Grand Canyon National Park, Ariz. ..........................................................................41

23. Rainfall, wind, and sand-transport data collected at weather station 

Pal L along the Colorado River corridor in Grand Canyon National Park, 

Ariz., from November 2003 to January 2006...............................................................................42

24. Rainfall, wind, and sand-transport data collected at weather station 

Pal U along the Colorado River corridor in Grand Canyon National Park, 

Ariz., from November 2003 to January 2006...............................................................................43

25. Aerial photographs taken in May 1965 and May 2004 of Comanche area 

along the Colorado River corridor in Grand Canyon National Park, Ariz..............................45

26. Rose diagrams of sand-transport potential calculated from wind data 

collected at weather station Com along the Colorado River corridor in 

Grand Canyon National Park, Ariz., from April 2004 to January 2006....................................46

27. Rainfall, wind, and sand-transport data collected at weather station 

Com along the Colorado River corridor in Grand Canyon National Park, 

Ariz., from April 2004 to January 2006.........................................................................................47

28. Aerial photographs taken in May 1965, May 2004, and April 2004 of area 

by mouth of Forster Canyon along the Colorado River corridor in Grand 

Canyon National Park, Ariz...........................................................................................................48

29. Rose diagrams of sand-transport potential calculated from wind data 

collected at weather station For along the Colorado River corridor in 

Grand Canyon National Park, Ariz., from April 2004 to January 2006....................................49

30. Rainfall, wind, and sand-transport data collected at weather station For 

along the Colorado River corridor in Grand Canyon National Park, Ariz., 

from April 2004 to January 2006...................................................................................................50

31. Aerial photographs taken in May 1965 and May 2004 of 202.9 Mile area 

along the Colorado River corridor in Grand Canyon National Park, Ariz..............................51

32. Rose diagrams of sand-transport potential calculated from wind data 

collected at weather station 202.9 along the Colorado River corridor in 

Grand Canyon National Park, Ariz., from April 2004 to January 2006....................................52

33. Rainfall and wind data collected at weather station 202.9 along the 

Colorado River corridor in Grand Canyon National Park, Ariz., from 

April 2004 to January 2006 ............................................................................................................53

34. Aerial photographs taken in May 1965 and May 2004 of Arroyo Grande 

area along the Colorado River corridor in Grand Canyon National Park, 

Ariz....................................................................................................................................................54

35. Study site at the Dumont Dunes in the Mojave Desert, southern Calif., 

showing location of experiment in late February 2004 ............................................................58
36. Histograms of shear velocity (u*) measured during experiment at the 

Dumont Dunes in the Mojave Desert, southern Calif., and two tests 

at Malgosa along the Colorado River corridor in Grand Canyon National 

Park, Ariz..........................................................................................................................................60

37. Sand flux (q) predicted for various shear velocities (u*) by eight eoliansediment-transport models. .........................................................................................................62

38. Total area of various types of sedimentary deposits mapped from aerial 

photographs in the Glen Canyon reach of the Colorado River corridor in 

Grand Canyon National Park, Ariz...............................................................................................67

39. Total area of various types of sedimentary deposit mapped from aerial

 photographs of the Lees Ferry reach of the Colorado River corridor in 

Grand Canyon National Park, Ariz...............................................................................................68

40. Total area of various types of sedimentary deposit mapped from aerial 

photographs in the Redwall Gorge reach of the Colorado River corridor

 in Grand Canyon National Park, Ariz..........................................................................................69

41. Total area of various types of sedimentary deposit mapped from aerial 

photographs of the Point Hansbrough reach of the Colorado River 

corridor in Grand Canyon National Park, Ariz. ..........................................................................70

42. Total area of various types of sedimentary deposits mapped from aerial 

photographs of the Little Colorado River reach of the Colorado River 

corridor in Grand Canyon National Park, Ariz. ..........................................................................71

Tables

1. Summary of sedimentary processes affecting archeologic sites at 

Palisades, Grand Canyon National Park, Ariz. ............................................................................9

2. Summary of sedimentary processes affecting archeologic sites at 

Lower Comanche, Grand Canyon National Park, Ariz. ..............................................................9

3. Summary of sedimentary processes affecting archeologic sites at 

Arroyo Grande, Grand Canyon National Park, Ariz. .................................................................10

4. Eolian-sediment-transport models tested in the Dumont Dunes in 

Death Valley, Calif., and the dune field at Malgosa at Grand Canyon 

National Park, Ariz..........................................................................................................................57

5. Comparison of predicted sand flux with sand flux measured by using 

sand traps during experiments in the Dumont Dunes and the dune 

field at Malgosa..............................................................................................................................59

6. Reaches of the Colorado River, with corresponding river miles, analyzed 

by using a GIS database compiled by the Utah State University. ..........................................66

7. Dates of and riverflow in aerial photographs included in the Utah State 

University’s GIS database, with available mapped river reaches in each 

aerial photograph...........................................................................................................................66

VI
1

Executive Summary

This report summarizes a 3-year study of eolian sedimentary processes in the Colorado River corridor, Grand Canyon 

National Park, Ariz., and discusses the relevance of those 

processes to the preservation of archeologic sites. The results 

reported here are based on detailed sedimentologic and geomorphologic investigations in three reaches of the river corridor, 

as well as continuous measurements of wind, rainfall, and sand 

transport at six sites for as long as 26 months, short-term field 

study at 35 other sites, examination of historical aerial photographs, and review of data collected and analyzed during previous studies. The data generated by this study, which involved 

collaboration with scientists of the U.S. Geological Survey 

(USGS) Grand Canyon Monitoring and Research Center, the 

National Park Service, Northern Arizona University, the Hopi 

Tribe, and GeoArch, Inc., were previously published by Draut 

and Rubin (2005, 2006, 2008) and Draut and others (2005, in 

press). This report, which supersedes that by Draut and Rubin 

(2007), provides an overview of the results and contains new 

conclusions regarding eolian sedimentary processes in the Colorado River ecosystem and their relevance to the preservation of 

archeologic sites.

At many of the study sites, eolian sediment serves as a substrate on which archeologic sites were formed (many sites were 

also built on fluvial and slopewash sediment) and, commonly, 

as a surficial deposit (cover) inferred to help preserve cultural 

materials. Over time, many cultural artifacts are exposed by 

wind deflation of the overlying sediment, forming a lag deposit 

on the land surface. Archeologic material also is vulnerable to 

erosion by gully incision. Incision of gullies and arroyos into 

sedimentary deposits during rainfall runoff is an erosive process 

counteracted by transport and deposition of eolian sediment 

because gullies are natural traps for windblown sand. The ability of eolian sediment transport to inhibit gully formation and to 

heal small gullies (<1 m wide or deep) is a major factor controlling the geomorphic evolution of Grand Canyon sedimentary 

deposits. Rainfall and sand-transport rates measured during this 

study showed that areas with heavy rainfall but abundant windblown sand may have no gullies (which form episodically but 

are quickly filled by eolian sediment), whereas areas of relatively 

low rainfall and low sand-transport rates can be substantially 

eroded by gullies and arroyos, destabilizing archeologic sites. 

Many eolian dunes in Grand Canyon show evidence of 

reduced sand supply relative to some time in the past, with 

vegetation and biologic soil crust covering relict duneforms. 

Vegetation and soil crusts indicate an absence of eolian sedimentation and a decrease in dune mobility relative to past times 

when the supply and transport of eolian sediment were abundant 

enough to form dunes. Some dunes with substantially reduced 

sand supply (and with well-developed vegetation and soil crust) 

have insufficient active eolian sedimentation to counteract 

gully incision; where present, large gullies and arroyos erode 

and degrade such dune fields and many of the archeologic sites 

within them.

The availability and transport of eolian sediment has 

important implications for the management of Glen Canyon 

Dam operations, which regulate the flow of the Colorado 

River through Grand Canyon. Because fluvial sandbars now 

provide the greatest source of eolian sediment in the river 

corridor, the alongshore and cross-shore dimensions of unvegetated, dry fluvial sandbars directly affect the entrainment and 

transport of eolian sediment. Therefore, depending on location 

and wind direction, fluvial-sandbar area and dimensions also 

can substantially affect eolian sediment transport to dune fields 

in which archeologic sites are covered by windblown sand. 

This relation between fluvial sandbars and many of the eolian 

deposits in Grand Canyon implies that the availability of 

eolian sediment is affected by dam operations that increase or 

decrease the area of open, dry fluvial sedimentary deposits. An 

increase in sandbar area due to dam operations could increase 

eolian sediment transport to specific dune fields and associated 

archeologic sites in areas with an appropriate dominant wind 

direction. This report discusses criteria for evaluating the sensitivity of archeologic sites to dam operations with regard to 

eolian sedimentation.

We distinguish two types of eolian deposit in the Colorado River corridor: (1) modern fluvial-sourced (MFS) deposits, which formed as the wind transported sand inland from a 

river-level sandbar, creating an eolian dune field downwind; 

and (2) relict fluvial-sourced (RFS) deposits, which formed 

as the wind eroded and redistributed sediment of extensive 

predam flood deposits. MFS deposits generally are smaller 

and more common in Grand Canyon than are RFS deposits. 

In areas of RFS deposits, the dominant wind direction may 

or may not be appropriate to transport sand from the river 

(non-flood-stage fluvial sandbars) to local eolian dune fields. 

Archeologic material is known to occur in eolian deposits of 

both types. 

Both MFS and RFS deposits are sensitive to dam operations for different reasons. MFS deposits, situated directly 

downwind from fluvial sandbars, receive an amount of windblown sand as a function of wind velocity, dimensions of 

exposed dry fluvial sandbars, and any barriers (such as vegetation) that exist between the fluvial sediment and its associated 

eolian deposits. Fluvial-sandbar area and riparian vegetation 

have been shown, by numerous studies, to respond to dam 

operations. Therefore, changes in either fluvial-sandbar area or 

riparian vegetation can affect the delivery of eolian sediment 

to MFS dune fields downwind. RFS deposits include eolian 

coppice dunes (vegetated sand mounds), which compose the 

uppermost, wind-reworked part of predam terraces. Predam 

terraces are largely alluvial in composition and contain sediment deposited by floods higher than any postdam floods 

have been (≥5,660 m3

/s). Because sediment-rich floods of that 

magnitude no longer occur in this regulated river, the fluvial 

deposits from which extensive RFS dune fields formed no 

longer constitute an active sand source; no substantial new 

deposition is likely to occur on those dune fields as long as no 

large sediment-rich floods occur. As vegetation and biologic 

soil crust colonize RFS coppice-dune fields over time, active 
2 The role of Eolian Sediment in the Preservation of Archeologic Sites Along the Colorado River Corridor

eolian sediment transport decreases within them, such that 

these areas become increasingly unable to compensate for 

precipitation-induced gully erosion. As a result, large gully 

and arroyo systems can form on predam terraces and associated RFS dune fields.

Analysis of the effects of the November 2004 controlledflood experiment on eolian sediment transport indicates that 

in areas where sandbars are enlarged by floods, sediment-rich 

controlled floods can be an effective means to restore sediment 

deposition locally in eolian dune fields above the controlledflood stage. Sandbar-building riverflows of about 1,270 m3

/s 

are much more likely to enhance eolian sedimentation on MFS 

than on RFS deposits because of the direct link between fluvial 

sandbars and MFS dune fields downwind. 

Our data suggest that the restoration potential for archeologic sites in eolian deposits can be optimized by using dam 

operations (controlled floods and postflood flows) that maximize the open sand area on fluvial sandbars during the spring 

windy season (April through early June), when eolian sediment transport is greatest. To effect the greatest sand transport to eolian deposits and associated archeologic material, 

riverflows that follow sandbar-building high flows would need 

to be managed to retain and maximize high-elevation, open, 

dry sandbar area. In spring 2005, the first windy season after 

the November 2004 high flow, the one study site with a clear 

MFS-type link between a fluvial sandbar and eolian dunes and 

with substantial remaining flood sediment (not entirely eroded 

by high fluctuating flows, as at other study sites), sand-transport rates were significantly higher than in the spring 2004 

windy season. At the same site, gully erosion was effectively 

counteracted by deposition of eolian sediment derived from 

the 2004 flood deposit. If controlled high flows were followed 

by low fluctuating flows (as defined in the 1996 Record of 

Decision signed by the Secretary of the Interior) or steady low 

flows rather than the experimental high daily flow fluctuations 

that occurred from January to March 2005, windblown sand 

would be more likely to be transported to and deposited in gullies, and erosion of eolian deposits and associated archeologic 

sites might be reduced. Operating Glen Canyon Dam under 

low fluctuating flows (or steady low flows) between the end 

of a controlled flood and the start of a spring windy season is 

predicted to maintain the postflood sandbar area longer than 

in winter 2005, leaving more sand available to be blown into 

higher elevation dune fields during the subsequent spring 

windy season.

Sedimentation patterns documented during this study 

indicate that eolian deposits above the riparian zone can 

respond to dam operations and that archeologic sites within 

these deposits can be consequently affected. The sensitivity of eolian deposits to dam operations could have either 

detrimental or restorative results. If reduction of open, dry 

fluvial-sandbar area causes a corresponding reduction in sand 

transport to and deposition on an eolian dune field downwind, 

then sand transport to and deposition on that same dune field 

can be enhanced by enlarging the area of the fluvial sandbar 

serving as a sand source for the dune field. As shown by this 

study, an increase in eolian sediment transport in the dune 

field as a result of dam operations can counteract deflation 

and gully incision there, potentially leading to greater preservation of associated archeologic sites. Protection of cultural 

artifacts in Grand Canyon on geologic time scales is unrealistic because of continual downcutting and backwasting of the 

bedrock canyon. However, preservation of archeologic sites 

likely could be enhanced on decadal to centennial time scales 

by restoring fluvial and eolian sedimentation that resembles 

more closely predam processes, including large, sediment-rich 

floods that once left fluvial deposits from which sediment was 

remobilized by wind.
3

Introduction

Since the closure of Glen Canyon Dam in 1963, the natural hydrologic and sedimentary systems along the Colorado 

River in the Grand Canyon reach have changed substantially 

(see, for example, Andrews, 1986; Johnson and Carothers, 

1987; Webb and others, 1999b; Rubin and others, 2002; Topping and others, 2003; Wright and others, 2005; Hazel and 

others, 2006b). The dam has reduced the fluvial sediment 

supply at the upstream boundary of Grand Canyon National 

Park by about 95 percent. Regulation of river discharge by 

dam operations has important implications for the storage and 

redistribution of sediment in the Colorado River corridor. In 

the absence of floods, sediment is not deposited at elevations 

that regularly received sediment before dam closure. Riparian vegetation has colonized areas at lower elevations than 

in predam time when annual floods removed young vegetation (Turner and Karpiscak, 1980). Together, these factors 

have caused a systemwide decrease in the size and number 

of subaerially exposed fluvial sand deposits since the 1960s, 

punctuated by episodic aggradation during the exceptional 

high-flow intervals in 1983–84, 1996, and 2004 and by sediment input from occasional tributary floods (Beus and others, 

1985; Schmidt and Graf, 1987; Kearsley and others, 1994; 

Hazel and others, 1999; Schmidt and others, 2004; Wright and 

others, 2005).

When the Bureau of Reclamation sponsored the creation 

of the Glen Canyon Environmental Studies (GCES) research 

initiative in 1982, research objectives included physical 

and biologic resources, whereas the effects of dam operations on cultural resources were not addressed (Fairley and 

others, 1994; Fairley, 2003). In the early 1980s, it was widely 

believed that because few archeologic sites were preserved 

within the river’s annual-flood zone, cultural features would 

not be greatly affected by dam operations. Recent studies, 

however, indicate that alterations in the flow and sediment 

load of the Colorado River by Glen Canyon Dam operations 

may affect archeologic sites within the river corridor, even 

above the annual flood limit (Hereford and others, 1993, 

Yeatts, 1996, 1997; Thompson and Potochnik, 2000; Draut 

and others, 2005). (The annual-flood zone is defined here by 

the mean annual predam flood of 2,410 m3

/s; the “predam 

flood limit,” the highest elevation at which fluvial deposits are 

present locally, was approximately equivalent to a rare, major 

flood of 8,500 m3/s; Topping and others, 2003.) Of about 500 

archeologic sites documented between Glen Canyon Dam and 

Separation Canyon (255 river miles), more than 330 are considered to be within the area of potential effect (APE) of dam 

operations (Fairley and others, 1994; Neal and others, 2000; 

Fairley, 2005). The APE was designated by the National Park 

Service (NPS) to include the area below the peak stage of the 

1884 flood; though previously believed to have reached 8,490 

m3/s, this flood was shown by Topping and others (2003) to 

have peaked at 5,940 m3/s.

Archeologic research and monitoring in Grand Canyon 

National Park focus increasingly on the potential effects of 

Glen Canyon Dam operations on the landscape in which 

these sites exist. Many archeologic sites in or on sedimentary deposits are being eroded, owing to eolian deflation and 

gully incision (Leap and others, 2000; Neal and others, 2000; 

Fairley, 2003, 2005). Hereford and others (1993) first suggested that gully incision of sedimentary deposits, and the base 

level to which small drainage systems respond, were linked 

to dam operations; they hypothesized that pronounced arroyo 

incision, which occurs during rainfall runoff, was caused by 

lowering of the effective base level at the mouths of ephemeral 

drainages to meet the new postdam elevation of high-flow 

sediment deposition, about 3 to 4 m below the lowest predam 

alluvial terraces. Thompson and Potochnik (2000) modified 

that hypothesis to include the restorative effects of fluvial 

deposition in the mouths of gullies and arroyos, presumed to 

raise effective base level at least temporarily, and new eolian 

deposition on predam alluvial deposits as wind reworks flooddeposited sand. Thompson and Potochnik (2000) concluded 

that sediment deprivation and fewer floods as a result of dam 

operations reduce the potential for new deposition that could 

heal gullies formed by rainfall runoff. Neal and others, following Lucchitta (I. Lucchitta, unpub. data, 1991), suggested that 

eolian deposition in incipient gullies is “one of the strongest 

restorative forces operating at archaeological sites.” Repeated 

high-resolution mapping after the 1996 controlled-flood 

The Role of Eolian Sediment in the Preservation of 

Archeologic Sites Along the Colorado River Corridor 

in Grand Canyon National Park, Arizona

By Amy E. Draut and David M. Rubin
4 The role of Eolian Sediment in the Preservation of Archeologic Sites Along the Colorado River Corridor

experiment (1,270 m3/s; see Webb and others, 1999b; Schmidt 

and others, 2001) confirmed that high riverflows can deposit 

sediment in arroyo mouths and suggested that those deposits 

can be a source for windblown sand which accumulates at 

higher elevation, causing sediment accretion above the floodstage elevation (Yeatts, 1997; Hazel and others, 2000, 2008).

This study began in 2003 as a collaborative effort between 

the USGS and the NPS, funded by the Bureau of Reclamation 

through the USGS Grand Canyon Monitoring and Research 

Center (GCMRC), to investigate the role of eolian sediment 

transport in the preservation of archeologic sites along the 

Colorado River corridor in Grand Canyon National Park and 

thereby to clarify the actual or potential effects of dam operations on eolian deposits and associated archeologic sites. Participants in this research included geologists and archeologists 

from the USGS (including the GCMRC), the NPS, Northern 

Arizona University, GeoArch, Inc., the Hopi Tribe, the Hualapai Nation, and the Western Area Power Administration.

Observations by this research group during reconnaissance in May 2003 formed the basis for more detailed sedimentologic and geomorphologic studies in the following year 

and led to the selection of sites at which weather stations were 

deployed to measure wind, precipitation, and eolian sediment 

transport continuously between late 2003 and early 2006. This 

report summarizes the results of that study and presents a final 

analysis and conclusions drawn from the data. Detailed discussions of data are omitted from this report but were presented 

by Draut and Rubin (2005, 2006, 2007, 2008) and Draut and 

others (2005).

Overview of Wind, Precipitation, and 

Eolian-Sediment-Transport Measurements

Wind, precipitation, and eolian-sediment-transport data, 

collected during this study at six sites, constitute the only 

continuous weather record available from the Colorado River 

corridor between November 2003 and January 2006, except 

for NPS temperature and rainfall measurements at Phantom 

Ranch (near river mile 88). Locations in the river corridor are 

commonly referred to by their distance (in miles) downstream 

from Lees Ferry, Ariz. (fig. 1); this report follows that convention and uses SI units for other measurements. River miles 

used here are those provided by the World Wide Web map 

server operated by the GCMRC (URL http://www.gcmrc.gov/

products/ims/ims.htm, accessed Apr. 2, 2008).

This study provided the first measurements at this temporal and spatial resolution of seasonal and regional variations in 

wind speed and direction and resulting eolian sediment transport, as well as of rainfall patterns within the interior of Grand 

Canyon. High-resolution records from weather stations can 

be used to identify rainfall events that caused gully incision 

and to predict eolian sediment redistribution, thus aiding other 

sedimentologic and geomorphologic studies of sedimentary 

deposits in the river corridor. Quantifying wind magnitude and 

direction was essential for identifying eolian-sediment-transport pathways in the vicinity of the study sites. This information was used to evaluate the potential sensitivity of certain 

study sites to dam operations. Detailed discussions of the data 

collected at weather stations, as well as electronic datafiles, 

were presented by Draut and Rubin (2005, 2006; see appendix 

1 for summaries of weather data from each study site).

A total of nine weather stations were deployed in the Colorado River corridor in Grand Canyon National Park (fig. 1) as 

part of this study: two weather stations at each of three sites in 

eastern Grand Canyon—an area known as “24.5 Mile” (river 

mile 24.8), Malgosa (river mile 57.9), and Palisades (river 

mile 66.1)—from November 2003 to January 2006; and one 

weather station at each of three study sites—Comanche (river 

mile 68.0) in eastern Grand Canyon, and Forster (river mile 

123.0) and 202.9 Mile (river mile 202.9) in western Grand 

Canyon—from April 2004 to January 2006. The weather 

stations were deployed in areas known to contain cultural artifacts, but were located such that the presence and operation of 

the instruments would not disturb the archeologic sites. Analysis of aerial photographs indicated that a reduction in open 

sand area had occurred at all six study sites after Glen Canyon 

Dam was constructed and that new deposition had occurred 

as a result of the 1996 controlled-flood experiment (Webb and 

others, 1999a). These criteria were intended to allow monitoring of the effects of similar controlled-flood experiments in the 

event that any such releases occurred during the 2-year operation of the weather stations; thus, the effects of the November 

2004 controlled-flood experiment were studied as part of 

this project. Wind and rainfall data were recorded digitally 

at 4-minute intervals at all weather stations; eolian sediment 

transport was measured on the basis of collection of sand in 

sand traps that were emptied during maintenance visits every 

4–8 weeks (Draut and Rubin, 2005, 2006).

At all study sites, the most common incidence of high 

wind velocities and, thus, the greatest potential for eolian 

sediment transport (as well as actual measured sand-transport 

rates) occurred during the spring windy season. In 2004, 

seasonal sediment transport peaked in April and May; in 2005, 

the peak was later, in May and early June. During the spring 

2004 and 2005 windy seasons, local maximum gusts were 

about 25 m/s, and daily local sand-transport rates were >100 

g/cm. At all weather stations, sand-transport rates during the 

spring windy season generally were 5 to 15 times higher than 

at other times of the year (see appendix 1). High winds occur 

outside of the spring windy season but then are more commonly accompanied by rain, such as during the summer and 

early fall monsoon season, and so these high winds cause little 

or no sediment transport because wet sand is too cohesive to 

move.

Wind direction was observed to change radically over 

short time intervals; wind velocity and dominant wind direction commonly varied on a diurnal cycle, with maximum 
5

gusts typically in the afternoon. At 24.5 Mile, Malgosa, and 

Palisades, where two weather stations were deployed at each 

study site, wind velocities and sand-transport rates were 

consistently higher at the higher elevation weather station than 

at river level, attributable in part to the presence of vegetation 

near the river, which reduces wind velocity and, thus, eolian 

sediment entrainment. Sand transport has been shown in many 

studies to decrease approximately exponentially as vegetation 

cover increases (Olson, 1958; Bressolier and Thomas, 1977; 

Ash and Wasson, 1983; Wasson and Nanninga, 1986; Buckley, 1987; Bauer and others, 1996; King and others, 2005). 

Wind velocity also can increase at higher elevations, given the 

reduced interaction of airflow with the canyon walls, although 

local topography can cause significant local variations in wind 

speed and direction.

Variations in sand-transport rates between study sites 

are related not only to variations in wind velocity, but also to 

other local factors that affect sediment-entrainment potential. 

Sand transport is likely reduced near the river because the 

moist, cohesive sediment that composes fluvial sandbars limits 

sediment entrainment by wind as the sand becomes cohesive 

when damp (Svasek and Terwindt, 1974; Sarre, 1988, 1989; 

McKenna Neuman and Nickling, 1989; Namikas and Sherman, 1995; Selah and Fryrear, 1995; Wiggs and others, 2004). 

In Grand Canyon, sandbars inundated by daily fluctuating 

flows released from the dam for hydropower generation commonly do not dry thoroughly before being inundated again the 

following day. Although the sand traps used in this study did 

not allow resolution of sand transport on the daily scales of 

riverflow fluctuations (no automated sand traps are available 

commercially that record sand transport at that resolution), this 

study documented a local increase in eolian sediment transport 

adjacent to a new dry (subaerial) sandbar deposited during the 

2004 controlled-flood experiment (Draut and Rubin, 2006).

The highest sand-transport rates were measured in 

“active” dune fields, that is, those with well-defined dune 

crests and sand shadows and with sparse or absent vegetation 

and biologic soil crust. On active dune fields, particularly at 

Malgosa and Forster (fig. 1), sand transport occurred by saltation and suspension at daily rates commonly of about 10 g/cm, 

but reached 100 to 1000 g/cm during the spring windy season. 

In contrast, less active eolian dune fields (those with substantial vegetation and soil crust, such as Palisades and Comanche) 

had daily sand-transport rates at least an order of magnitude 

lower (0.1–1 g/cmduring the nonwindy season and 1–10 g/

cmduring the windy season). Those measured differences are 

consistent with the results of previous studies that demonstrated lower sand-transport rates over vegetated dunes and 

over soil crusted surfaces (Leys and Eldridge, 1998; Belnap, 

2003; Goossens, 2004). The dune field at 24.5 Mile, which has 

both active and relatively inactive areas, had daily sand-transport rates more like those at Palisades and Comanche (about 

0 50 KILOMETERS

113 112 37

36

Comanche Palisades

202.9 Mile

Lake Mead

Lake

Powell

Grand Canyon National Park

Lees Ferry

Colorado

River

24.5 Mile

Malgosa

Forster

Phantom

Ranch

Arroyo

Diamond Creek Grande

25

Paria River

Little Colorado River

111

Glen 

Canyon 

Dam

ARIZONA

Figure 1. Colorado River corridor in Grand Canyon National Park, Ariz., showing locations of study sites. Data were 

collected from weather stations at 24.5 Mile, Malgosa, Palisades, Comanche, Forster, and 202.9 Mile; sedimentary 

profiles were studied at Palisades, Comanche, and Arroyo Grande. River reach between Lees Ferry and the Little 

Colorado River is known as Marble Canyon.

Overview of Wind, Precipitation, and Eolian-Sediment-Transport Measurements
6 The role of Eolian Sediment in the Preservation of Archeologic Sites Along the Colorado River Corridor

1 g/cm) than at active Malgosa and Forster (see appendix 1). 

The weather station near the river at Palisades (Pal L; see fig. 

20 for location), on a relict fluvial cobble-boulderbar, typically 

recorded daily sand-transport rates of about 0.01 g/cmthe 

lowest of all the study sitesapparently owing to a low sand 

supply and not to low wind velocities (Draut and Rubin, 

2006). 

Rainfall data collected throughout the 26-month study 

interval indicate considerable spatial and seasonal variations 

(see appendix 1). Daily rainfall recorded by the upper and 

lower rain gages at a single study site commonly differed 

by several tenths of a millimeter, and daily rainfall totals by 

as much as several millimeters. Rain gages recorded strong, 

spatially isolated storms, particularly during the summer and 

early fall thunderstorm season. Total annual rainfall varied by 

a factor of >2 over distances of about 10 km in 2005 (Draut 

and Rubin, 2006), when the weather stations at Malgosa and 

Palisades (fig. 1) recorded the highest and lowest rainfall measured during this study, respectively—a difference attributable 

to local topographic influence on the movement of weather 

systems. During the unusually wet winter of 2005, weather 

stations at study sites in western Grand Canyon recorded 

approximately twice the average rainfall recorded by weather 

stations at study sites in eastern Grand Canyon and Marble 

Canyon. The measured spatial variation in rainfall indicates 

that future sedimentologic and geomorphologic studies in 

Grand Canyon would benefit substantially from continued 

or expanded data collection at multiple sites along the river 

corridor because the rainfall records collected by the NPS at 

Phantom Ranch (near river mile 88) evidently are not valid for 

other parts of the canyon.

Overview of Sedimentologic and Geomorphologic Investigations

In May 2003, reconnaissance along the Colorado River 

corridor in Grand Canyon National Park was performed by 

personnel from the USGS, the Hopi and Hualapai Tribes, 

GeoArch, Inc., and the Western Area Power Administration, 

led by NPS archeologists J.R. Balsom, J.L. Dierker, and L.M. 

Leap. This group visited 38 archeologic sites at which eolian 

sediment was believed to be important either as the material 

underlying the site or as material forming a protective cover. 

Depositional environments of the sediment around these 

archeologic sites were determined, where possible, through 

identification of sedimentary textures characteristic of waterlain (fluvial or tributary flow) or eolian deposition (for example, Walker, 1963; Hunter, 1977; Rubin and Hunter, 1982, 

1987; Gladfelter, 1985; Rubin, 1987; Rubin and others, 1990; 

Schmidt, 1990; Southard and Boguchwal, 1990). The group 

performing this reconnaissance, while noting that the selected 

sites likely were not typical of all archeologic sites in the river 

corridor, determined (through digging shallow test pits into 

sediment to expose three-dimensional sedimentary structures) 

that much of the sediment beneath or above these particular 

archeologic sites had been transported by wind from fluvial 

deposits at the river margins (Draut and others, 2005). Several 

archeologic sites were built on or buried by sediment deposited directly by large floods of the Colorado River. Observations during the reconnaissance formed the basis for more 

detailed sedimentologic and geomorphologic investigations at 

a selected subset of the 38 archeologic sites the following year 

and for deployment of the weather stations discussed above.

The research group hypothesized that eolian sediment 

transport to archeologic sites apparently is limited largely 

by sand supply and vegetation cover rather than by wind. 

Reduction in open sand area on sandbars, and submergence 

of sandbars by daily riverflow fluctuations, can be expected 

to reduce eolian sediment transport to nearby dune fields with 

associated archeologic sites (Ash and Wasson, 1983; Buckley, 

1987; Namikas and Sherman, 1995; Wiggs and others, 2004). 

Reduced eolian sediment transport, in turn, can be expected to 

facilitate the growth of existing arroyos and the establishment 

of new ones, as discussed by Thompson and Potochnik (2000). 

Erosion of archeologic sites by arroyo incision was apparent 

at many of the sites visited in May 2003; repeat photographic 

images at those sites, taken by NPS personnel since the late 

1990s, support this observation (Leap and others, 2000). Some 

archeologic sites are affected by small drainages that might be 

repairable by modest increases in eolian sediment deposition. 

At some archeologic sites, filling of small (<1 m wide) gullies 

by eolian sediment would aid preservation of cultural features 

that have already been stabilized by construction of check dams; 

other areas are compromised by large drainages that could not 

reasonably be expected to fill with eolian sediment, given the 

current local geomorphology and observable sand supply.

Sedimentologic and geomorphologic investigations in 

May 2004 focused on the Palisades, Lower Comanche, and 

Arroyo Grande areas along the Colorado River corridor (figs. 

1 and 2). These river reaches are all characterized by alluvial 

terraces that represent multiple episodes of floodplain aggradation within the pool-and-drop bedrock canyon. The highest 

alluvial terraces at each study site contain deposits left by 

predam floods of >5,660 m3

/s (Hereford and others, 1993; 

Topping and others, 2003). The terraces at all three study sites 

contain arroyo networks (Patton and Schumm, 1981; Waters 

and Haynes, 2001; Webb and Hereford, 2001), as much as several meters deep and wide, that result from incision by local 

rainfall runoff. Coppice dunes partly cover the terrace surfaces 

at all three study sites. Talus piles commonly are present at 

the base of bedrock walls, and debris fans occur at the mouths 

of side-canyon tributaries. The May 2004 investigations 

complemented several previous studies, particularly those 

at Palisades, where geomorphologic mapping by Hereford 

(1993, 1996) and Hereford and others (1993, 1996) generated 

detailed interpretations of the surficial geology and radiocarbon dates; the same area was visited by Hereford and others 

(1993) and Thompson and Potochnik (2000) to formulate the 

base-level hypotheses discussed above. Grams and Schmidt 

(1999) used historical photographs to document a reduction 
7

in the extent of surficial sand deposits at Palisades since 1890. 

High-resolution topographic surveys by Yeatts (1996) and 

Hazel and others (2000) indicated aggradation of fluvial sand 

deposits at Palisades as a result of the March 1996 controlledflood experiment from Glen Canyon Dam, and inferred eolian 

migration of sediment to higher elevations during the following year. Topographic surveys documented about 25 m3

 of 

sediment deposition in an arroyo mouth at Palisades as a result 

of the November 2004 controlled-flood experiment; in the 6 

months after that experiment, the raised arroyo base level was 

not observed to have affected the topography of higher terrace 

areas at Palisades (Hazel and others, 2008). 

After viewing natural sedimentary exposures, the May 

2004 research group chose to focus on those that were most 

complete vertically and that offered good spatial coverage 

throughout varying terrain. Data were obtained by detailed 

examination of sedimentary profiles and numerous shallow 

test pits in alluvial terraces, coppice-dune fields, and, at Palisades, near the distal margin of a debris fan from a tributary 

canyon (fig. 2). Although the sedimentary deposits studied 

during this investigation were in the vicinity of archeologic 

sites, no cultural artifacts were exposed or collected. The 

presence of arroyos facilitated the exposure of vertical faces; 

at Palisades and Lower Comanche (fig. 1), three of the sedimentary sections studied in detail were exposed by digging 

test pits into areas without cultural artifacts. Thicknesses of 

sedimentary units were measured, and sedimentary structures, 

clast lithology, and sediment color were described. At selected 

sites, sediment samples were collected for grain-size analysis, 

using a Coulter laser particle-size analyzer at the GCMRC 

laboratory in Flagstaff, Ariz. Sedimentary structures were 

used to identify the number and thickness of fluvial deposits, 

eolian reworking of fluvial sediment, and interaction of those 

processes with local runoff sedimentation. Geomorphic and 

sedimentary processes that affect each studied archeologic site 

are summarized for Palisades, Lower Comanche, and Arroyo 

Grande in tables 1, 2, and 3, respectively; detailed discussions 

of each site were presented by Draut and others (2005). 

Identifying Fluvial and Eolian Deposits by Using 

Sediment Grain Size

In addition to describing depositional units by using 

sedimentary structures, we investigated the use of grain-size 

analysis to distinguish fluvial from eolian material. Previous 

studies have shown that grain size and moment statistics are of 

little use for identifying fluvial and eolian deposits when comparing samples from multiple geographic regions (Ahlbrandt, 

1979; Tucker and Vacher, 1980; Gladfelter, 1985), owing to 

variations in clast composition and weathering conditions. We 

analyzed particle-size distributions in 100 sediment samples 

from predam fluvial deposits, postdam fluvial deposits, and 

eolian deposits collected only within the Colorado River corridor of Grand Canyon (fig. 3) to assess whether this sedimentary system is consistent enough to use grain size to classify 

samples of unknown origin collected within this reach of 

the river corridor. (We refer here only to fine-grained fluvial 

deposits at flood-stage elevation that are relevant to archeology; deeper in the river channel, fluvial deposits include sediment grain sizes as large as boulders to which this discussion 

does not apply.) 

Although grain sizes within Colorado River fluvial deposits vary as a function of sand supply, riverflows, and proximity 

to flooding tributaries, this study found essentially no overlap 

between the textural characteristics of predam fluvial (fig. 

3A) and mature eolian deposits (fig. 3A) in Grand Canyon; 

the finest eolian deposits are coarser than the coarsest predam 

fluvial units sampled (fig. 3E; see Burke and others, 2003). 

The absence of overlap indicates that although the mature 

eolian deposits are assumed to have been derived largely 

from predam fluvial deposits, enough finer fluvial sediment is 

removed by wind that the grain-size distribution of the remaining (winnowed) sand in mature eolian deposits is characteristically coarser than in the original fluvial deposit (see Rubin 

and others, 2006). Grain-size distributions of eolian samples 

overlap, however, with those from postdam high-flow deposits 

(fig. 3F). The postdam fluvial samples shown here (deposited 

by the November 2004 high flow) are coarser, as a population, than the predam flood deposits (fig. 3D). The presence 

of coarser postdam fluvial deposits is consistent with previous analyses of other postdam flood deposits and reflects the 

observation that the sediment transported and deposited by the 

Colorado River coarsened after the closure of Glen Canyon 

Dam in response to limitation of the upstream sediment supply 

and winnowing of the fine sediment already in the river channel (Rubin and others, 1998; Topping and others, 2000a,b). 

Therefore, within the Colorado River corridor, grain 

size can be used to distinguish predam flood deposits (which 

underlie and overlie archeologic sites in Grand Canyon, unlike 

younger, lower-elevation postdam deposits) from mature 

eolian deposits if sedimentary structures are absent. Particle 

size as a diagnostic tool should still be used with caution even 

within one sedimentary system, unless the range of grain sizes 

for known eolian and fluvial deposits in that system is well 

defined. The difference in grain-size distribution between a 

fluvial deposit and its winnowed, eolian counterpart depends 

on the initial composition of the flood sediment and on the 

wind conditions affecting the sediment. Colorado River fluvial 

sediment that has undergone some wind reworking might not 

yet plot within the mature eolian field of figure 3C, limiting 

these diagnostic applications. 

Two Types of Eolian Deposit Defined for the 

Colorado River Corridor

Results of the sedimentologic and geomorphologic investigations of 2004, in combination with quantified seasonal 

wind directions and sand-transport potential, indicate two 

types of eolian deposit in the Colorado River corridor—modern fluvial-sourced (MFS) and relict fluvial-sourced (RFS)—

Overview of Sedimentologic and Geomorphologic Investigations
8 The role of Eolian Sediment in the Preservation of Archeologic Sites Along the Colorado River Corridor

Figure 2. Aerial photographs of study area sites along the Colorado River corridor in Grand Canyon National Park, Ariz. 

(fig. 1), with geomorphology shown in colored overlays. Numbered circles, sedimentary profiles measured in detail; 

circled Ts, test pits studied in less detail and to shallower depth. Riverflow is 226 m3/s in all photographs. A, Palisades. 

Geomorphic data from this study and Hereford and others (1993). Pale-green area in north is a debris fan; darker green 

strips along shoreline are a cobble bar, likely a reworked part of debris fan. Light-blue areas are relict (predam) terrace 

surfaces; darker blue areas are modern fluvial sandbars at an elevation within common dam-controlled flow fluctuations (<566 m3

/s). Yellow areas are coppice dunes. Orange area is a playalike surface where slopewash and colluvial 

sediment accumulate. Arroyo is outlined in white. B, Lower Comanche. Green area is a boulder bar. Blue area is fluvial 

deposits that form a narrow terrace. Yellow area is coppice dune. Orange area is a talus and colluvial slope drained by 

an arroyo outlined in white. C, Arroyo Grande. Light-blue and dark-blue areas are two terrace surfaces, one at higher 

and one at lower elevation, respectively. Yellow areas are eolian coppice dunes on the upper terrace and to east. 

Orange area is talus and colluvium with bedrock exposed. Arroyo is outlined in white.

A B

C
9

Site Age and 

affiliation 

of site 

Sediment on which 

site was originally 

built 

Sediment 

overlying 

site 

Sedimentary and 

geomorphic 

characteristics 

C:13:033 Uncertain; 

probably 

Pueblo I–III 

Debris-fan cobbles, 

gravel 

Eolian (minor) Dominated by debris-flow 

deposition 

C:13:098 Historic Debris-fan cobbles, 

gravel 

None Remains of 19th century cabin 

built on debris-fan sediment 

C:13:099 Pueblo I–II Fluvial; slopewash 

sand, gravel 

Eolian; distal 

debris-flow 

material 

Interbedding of fluvial, eolian, 

debris-flow and slopewash 

sediment 

C:13:100 Pueblo I–II Fluvial Fluvial and

eolian 

Fluvial sediment modified by 

wind 

C:13:101 Pueblo I–II Rounded cobbles, 

likely fluvial 

Eolian (minor) Coppice dunes overlying

rounded cobbles 

C:13:272 Pueblo I–II Debris-fan cobbles, 

gravel 

Fluvial and

eolian 

Fluvial sediment modified by 

wind into coppice dunes; 

bioturbated 

C:13:334 Pueblo I–II Fluvial; ponded

slopewash 

Fluvial Eroding out of apparent fluvial 

deposit 

C:13:336 Pueblo I–II Likely fluvial (artifacts 

not in original position) 

Fluvial and

eolian 

Fluvial sediment reworked by

wind into coppice dunes 

C:13:355 Pueblo II Fluvial; distal debris 

flow 

Fluvial and

eolian 

Area dominated by debris fan, 

smaller volumes of fluvial and

eolian sediment 

Table 1. Summary of sedimentary processes affecting archeologic sites at Palisades, Grand Canyon National Park, Ariz. 

[Site numbers assigned by the National Park Service. See Draut and others (2005) for detailed discussions of sedimentary processes in these areas. Prehistoric 

sites were dated by radiocarbon methods and artifact identification to the Pueblo I and Pueblo II (PI and PII) periods (Fairley and others, 1994; Hereford, 1996), although there is some evidence for Preformative occupation (Dierker and Downum, 2004). The historical site is associated with mining activity and was occupied 

from A.D. 1890 to 1910]

Site Age and affiliation 

of site 

Sediment on 

which site was 

originally built 

Sediment 

overlying site 

Sedimentary and 

geomorphic 

characteristics 

C:13:273 Early Formative

(Basketmaker III) 

Fluvial, eolian; 

colluvial 

Eolian (minor) Fluvial and eolian deposits 

interbedded with 

slopewash colluvium. 

C:13:274 Pueblo I–II Eolian None Eolian substrate overlies 

distal debris-fan sediment. 

C:13:333 Pueblo I–II Eolian Eolian (minor) Site destabilized by eolian

deflation and dune

migration. 

C:13:335 Pueblo I–II Eolian Eolian Exposed by eolian

deflation. 

C:13:337 Pueblo I–II Eolian None Eolian dunes; site in 

interdune area. 

C:13:373 Prehistoric to Early 

Historic Hopi 

Eolian Eolian Site destabilized by eolian

deflation and dune

migration. 

Table 2. Summary of sedimentary processes affecting archeologic sites at Lower Comanche, Grand Canyon National Park, Ariz. 

[Site numbers assigned by the National Park Service. Most cultural features in this area date to the Late PI–Early PII Formative period (about A.D. 900–1000; Fairley and 

others, 1994). At least one site contains artifacts related to late prehistoric and early historical use by the Hopi Tribe (Fairley and others, 1994). Early Formative age for 

site C:13:273 is based on radiocarbon ages obtained on a hearth feature by Yeatts (1998)]

Overview of Sedimentologic and Geomorphologic Investigations
10 The role of Eolian Sediment in the Preservation of Archeologic Sites Along the Colorado River Corridor

distinguishable by the relative positions and orientations of 

eolian deposits and modern (<1,270 m3/s) fluvial deposits 

and by the dominant wind directions causing eolian sediment 

transport in each setting.

MFS dune fields, directly downwind from recent (postdam) fluvial deposits, formed as the wind transported sand 

inland from a river-level sandbar, creating the dune field 

downwind. An example of an MFS deposit, at the mouth of 

Forster Canyon (river mile 123.0), is shown in figure 4A. In 

this area, the dominant wind direction (as measured during this 

study) is from the north-northeast, dune configuration indicates net sand transport to the south-southwest, and high wind 

velocities (>20 m/s during the spring windy season) transport 

sediment away from a river-level sandbar to form a dune field 

downwind. Within this active dune field, daily sand-transport 

rates of about 100 g/cmwere common in 2004 and 2005, and 

dune-surface elevations were observed to increase or decrease 

locally by tens of centimeters between equipment-maintenance 

visits every 6–8 weeks. 

RFS deposits formed as the wind eroded and redeposited 

sediment that composed extensive predam flood deposits, 

generating eolian dunes essentially in place over parts of 

fluvial terraces. Whether or not RFS deposits are downwind 

of modern fluvial sandbars, their most substantial sediment 

Site Sediment on 

which site was 

originally built 

Sediment 

overlying site 

Sedimentary and 

geomorphic characteristics 

G:03:064, F1 Protohistoric to 

Early Historic Pai 

Eolian Eolian (minor) Coppice dunes on upper terrace

surface 

G:03:064, F2 Protohistoric to 

Early Historic Pai 

Eolian Eolian (minor) Coppice dunes on upper-terrace

surface 

G:03:064, F3 Protohistoric to 

Early Historic Pai 

Eolian Eolian (minor) Coppice dunes on upper-terrace

surface 

G:03:064, F4 Protohistoric to 

Early Historic Pai 

Eolian Eolian (minor) Interdune area in coppice-dune field; 

arroyo incision affects feature stability 

G:03:064, F5 Protohistoric to 

Early Historic Pai 

Eolian Eolian (minor) Interdune area in coppice-dune field; 

affected by eolian deflation 

G:03:064, F6 Protohistoric to 

Early Historic Pai 

Terrace surface

(dominantly fluvial) 

None Arroyo incision affects terrace surface

in vicinity of this feature. 

G:03:064, F7 Protohistoric to 

Early Historic Pai 

Terrace surface

(dominantly fluvial) 

None Surface of upper terrace 

G:03:064, F8 Protohistoric to 

Early Historic Pai 

Terrace surface

(dominantly fluvial) 

None Surface of upper terrace 

G:03:064, F9 Protohistoric to 

Early Historic Pai 

Terrace surface

(dominantly fluvial) 

None Surface of upper terrace 

G:03:064, F10 Protohistoric to 

Early Historic Pai 

Terrace surface

(dominantly fluvial) 

None Surface of upper terrace 

G:03:064, F11 Protohistoric to 

Early Historic Pai 

Terrace surface

(dominantly fluvial) 

None Surface of upper terrace 

G:03:064, F12 Protohistoric to 

Early Historic Pai 

Eolian Eolian (partly 

covers feature) 

Small coppice dunes on upper-terrace

surface. Feature affected by arroyo

incision. 

G:03:064, F13 Protohistoric to 

Early Historic Pai 

Eolian None Small coppice dunes on upper-terrace

surface. Feature affected by arroyo

incision. 

G:03:064, F14 Protohistoric to 

Early Historic Pai 

Interbedded 

fluvial/eolian/colluvial 

Eolian Exposed in small drainage within 

upper terrace 

G:03:064, F15 Protohistoric to 

Early Historic Pai 

Colluvium None Near landward edge of upper terrace, 

in area dominated by slopewash 

sedimentation 

N.a. Unknown Slopewash colluvium 

and eolian 

Fluvial, eolian, 

and colluvial 

Hearth feature exposed in arroyo wall

within upper terrace 

Age and

aliation

of site

Table 3. Summary of sedimentary processes affecting archeologic sites at Arroyo Grande, Grand Canyon National Park, Ariz.

[Site G:03:064 includes 15 separate features, generally associated with the protohistoric and Early Historic-era Pai culture related to the Paiute and Hualapai Tribes. Many features were 

built on eolian sediment directly, but this relatively thin eolian substrate is underlain by volumetrically more substantial flood deposits. N.a., not assigned]
11

source is not the modern, presently active sandbars (those containing fluvial sediment transported by riverflows at or below 

approximately 1,270 m3/s), but larger predam flood deposits 

(see Burke and others, 2003), for example, the coppice-dune 

field at Palisades (fig. 4B). This study and those by Hereford 

and others (1993, 1996) showed that the Palisades area is 

underlain by extensive predam fluvial deposits; the eolian 

dune field lies atop part of the fluvial terrace. The dominant 

direction of sediment-transporting winds measured at Palisades over >2 years was from the south-southeast (Draut and 

Rubin, 2006). If that direction is representative of long-term 

local weather conditions, then only minor amounts of sedi20

40

60

80

100

0.01 0. 1 1

20

40

60

80

100

0.01 0. 1 1

20

40

60

80

100

0.01 0. 1 1

20

40

60

80

100

0.01 0. 1 1

20

40

60

80

100

0.01 0. 1 1

E

Predam

fluvial

deposits

Eolian

deposits

20

40

60

80

100

0.01 0. 1 1

A B C

D F

Predam

fluvial

deposits

Postdam

(November 2004)

fluvial deposits Eolian deposits

Predam

fluvial

deposits

Postdam

(November

2004) fluvial

deposits

Postdam

(November

2004) fluvial

deposits

Eolian

deposits

GRAIN SIZE, IN MILLIMETERS

CUMULATIVE PERCENTAGE OF FINER SEDIMENT

Figure 3. Grain-size distributions, obtained by using laser particle-size analysis, in fluvial and eolian deposits along the Colorado River corridor in Grand Canyon National Park, Ariz. (fig. 1). Cumulative percentage of the sediment sample that is finer 

than the corresponding grain diameter shown on the horizontal axes, ranging from 0.037 mm (coarse silt) to 1.000 mm (boundary between coarse and very coarse sand; Boggs, 1995). A, Grain-size distributions in 27 sediment samples from 10 different 

fluvial strata, all deposited by Colorado River floods that predated closure of Glen Canyon Dam. Samples were identified as 

fluvial deposits by presence of unequivocal sedimentary structures. Multiple samples were collected from some flood deposits because grain size commonly varies vertically within each deposit (Rubin and others, 1998). B, Grain-size distributions 

in 63 samples from 10 different sedimentary deposits from November 2004 experimental flood in Grand Canyon. C, Grain-size 

distributions in sediment from 10 eolian deposits in Grand Canyon. D, Comparison of predam fluvial deposits in figure 3A

(solid-outlined light-gray field) with postdam (Nov. 2004) deposits in figure 3B (dashed-outlined darker gray field). Deposits of 

2004 flood are coarser and show a tighter distribution than the predam deposits. E, Comparison of predam fluvial deposits in 

figure 3A (light-gray field) with eolian deposits in figure 3C (dark-gray field). F, Comparison of the postdam (Nov. 2004) flood 

deposits in figure 3B (dashed-outlined medium-gray field) with eolian deposits in figure C (dark-gray field).

Overview of Sedimentologic and Geomorphologic Investigations
12 The role of Eolian Sediment in the Preservation of Archeologic Sites Along the Colorado River Corridor

ment are transported by wind from river-level sandbars to 

the eolian dune field at Palisades, where the dunes apparently 

formed from wind erosion and redeposition of sediment that 

composed the predam fluvial deposits. Although some migration of eolian dunes is apparent today in the northern part of 

the Palisades dune field, generally this dune field is inactive 

(relative to such study sites as Malgosa and Forster) and has 

well-established vegetation and biologic soil crust. Although 

some new sediment probably is occasionally transported into 

the dune field from river-level sandbars (Yeatts, 1996), given 

appropriate short-term wind conditions, the dominant direction 

of sand-transporting wind measured at Palisades in this study 

indicates that wind likely causes a net loss of sand from this 

dune field to the northwest (where it can be lost into the river) 

at daily rates of about 1 g/cm. Continued erosion of eolian and 

fluvial deposits by gullies causes substantial additional loss of 

sediment at Palisades. Because the mechanism of formation of 

this RFS deposit was linked inextricably with the deposition 

of fluvial sediment during large, sediment-rich predam floods, 

substantial new sediment will probably not be supplied to the 

Palisades dune field without similar large, sediment-rich floods 

in the future.

MFS deposits generally are smaller and more common in 

Grand Canyon than are RFS deposits. Eolian deposits of both 

types are known to contain archeologic material. For different 

reasons, both MFS and RFS dune fields should be considered sensitive to Glen Canyon Dam operations. Because they 

are directly downwind from fluvial sandbars, MFS deposits 

receive some windblown sand as a function of wind velocity, exposed dry fluvial-sandbar area, and sediment-trapping 

vegetation between the fluvial deposit and its associated eolian 

deposits. Fluvial-sandbar area and riparian vegetation have 

been shown in numerous studies to respond to dam operations, 

and so changes to either condition can affect the delivery of 

eolian sediment to MFS dune fields downwind. 

The dimensions (length and width) of fluvial sandbars 

relative to the local wind direction control the supply of windblown sediment inland that forms MFS deposits and potentially covers local archeologic sites. For example, a 2-m-wide 

sandbar that extends 50 m along the riverbank will be able 

to supply more windblown sand inland and downwind to a 

longer strip of shoreline than will a 10-m-wide and 10-m-long 

sandbar, assuming that equilibrium sand transport is attained 

Figure 4. Aerial photographs showing two types of eolian deposit defined for the Colorado River corridor in Grand Canyon National Park, Ariz. 

(fig. 1). Green arrows indicate dominant direction of local wind with high-enough velocity to transport sand (obtained from vector sums of 

4-minute wind-velocity measurements collected over many months; see Draut and Rubin, 2005, 2006). Black dashed lines, edges of eolian dune 

fields; red asterisks, nearby modern fluvial sand deposits. A, Modern fluvial-sourced (MFS) deposits at the mouth of Forster Canyon (river mile 

123.0, fig. 1) directly downwind from fluvial sand deposits. In this area, dominant wind direction is from north-northeast, transporting sand away 

from a river-level sandbar to form a dune field downwind. B, Relict fluvial-sourced (RFS) deposits at Palisades (river mile 66), formed as wind reworked sediment deposited by large predam floods, generating eolian dunes basically in place across parts of fluvial terraces. Dominant wind 

direction in this area is from south-southeast. Modern fluvial sand deposits are not directly upwind of eolian dune field, and so little sediment 

from those sandbars reaches dunes.
428429430

431432

27 3629 45 55 59 60 

427

430. 403

430. 530

429. 317

430. 799

431. 435

430. 887

431. 062

Distal debris-flowsediment 

798.898

800.742

800.619

800.972

800

46 106 117 137

798

799

801

797796795

60 72 85 96 175

794

793

792

796. 147

2

795. 874

4

5

793. 395 6

795. 525

797. 480

3

Fluvial sediment

Eolian sediment

Slopewash and colluvial sediment

Sedimentarytextureinconclusive

A B 

CROSS-SHORE DISTANCE FROM RIVER, IN METERS

ELEVATION, IN METERS

Figure 5. Sedimentary profiles at Palisades (A) Lower Comanche (B) Arroyo Grande (C) study sites in Grand Canyon National Park, Ariz. (fig. 1). Ele

enced to NAVD88 (1999) datum; numbers above each profile are elevation of land surface (in meters). 1,270-m3/s flood stage is equivalent to elevat

Palisades, 789 m at Comanche, and 425 m at Arroyo Grande. Stage-discharge relations for Palisades and Comanche from Hazel and others (2006a)Grande are estimates only. Numbers below each profile indicate stratigraphic sections by which these profiles are identified in detailed discussion others (2005). Colors of individual units within each profile correspond to inferred depositional environment (assigned on the basis of sedimentary composition, and, for about 10 individual strata, grain-size distribution). Slopewash and colluvial sediments are derived from local bedrock and taluthose for which a depositional setting was not assigned, either because sedimentary textures were inconclusive or because those parts of profilesible. Width of each sedimentary unit is a schematic representation of its grain size (the wider the unit, the coarser the sediment); some units coarGrain-size properties were determined primarily by using grain-size-comparator charts. 
14 The role of Eolian Sediment in the Preservation of Archeologic Sites Along the Colorado River Corridor

during wind events over each sandbar, even though the two 

sandbars have identical area (100 m2). Sensitivity of MFS 

deposits to dam operations is, therefore, a function not only of 

postdam changes in the area of fluvial sandbars but also of the 

dimensions of the remaining open, dry sandbar and its position 

relative to eolian deposits (and any archeologic sites) inland of 

the river.

RFS deposits include eolian coppice dunes that compose 

the uppermost, wind-reworked part of predam terraces that are 

largely alluvial in composition, containing sediment deposited by floods higher than any postdam floods (≥5,660 m3

/s). 

Sediment-rich floods of predam magnitude no longer occur in 

this regulated river, and so the relict fluvial deposits no longer 

constitute an active sediment source. Therefore, no substantial new deposition is likely to occur on RFS dune fields in 

the absence of large sediment-rich floods. As vegetation and 

biologic soil crust grow on RFS coppice-dune fields over time, 

active eolian sediment transport decreases within them, such 

that these areas become increasingly unable to compensate for 

precipitation-induced gully erosion. As a result, large gully 

and arroyo systems can form on predam terraces and associated RFS dune fields (figs. 2A, 2C).

Sedimentary Environments—Implications for 

the Preservation of Archeologic Sites

Fluvial deposits are the most common substrate underlying the archeologic sites at Palisades and Arroyo Grande (fig. 

1). Fluvial deposition was observed generally to decrease 

with increased elevation and distance from the river as locally 

derived slopewash and colluvial sediment became more 

conspicuous (fig. 5). The abundance of fluvial sediment does 

not decrease regularly away from the river, however, partly 

because eolian modification can occur across much of an 

alluvial terrace almost irrespective of distance from the river 

(although wind velocities generally are lower at the river 

margin, where vegetation commonly is thick). In the Colorado River corridor, wind velocity (and eolian modification 

of fluvial sediment) typically peaks during the spring windy 

season, as discussed above. Although eolian dunes are present 

on terrace surfaces at Palisades and Arroyo Grande, eolian 

sediment was observed to be more important as a protective 

cover in those areas than as the substrate on which cultural 

features were formed. At Lower Comanche, in contrast, five 

of the six archeologic sites were formed on and are partly 

buried by eolian sediment; however, the largest and most 

extensive archeologic site at Lower Comanche is not in the 

eolian dune field but on a lower elevation terrace constructed 

of fluvial, eolian, and slopewash deposits. In all three areas, 

geomorphic processes that affect the condition of archeologic 

sites today include arroyo incision, wind action, and episodic 

local deposition of slopewash and debris-flow sediment. 

Arroyo incision and eolian deflation contribute to exposure 

and erosion of cultural artifacts in all three areas: eolian 

deflation exposes artifacts that may then be washed away by 

rainfall runoff, and dune migration (particularly at Lower 

Comanche) causes downslope movement of artifacts as the 

sand surface shifts underneath. Episodic deposition of flood 

sediment at Palisades and Arroyo Grande no longer occurs at 

elevations high enough to affect archeologic sites under the 

present dam-controlled flow regime of the Colorado River.

Many archeologic sites, including most of those at Palisades, Lower Comanche, and Arroyo Grande (fig. 1), were 

formed on terraces that consist largely of Colorado River alluvium. Many of those sites are preserved today by having been 

buried by flood deposits and eolian dunes. From prehistoric 

times until the closure of Glen Canyon Dam in 1963, the highest-elevation fluvial deposition in this river corridor occurred 

during spring snowmelt floods that regularly exceeded even 

the highest postdam riverflows: the highest postdam riverflow, 

2,750 m3

/s, occurred in 1983, while the predam 8-year flood 

level was 3,540 m3/s (Topping and others, 2003). Annual 

sediment-rich floods occurred concurrently with, or receded 

during, the spring windy season, when wind would have remobilized sand from recent flood deposits to form eolian dune 

fields. The modern absence of sediment-rich floods eliminates 

the mechanism for depositing sediment at the elevations of 

prehistoric alluvium, as well as the source of new sediment for 

eolian deposits. Dam operations have thus substantially altered 

the fluvial and eolian processes that acted on the prehistoric, 

inhabited landscape. This alteration potentially hinders the 

preservation of tens to hundreds of archeologic sites, including 

most of those visited in this study, by limiting the fluvial and 

eolian sediment available to bury and cover them. (The NPS 

lists several hundred archeologic sites as potentially affected 

by dam operations, but we refer only to those that were studied 

at this level of sedimentary detail for this project.) Therefore, 

preservation of archeologic sites might be enhanced by restoring fluvial and eolian deposition to resemble more closely 

those processes that occurred before the river was dammed—

large, sediment-rich floods that left fluvial sand deposits from 

which sand was remobilized by wind. 

Fluvial deposits form the most extensive base on which 

the archeologic sites at Palisades and Arroyo Grande (fig. 

1) were formed, spanning hundreds of square meters in area 

(see Hereford and others, 1996). Moderate (about 1,270 m3

/s) 

controlled Colorado River high flows, as released in 1996 

and 2004, can enlarge sandbars (at least temporarily) that 

supply sand to eolian deposits covering archeologic sites at 

higher elevations. To effect a large-scale restoration of fluvial 

terraces, however, a riverflow of >4,810 m3/s would likely be 

needed, on the basis of stage-discharge relations developed for 

Palisades from historical-flood debris (Draut and others, 2005; 

Hazel and others, 2006b), although we recognize that stagedischarge curves can vary, owing to episodic constriction of 

the river channel by debris flows. To cause deposition instead 

of erosion, flood waters also would require high suspendedsediment concentrations (Hazel and others, 2006a; Topping 

and others, 2006). The suspended-sediment concentrations 

measured for predam riverflows >1,000 m3

/s were within an 

order of magnitude of 0.1 g/L (Topping and others, 2000b); 
15

it is not known what the suspended-sediment concentration 

would be in a postdam flood of 4,810 m3/s. In general, the 

average annual postdam sediment load is about 5–15 percent 

of average predam values (varying locally relative to tributaries). An experimental flow of the magnitude needed to inundate predam fluvial terraces at Palisades, about 4,810 m3

/s, 

would be nearly 4 times higher than the highest experimental 

flows currently under consideration by the Glen Canyon Dam 

Adaptive Management Program. Suspended-sediment concentrations also would probably be too low in such a high flow to 

have a substantial restorative effect unless the flood followed 

an exceptionally large input of tributary sediment or sediment 

were added artificially downstream of Glen Canyon Dam. If 

a sediment-rich, high-discharge dam release were to deposit 

a large volume of new high-elevation fluvial deposits, those 

deposits could then act as a source for windblown sediment, 

which could be transported to MFS dune fields and reworked 

to form or replenish RFS dune fields. Increased transport of 

eolian sediment to dune fields is expected to inhibit erosion by 

filling small gullies, which act as natural traps for windblown 

sand (documented in filled paleogullies by Thompson and 

Potochnik, 2000, and observed during this study in several 

paleogully exposures and in modern dune fields; Draut and 

Rubin, 2006), and by providing additional protective cover to 

archeologic sites. 

Controlled dam releases of about 1,270 m3

/s in 1996 

and 2004 deposited sand in arroyo mouths at Palisades and 

elsewhere (Yeatts, 1996; Topping and others, 2006; Hazel and 

others, 2008), possibly increasing the preservation potential 

of some archeologic sites by temporarily raising the effective 

base level to which arroyos incise (Hereford and others, 1993). 

This effect is likely short lived, however, because runoff from 

local rainstorms can quickly remove the new deposits in arroyo 

mouths and lower the effective base level once again. Relatively few data are available concerning the effects of sediment 

deposition during controlled floods and the ability of sediment 

deposition to control arroyo base level on various time scales; 

such data would definitively support or refute the still-debated 

hypotheses of Hereford and others (1993) and Thompson and 

Potochnik (2000). Local climate, drainage area, substrate composition, and river-related sediment and base-level effects all 

contribute to arroyo incision and healing (Waters and Haynes, 

2001; Webb and Hereford, 2001), although arroyo incision 

remains incompletely understood. Arroyo-incision processes 

in the Colorado River ecosystem could be clarified by repeated 

high-resolution mapping of gullies and affected archeologic 

sites to measure local erosion and deposition rates, and by 

measuring rainfall and other climatic parameters that vary 

widely within the complex canyon topography. It is noteworthy that Palisades and Lower Comanche, where large arroyos 

erode multiple archeologic sites, were the two areas with the 

least rainfall of the six sites monitored during this 26-month 

study (Draut and Rubin, 2006). If our data are representative of 

longer term, regional variation in rainfall, then enhanced local 

precipitation might be eliminated as a possible cause of recent 

preferential arroyo formation at those sites. 

In general, dam operations are less likely to affect 

deposition of slopewash and debris-flow sediment than to 

affect fluvial and eolian deposits. However, deposits resulting 

from local runoff will vary in their extent and location from 

predam condition if the base level onto which local sediment 

is delivered is lowered. For example, if the configuration of 

eolian dunes changes or if a new gully breaches the dune field 

(as at Palisades), slopewash events may cause additional gully 

incision that drains to the river instead of allowing slopewash 

and colluvial sediment to accumulate in ponded areas. Loss 

of slopewash sediment would have the greatest effect farthest from the river, where the proportion of such sediment is 

highest. At our study sites, slopewash and colluvial sediment 

composed only thin overlying layers relative to the thicker 

cover provided by fluvial and eolian deposits. However, 

multiple exposures that we observed in other areas of the river 

corridor include interbedded eolian and local sediment—a thin 

stratum of poorly sorted debris-flow sediment that can form a 

resistant cap protecting the underlying, more easily erodible 

eolian sediment. Therefore, reduction in the accumulation of 

cap-forming slopewash sediment (caused by a reconfiguration 

of local slopewash drainage) could lead to an increase in the 

erosion of eolian sediment.

Criteria for Identifying Site Sensitivity 

to Dam Operations

In this study, we combined analysis of prehistoric sedimentary and geomorphic environments with that of modern 

eolian processes to assess the sensitivity of specific archeologic sites to dam operations. Site-specific evaluation of 

archeologic sites is important because the relative roles of fluvial, eolian, and other sedimentation processes, as well as local 

wind and precipitation patterns, differ widely among sites in 

the same reach of the river corridor. We proposed a series of 

steps to determine the role of eolian sediment in preserving 

any given archeologic site, and then to assess the effect of 

dam operations on eolian sedimentation at that site (Draut and 

others, 2005); three case studies using those criteria were presented by Draut and Rubin (2008). Here, we summarize those 

site-evaluation criteria and case studies briefly. These guidelines were formulated specifically to apply to eolian sedimentation, although our approach could be modified to address a 

wider range of processes and their interaction with cultural 

features. We reiterate that although the guidelines below refer 

only to eolian sedimentation and, specifically, to MFS deposits, predam fluvial terraces with associated archeologic sites 

(as well as all RFS deposits, for the reasons outlined above) 

should be considered sensitive to dam operations because the 

absence of sediment-rich floods of about 2,830 m3

/s eliminates 

the mechanism by which those deposits formed and received 

significant amounts of new sediment.

An important first step in evaluating the factors that 

enhance preservation of archeologic sites is to determine the 

depositional context of the sediment on which the site was 

Criteria for Identifying Site Sensitvity to Dam Operations
16 The role of Eolian Sediment in the Preservation of Archeologic Sites Along the Colorado River Corridor

built and by which the site has been buried (covered). Depositional settings can be inferred by examining geomorphic 

features, sedimentary structures on the land surface, and 

sedimentary structures in the subsurface viewed in vertical 

section (sedimentary profiles). Field investigations can be 

supplemented by laboratory analyses of sediment particle-size 

distributions, as discussed above, and by radiocarbon dating 

of materials that contain organic matter or charcoal (whether 

cultural or noncultural). Radiocarbon dating not only provides 

information on the date of cultural occupation but also can be 

used to determine recurrence intervals of floods and debris 

flows in the study area, events that may have affected occupation by prehistoric cultures (for example, Hereford and others, 

1996, 2000).

If field study of surface geomorphology and sedimentary 

horizons determines that eolian deposition has buried and (as 

is commonly inferred) preserved a given archeologic site, then 

the possible loss of some of the eolian sediment that previously covered the site needs to be determined. Recognizing 

whether eolian sediment cover has been lost, by wind deflation 

or gully incision, is a step in assessing the risk of impending archeologic site degradation, or the degree to which such 

degradation has already occurred. If no loss of eolian sediment is suspected at a particular site, that site may not be at 

immediate risk of artifact loss. Future loss of eolian sediment 

at an archeologic site could be documented most accurately 

by repeated high-resolution mapping to measure changes in 

the elevation of a deflating land surface, or in the depth and 

width of growing gullies. If quantitative survey methods are 

unavailable, loss of sediment can be qualitatively identified by 

repeated ground-based photography and geomorphic evidence 

of deflation, including winnowed lag deposits on the land 

surface, pedestal formation, especially around plants (although 

erosion by rainfall can also leave small-scale pedestal features), and exhumation of plant roots. 

Deflation of eolian deposits represents a net loss of sediment from an area where net deposition has formerly occurred. 

Such a situation would arise from a change in the balance 

between the sediment supply and the sediment-transport capacity of local winds. If local wind conditions are assumed not to 

have changed significantly and a decrease in sediment supply 

is likely, the next step in this evaluation is to identify the source 

of the eolian sediment that buried the archeologic site. Source 

areas for eolian sediment are most readily identifiable by 

monitoring local wind conditions. The longer the time interval 

over which winds are monitored, the more accurate the resulting eolian-sediment-transport predictions will be. In Grand 

Canyon, the most important sources of new sediment from 

which wind can mobilize sand are fluvial sandbars. Records of 

wind speed and direction, such as those obtained during this 

study, can be used to generate vector sums that demonstrate the 

potential for eolian sediment transport over time (Draut and 

Rubin, 2005, 2006). If long-term weather monitoring is not feasible, recent local wind conditions can be inferred in the field 

from the orientation of ripple structures, sand shadows (which 

form in the lee of obstacles), and dune morphology (slipfaces). 

The presence of biologic soil crusts also indicates that 

eolian deposits now receive little or no active sand deposition. 

Soil crusts, which are dark-colored microbiotic soils that compose ≤70 percent of desert soils in the Southwestern United 

States, are dominated by cyanobacteria that live symbiotically 

with mosses and lichens. The crusts begin to form in 6–24 

months and require ≥5 years without disturbance to develop 

fully into a community. Although biologic soil crust may 

survive after being subjected to shallow burial, as the biota 

extend sheaths to the land surface to resume photosynthesis, 

deeper burial (>0.5 cm in quartz sands) will kill the crust 

(Belnap and Eldridge, 2003; J. Belnap, written comm., 2006). 

Therefore, if an area with eolian duneforms on the land surface also contains well-developed soil crust, this observation 

implies that although sediment accumulated there in the past 

(forming the dunes), it has been years since any substantial 

amount of windblown sand was last deposited on that surface. 

Similarly, abundant vegetation on the surfaces of eolian dunes 

implies that the duneforms are now relatively immobile and 

not undergoing rapid deposition or migration. Vegetation and 

biologic soil crust on dunes do not directly indicate deflation 

(loss of eolian sediment) but an absence, or near absence, of 

deposition in an area where it had formerly occurred. In an 

eolian dune field where sediment supply becomes limited, the 

land surface can first deflate (as wind transports more sediment out of than into the dune field), and then, after several 

years of limited sediment input and deposition, vegetation and 

biologic soil crust can colonize the deflated land surface and 

reduce additional deflation by armoring the relict duneforms 

(Leys, 1990; Leys and Eldridge, 1998; Belnap, 2003). 

In a dune field where dunes become less mobile over time 

(and where vegetation and biologic soil crust have grown), 

dune “stability” should not be confused with the “stability” of 

archeologic sites. An archeologic site in a deflated, vegetated 

dune field can be eroded by gully incision, as is commonly 

observed in Grand Canyon dune fields (such as those at 

Palisades, Comanche, Tanner/Cardenas [about river mile 

70], Arroyo Grande, and 202.9 Mile, fig. 1). In those areas, 

where dunes are relatively immobile, gully incision proceeds 

with little or no counteraction by eolian sediment deposition, 

thereby ultimately destabilizing dunes and associated archeologic sites.

After local wind conditions have been monitored to 

identify a sand source, possible decrease in the area of that 

sand source needs to be addressed. Aerial photography and 

repeated high-resolution mapping have been used to document 

historical changes in sandbar area and structure throughout 

the Colorado River corridor in Grand Canyon National Park 

(for example, Schmidt and others, 2004). Oblique, groundbased photography can effectively document other changes 

in source-area characteristics that might affect the ability of 

sandbars to serve as sources of eolian sediment. Important 

changes in sand-source quality might include a decrease in 

area due to sandbar erosion; growth of vegetation; increased 

moisture content of the open sand area (more frequent inundation by flow fluctuations); greater surface exposure of rocks, 
17

driftwood, or other obstacles that inhibit wind; or formation of 

soil crust on the land surface.

If the supply of windblown sediment to a particular site 

in an MFS dune field appears to have declined, the probability 

that renewed deposition of eolian sediment could enhance the 

preservation of associated archeologic sites needs to be determined. Sites at which increased eolian deposition would substantially protect cultural features are those at which the greatest degradation occurs owing to deflation of sediment cover 

by wind, or from incision by gullies that are small enough to 

be healed by windblown sand (<1 m wide or deep, judging by 

a few exposures of filled gullies observed during this study 

and by Thompson and Potochnik, 2000). Eolian sedimentation is unlikely to prevent the loss of cultural features that are 

threatened more immediately by incision of a major arroyo or 

side-canyon channel than by deflation or minor gullies.

These steps thus provide a method for evaluating the 

sensitivity of a particular MFS deposit (and any associated 

archeologic sites) to dam operations by assessing how closely 

the condition of the eolian deposit is linked to that of nearby 

fluvial sandbars, which, in turn, are greatly affected by the 

dam-controlled flow and sediment content of the river (for 

example, Wiele and others, 1996; Webb and others, 1999a; 

Schmidt and others, 2004; Topping and others, 2006). Archeologic sites can be preserved in several ways by using the 

increase in cover and gully-filling ability of additional eolian 

sediment. At some sites, erosion control by check dams can 

keep gullies small enough to be partially or fully healed by 

windblown sand. Localized mitigation efforts by the NPS and 

collaborating tribes might substantially restore site conditions 

in such areas (Leap and Coder, 1995; Balsom and others, 

2005). In many areas, however, especially if a larger scale 

solution is desired, preservation of archeologic sites that rely 

on eolian sediment cover can be achieved only by restoring 

the source areas from which the eolian sediment is derived. 

Because Colorado River sand deposits constitute the largest 

source of new sediment mobilized by wind, increasing dry, 

open sandbar area is the most effective way to enhance the 

potential for transport to and deposition on MFS dune fields 

and associated archeologic sites. Restoring sandbars by using 

controlled high riverflows under sediment-enriched conditions 

could be the most effective way to restore eolian deposits and 

preserve archeologic sites above the flood stage (Yeatts, 1997; 

Fairley, 2005; Draut and Rubin, 2006).

Three Case Studies

This study identified archeologic sites at which (1) erosion apparently is linked to dam operations, (2) erosion is not 

linked to dam operations, and (3) the connection between dam 

operations and site degradation remains unclear. Case studies of these three situations are presented in this subsection. 

The locations of the studied archeologic sites cannot legally 

be disclosed, and so they are referred to here simply as sites 1 

through 3. 

Site 1 is considerably sensitive to dam operations. On the 

basis of geomorphologic observations and a shallow test pit 

dug into sediment near the site in May 2003, eolian sediment 

forms both the substrate on which this site was built and the 

cover that has kept the roasting feature and artifact scatter 

largely intact. Site 1, located near the land, upper-elevation 

end of an eolian dune field, has undergone loss of eolian sediment, as shown by downslope movement of artifacts as the 

land surface has deflated (determined by years of monitoring 

by the NPS). Although the dune field shows evidence of active 

sand transport in the vicinity of the site, much of the dune field 

has undergone pronounced deflation and soil-crust growth, 

indicating little or no active sand deposition at present. The 

source of the eolian sediment that partly covers site 1 is a fluvial sandbar about 80 m directly upwind of the site, identified 

on the basis of wind conditions monitored at a weather station 

near site 1 for >1 year. Therefore, the eolian deposit at site 1 is 

considered to be MFS. Comparison of oblique historical photographs indicates a major decrease in the area and volume of 

the site 1 river-level sandbar from predam (1920s) to postdam 

(1970s) time (Turner and Karpiscak, 1980), a trend confirmed 

by comparison of aerial photographs of the area taken in the 

1960s and 1990s. This decrease in sandbar area and volume 

suggests that deflation and limited sand transport in the dune 

field are related to the loss, since dam closure, of the fluvial 

sandbar about 80 m upwind. Site 1 presently is intact enough 

that it could be better preserved, given additional eolian sediment cover. The archeologic site and its surroundings are not 

affected by gully incision, visitor trails, or any other degradation processes. 

The apparent sensitivity of site 1 to dam operations implies 

that restoration of the fluvial sandbar could enhance windblown 

sediment delivery to the associated MFS dune field, helping to 

cover the cultural artifacts there. The site 1 sandbar received 

substantial new sediment during the 1996 and November 2004 

controlled floods (on the basis of preflood and postflood aerial 

photographs and visits). Sand-transport rates measured at the 

site before and after the 2004 flood showed greater sand flux 

during the spring 2005 windy season than during the spring 

2004 windy season, even though wind conditions in spring 

2004 had a greater sand-transport potential than those in spring 

2005. Therefore, site 1 provides an example of dam operations rebuilding a sandbar, thus enhancing sand transport to an 

archeologically important MFS deposit.

Site 2 shares many characteristics with site 1 in that it 

contains cultural features built on and buried by eolian sediment. A natural cross-section exposure reveals debris-flow 

sediment underlying the eolian dune field in the area of site 2. 

Advanced deflation and well-developed biologic soil crust are 

apparent throughout the upper part of the dune field. Although 

wind conditions were not monitored in the immediate area, 

the orientations of dunes and sand shadows in the lower, more 

active part of the dune field, which was photographed during 

four visits in multiple seasons, indicate that the source of the 

eolian sediment is a fluvial sandbar about 70 m upwind of the 

site. Aerial photographs show a pronounced decrease in open 

Criteria for Identifying Site Sensitvity to Dam Operations
18 The role of Eolian Sediment in the Preservation of Archeologic Sites Along the Colorado River Corridor

sand area on the sandbar between the 1960s and 1990s, as well 

as an increase in vegetation cover on the eolian dune field. 

Thus far, evidence suggests that deflation and reduced sand 

mobility on the dune field are linked to postdam shrinkage 

of the river-level sandbar which serves as the sand source for 

that MFS dune field. However, although the general condition 

of the dune field likely responds to dam operations, the rapid 

degradation of site 2 cannot be linked to Glen Canyon Dam 

because other factors unrelated to windblown sand affect the 

site on shorter time scales. A large tributary channel where 

major floods and debris flows are known to have occurred in 

historical time has incised into eolian sediment at the edge of 

the dune field (fig. 6). The cultural features at site 2 are eroded 

more substantially by episodic tributary activity than by processes that could be reduced or reversed with more windblown 

sand (eolian deflation or formation of small gullies).

In contrast to sites 1 and 2, where archeologic-site sensitivity to dam operations can be either confirmed or refuted, 

respectively, site 3 presents a situation in which the effect of 

dam operations remains unclear even after detailed study. Similar to sites 1 and 2, site 3 was built on and buried by eolian 

sediment; the site is situated in a large, sparsely vegetated 

dune field. Individual features show evidence of some loss of 

the eolian sediment that previously covered them, including 

deflation, slumping, and downslope movement of artifacts 

associated with dune migration. Some minor biologic soil 

crust is present, but most of the dune field appears to be undergoing active sand transport. The dominant local wind direction, measured near site 3 for >1 year, indicates that the most 

likely sand source for this dune field is a large, predam fluvial 

terrace upwind, making the dune field RFS type. The modern 

morphology of the fluvial terrace suggests a substantial loss 

of sediment from, as well as of eolian sediment-entrainment 

capacity in, this source area. The terrace is incised by an 

arroyo network several meters deep and wide, and its surface 

has been colonized by abundant vegetation and biologic soil 

crust, observations consistent with the fact that no postdam 

floods have reached the level of this terrace. 

Figure 6. Sedimentary material in area where a tributary channel erodes an eolian deposit containing cultural material 

(site 2) along Colorado River corridor in Grand Canyon National Park, Ariz. (fig. 1). Poorly sorted sediment exposed in 

lower part of nearly vertical bank is interpreted as a deposit from a tributary debris flow. Fine, light-colored eolian sand 

was deposited later, overlying debris-flow sediment; formation of archeologic site apparently was synchronous with 

formation of eolian deposit, because cultural material is being eroded out at a level approximately halfway through eolian 

deposit thickness. 
19

Although surface conditions in the eolian dunes may 

be related to postdam reduction of sediment from the fluvial 

terrace upwind, it is unclear whether or not site 3 would be 

better preserved if new deposition from a large, sedimentrich flood were to increase sand transport from the terrace 

to the RFS dune field. Eolian processes are responsible for 

the disturbance of artifacts at site 3, but the dune migration 

that affects them is a natural process endemic to active dune 

fields. In a natural system, continued dune migration would 

be expected eventually to cover the site. Over time scales 

of years to decades, migrating dunes in an unaltered eolian 

system would expose and cover any given part of the dune 

field repeatedly, and downslope movement of artifacts would 

be expected as the sand shifts under them. Dunes near the 

site would need to be surveyed repeatedly over decades to 

determine whether or not dune migration will continue as 

it would naturally with plentiful sediment, or whether the 

dune field will show signs of exacerbated sediment-supply 

limitation in the future (increases in vegetation, biologic soil 

crust, or winnowed lag deposits and decrease in the mobility 

of duneforms), which might indicate that sediment deprivation caused by dam operations had prolonged the exposure 

of these artifacts, thereby increasing the risk of their damage 

and loss.

As outlined above, we can determine in many cases 

through careful, site-specific field study whether and to what 

degree a particular archeologic site is sensitive to the effects 

of Glen Canyon Dam operations. Although in-place preservation of cultural artifacts on geologic time scales is unrealistic, owing to continual downcutting and backwasting in this 

bedrock canyon, preservation of archeologic sites could be 

enhanced on decadal to centennial time scales by restoring 

fluvial and eolian sedimentation to resemble more closely 

the processes that occurred before the river was regulated 

by upstream dams, including large, sediment-rich floods that 

left fluvial deposits from which sediment was remobilized by 

wind.

Effects of the November 2004 Controlled-Flood Experiment on Eolian 

Sediment Transport

Archeologic sites that depend on a supply of windblown 

sediment from fluvial sandbars for their continued preservation can receive an increase in eolian sediment after restoration of sandbars by high releases from Glen Canyon Dam. 

Sandbar restoration was the primary goal of the controlledflood experiment on the Colorado River in November 2004, 

the second such experiment. To ensure a greater sand supply 

in the upstream reach than was available during the first 

controlled-flood experiment in March 1996 (Webb and others, 

1999b; Patten and others, 2001; Schmidt and others, 2001), 

the 2004 controlled flood occurred after substantial amounts 

of sand had recently been supplied to upper Marble Canyon 

by the Paria River and other tributaries, and after an interval 

of lower dam releases designed to minimize sediment export. 

Conditions during the 2004 high flow therefore represented 

sediment enrichment in the river channel relative to conditions 

during the 1996 flood (Topping and others, 2006).

The design of the 2004 controlled-flood experiment 

included a 60-hour steady riverflow of 1,160 m3

/s released 

from Glen Canyon Dam on November 22 and 23. Postflood 

surveys indicated that the area and volume of sandbars in 

Marble Canyon above approximately river mile 40 were 

significantly greater than before this high flow and that 

approximately half of the surveyed sand deposits were much 

larger than immediately after the 1996 controlled flood (Hazel 

and others, 2005; Topping and others, 2006). Below approximately river mile 40, localized deposition and erosion were 

documented, and a consistent pattern of sandbar aggradation 

could not be demonstrated, implying that in future high-flow 

experiments, more sand must be present in the river channel 

to achieve deposition on sandbars throughout the canyon (Topping and others, 2006). 

In addition to the sandbar surveys after the 2004 controlled-flood experiment (Hazel and others, 2005), fluvial 

sand deposits at our study sites were photographed immediately before and after the flood (in November and December 

2004, respectively) and again at multiple times during 2005; 

preflood and postflood photographs were published by Draut 

and Rubin (2005, 2006). The duration of this study included 1 

year of preflood data and >1 year of postflood data. Study sites 

were chosen partly because new fluvial sand deposition had 

occurred at them during the 1996 controlled-flood experiment. 

Therefore, similar deposition was predicted to occur at these 

sites during the November 2004 high flow. On the basis of 

wind conditions monitored in the year before the controlledflood experiment (Draut and Rubin, 2005), the greatest potential for redistribution of new, flood-deposited sediment was 

predicted to occur during the spring 2005 windy season. 

At all six weather-station sites (fig. 1), major deposition 

of new fluvial sand occurred as a result of the November 2004 

controlled flood (Draut and Rubin, 2005, 2006). The substantial deposition in those areas during a sediment-rich Colorado 

River high flow implies that to the extent that such flows can 

restore the sandbars, controlled floods are also an effective 

management option to increase the availability of sediment to 

MFS deposits. In addition to depositing a substantial amount 

of new sand on many sandbars, the November 2004 high flow 

also facilitated eolian sediment entrainment because the new 

sediment covered vegetation, rocks, and driftwood, decreasing the roughness of the land surface and thereby promoting 

sediment entrainment by wind (Lettau, 1969; Marshall, 1971; 

Raupach and others, 1993; Gillies and others, 2000; King and 

others, 2005).

However, if maximizing eolian redistribution of sediment is one of the management goals of a controlled flood, 

riverflows that occur between the time of the flood and the 

next windy season must also be managed to maximize open, 

Effects of the November 2004 Controlled-Floof Experiment on Eolian Sediment Transport
20 The role of Eolian Sediment in the Preservation of Archeologic Sites Along the Colorado River Corridor

dry sandbar area during that windy season (April−early June). 

Much of the 2004 flood-deposited sand was eroded by high, 

daily flow fluctuations that ranged from 142 to 566 m3/s from 

January to March 2005, before the spring windy season began 

(Draut and Rubin, 2006). For example, at Malgosa (river mile 

57.9, fig. 1), a new sand deposit, 1.5 m thick and more than 

10 m wide, formed during the flood but was eroded almost 

entirely during the next 4 months (fig. 7). Sites a short distance 

downstream of the Little Colorado River, such as Palisades 

and Comanche, 7.4 and 10.4 km, respectively, below the 

confluence with the main stem, showed a less pronounced loss 

of sand during January–March 2005 flow fluctuations than 

did Marble Canyon, presumably because flooding of the Little 

Colorado River in February 2005 (about 70 m3/s) provided 

additional sand to these nearby areas.

At the study sites where flood deposits were entirely 

eroded before the 2005 windy season began, sand-transport 

rates measured during the spring 2005 windy season were 

comparable to or lower than those measured during the 

spring 2004 windy season, given similar wind conditions. At 

24.5 Mile, however, where approximately half of the flooddeposited sand remained at the start of the spring 2005 windy 

season, sand-transport rates measured near the river during the 

spring 2005 windy season were approximately double those 

Figure 7. Study site at Malgosa (river mile 57.9) along the Colorado River corridor in Grand Canyon National Park, Ariz., showing effects of 

November 2004 flood and subsequent fluctuating flows. Study site is on river right, near weather station Mal L (see fig. 14 for location). Photographs from Draut and Rubin (2006). A, Preflood photograph taken November 17, 2004, at a riverflow of 226 m3

/s. B, Postflood photograph taken 

December 9, 2004, at a riverflow of about 226 m3

/s. New sand deposited at site during flood was approximately 2 m thick (note person for scale). 

C, After several months of 142 to 566-m3

/s daily flow fluctuations, flood deposit had been eroded substantially, exposing many rocks in center of 

beach that were present before flood. Photograph taken March 13, 2005, during riverflow of about 226 m3

/s. D, By late spring 2005, flood deposit 

had been almost entirely removed, and state of sandbar was nearly identical to preflood state. Photograph taken May 28, 2005, during riverflow 

of 226 m3

/s.
21

in spring 2004 (Draut and Rubin, 2006), even though wind 

conditions there in spring 2005 had less capacity to transport 

sediment than in spring 2004 (see appendix 1). The increase in 

sand transport near the river in spring 2005 relative to spring 

2004 is interpreted as a result of an increase in the area of 

available sand upwind and a decrease in the roughness of the 

land surface where 2004 flood sediment was still present. No 

similar increase in sand flux relative to the previous year was 

measured at the upper-elevation station in the same dune field. 

The dominant wind direction at 24.5 Mile transports sand 

from the west-southwest to the east-northeast (from river level 

to the upper part of the MFS dune field; see appendix 1). Sandtransport measurements at 24.5 Mile suggest that although 

the influence of the new flood sediment was measurable near 

river level (at the lower of the two weather stations) in spring 

2005, its effects had not yet propagated to the upper part of 

the dune field. In many areas of the river corridor, new sand 

would need to reach the highest parts of eolian dune fields in 

order to increase sand transport to archeologic sites. Because 

the sand flux measured at the upper weather station at 24.5 

Mile exceeded that measured at the lower station, even with 

the new flood sand present (Draut and Rubin, 2006), the net 

sand flux into the dune field was still negative even after the 

controlled-flood experiment. Had the sandbar near the lower 

station been as large during the spring 2005 windy season as it 

was immediately after the November 2004 controlled flood, the 

sand flux into the dune field might have balanced or exceeded 

that out of the dune field, resulting in net sediment gain. At 

this same site, the restorative function of eolian sediment 

derived from the flood deposit was still apparent >1 year after 

the controlled-flood experiment. In January 2006, a new gully 

that had recently begun to incise into the eolian dune field was 

photographed at 24.5 Mile. The orientation of the gully and 

of wind ripples in the sand indicated that sediment filling the 

lower part of the gully had blown inland from the November 

2004 controlled-flood deposit, an observation consistent with 

the dominant wind direction recorded at 24.5 Mile during the 

preceding 26 months (Draut and Rubin, 2006). The ability of 

gullies to act as natural traps for windblown sand could contribute to slowing or cessation of erosional processes that affect the 

stability and preservation of archeologic sites in eolian deposits 

(for example, Thompson and Potochnik, 2000).

 Effects of the November 2004 controlled-flood experiment on eolian sediment transport, therefore, indicate that 

increasing the area of sandbars can increase sediment deposition in eolian dune fields above the flood-stage elevation. 

Sandbar-building floods have a greater potential to enhance 

eolian sedimentation on MFS deposits than on RFS deposits, as 

defined above (fig. 4), because of the direct link between active 

fluvial sandbars (at or below the 1,270-m3

/s flood stage) and 

MFS dune fields downwind. To substantially restore RFS dune 

fields would require sediment-rich floods on the scale of predam 

spring snowmelt floods, at least several times as high as those 

conducted experimentally thus far and for a longer duration. 

Therefore, any future controlled high flows on the scale of the 

2004 experiment would probably substantially enhance eolian 

deposition on MFS dune fields (provided that postflood flows 

are managed to maintain the size and condition of new fluvial 

deposits throughout the next windy season) but have little effect 

on eolian sediment transport into RFS dune fields.

The high daily flow-fluctuation schedule (142−566 m3

/s) 

of experimental flows was conducted during January–March 

2003, 2004, and 2005 to suppress nonnative fish populations. 

Each of those high-fluctuating-flow intervals exported approximately twice as much fluvial sediment as under modified low 

fluctuating flow (MLFF) operations of Glen Canyon Dam for 

comparable-volume months and sediment influx (S.A. Wright, 

oral commun., 2006). Therefore, operation under low fluctuating flows (or steady low flow) between the end of a controlled 

flood and the start of spring high winds is predicted to maintain much more of the postflood sandbar area until the wind 

can redistribute flood sediment into higher elevation eolian 

deposits during the subsequent spring windy season.

Recommended Future Research

To evaluate the degree to which the presence and operation of Glen Canyon Dam may influence the preservation of 

archeologic sites in the Colorado River corridor (fig. 1), sitespecific stratigraphic and geomorphic knowledge is needed. 

Establishment of the local importance of fluvial, eolian, and 

other processes in predam and postdam time is an important prerequisite for accurate assessments of dam effects, 

and archeologic-site sensitivity to dam operations must be 

evaluated on a site-by-site basis because the relative roles of 

various sedimentation processes differ widely between sites, 

even within the same river reach. Future sedimentologic and 

geomorphologic studies could assess the sensitivity to dam 

operations of additional archeologic sites not included in this 

study. It would be highly informative to include field analysis 

of vertical sediment profiles (identifying depositional environments by using sedimentary structures) in any future excavation of archeologic sites in the river corridor. 

Wind, rainfall, and sand-transport data collected during 

the 26 months of this study span various weather conditions 

but still are probably not representative of long-term climate 

in the Grand Canyon region. A long-term weather-monitoring 

program would allow climate patterns and potential-sandtransport measurements to be refined with greater accuracy. 

To represent weather conditions at high spatial resolution over 

the entire Colorado River corridor in Grand Canyon National 

Park, many stations would be required. To represent spatial 

variation reasonably, at least five (preferably more) weather 

stations should be distributed between Lees Ferry and Diamond Creek (river miles 0−226, fig. 1). Although the stations 

used in this study monitored weather conditions that were 

directly relevant to archeologic sites (wind, rainfall, and sand 

transport), a longer term weather-monitoring program could 

use additional equipment to measure air temperature, relative humidity, barometric pressure, and other parameters to 

generate a broader scale climatic record in the Colorado River 

Recommended Future Research
22 The role of Eolian Sediment in the Preservation of Archeologic Sites Along the Colorado River Corridor

corridor that would be useful for physical, biologic, and cultural research. The measured broad spatial variation in rainfall 

documented during this study indicates that future sedimentologic and geomorphologic studies in the canyon would benefit 

substantially from continued or expanded weather monitoring 

at multiple sites along the Colorado River corridor because 

the rainfall records collected by the NPS at Phantom Ranch 

cannot be considered valid for other parts of the canyon. 

As a step to realizing those objectives, new weather stations were installed in early 2007 to measure wind speed and 

direction, precipitation, sand transport, air temperature, relative humidity, and barometric pressure. These stations, at 24.5 

Mile, 60 Mile, Palisades, 70 Mile, 136 Mile, 202.9 Mile, and 

223 Mile (fig. 1), allowed monitoring of local effects of the 

March 2008 controlled-flood experiment on sand flux. Data 

from those weather stations are not yet available.

Recording climatic data in the Colorado River corridor is only one step to identifying the complex geomorphic 

processes that affect the condition of eolian deposits, and, by 

extension, of many archeologic sites. The information gathered and presented in this and our previous reports could form 

the basis for a wide array of future modeling studies. It is 

becoming increasingly clear that eolian transport and deposition of sediment affects the condition of archeologic sites in 

the river corridor and that the availability of sediment from 

open sand areas on fluvial sandbars is an integral component 

of these processes. Although eolian-sediment-transport modeling formed a component of this study (see appendix 2), we 

suggest three additional research initiatives to address these 

issues in more detail: 

1. A detailed aerodynamic-modeling study of one or more 

sites that would involve numerical representation of airflow, including dynamic interactions with obstacles, slope, 

and irregular spatial boundaries.

2. Construction of a new sand-trap design that would allow 

higher temporal resolution of sand-transport response to 

specific, short-duration wind conditions. Future research 

in these two linked directions would lead to a better 

understanding of the eolian-sediment-transport systems that affect natural and cultural resources in Grand 

Canyon. 

3. Because of the approximately exponential inverse relation 

between eolian sediment transport and vegetation cover 

(Bressolier and Thomas, 1977; Buckley, 1987), studying the response of eolian sediment transport to localized 

removal of riparian vegetation would be informative. 

Such areas as the sandbar downstream of 202.9 Mile or 

along the east bank of the river near Comanche are possible sites where vegetation removal could promote additional eolian sediment transport, given that eolian dune 

fields are nearby and vegetation cover is known to have 

increased locally in postdam time (see appendix 1). To 

promote sand transport effectively, near-complete removal 

of vegetation would be needed; nearbed wind velocities 

are negligible on surfaces with about 40-percent vegetation cover (Buckley, 1987), and in many riparian areas of 

Grand Canyon, the vegetative cover is much denser. We 

recommend that in future vegetation-removal projects, 

wind conditions and sand transport should be monitored 

at study sites for several months, ideally spanning a spring 

windy season before and a spring windy season after 

vegetation removal, to assess possible effects. 

Conclusions

Eolian sediment serves as a substrate on which many 

archeologic sites in the Colorado River corridor were formed 

(in many areas also in association with fluvial and slopewash 

sediment), and, more commonly, as a surficial deposit covering archeologic material. Without sufficient eolian sediment, 

cultural artifacts are exposed by wind deflation of the overlying sediment, forming a lag deposit on the land surface. Many 

eolian dune fields in Grand Canyon show evidence of reduced 

sediment supply in the form of vegetation and biologic soil 

crust covering relict duneforms. The presence of well-developed 

microbiotic soil crusts and colonization by grasses indicates a 

lack of sediment deposition and a decrease in dune mobility relative to times in the past when the supply and transport of eolian 

sediment were great enough to generate dunes. Sand-transport 

rates on dune fields in Grand Canyon with well-developed vegetation and biologic soil crust are typically a tenth of those on 

dunes without vegetation or soil crust. Although vegetation and 

biologic soil crust limit the mobility (migration) of dunes relative to their earlier state of sediment abundance, this observation does not imply that dunes and associated archeologic sites 

cannot erode. Dunes with substantially reduced sand supply 

(and with vegetation and soil crust) are less likely to have sufficient sediment transport and deposition to counteract gully 

incision. In these vegetated, soil-crusted dunes, large gullies and 

arroyos are more likely to form and cause major erosion and 

degradation of dunes and archeologic sites.

Reduction in the source areas that provide windblown 

sand to eolian deposits is evident from comparison of aerial 

photographs taken in the 1960s with modern images. At the 

study sites (fig. 1), many fluvial sandbars are smaller, and 

riparian vegetation is more abundant, now than in 1965, consistent with the results of previous studies in many other areas 

of the Colorado River corridor (Turner and Karpiscak, 1980; 

Beus and others, 1985; Schmidt and Graf, 1987; Kearsley and 

others, 1994; Leschin and Schmidt, 1995; Hazel and others, 

1999; Schmidt and others, 2004).

The problem of archeologic-site preservation in postdam 

time is essentially a competition between two processes—precipitation runoff, which creates gullies that erode sedimentary 

deposits (as well as overland flow that can wash artifacts into 

gullies); and eolian sediment transport, which fills in small 

gullies, inhibiting their growth (gullies act as natural traps for 

windblown sand). The ability of eolian sediment transport to 
23

counteract gully formation and heal small (<1 m wide and 

deep) gullies is a major factor controlling the geomorphic 

evolution of Grand Canyon sedimentary deposits. Areas where 

abundant rainfall and high sand-transport rates were measured 

during this study can lack gullies (which form episodically but 

are quickly filled by windblown sand), whereas areas where 

little rainfall and little sand transport were measured have 

been substantially eroded by gullies and arroyos, destabilizing 

archeologic sites. Although many factors (long-term climatic 

fluctuations, drainage-basin geometry, substrate composition, 

and effective base level) contribute to gully formation, we 

infer that the arroyo incision would not have progressed so far 

in some areas if eolian-sediment-transport rates were significantly higher. For example, several kilometers upstream of the 

deeply incised Palisades terrace, gullies typically are absent 

in the dune field at Malgosa—a study site that had twice the 

rainfall and 10 times the sand-transport rate of Palisades.

Two types of eolian deposit occur in the Colorado River 

corridor, defined by the relative positions of the deposits and 

nearby fluvial sandbars and the locally dominant direction 

of eolian sediment transport. Modern fluvial-sourced (MFS) 

deposits formed as the wind transported sand inland from a 

river-level sandbar, creating an eolian dune field downwind; 

and relict fluvial-sourced (RFS) deposits formed by in-place 

wind reworking of predam flood deposits. Both MFS and RFS 

deposits are known to contain archeologic material, and both 

types of deposits are sensitive to dam operations, but for different reasons. Changes in dry, open, fluvial-sandbar dimensions (a 

function of dam operations) affect eolian sediment transport to 

MFS dune fields downwind; we have defined criteria to judge 

the sensitivity to dam operations of particular archeologic sites 

within MFS deposits. RFS deposits compose the uppermost, 

wind-reworked part of predam terraces that are largely alluvial, containing sediment deposited by riverflows ≥5,000 m3

/s. 

Because sediment-rich floods of that magnitude do not occur in 

the regulated Colorado River, fluvial deposits from which RFS 

dune fields formed no longer constitute an active sand source, 

and so no substantial new deposition is likely to occur on RFS 

dune fields in the absence of large, sediment-rich floods. 

Management of Glen Canyon Dam operations affects 

eolian sediment transport in the Colorado River corridor 

through Grand Canyon. If the size and number of the fluvial 

sandbars from which wind remobilizes sand can be increased 

by controlled, sediment-rich flows of about 1,270 m3

/s, then 

windblown sand transport can significantly increase in the 

vicinity of new flood deposits, and new flood sand can be 

transported by wind to elevations above the flood stage, 

replenishing sediment in MFS deposits. All of those processes 

were documented on seasonal time scales during this study 

after the November 2004 1,160-m3/s controlled-flood experiment. Eolian sediment transport to eolian dune fields will be 

greatest if postflood dam operations maximize the area and 

number of fluvial sandbars during the spring windy season 

(between April and early June), when sand-transport rates are 

about 5 to 15 times higher than in other seasons. After the 

November 2004 controlled flood, newly deposited sandbars 

were eroded substantially by daily flow fluctuations of 142 to 

566 m3/s between January and March 2005, before the spring 

windy season began. Sandbar erosion by high daily flow 

fluctuations removed much of the sand that was potentially 

available for eolian redistribution, limiting the effects of the 

2004 flood on archeologic sites. Because high fluctuating 

flows export approximately twice as much fluvial sand as is 

exported by modified low fluctuating flow (MLFF) operations 

of Glen Canyon Dam, more eolian sediment would be available to be blown inland (to MFS dune fields and the associated 

archeologic sites) if sandbar-building floods were followed 

by low fluctuating flows rather than by high daily fluctuations. Operating under low fluctuating flows or steady low 

flows between the end of a controlled flood and the start of the 

spring windy season is predicted to retain more of the postflood sandbar area until the next spring windy season, when 

wind can transport sand into eolian deposits above flood-stage 

elevation. If sandbars could be rebuilt to the extent that they 

remained larger throughout the year, or retained sediment from 

one flood to the next, overall eolian sediment transport would 

be greater than under present conditions, even though sandbars 

would still be partially eroded between floods.

Preservation of archeologic sites along the Colorado 

River corridor in Grand Canyon National Park on geologic 

time scales is unrealistic, owing to continual downcutting and 

backwasting of the bedrock canyon. On decadal to centennial 

time scales, tens to hundreds of archeologic sites in Grand 

Canyon could be better preserved by restoring fluvial and 

eolian sedimentation to resemble more closely those processes 

that occurred before the river was regulated by upstream dams, 

including sediment-rich floods that left fluvial deposits from 

which sediment was remobilized by wind.

Acknowledgments

This research was supported by the Bureau of Reclamation through the Grand Canyon Monitoring and Research 

Center (GCMRC), in cooperation with the National Park Service (NPS). We thank the following people for their collaboration at many stages of this project: J. Balsom, M. Barger, K. 

Burnett, S. Davis, B. Dierker, J. Dierker, J. Draut, H. Fairley, 

C. Fritzinger, A. Fuller, S. Goeking, guides and students from 

Grand Canyon Youth, R. Griffiths, J. Grissom, D. Harris, G. 

Hatcher, J. Hazel, S. Hueftle, R. Hunter, L. Jackson, S. Jones, 

M. Kaplinski, K. Killoy, J. Logan, T. Melis, F. Nials, M. Piller, 

S. Reeder, M. Rubin, J. Running, T. Sabol, E. Todd, D. Topping, R. Tusso, N. Voichick, S. Wright, S. Wyse Mietz, and 

M. Yeatts. D. Sherman (Texas A&M University) provided 

shear-velocity values for two of the eolian-sediment-transport 

models evaluated in appendix 2. J. Johnson and R. McDonald 

provided constructive reviews of the manuscript. We thank P. 

McCredie, G. Havach, L. Schmit, and T. Suzuki for their editorial work. We thank R. Hereford, D. Topping, and R. Hunter 

for their helpful comments and discussions on this report.

Acknowledgments
24 The role of Eolian Sediment in the Preservation of Archeologic Sites Along the Colorado River Corridor

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Geology, v. 29, p. 399–402.

Webb, R.H., and Hereford, R., 2001, Floods and geomorphic 

change in the southwestern United States—an historical 

perspective: Federal Interagency Sedimentation Conference, 

7th, Reno, Nev. 2001, Proceedings, v. 1, p. IV30−IV37.

Webb, R.H., Schmidt, J.C., Marzolf, G.R., and Valdez, 

R.A., eds., 1999a, The controlled flood in Grand Canyon: 

Washington, D.C., American Geophysical Union Geophysical 

Monograph 110, 367 p.

Webb, R.H., Wegner, D.L., Andrews, E.D., Valdez, R.A., and 

Patten, D.T., 1999b, Downstream effects of Glen Canyon 

Dam on the Colorado River in Grand Canyon—A review, in

Webb, R.H., Schmidt, J.C., Marzolf, G.R., and Valdez, R.A., 

eds., The controlled flood in Grand Canyon: Washington, 

D.C., American Geophysical Union, Geophysical Monograph 

110, p. 1–21.

White, B.R., 1979, Soil transport by winds on Mars: Journal of 

Geophysical Research, v. 84, p. 4643–4651. 

Wiele, S.M., Graf, J.B., and Smith, J.D., 1996, Sand deposition 

in the Colorado River in the Grand Canyon from flooding of 

the Little Colorado River: Water Resources Research, v. 32, 

p. 3579–3596.

Wiggs, G.F.S., Baird, A.J., and Atherton, R.J., 2004, The 

dynamic effects of moisture on the entrainment and transport 

of sand by wind: Geomorphology, v. 59, p. 13–30.

Williams, G., 1964, Some aspects of the eolian saltation load: 

Sedimentology, v. 3, p. 257–287.

Wright, S.A., Melis, T.S., Topping, D.J., and Rubin, D.M., 2005, 

Influence of Glen Canyon Dam operations on downstream 

sand resources of the Colorado River in Grand Canyon, in 

Gloss, S.P., Lovich, J.E., and Melis, T.S., eds., The state 

of the Colorado River ecosystem in Grand Canyon: U.S. 

Geological Survey Circular 1282, p. 17–31.

Yeatts, M., 1996, High elevation sand deposition and retention 

from the 1996 spike flow—An assessment for cultural 

resources stabilization, in Balsom, J.R., and Larralde, S., eds., 

Mitigation and monitoring of cultural resources in response 

to the experimental habitat building flow in Glen and Grand 

Canyons, Spring 1996: Flagstaff, Ariz., Report to Bureau of 

Reclamation, and Grand Canyon Monitoring and Research 

Center, p. 124–158.

Yeatts, M., 1997, High elevation sand retention following the 

1996 spike flow: Flagstaff, Ariz., report to the Grand Canyon 

Monitoring and Research Center, 15 p.

Yeatts, M., 1998, 1997 data recovery at five sites in the Grand 

Canyon—final report: Grand Canyon National Park, River 

Corridor Monitoring Project Report 60.

Zingg, A.W., 1953, Wind tunnel studies of the movement of 

sedimentary material, in Proceedings of the 5th Hydraulic 

Conference Bulletin (Studies in Engineering, v. 34): Iowa 

City, Iowa State University, p. 111–135. 

Zobeck, T.M., Sterk, G., Funk, R., Rajot, J.L., Stout, J.E., 

and Van Pelt, R.S., 2003, Measurement and data analysis 

methods for field-scale wind erosion studies and model 

validation: Earth Surface Processes and Landforms, v. 28, p. 

1163–1188.
29

This appendix summarizes wind, rainfall, and sand-transport measurements at six study sites (nine weather stations) 

along the Colorado River corridor in Grand Canyon National 

Park between November 2003 and January 2006 and provides 

conclusions specific to each site. Technical specifications of 

instruments and data-processing methods were discussed by 

Draut and Rubin (2005) and are summarized briefly here.

Mean wind velocity, maximum gust, and mean wind 

direction were measured digitally at each weather station with 

a 4-minute sampling interval. Sand flux was monitored by 

using traps that were emptied during maintenance visits every 

4–8 weeks. Sand-transport measurements are based on cumulative values representing the interval between maintenance 

visits. 

The total mass of sand collected from each trap during 

each maintenance visit was weighed, and sand-transport 

rates were calculated for each interval between collections by 

integration from 0 to 1 m of a curve fitted to the mass-versusheight data. The amount of sediment transport represented 

by the lowermost 1 m generally accounts for more than 99 

percent of the total sediment transport (Zobeck and Fryrear, 

1986; Vories and Fryrear, 1991; Sterk and Raats, 1996; Zobeck 

and others, 2003). The curve-fitting procedure uses a fiveparameter combined power-law and exponential function that 

has been shown to model vertical sand flux more accurately 

than either power-law (Zobeck and Fryrear, 1986; Fryrear and 

others, 1991) or exponential (Vories and Fryrear, 1991) fits 

alone (Sterk and Raats, 1996). The actual mass flux is considered to span an efficiency range of 70–130 percent in “big 

spring number eight” (BSNE) sand traps for grain sizes and 

wind velocities measured at the various study sites (Goossens 

and others, 2000).1

 This efficiency range was used to estimate error in the sand-transport data. Although this estimate 

constitutes a conservative treatment of the data, it is the best 

available for these bulk sand-transport data. (The exact correspondence between wind velocities and local sand-transport 

rate is unknown.) 

Grain-size analyses were performed on surface-sand samples from each instrument tripod at the time of initial deployment. Median grain size (d50), obtained by laser particle-size 

analysis (Draut and Rubin, 2006), allowed estimation of the 

critical threshold of motion (minimum wind velocity needed 

to mobilize and transport sand grains of a certain size) for sand 

at the study sites, taken to be about 2 m/s by using the formulation of Bagnold (1941; see appendix 2). In analyzing the 

wind data, we consider not only wind velocity but the sandtransport potential due to a given wind velocity. To represent 

this potential, we use a proxy variable, Qp, calculated for all 

the data points at which the wind velocity (u) exceeded the 

critical threshold of motion (ucrit), which is defined as the cube 

of the difference between the measured wind velocity and the 

critical threshold of motion: 

 

 (1)

This relation follows the convention used to construct 

eolian-sediment-transport models, such as those of Kawamura (1951) and Lettau and Lettau (1977), but substitutes 

wind velocity for shear velocity (see appendix 2). Although 

the units of Qp (m3

/s3) do not directly translate to a sand flux, 

comparison of the spatial and temporal variations in relative 

Qp values yields useful information about sand-transport 

potential. For the data points at which u<ucrit, Qp was set equal 

to zero, indicating that no sand transport would occur. Dominant wind directions causing sand transport were then calculated by using vector sums of Qp values from the 4-minute 

wind measurements. Monthly vector sums of Qp values for 

each weather station were reported by Draut and Rubin (2005, 

2006). 

The error in each wind-direction measurement is estimated at ≤10° (5° for the manufacturer’s stated accuracy of the 

anemometer plus 5° for operational error). For the magnitude 

component of wind velocity, analyses include an error of 0.5 

m/s at u <17 m/s and ±3 percent at u between 17 and 30 m/s

(manufacturer’s stated accuracy). Measurement errors are not 

expected to affect net (dominant) wind-velocity calculations 

significantly, except where winds blew often from opposing 

directions, such as at 202.9 Mile (fig. 1). For all other study 

sites, wind directions were consistent enough that measurement errors would not significantly affect the reported dominant wind and sand-transport directions.

24.5 Mile

Two weather stations were deployed in an eolian dune 

field on the downstream side of a debris fan at 24.5 Mile (fig. 

8)—one near river level (weather station 24.5 L, fig. 8B) and 

one at the upper end of the dune field (weather station 24.5 U; 

Draut and Rubin, 2005, 2006). The dune-field area between 

the two weather stations undergoes active sand transport and 

has little vegetation or biologic soil crust. An approximately 

equal area at the north (upstream) end of the dune field is 

relatively inactive, with a well-developed soil crust and evidence of deflation of the land surface. Comparison of aerial 

1

Ideally, sand traps would be isokinetic (100-percent efficiency), meaning that the sand trap would not disrupt airflow around it and would capture 

100 percent of the sediment in transport locally per unit width. No perfectly 

isokinetic sand traps have been designed. A sand trap operating at <100 percent efficiency diverts airflow away from the trap orifice, and the amount of 

captured sediment underrepresents the amount of sediment transport locally. 

A sand trap operating at >100 percent efficiency diverts air flow into the trap, 

thereby overrepresenting the amount of sediment transport locally per unit 

width.

3 .

Appendix 1. Site-Specific Observations

Appendix 1
30 The role of Eolian Sediment in the Preservation of Archeologic Sites Along the Colorado River Corridor

photographs taken in 1965 and 2004 (fig. 8) shows a decrease 

in the area of river-level sandbars and an increase in riparian 

vegetation at 24.5 Mile in postdam time. Notably, a river-level 

sandbar at the west end of the eolian dune field (sandbar a, fig. 

8) is clearly visible in 1965 photographs but much smaller or 

absent in recent photographs (see fig. 39 of Turner and Karpiscak, 1980). This sandbar was temporarily enlarged by the 1996 

controlled-flood experiment (on the basis of aerial-photographic analysis) and again by the November 2004 controlledflood experiment (Draut and Rubin, 2006), after which it was 

partially eroded by daily flow fluctuations. A second fluvial 

sand deposit (sandbar b, fig. 8) is now smaller than in 1965 

and is partly covered by vegetation, and riparian vegetation is 

more abundant there today than in 1965. 

Wind with velocity high enough to transport sediment 

consistently came from the west-southwest at 24.5 Mile (figs. 9, 

10). Therefore, the eolian dune field is directly downwind of the 

river-level sandbar (a, fig. 8) and is defined as an MFS deposit. 

Daily sand-transport rates were typically about 1 g/cm in 

the dune field at 24.5 Mile; daily sand-transport rates at the 

upper end of the dune field were consistently higher than those 

measured near river level by a factor of 2 to 4, consistent with 

the higher wind velocities measured at weather station 24.5 

U (figs. 8B, 11, 12). Given the projected strong link between 

sediment composing the fluvial deposit (sandbar a, fig. 8) and 

the eolian dune field, it was not surprising that replenishment of 

sediment on this sandbar during the 2004 controlled flood was 

followed by a measured increase in eolian sediment transport 

near river level (recorded at weather station 24.5 L) in the 

spring 2005 windy season, relative to the spring 2004 windy 

season. The sand flux at weather station 24.5 L was higher in 

spring 2005 than in spring 2004, even though the sand-transport 

potential of wind measured there was about 30 percent lower 

in spring 2005 (total Qp=4,150 m3

/s3 in April and May 2005, in 

comparison with 5,970 m3/s3 in April and May 2004). No similar increase in sand flux relative to the previous year was measured at weather station 24.5 U (fig. 12), where the sand-transport potential of wind was similar in spring 2004 and spring 

2005. Because the sand flux measured at weather station 24.5 U 

in spring 2005 exceeded that measured at weather station 24.5 

L, even with the new flood deposit present, the net sand flux 

into this dune field was still negative, indicating deflation of its 

land surface. Given wind conditions similar to those measured 

in 2005, the sand flux at weather station 24.5 L would need to 

be about 50 percent higher than that measured in 2005 to equal 

that at weather station 24.5 U, indicating that the dune field 

underwent no net gain or loss of sediment. We speculate that 

if the sandbar near weather station 24.5 L had been as large 

Figure 8. Aerial photographs taken in May 1965 (A) and May 2004 (B) of 24.5 Mile area along the Colorado River corridor in Grand Canyon 

National Park, Ariz. (fig. 1). Riverflow in May 1965 was between 680 and 792 m3

/s, and in May 2004 was 226 m3/s. Fluvial sand deposits (a and b). 

Modern extent of eolian dune field is indicated in figure 8B. Red dots, weather stations 24.5 L (lower) and 24.5 U (upper). Note the increase in 

riparian vegetation and decrease in open sand area since 1965. 
31

during the spring 2005 windy season as it was immediately 

after the November 2004 flood (having been reduced to half its 

postflood area by high daily flow fluctuations between January 

and March 2005), the sand flux into the dune field might have 

equaled or exceeded that measured at weather station 24.5 U, 

resulting in net sediment gain in the dune field. 

Archeologic sites built on and buried by eolian sediment 

are known to occur in the vicinity of 24.5 Mile. Because this 

area is an MFS dune field in which an eolian deposit receives 

sediment from a fluvial sandbar directly upwind, changes in 

the amount of fluvial sediment available from this sandbar can 

be expected to affect the preservation of archeologic sites in 

the eolian deposit to which this fluvial sediment is linked. The 

relatively inactive northern part of the dune field at 24.5 Mile 

has probably undergone deflation as a result of the decrease 

in sand source upwind (sandbar a, fig. 8) since the 1960s. 

The growth of the same fluvial sand deposit during the 2004 

530

1,150

1,010

1,080

992

4,730

5,310

378

A

B

45

840

305

1,455

561

4,256

3,082

76

Figure 9. Rose diagrams of sand-transport potential calculated from 

2 years of wind data collected at weather station 24.5 L (fig. 8B) along 

the Colorado River corridor in Grand Canyon National Park, Ariz. (fig. 

1). Numbers for 2004 (A) and 2005 (B) are total values of proxy variable Qp for each of eight directional half-quadrants, indicating total 

potential for eolian sediment transport from each compass sector. 

Vector sum of 2004 data yields a net Qp value of 7,350 m3

/s3 from a direction of 244°; vector sum of 2005 data yields a net Qp value of 5,974 

m3

/s 3 from a direction of 244°. 

A

B

9

843

1,530

1,250

3,000

28,200

9,380

45

7

896

474

1,181

5,521

16,498

13,414

34

Figure 10. Rose diagrams of sand-transport potential calculated 

from 2 years of wind data collected at weather station 24.5 U (fig. 8B) 

along the Colorado River corridor in Grand Canyon National Park, 

Ariz. (fig. 1). Numbers are values of proxy variable Qp for each of 

eight directional half-quadrants, indicating total potential for eolian 

sediment transport from each compass sector. Vector sum of 2004 

data yields a net Qp value of 35,800 m3

/s3 from a direction of 229°; 

vector sum of 2005 data yields a net Qp value of 23,607 m3

/s3 from a 

direction of 244°.

Appendix 1
32 The role of Eolian Sediment in the Preservation of Archeologic Sites Along the Colorado River Corridor

N D J F M A M J J A S O N D

5

10

15

20

25

30

35

40 J F M A M J J A S O N D J

2004 2005

1

2

3

4

5 N D J F M A M J J A S O N D J F M A M J J A S O N D J

2

4

6

8

10

12

14

16 N D J F M A M J J A S O N D J F M A M J J A S O N D J

J F M A M J J A S O N D J

0

1

2

3

4 N D J F M A M J J A S O N D

YEAR

DAILY TOTAL RAINFALL, 

IN MILLIMETERS

DIURNAL MAXIMUM GUST,

IN METERS PER SECOND

DIURNAL AVERAGE WIND VELOCITY,

IN METERS PER SECOND

DAILY SAND TRANSPORT, 

IN GRAMS PER CENTIMETER

Figure 11. Rainfall, wind, and sand-transport data collected at weather station 24.5 L (fig. 8B) along the Colorado River corridor in Grand Canyon 

National Park, Ariz. (fig. 1), from November 2003 to January 2006. Daily sand transport is plotted in grams per day between ground surface and 

a height of 1 m (elevation of uppermost sand trap), normalized to a width of 1 cm. To obtain these values, sand mass collected from four traps 

during each maintenance visit was integrated over a width of 1 m and divided by number of days since traps had last been emptied. Wind data 

from upper (2.0-m height) anemometer only are presented as diurnal average wind velocity and diurnal maximum gust, using daytime (0600–

1800 h) and nighttime (1800–0600 h) averages of data collected at 4-minute intervals. Daily total rainfall is summed over 24-hour intervals.
33

5

10

15

20

25

30

35

40

N D J F M A M J J A S O N D

4

8

12

16

1

2

3

4

5 N D J F M A M J J A S O N D

N D J F M A M J J A S O N D

1

2

3

4

5

N D J F M A M J J A S O N D J F M A M J J A S O N D J

J F M A M J J A S O N D J

J F M A M J J A S O N D J

J F M A M J J A S O N D J

2004 2005

YEAR

DAILY TOTAL RAINFALL, 

IN MILLIMETERS

DIURNAL MAXIMUM GUST,

IN METERS PER SECOND

DIURNAL AVERAGE WIND VELOCITY,

IN METERS PER SECOND

DAILY SAND TRANSPORT, 

IN GRAMS PER CENTIMETER

Figure 12. Rainfall, wind, and sand-transport data collected at weather station 24.5 U (fig. 8B) along the Colorado River corridor in Grand Canyon National Park, Ariz. (fig. 1) from November 2003 to January 2006. Daily sand transport is plotted in grams per day between ground surface 

and a height of 1 m (elevation of uppermost sand trap), normalized to a width of 1 cm. To obtain these values, sand mass collected from four 

traps during each maintenance visit was integrated over a width of 1 m and divided by number of days since traps had last been emptied. Wind 

data from upper (2.0-m height) anemometer only are presented as diurnal average wind velocity and diurnal maximum gust, using daytime 

(0600–1800 h) and nighttime (1800–0600 h) averages of data collected at 4-minute intervals. Daily total rainfall is summed over 24-hour intervals. 

Sand-transport data collected on November 15, 2005, were underestimated by an unknown amount, and those collected on January 12, 2006, 

correspondingly overestimated, because a mouse had contaminated lowermost (0.1-m height) sand trap at study site.

Appendix 1
34 The role of Eolian Sediment in the Preservation of Archeologic Sites Along the Colorado River Corridor

controlled flood, the resulting increase in sand flux into the 

dune field, and the filling of a small gully by windblown sand 

derived from the 2004 flood deposit (Draut and Rubin, 2006) 

all indicate that an increase in sandbar area can result in an 

increase in eolian sediment transport to, and deposition on, 

MFS deposits and associated archeologic sites.

The west-southwest dominant wind direction (and the same 

projected net sand-transport direction) measured at 24.5 Mile 

may be extrapolatable for some short distance upstream and 

downstream. Because wind conditions vary with local topography, however, extrapolation of these results for greater distances 

is not recommended, and any such extrapolation should be 

considered only speculative. However, because the orientation 

of the canyon around 24.5 Mile remains approximately constant 

(trending northeast and varying by ≤10° between river miles 

22.5 and 25.0), similar net eolian sediment transport could be 

anticipated for other sedimentary deposits between river miles 

22.5 and 25.0. Aerial photographs of the largest fluvial sandbar 

presently in that river reach (at river mile 23.5) indicate that 

this sandbar is now smaller and that vegetation in the area has 

increased since 1965 (fig. 13), similar to the changes apparent 

at 24.5 Mile. If a west-southwest dominant wind direction is 

assumed for 23.5 Mile, the small eolian deposit immediately 

northeast of the fluvial sandbar also is likely an MFS deposit in 

which sedimentation is linked to sand supply from the fluvial 

sandbar at 23.5 Mile. The eolian dune field at 23.5 Mile, which 

is approximately half the size of that at 24.5 Mile, was not 

investigated during this study.

The weather stations at 24.5 Mile from which data are 

reported here were removed in January 2006, and new weather 

stations were deployed in February 2007 at the same locations 

(24.5 L and 24.5 U, fig. 8) to monitor wind speed and direction, precipitation, temperature, relative humidity, barometric 

pressure, and eolian sand transport. Data from these new 

weather stations are not yet available.

Malgosa

The eolian dune field on the downstream, south side of the 

Malgosa Canyon debris fan (river mile 57.9, fig. 14) was one 

of the most active observed during this study. Wind direction 

there is most commonly aligned with the main canyon, from 

either the south-southeast or the north-northwest (figs. 15, 16). 

Wind records from Malgosa commonly show daily fluctuations in wind velocity, with higher-velocity, more consistently 

from the south-southeast in the afternoons (Draut and Rubin, 

2005, 2006). Wind gusts >20 m/s were frequent during 2004 

and 2005 in the upper part of the dune field (figs. 17, 18); daily 

sand-transport rates of about 10 to 100 g/cm were typical, 

and in May 2004 a 2-day event was recorded during which 

daily sand-transport rates were >4 kg/cm. Wind velocities 

Figure 13. Aerial photographs taken in May 1965 (A) and May 2004 (B) of 23.5 Mile area along the Colorado River corridor, Grand Canyon 

National Park, Ariz. (fig. 1). Riverflow in May 1965 was between 680 and 792 m3/s, and in May 2004 was 226 m3/s. Small eolian dune field shown 

in figure 13B. If dominant wind direction is assumed to be the same at both 23.5 Mile and 24.5 Mile, then eolian dune field is directly downwind 

from a fluvial sandbar.
35

high enough to transport sediment of the grain size found in 

the dune field at Malgosa (>2 m/s) blow dominantly from the 

south-southeast, such that the net sand transport direction is 

upstream with respect to the Colorado River. This dominant 

wind direction is consistent with the dune morphology on the 

south side of the Malgosa debris fan, which has north-facing 

slipfaces that indicate north dune migration. Therefore, the 

primary sediment source for this dune field is the fluvial sandbar immediately upwind of the dune field (sandbar a, fig. 14). 

A second sandbar, across the river and about 200 m downstream (sandbar b, fig. 14), also occasionally provides a minor 

amount of sediment to the dune field. (In May 2004, sand was 

observed to blow from sandbar b across the river into the dune 

field upstream of sandbar a.) The orientation of the eolian 

dunes with respect to fluvial sandbars, together with the dominant wind direction measured from November 2003 to January 

2006, implies that the dune field at Malgosa is an MFS deposit 

in which eolian sedimentation is directly linked to sediment 

supply from one or more fluvial sandbars upwind.

The higher riverflow in 1965 aerial photographs relative 

to those taken since the mid-1990s, and the generally low 

elevation of sandbars a and b today, make it difficult to compare fluvial-sandbar area between the two sets of photographs 

shown in figure 14. Aerial photographs do, however, show an 

increase in vegetation along the riparian zone and in the dune 

field at Malgosa itself in 2004 relative to 1965 (fig. 14). The 

increase in vegetation in the dune field since the 1960s suggests that the dunes have become less mobile. Dunes on the 

north side of Malgosa Creek (a tributary of the Colorado River 

that is dry except after recent heavy rain) can be considered 

inactive relative to those on the south side of Malgosa Canyon 

and have well-developed vegetation and biologic soil crust. 

The differences in dune surfaces between the north and south 

sides of Malgosa Creek are illustrated in figure 19. These 

differences are attributable to the trapping of eolian sand in 

the Malgosa Canyon channel between the two parts of the 

dune field—the southern dunes migrate north, but their sand is 

removed by episodic runoff in Malgosa Canyon before signifiFigure 14. Aerial photographs taken in May 1965 (A) and May 2004 (B) of Malgosa area along the Colorado River corridor in Grand Canyon National Park, Ariz. (fig. 1). Riverflow in May 1965 was from 680 to 792 m3

/s, and in May 2004 was 226 m3/s. Fluvial sand deposits (a and b). Red dots, 

weather stations Mal L (lower) and Mal U (upper). Most active area of eolian dune field on downstream side of Malgosa Canyon debris fan is 

indicated in figure 14B. Box in figure 14B indicates area of photograph in figure 19A. Note increase in riparian vegetation since 1965.

Appendix 1

A
36 The role of Eolian Sediment in the Preservation of Archeologic Sites Along the Colorado River Corridor

cant amounts of sand can reach the northern part of the dune 

field. Only sediment carried in suspension during high winds 

can be expected to reach the northern part of the dune field; 

sand carried north by saltation or reptation will be trapped 

in the tributary drainage and unavailable to the northern part 

of the dune field. Sand-transport rates were not measured in 

the dunes north of Malgosa Canyon during this study. The 

presence of substantial sand dunes on the northern part of the 

Malgosa debris fan, although they are now fairly inactive, suggests a greater sediment supply to the northern part of the dune 

field in the past than today.

A

B

575

237

20,400

81,600

15,300

326

219

2,720

1,180

167

814

36,714

22,303

54

9

353

A

B

241

49,101

9

379,280

434,920

586

46

11 ,136

13

80,900

259

702,000

176,000

380

13

22,100

Figure 15. Rose diagrams of sand-transport potential calculated from 

2 years of wind data collected at weather station Mal L (fig. 14B) 

along the Colorado River corridor in Grand Canyon National Park, Ariz. 

(fig. 1). Numbers for 2004 (A) and 2005 (B) are values of proxy variable Qp for each of eight directional half-quadrants, indicating total 

potential for eolian sediment transport from each compass sector. 

Vector sum of 2004 data, excluding period of inactivity from November 

17, 2004, to December 9, 2004, when weather station was temporarily dismantled and stored on higher ground during and shortly after 

November 2004 high-flow experiment, yields a net Qp value of 107,000 

m3/s3 from a direction of 132°; vector sum of 2005 data, ending when 

datalogger failed on September 19, 2005, yields a net Qp value of 

56,148 m3

/s3 from a direction of 154°.

Figure 16. Rose diagrams of sand-transport potential calculated from 

2 years of wind data collected at weather station Mal U (fig. 14B) 

along the Colorado River corridor in Grand Canyon National Park, Ariz. 

(fig. 1). Numbers for 2004 (A) and 2005 (B) are values of proxy variable 

Qp for each of eight directional half-quadrants, indicating total potential for eolian sediment transport from each compass sector. Vector 

sum of 2004 data yields a net Qp value of 757,000 m3

/s3 from a direction 

of 143°; vector sum of 2005 data yields a net Qp value of 725,880 m3

/s3

from a direction of 156°.
37

1

2

3

4

5

6

7

8 N D J F M A M J J A S O N D

5

10

15

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25 N D J F M A M J J A S O N D

10

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50 N D J F M A M J J A S O N D

N D J F M A M J J A S O N D

40

50 J F M A M J J A S O N D J

J F M A M J J A S O N D J

J F M A M J J A S O N D J

J F M A M J J A S O N D J

2

4

Vertical scale broken

2004 2005

YEAR

DAILY TOTAL RAINFALL, 

IN MILLIMETERS

DIURNAL MAXIMUM GUST,

IN METERS PER SECOND

DIURNAL AVERAGE WIND VELOCITY,

IN METERS PER SECOND

DAILY SAND TRANSPORT, 

IN GRAMS PER CENTIMETER

Figure 17. Rainfall, wind, and sand-transport data collected at weather station Mal L (fig. 14B) along the Colorado River corridor in Grand Canyon National Park, Ariz. (fig. 1) from November 2003 to January 2006. Record ended on September 19, 2005, when datalogger ceased to function. 

Daily sand transport is plotted in grams per day between ground surface and a height of 1 m (elevation of uppermost sand trap), normalized to 

a width of 1 cm. To obtain these values, sand mass collected from four traps during each maintenance visit was integrated over a width of 1 

m and divided by number of days since traps had last been emptied. Wind data from upper (2.0-m height) anemometer only are presented as 

diurnal average wind velocity and diurnal maximum gust, using daytime (0600–1800 h) and nighttime (1800–0600 h) averages of data collected at 

4-minute intervals. Daily total rainfall is summed over 24-hour intervals.

Appendix 1
38 The role of Eolian Sediment in the Preservation of Archeologic Sites Along the Colorado River Corridor

10

20

30

40

50 N D J F M A M J J A S O N D

5

10

15

20

25 N D J F M A M J J A S O N D

1

2

3

4

5

6

7

8 N D J F M A M J J A S O N D

50

100

150

4,000

5,000 N D J F M A M J J A S O N D

Ve rtical scale broken

J F M A M J J A S O N D J

J F M A M J J A S O N D J

J F M A M J J A S O N D J

J F M A M J J A S O N D J

= Minimum estima te

2004 2005

YEAR

DAILY SAND TRANSPORT, 

IN GRAMS PER CENTIMETER

DAILY TOTAL RAINFALL, 

IN MILLIMETERS

DIURNAL MAXIMUM GUST,

IN METERS PER SECOND

DIURNAL AVERAGE WIND VELOCITY,

IN METERS PER SECOND

Figure 18. Rainfall, wind, and sand-transport data collected at weather station Mal U (fig. 14B) along the Colorado River corridor in Grand 

Canyon National Park, Ariz. (fig. 1) from November 2003 to January 2006. Daily sand transport is plotted in grams per day between ground 

surface and a height of 1 m (elevation of uppermost sand trap), normalized to a width of 1 cm. To obtain these values, sand mass collected from 

four traps during each maintenance visit was integrated over a width of 1 m and divided by number of days since traps had last been emptied. 

Wind data from upper (2.0-m height) anemometer only are presented as diurnal average wind velocity and diurnal maximum gust, using daytime 

(0600–1800 h) and nighttime (1800–0600 h) averages of data collected at 4-minute intervals. Daily total rainfall is summed over 24-hour intervals. 

Sand-transport data collected in January 2005 and January 2006 (red circles) are minimum estimates because one or more sand traps had been 

deployed incorrectly.
39

Malgosa had not only the highest daily sand-transport 

rates measured at any study site but also the heaviest rainfall 

(figs. 17, 18). Annual rainfall at Malgosa totaled 270 mm 

in 2005, twice that measured at the next-nearest study site 

(Palisades, 12 km downstream). Heavy rainfall at Malgosa 

relative to other sites was common on an event-by-event basis. 

The marked differences between the rainfall at Malgosa and 

elsewhere are attributable to local topography, although this 

interpretation is poorly constrained, and only 26 months of 

rainfall data are available from this study, possibly not accurately representing long-term conditions. The Malgosa Canyon 

tributary trends northeast and drains the east side of the Walhalla Plateau, southeast of the main Kaibab monocline. The 

orientation of Malgosa Canyon and the drainage-basin geometry may affect movement of local weather systems, possibly 

funneling east-moving storms in a way that could account for 

the significantly heavier rainfall recorded near river level at 

Malgosa relative to other study sites (Draut and Rubin, 2006).

Although Malgosa received more rainfall than other areas 

of Grand and Marble Canyons during this study, the active 

dune field there is not incised by gullies. A few small ephemeral gullies were observed there that were rapidly filled by 

windblown sand, but they did not grow large enough to cause 

substantial erosion. This relation among precipitation, gully 

incision, and the restorative effects of eolian sand contrasts 

with the conditions at Palisades, as discussed in detail below, 

where major gullies occur in an area that received less rainfall 

than other study sites. Eolian sediment transport at Palisades, 

however, was no more than a tenth of that at Malgosa and so is 

apparently unable to heal gullies of the size now there.

The November 2004 controlled-flood experiment resulted 

in deposition of a major new sandbar at Malgosa (a, fig. 14) ≤2 

m thick and >10 m wide. High daily flow fluctuations for the 

first 3 months of 2005 eroded this sand deposit almost entirely. 

By May 2005, the new sandbar’s condition appeared almost 

identical to its preflood condition (fig. 7). Because the sandbar had eroded so significantly before the spring 2005 windy 

season began, it was not surprising that sand-transport rates 

measured at the weather stations in the Malgosa area in spring 

2005 were no higher than in spring 2004 (figs. 17, 18).

Palisades

We analyzed sedimentary profiles at Palisades (Palisades 

of the Desert), near river mile 66, in addition to deploying two 

weather stations there that measured wind velocity, rainfall, 

and sand transport from November 2003 to January 2006. 

Detailed discussions of these data (figs. 2A, 5A; table 1) were 

presented by Draut and others (2005). 

The Palisades area forms the upstream part of the geomorphic reach of the canyon described by Schmidt and Graf (1987) 

as the Furnace Flats reach. As discussed in the section above 

entitled “Overview of Sedimentologic and Geomorphologic 

Investigations,” the alluvial terraces in this river reach represent 

multiple episodes of floodplain aggradation in predam time, by 

distinct fluvial sedimentary structures in the studied profiles. 

The areal extent of fluvial deposits indicates that the entire 

terraced area at Palisades was submerged episodically during 

predam high flows (see Hereford and others, 1993, 1996; 

Hereford, 1996). No postdam flows (since 1963) have inundated most of the terrace. A stage-discharge relation determined 

from driftwood deposits indicated that the terraced area was 

almost entirely inundated by a riverflow of about 5,940 m3

/s 

(Draut and others, 2005; Hazel and others, 2006a), a flood level 

reached most recently in 1884. Reworking of fluvial sediment 

by wind was common in predam time, as evidenced by eolian 

deposits interbedded with fluvial deposits; eolian material was 

Figure 19. Zones within dune field at Malgosa along the Colorado River corridor in Grand Canyon National Park, Ariz. (fig. 1). A, Duneforms 

in background, north of the Malgosa Creek tributary (in midground), 

are covered with abundant grass and other vegetation; biologic 

soil crust also occurs there, indicating little active eolian sediment 

deposition. View northward (upstream with respect to the Colorado 

River) from top of a dune crest just south of tributary. B, Southern part 

of dune field (south of Malgosa Creek), where vegetation is much 

sparser than in area of figure 19A and daily sand-transport rates 

reach hundreds of grams per centimeter. 

Appendix 1
40 The role of Eolian Sediment in the Preservation of Archeologic Sites Along the Colorado River Corridor

also observed interbedded with “ponded,” playalike sediment 

deposits where slopewash runoff had formed small, isolated 

pools on the east side of the terrace. Aerial photographs indicate that vegetation in the terraced area has increased somewhat since 1965, while that in the riparian zone has increased 

substantially (fig. 20). Deepening of the now-substantial 

arroyo at Palisades (fig. 2A) since the 1960s is believed to have 

occurred after this local drainage breached predam alluvium 

exposures and eolian dunes in the late 1970s or early 1980s and 

began to drain directly to the Colorado River (Hereford and 

others, 1993; Thompson and Potochnik, 2000). 

Six of the nine archeologic sites at Palisades were formed 

in or on fluvial sediment, some of which had been reworked 

by wind (table 1; see Draut and others, 2005). Five of these 

nine archeologic sites are preserved at least partly by a cover 

of eolian sediment, with minor contributions from eolian sedimentary cover at two additional sites. Erosion associated with 

arroyo incision affects two of the archeologic sites. Exposure 

of cultural artifacts is attributable at least partly to eolian deflation at five of the archeologic sites at Palisades. 

The greater abundance of fluvial relative to eolian sediment in vertical profiles indicates that the eolian coppice dunes 

on the terrace surface apparently formed by wind reworking of 

the extensive predam flood deposits which underlie the Palisades area, and so the dune there is defined as an RFS deposit 

(fig. 4B; Hereford, 1996). Wind directions generally align with 

the north-south orientation of the river in this area, with winds 

blowing from either the north or the south, although the dominant wind direction at Palisades (at velocities great enough to 

transport sand) is from the south-southeast (figs. 21, 22; Draut 

and Rubin, 2005, 2006). Daily sand-transport rates were about 

1 g/cm within the coppice dunes but only about 0.1 g/cm on 

a cobble deposit at the river edge (figs. 23, 24). Given the 

dominant wind direction from the south-southeast, significant 

amounts of sediment are probably not transported by wind 

from river-level sandbars (see fig. 20 for locations) into the 

Figure 20. Aerial photographs taken in May 1965 (A) and May 2004 (B) of Palisades area along the Colorado River corridor in Grand Canyon 

National Park, Ariz. (fig. 1). Riverflow in May 1965 was between 680 and 792 m3/s, and in May 2004 was 226 m3/s. Fluvial sand deposits (a, b, and 

c). Red dots, weather stations Pal L (lower) and Pal U (upper). Most-active area of eolian dune field is indicated in figure 20B. Note increase in 

riparian vegetation and decrease in open sand area since 1965.
41

coppice dunes at Palisades. Although some migration of eolian 

dunes is apparent today in the northern part of the dune field, 

generally these dunes are relatively inactive, and vegetation 

and biologic soil crust are well established. 

Some new sediment probably is occasionally transported 

into the dune field from river-level sandbars (Yeatts, 1996); 

however, the net wind direction measured during this study 

indicates a probable net loss of sediment from this dune field 

northwest (where it can be lost into the river). As discussed 

above, gully and arroyo incision causes episodic additional 

erosion of eolian sediment at Palisades. Because the formation 

of this RFS deposit was linked to deposition of fluvial sediment during large, sediment-rich predam floods, substantial 

new sediment will probably not be supplied to the dune field 

at Palisades without similar large, sediment-rich floods in 

A

B

3,070

12,500

7,130

45,200

24,600

4,490

7,990

15,300

2,758

9,969

938

10,982

68,253

9,327

1,334

4,076

Figure 21. Rose diagrams of sand-transport potential calculated from 

2 years of wind data collected at weather station Pal L (fig. 20B) along 

the Colorado River corridor in Grand Canyon National Park, Ariz. (fig. 

1). Numbers for 2004 (A) and 2005 (B) are values of proxy variable Qp

for each of eight directional half-quadrants, indicating total potential 

for eolian sediment transport from each compass sector. Vector sum 

of 2004 data yields a net Qp value of 38,800 m3/s3 from a direction of 

149°; vector sum of 2005 data yields a net Qp value of 68,171 m3/s3 from 

a direction of 179°.

A

B

1,61 1

63,272

5,918

172,900

39,082

365

134

4,864

17,600

109,000

9,930

304,000

313,000

11,200

2,910

18,700

Figure 22. Rose diagrams of sand-transport potential calculated from 

2 years of wind data collected at weather station Pal U (fig. 20B) along 

the Colorado River corridor in Grand Canyon National Park, Ariz. (fig. 

1). Numbers for 2004 (A) and 2005 (B) are values of proxy variable Qp

for each of eight directional half-quadrants, indicating total potential 

for eolian sediment transport from each compass sector. Vector sum 

of 2004 data yields a net Qp value of 467,000 m3

/s3 from a direction 

of 155°; vector sum of 2005 data, collected while datalogger used a 

4-minute sampling interval (Jan. 1, 2005−Apr. 2, 2005, and Sept.18, 

2005−Jan. 14, 2006), yields a net Qp value of 154,890 m3/s3 from a direction of 132°.

Appendix 1
42 The role of Eolian Sediment in the Preservation of Archeologic Sites Along the Colorado River Corridor

1

2

3

4

5

6

7

8 N D J F M A M J J A S O N D

5

10

15

20

N D J F M A M J J A S O N D

5

10

15

20 N D J F M A M J J A S O N D J F M A M J J A S O N D J

2004 2005

N D J F M A M J J A S O N D

0.005

0.010

0.015

0.020

0.025 J F M A M J J A S O N D J

J F M A M J J A S O N D J

J F M A M J J A S O N D J

YEAR

DAILY TOTAL RAINFALL, 

IN MILLIMETERS

DIURNAL MAXIMUM GUST,

IN METERS PER SECOND

DIURNAL AVERAGE WIND VELOCITY,

IN METERS PER SECOND

DAILY SAND TRANSPORT, 

IN GRAMS PER CENTIMETER

Figure 23. Rainfall, wind, and sand-transport data collected at weather station Pal L (fig. 20B) along the Colorado River corridor in Grand Canyon National Park, Ariz. (fig. 1) from November 2003 to January 2006. Daily sand transport is plotted in grams per day between ground surface 

and a height of 1 m (elevation of uppermost sand trap), normalized to a width of 1 cm. To obtain these values, sand mass collected from four 

traps during each maintenance visit was integrated over a width of 1 m and divided by number of days since traps had last been emptied. Wind 

data from upper (2.0-m height) anemometer only are presented as diurnal average wind velocity and diurnal maximum gust, using daytime 

(0600–1800 h) and nighttime (1800–0600 h) averages of data collected at 4-minute intervals. Daily total rainfall is summed over 24-hour intervals.
43

Figure 24. Rainfall, wind, and sand-transport data collected at weather station Pal U (fig. 20B) along the Colorado River corridor in Grand Canyon 

National Park, Ariz. (fig. 1) from November 2003 to January 2006. In April 2005, datalogger began to malfunction, and rain gage ceased to function. 

Operation resumed on May 30, 2005, but with datalogger incorrectly programmed to record data every 4 hours instead of every 4 minutes. Datalogger was reprogrammed to record at 4-minute intervals on September 18, 2005, after which operation proceeded normally but without a functioning 

rain gage, until weather station was removed on January 14, 2006. Daily sand transport is plotted in grams per day between ground surface and a 

height of 1 m (elevation of uppermost sand trap), normalized to a width of 1 cm. To obtain these values, sand mass collected from four traps during 

each maintenance visit was integrated over a width of 1 m and divided by number of days since traps had last been emptied. Wind data from upper 

(2.0-m height) anemometer only are presented as diurnal average wind velocity and diurnal maximum gust, using daytime (0600–1800 h) and nighttime (1800–0600 h) averages of data collected at 4-minute intervals. Daily total rainfall is summed over 24-hour intervals.

5

10

15

20 N D J F M A M J J A S O N D

5

10

15

20

N D J F M A M J J A S O N D

1

2

3

4

5

6

7

8 N D J F M A M J J A S O N D

N D J F M A M J J A S O N D

2

4

6

8

10 J F M A M J J A S O N D J

Logging every 4 hour s

instead of 4 minutes

J F M A M J J A S O N D J

J F M A M J J A S O N D J

J F M A M J J A S O N D J

R ain gage not working after 4/2 /0 5

2004 2005

YEAR

DAILY TOTAL RAINFALL, 

IN MILLIMETERS

DIURNAL MAXIMUM GUST,

IN METERS PER SECOND

DIURNAL AVERAGE WIND VELOCITY,

IN METERS PER SECOND

DAILY SAND TRANSPORT, 

IN GRAMS PER CENTIMETER

Appendix 1
44 The role of Eolian Sediment in the Preservation of Archeologic Sites Along the Colorado River Corridor

the future. Controlled, sediment-rich Colorado Riverflows of 

about 1,270 m3/s can enlarge the fluvial sand deposits shown 

in figure 20 at least temporarily, and substantial deposition on 

sandbars (and in arroyo mouths) was documented at Palisades 

after high flows in 1996 (Yeatts, 1996) and 2004 (Draut and 

Rubin, 2006; Hazel and others, 2008). However, flows of that 

magnitude are unlikely to promote substantial eolian sediment 

transport into the dune field, given the dominant wind direction measured during this study and the positions of sandbars a 

through c (fig. 20) relative to the eolian dunes.

As mentioned above, during this study the annual rainfall 

measured at Palisades was significantly less than that measured 12 km upstream at Malgosa (in 2005, the 135 mm 

recorded at Palisades was less than half that measured at Malgosa; figs. 23, 24). Palisades had the least total annual rainfall 

of any study site, though similar to that measured nearby at 

Comanche (river mile 68, where 138 mm of rain fell in 2005). 

The much-studied arroyo at Palisades has, therefore, reached 

its advanced state of terrace incision despite its position in 

a reach of the Colorado River with relatively little rainfall, 

at least as measured during this 26-month study. Although 

many factors contribute to gully incision (including long-term 

climate, drainage-basin geometry, substrate composition, and 

effective base level), we infer that arroyo incision would not 

have progressed so far if eolian sediment transport within the 

Palisades terrace area were an order of magnitude greater than 

today. A short distance upstream, gullies are typically absent 

from the dune field at Malgosa—a site with twice the rainfall 

but 10 times the sand-transport rate at Palisades. Active eolian 

sediment transport at Malgosa more than accommodates the 

episodic gully incision there, and gullies (which act as natural 

traps for windblown sand) are quickly healed, similar to the 

situation observed at 24.5 Mile in January 2006 (Draut and 

Rubin, 2006). 

The weather stations at Palisades from which data are 

reported here were removed in January 2006. In February 

2007, a new weather station was deployed at Palisades dune 

field (Pal U, fig. 20) to monitor wind speed and direction, 

rainfall, temperature, relative humidity, barometric pressure, 

and sand transport. Data from this new weather station are not 

yet available.

Comanche

As discussed above, we analyzed sedimentary profiles 

at Lower Comanche (near river miles 68–69) in May 2004 

(fig. 5B). One weather station (Com; see Draut and Rubin, 

2005, 2006) measured wind velocity, precipitation, and sand 

transport in the northern part of the Lower Comanche area 

between April 2004 and January 2006. Detailed discussions 

of these data were presented by Draut and others (2005) (see 

figs. 2B and 5B and table 2).

The stratigraphy of the southern, arroyo-incised part 

of the Comanche area (that is, Lower Comanche) indicated 

multiple episodes of fluvial sedimentation, followed by 

reworking at the land surface by wind and local rainfall 

runoff. Eolian climbing ripples were present in some sedimentary deposits; much of the silt and fine sand did not 

contain preserved, diagnostic sedimentary structures. Colluvium (recognized by sandstone and shale clasts derived 

from local bedrock) was present in all six of the sedimentary 

profiles studied at Lower Comanche. Five of the six archeologic sites in the vicinity are within eolian dunes (table 2), of 

which four were originally on eolian sediment and the fifth 

was built on an interdune, playalike surface. Four archeologic sites were at least partly buried by eolian sediment, two 

of which have only minor sediment cover (<10 cm thick). 

Three of the five archeologic sites within the dune field are 

affected by active eolian deflation and dune migration. The 

one cultural site not in or among the large coppice dunes at 

Lower Comanche (site C:13:273, table 2) was constructed on 

a terrace that contained slopewash sediment interbedded with 

lighter colored, better sorted fine sand and silt with poorly 

preserved sedimentary structures that appeared to grade 

laterally into both fluvial and eolian deposits. 

On the basis of field relations between fluvial and eolian 

deposits, the eolian dunes in the Comanche area most likely 

originated from reworking of large, predam flood deposits—

some in place and some immediately southeast (upwind) of 

the dune area—similarly to those at Palisades. Therefore, the 

large eolian dune field at Comanche is defined primarily as an 

RFS deposit. The dominant wind direction (net potential sandtransport direction) identified for Comanche in 2004 and 2005 

is from the southeast, directed upstream (fig. 26). A substantial 

component of potential sediment transport is from the south, 

however, implying that some sediment from non-flood-stage 

fluvial deposits may reach the eolian dunes. If sand is indeed 

blown from river-margin sandbars (a, fig. 25), this sediment 

supply has probably diminished since the 1960s because the 

open sand area has decreased and riparian vegetation has 

increased between the sandbar and eolian dunes in postdam 

time (fig. 25). A decrease in open sand area and an increase in 

vegetation are similarly apparent at sandbar b (fig. 25), several 

hundred meters downstream and to the south-southeast of 

sandbar a, where the November 2004 controlled flood substantially increased the open sand area. The new flood sand 

was eroded so rapidly by high daily flow fluctuations in early 

2005 that 6 months after the flood, the state of the beach was 

virtually identical to that before the flood (Draut and Rubin, 

2006). Postflood daily sand-transport rates during the spring 

2005 windy season were higher, however, than in spring 2004, 

by a factor of ≤2 (daily sand-transport rates in this dune field 

are typically about 0.1 g/cm, reaching >1 g/cm during spring 

winds; fig. 27).

Given the proximity of Palisades to Comanche (about 

5 km apart), the consistent north-south orientation of the 

main canyon between them, and the similar south-southeast 

dominant wind direction measured in both areas, we can 

reasonably extrapolate similar net eolian-sediment-transport 

pathways for the reach of the Colorado River corridor 

between these two areas. Few fluvial sandbars occur on river 
45

right (west bank) in that reach, except for a small deposit at 

the Lava-Chuar campsite (river mile 65.3). Open sand area 

is greater on river left (east bank), with some fluvial deposits from which sand is likely remobilized and transported 

predominantly north-northwest. The dominant sand-transport 

direction calculated for both Palisades and Comanche is such 

that new fluvial deposits left by riverflows of about 1,270 

m3/s will probably not act as major sand sources for adjacent 

dune fields on river left. Instead, in those areas and presumably along the intervening approximate 5 km of the Colorado 

River corridor, the net sand-transport direction from fluvial 

sandbars on river left is upstream and to the river, where 

windblown sand would become entrained in the water. 

Immediately downstream of Lower Comanche, the 

canyon widens and makes several tight bends in the Tanner 

area (river miles 69–71). Given the substantial topographic 

variations between Comanche and Tanner, we cannot reasonably extrapolate a similar north-northwest dominant sandtransport direction downstream of Lower Comanche, where 

wind conditions would need to be measured independently to 

identify eolian-sediment-transport pathways in that area. Data 

from two weather stations deployed at river mile 70 in early 

2007 should clarify sand-transport rates and directions in that 

reach of the Colorado River corridor.

Because many of the archeologic sites in the Comanche area are associated with eolian sediment that locally 

is apparently sourced from predam and, to a lesser extent, 

postdam fluvial deposits, the occurrence or nonoccurrence of 

sediment-rich floods is linked to sedimentary processes in the 

dune field, likely affecting the preservation of archeologic 

Figure 25. Aerial photographs taken in May 1965 (A) and May 2004 (B) of Comanche area along the Colorado River corridor in Grand Canyon 

National Park, Ariz. (fig. 1). Riverflow in May 1965 was between 680 and 792 m3

/s, and in May 2004 was 226 m3/s. Fluvial sand deposits (a and b) 

red dot, weather station Com. Modern extent of eolian dune field is indicated in figure 25B. Note increase in riparian vegetation and decrease in 

open sand area since 1965.

Appendix 1
46 The role of Eolian Sediment in the Preservation of Archeologic Sites Along the Colorado River Corridor

sites there. As with several other large eolian dune fields in 

Grand Canyon, however (see discussion of site 3 in the subsection above entitled “Three Case Studies”), it is uncertain 

whether the archeologic sites at Comanche would be better 

preserved if new flood sediment were available to be blown 

into the dune field, because many of these sites are naturally exposed by dune migration over time. If the dune field 

at Comanche is significantly affected by sediment-supply 

limitation in the future (that is, by the effects of dam operations), vegetation and biologic soil crust will increase in this 

dune field, indicating a decrease in mobility of the eolian 

sediment composing the dunes. Continued monitoring and 

topographic surveys of dunes by the National Park Service 

would indicate whether, and how rapidly, dune migration and 

sand transport occur. As eolian sediment transport decreases 

in a sediment-supply-limited dune field and dune-migration 

rates correspondingly decrease, the risk of archeologic-site 

destabilization by dune migration is diminished. However, 

although cultural artifacts then will less likely be disturbed 

by dune migration, the risk of site erosion by gully incision 

will increase because with less sand transport, gullies that 

form during rain runoff will have less opportunity to be filled 

by eolian sand. 

Forster

The study site at the mouth of Forster Canyon (river 

mile 123.0) is in an eolian dune field south-southwest of a 

small fluvial sand deposit opposite the tail waves of Forster 

rapid (sandbar a, fig. 28). Higher riverflow in aerial photographs taken in 1965 relative to those taken in the 1990s and 

2000s makes it difficult to determine accurately changes in 

the area of the sandbars at Forster (a−c, fig. 28), although the 

more recent photographs clearly show an increase in riparian 

vegetation covering a formerly open sand area. 

One weather station deployed in the eolian dune field 

at Forster from April 2004 to January 2006 had multiple 

equipment failures related to adverse conditions caused by 

high winds and abundant windblown sand. During its operation, however, the station recorded wind directions almost 

exclusively from the north and northeast (oriented up the 

axis of Forster Canyon, perpendicular to the trend of the 

Colorado River in this area), with a dominant wind direction 

from the north-northeast (fig. 29). Therefore, the eolian dune 

field at Forster (figs. 5A and 28B) is directly downwind of 

the fluvial sand deposit (sandbar a, fig. 28) and is defined as 

an MFS deposit. Daily sand-transport rates within this dune 

field were among the highest measured during this study 

(commonly >100 g/cm, fig. 30), and the sand surface was 

observed to aggrade and deflate repeatedly at the weather 

station by tens of centimeters on a time scale of weeks. 

Forster was the site of the highest wind speed measured 

during this study, a gust in July 2004 of 29 m/s. Aside from 

the main dune field at Forster, eolian sediment also occurs at 

elevations tens of meters above the river, where the sediment is deposited on a steep, vegetated, sloping canyon wall 

on the south side (left bank) of the river. These eolian slope 

deposits, which are visible at the bottoms of figures 28A and 

28B and shown obliquely in figure 28C, are downwind of 

the sandbars (a−c, fig. 28) and assumed to have been sourced 

from them. If those three fluvial deposits serving as sand 

2,324

4,125

750

6,816

11 ,423

1,695

81

215

A

B

1,710

9,270

2,720

10,900

4,550

104

93

1,320

Figure 26. Rose diagrams of sand-transport potential calculated 

from wind data collected at weather station Com (fig. 20B) along the 

Colorado River corridor in Grand Canyon National Park, Ariz. (fig. 1) 

from April 2004 to January 2006. Numbers for 2004 (A) and 2005 (B) 

are values of proxy variable Qp for each of eight directional halfquadrants, indicating total potential for eolian sediment transport from 

each compass sector. Vector sum of April–December 2004 data yields 

a net Qp value of 10,200 m3

/s3 from a direction of 98°; vector sum of 

2005 data yields a net Qp value of 13,308 m3/s3 from a direction of 153°.
47

5

10

15

20

N D J F M A M J J A S O N D

5

10

15

20 N D J F M A M J J A S O N D

N D J F M A M J J A S O N D

N D J F M A M J J A S O N D J F M A M J J A S O N D J

1

2

3

4

5

J F M A M J J A S O N D J

J F M A M J J A S O N D J

J F M A M J J A S O N D J

1

2

3

4

5

2004 2005

YEAR

DAILY TOTAL RAINFALL, 

IN MILLIMETERS

DIURNAL MAXIMUM GUST,

IN METERS PER SECOND

DIURNAL AVERAGE WIND VELOCITY,

IN METERS PER SECOND

DAILY SAND TRANSPORT, 

IN GRAMS PER CENTIMETER

Figure 27. Rainfall, wind, and sand-transport data collected at weather station Com (fig. 20B) along the Colorado River corridor in Grand Canyon 

National Park, Ariz. (fig. 1) from April 2004 to January 2006. Daily sand transport is plotted in grams per day between ground surface and a 

height of 1 m (elevation of uppermost sand trap), normalized to a width of 1 cm. To obtain these values, sand mass collected from four traps 

during each maintenance visit was integrated over a width of 1 m and divided by number of days since traps had last been emptied. Wind data 

from upper (2.0-m height) anemometer only are presented as diurnal average wind velocity and diurnal maximum gust, using daytime (0600–

1800 h) and nighttime (1800–0600 h) averages of data collected at 4-minute intervals. Daily total rainfall is summed over 24-hour intervals.

Appendix 1
48 The role of Eolian Sediment in the Preservation of Archeologic Sites Along the Colorado River Corridor

sources were enlarged, it is probable that new eolian sediment in turn also would accumulate in the dune field and on 

eolian deposits of the adjacent canyon-wall slope.

Aerial photographs taken before and after the 1996 

controlled-flood experiment show an increase in the area of 

one sandbar (a, fig. 28) at the upstream end of the dune field 

at Forster. Although the schedule of flood-related fieldwork 

did not permit this beach to be photographed immediately 

before or after the November 2004 controlled flood, visual 

observations, including a shallow sedimentary profile dug in 

early 2005, indicated that new sand was deposited there as a 

result of this flood. High daily flow fluctuations from January to March 2005 caused partial erosion of the new flood 

deposit, such that tamarisk roots were exposed in March 

2005 that had not been visible before the November 2004 

flood. Sand-transport rates measured during the spring 2005 

windy season were significantly higher than those measured 

in spring 2004 (fig. 30), but sand-trap malfunctions during 

spring 2004 and anemometer malfunctions in spring 2005 

prevented thorough comparison of preflood and postflood 

spring wind conditions and sand transport at Forster.

Known archeologic sites in the Forster area include 

several sites built on and buried by eolian sediment. Dune 

migration causes many cultural artifacts to be exposed and 

covered repeatedly. Because this MFS deposit is unusually active, with frequent high winds that move significant 

Figure 28. Aerial photographs taken in May 1965 (A), May 2004 (B), and April 2004 (C ) of area by mouth of Forster Canyon along the Colorado 

River corridor in Grand Canyon National Park, Ariz. (fig. 1). Riverflow in May 1965 was between 680 and 792 m3

/s, and in May 2004 was 226 m3/s. 

Fluvial sand deposits (a, b, and c; sandbar c is mostly obscured by high flow in 1965 photograph). Red dot, weather station For. Modern extent 

of eolian dune field is indicated in figure 28B. In figure 28C, light-colored eolian deposits on slopes above river, downwind from fluvial sand 

deposits. (Dominant wind direction at Forster is from north-northwest.) View southwestward toward river left near sandbar b. Note increase in 

riparian vegetation and decrease in open sand area since 1965.
49

amounts of sand, sediment supply to the dune field at Forster is strongly linked to the amount of sediment available at 

the upstream sandbar (a, fig. 28). Forster is an area of Grand 

Canyon where the canyon orientation changes substantially 

within several kilometers of the study site; therefore, a dominant north-northeast wind direction should not be assumed 

for other areas upstream and downstream.

202.9 Mile

One weather station on river right (west bank, river 

mile 202.9) operated from April 2004 to January 2006. The 

study site (fig. 1) includes an eolian dune field near river 

level that is covered by trees and abundant other vegetation. 

The heavy vegetation has grown on the dune field and on a 

large river-level sandbar (a, fig. 31) just downstream from 

the dune field since the 1960s and now covers much of what 

was previously an open sand area. Immediately upstream 

of the weather station, an eolian dune field shows evidence 

of erosion by deflation, some biologic soil crust, and gully 

incision. The purpose of monitoring this site was to identify 

the sand source for the eroding, high-elevation dune field 

by measuring the dominant wind direction that could cause 

sand transport. Identifying the sand source could establish 

the degree to which vegetation encroachment downstream 

of the site may have affected the condition of the upper dune 

field by limiting eolian sediment transport from its sand 

source.

Data collected from April to December 2004 at 202.9 

Mile indicated that the dominant sand-transport direction 

was north (from downstream, fig. 32). Those initial data 

supported the hypothesis that the large sandbar (a, fig. 

31) formerly provided a sand source to the dune field on 

the debris fan, implying, in turn, that reduction in sandentrainment potential from the newly vegetated sandbar had 

affected or could affect the condition of the eolian deposits 

downwind (upstream) of this sandbar. Wind conditions 

there in 2005, however, indicated a more complex situation. 

Although upstream and downstream winds nearly balanced 

each other at the study site in 2005, a tertiary component 

from the northwest yielded a vector sum showing net sand 

flux to the river (figs. 32, 33). Thus, the longer record now 

available from 202.9 Mile suggests that although the loss of 

a potential sand source (the now-vegetated sandbar) downstream from this site may affect the condition of the dune 

field, the sediment supply from other sources could also 

affect eolian deposition and erosion processes there. The net 

vector sums of Qp values from 2005 wind data (1,286 m3

/

s3 from 283°) indicated a weaker sand-transport potential to 

the east, however, than to the north, as implied by the net 

vector sum of Qp values from 2004 wind data (2,160 m3/s3

from 194°). Deployment of a new weather station at 202.9 

Mile in March 2007 could clarify the eolian-sediment-transport regime at this site by providing longer-term wind data.

B

60,638

44,404

328

49

145

24

35

45

A

106,000

117,000

239

295

617

173

87

431

Figure 29. Rose diagrams of sand-transport potential calculated 

from wind data collected at weather station For (fig. 28B) along the 

Colorado River corridor in Grand Canyon National Park, Ariz. (fig. 

1) from April 2004 to January 2006. High winds caused repeated 

problems during weather-station operation, resulting in data gaps of 

several hours to months (see fig. 30). Numbers for 2004 (A) and 2005 

(B) are values of proxy variable Qp for each of eight directional halfquadrants, indicating total potential for eolian sediment transport from 

each compass sector. Vector sum of 2004 data yields a net Qp value 

of 219,000 m3

/s3 from a direction of 21°; vector sum of data for two extensive intervals of normal operation during 2005 (Jan. 1, 2005−Apr. 3, 

2005, and Sept. 20, 2005−Dec. 31, 2005) yields a net Qp value of 101,070 

m3

/s3 from a direction of 26°.

Appendix 1
50 The role of Eolian Sediment in the Preservation of Archeologic Sites Along the Colorado River Corridor

J F M A M J J A S O N D J

4

8

12

16

20

24

28

32 N D J F M A M J J A S O N D

4

8

12

16

20

24

28

32 N D J F M A M J J A S O N D

1

2

3

4

5

6

7 N D J F M A M J J A S O N D

N D J F M A M J J A S O N D

J F M A M J J A S O N D J

J F M A M J J A S O N D J

J F M A M J J A S O N D J

2004 2005

100

200

300

400

500

700

600

YEAR

DAILY TOTAL RAINFALL, 

IN MILLIMETERS

DIURNAL MAXIMUM GUST,

IN METERS PER SECOND

DIURNAL AVERAGE WIND VELOCITY,

IN METERS PER SECOND

DAILY SAND TRANSPORT, 

IN GRAMS PER CENTIMETER

Figure 30. Rainfall, wind, and sand-transport data collected at weather station For (fig. 28B) along the Colorado River corridor in Grand Canyon 

National Park, Ariz. (fig. 1) from April 2004 to January 2006. High winds caused repeated problems during weather-station operation, resulting 

in data gaps of several hours to months. Red dots, sand-trap data points that are only minimum estimates of sand transport because during 

those maintenance visits, lowermost trap was completely filled with sand. Daily sand transport is plotted in grams per day between ground 

surface and a height of 1 m (elevation of uppermost sand trap), normalized to a width of 1 cm. To obtain these values, sand mass collected from 

four traps during each maintenance visit was integrated over a width of 1 m and divided by number of days since traps had last been emptied. 

Wind data from upper (2.0-m height) anemometer only are presented as diurnal average wind velocity and diurnal maximum gust, using daytime 

(0600–1800 h) and nighttime (1800–0600 h) averages of data collected at 4-minute intervals. Daily total rainfall is summed over 24-hour intervals.
51

Arroyo Grande

Arroyo Grande is on land managed jointly by the Hualapai Nation and the National Park Service. The study site covered an area of about 250 m by 70 m; the nearest side-canyon 

tributaries enter the Colorado River >1 km upstream and 300 

m downstream of the study site (fig. 2C). A large eddy is 

present on river left (north bank) in the Arroyo Grande area 

even at nonflood stage. An arroyo network, ≤5 m deep, has 

incised two levels of predam alluvial terraces in this area 

(fig. 2C; white arrow, fig. 34). Eolian coppice dunes, most 

of which are now relatively inactive, with sparse vegetation 

and biologic soil crust, are present on the terraces. Terrace 

surfaces are deflated, as indicated by exposed plant roots and 

the formation of pedestals containing pebbles and cultural 

artifacts ≤5 cm above the surrounding land surface. Four 

archeologic-site complexes are present in alluvial-terrace and 

tributary-delta parts of the Arroyo Grande area, the largest of 

which (site G:03:064, table 3) is affected by the arroyo. The 

study site contains 15 documented cultural features on the 

land surface and several additional features exposed within 

the arroyo walls (table 3).

Colorado River flood deposits dominate the stratigraphic record around the largest archeologic site complex 

(site G:03:064, table 3) at Arroyo Grande. Sedimentary 

profiles within the upper terrace (fig. 2C) indicated that the 

proportion of fluvial sediment generally increases to the 

river. The record of flood deposition is best preserved in 

sedimentary profiles nearest to the river, with 15 individual 

flood events evident in one profile (Draut and others, 2005). 

All the profiles showed evidence of subaerial reworking and 

incorporation of colluvial and slopewash sediment between 

floods. The repeated occurrence of fluvial deposits overlain 

by subaerial sediment led to the description of a “flood couplet” facies consisting of a lower fluvial and an upper subaerial member (Draut and others, 2005, 2008). Bioturbation 

Figure 31. Aerial photographs taken in May 1965 (A) and May 2004 (B) of 202.9 Mile area along the Colorado River corridor in Grand Canyon National Park, Ariz. (fig. 1). Riverflow in May 1965 was between 680 and 792 m3

/s, and in May 2004 was 226 m3/s. Large fluvial sand deposit (a); red 

dot, weather station 202.9. Modern extent of eolian dune field, on downstream (south) side of a small debris fan, is shown is figure 31B. Dominant wind direction varies widely at 202.9 Mile, with calculations yielding a net potential for eolian sediment transport from the south-southwest 

in 2004 and from the west in 2005. Note increase in riparian vegetation and decrease in open sand area since 1965.

Appendix 1
52 The role of Eolian Sediment in the Preservation of Archeologic Sites Along the Colorado River Corridor

and the presence of lithic clasts in the upper parts of flood 

couplets (derived from local gneissic bedrock) indicated 

reworking of flood sediment at the land surface. Similar to 

the Lower Comanche site, the channel-fill deposits exposed 

at Arroyo Grande indicate multiple episodes of gully formation and filling during past subaerial exposure. Eolian sediment constituted a relatively minor volume in the measured 

sections. The most likely sediment source for the small, 

deflated coppice dunes visible on the land surface today is 

from reworking of the extensive fluvial deposits that created 

the terrace morphology in the area. Therefore, the eolian 

dunes at Arroyo Grande, as at Palisades, can be considered 

relict features that formed by in-place eolian reworking of 

large, predam flood deposits, and so this dune field is defined 

as an RFS deposit.

The abundance of charcoal and ash material in many 

strata at Arroyo Grande is attributable to grass fires during 

times of subaerial exposure, which probably were deliberately set by the inhabitants in the area, although lightning 

strikes could also have caused occasional fires. The Hualapai 

and Southern Paiute Tribes, both with ancestral ties to the 

Arroyo Grande area, have cultural traditions that include the 

deliberate setting of grass fires to initiate seed germination 

and to prevent other, larger fires from starting (Jackson and 

Bullets, oral communs., 2004). The setting of grass fires was 

practiced at prescribed times of the year and continues today. 

Other possible reasons for deliberately set grass fires include 

hunting and warfare (Powell, 1878; Kelly and Fowler, 1986; 

Boyd, 1999).

Of the 16 cultural features that we examined at Arroyo 

Grande, 15 are exposed at the land surface (table 3); 14 

features were formed on the upper terrace surface, of which 

7 are within coppice dunes on the terrace surface and the rest 

partly covered by eolian sediment. Of the two cultural features not formed on the upper-terrace surface, one was built 

on colluvium near the land edge of the terrace, and the other 

(an unnamed site) was exposed within an arroyo wall. 

Comparison of aerial photographs taken in 1965 and 

2004 shows a substantial decrease in open sand area along 

several hundred meters of river left (north bank) in postdam 

time (even though the 2004 photographs were taken during 

a much lower riverflow; fig. 34), as well as a substantial 

increase in riparian vegetation. Although we did not derive a 

stage-discharge relation for the Arroyo Grande area, we estimate that a riverflow of about 5,660 m3

/s, a flood level last 

reached in 1884, would probably inundate the upper terrace 

(recognizing that stage-discharge relations are episodically 

altered when debris flows constrict the river channel and 

cause water to pool upstream of the constriction). Because 

the eolian dune field at Arroyo Grande is apparently an RFS 

deposit, on the basis of sedimentary profiles through the 

dunes and underlying terrace, the postdam absence of sediment supply to this terrace by floods has removed the major 

source of sediment to the eolian dunes as well. Although 

we do not know the extent to which lower-elevation fluvial 

sandbars (≤1,270-m3

/sstage) contributed windblown sand to 

the dunes in predam time, any eolian sediment probably does 

not reach the dune field from the small river-level sandbars 

still present in this area because thick riparian vegetation 

now separates the fluvial sandbars from the eolian dune 

field. Therefore, a riverflow of 1,270 m3

/s would probably 

50 m

219

3,542

44

182

3,946

448

0.22

1,293

A

B

578

1,780

74

1,390

2,730

1,810

67

1,400

Figure 32. Rose diagrams of sand-transport potential calculated 

from wind data collected at weather station 202.9 (fig. 31B) along the 

Colorado River corridor in Grand Canyon National Park, Ariz. (fig. 1) 

from April 2004 to January 2006. Numbers for 2004 (A) and 2005 (B) 

are values of proxy variable Qp for each of eight directional halfquadrants, indicating total potential for eolian sediment transport from 

each compass sector. Vector sum of 2004 data, excluding data gaps 

from September to November 2004 (see fig. 33), yields a net Qp value 

of 2,160 m3/s3 from a direction of 194°; vector sum of 2005 data yields a 

net Qp value of 1,286 m3/s3 from a direction of 283°.
53

4

8

12

16

N D J F M A M J J A S O N D

1

2

3

4

5 N D J F M A M J J A S O N D

5

10

15

20

N D J F M A M J J A S O N D J F M A M J J A S O N D J

No rain gage

6/10/05 to 9/2 2/05

2004 2005

J F M A M J J A S O N D J

J F M A M J J A S O N D J

YEAR

DAILY TOTAL RAINFALL, 

IN MILLIMETERS

DIURNAL MAXIMUM GUST,

IN METERS PER SECOND

DIURNAL AVERAGE WIND VELOCITY,

IN METERS PER SECOND

Figure 33. Rainfall and wind data collected at weather station 202.9 (fig. 31B) along the Colorado River corridor in Grand Canyon National Park, 

Ariz. (fig. 1) from April 2004 to January 2006. Data gaps were caused by animals chewing through cables and short-circuiting datalogger. No 

sand traps were used, and rain gage was not operational from June 10, 2005, to September 22, 2005. Daily sand transport is plotted in grams per 

day between ground surface and a height of 1 m (elevation of uppermost sand trap), normalized to a width of 1 cm. To obtain these values, sand 

mass collected from four traps during each maintenance visit was integrated over a width of 1 m and divided by number of days since traps had 

last been emptied. Wind data from upper (2.0-m height) anemometer only are presented as diurnal average wind velocity and diurnal maximum 

gust, using daytime (0600–1800 h) and nighttime (1800–0600 h) averages of data collected at 4-minute intervals. Daily total rainfall is summed 

over 24-hour intervals.

not deposit new sediment that would blow into the dune field 

(although the dominant wind direction at Arroyo Grande 

was not measured during this study) because such dense 

vegetation separates the dune field from the river in almost 

every direction. The dominant direction of winds capable of 

transporting sand is likely from the east on the basis of the 

slipface orientation of a large, active dune at the east edge of 

the study site (Draut and others, 2005).

Appendix 1
54 The role of Eolian Sediment in the Preservation of Archeologic Sites Along the Colorado River Corridor

Figure 34. Aerial photographs taken in May 1965 (A) and May 2004 (B) of Arroyo Grande area along the Colorado River corridor in Grand 

Canyon National Park, Ariz. (fig. 1). Riverflow in May 1965 was between 680 and 792 m3/s and in May 2004 was 226 m3/s. Modern extent of eolian 

dune field, on downstream (south) side of a small debris fan, is indicated in figure 34B, along with location of arroyo (see fig. 2C ). Note great 

increase in riparian vegetation since 1965; extensive fluvial sand deposits visible in riparian zone in 1965 were no longer present as open sand 

areas in 2004, despite lower riverflow.
55

Introduction

A question remains regarding the evolution of eolian 

deposits along the Colorado River corridor in Grand Canyon 

National Park: to what extent has the sediment supply to 

individual sand deposits been limited by Glen Canyon Dam 

operations? Eolian sediment transport has always been somewhat restricted by confinement within this bedrock canyon—

dune fields can become only so large before reaching canyon 

walls, the river, large talus piles, and other spatial limitations. 

This study indicates, however, that eolian sediment transport 

is now more limited than in predam time because the supply 

of windblown sand to some eolian deposits (particularly MFS 

deposits) increases or decreases in response to changes in 

fluvial-sandbar area upwind. Dam operations are known to 

have reduced the area, volume, and number of fluvial sandbars 

overall. 

We have investigated whether eolian-sediment-transport 

models (based empirically on field and wind-tunnel experiments) can be used to discern sediment-supply limitation from 

field measurements of wind velocity and sand transport. If 

the sand flux predicted under given wind conditions closely 

matches that measured under the same conditions in the field, 

where sediment supply is not limited by sand availability, soil 

crusts, vegetation, or bed roughness, then sediment-supply 

limitation might be inferable in other field settings where the 

same models consistently overpredict measured sand flux. Thus, 

the inferred sediment-supply limitation could be caused by one 

or more factors (unavailability of sand, presence of vegetation or soil crusts, bed roughness), and further study would be 

needed to identify which possible causes were relevant. The 

experiments discussed here were conducted as part of the Grand 

Canyon eolian-sedimentation study but involved fieldwork in 

the Dumont Dunes of southern Death Valley, Calif., as well as 

in Grand Canyon National Park, Ariz. 

We tested eight eolian-sediment-transport models (table 4) 

in an experiment in the Dumont Dunes, a desert environment 

with essentially unlimited open sand area and without vegetation or soil moisture, factors that commonly affect comparable 

studies conducted in coastal sand dunes. Comparison of the 

measured sand flux with those predicted by the various models 

indicates that although these eight models may perform better 

in this field setting, where sources of uncertainty have been 

minimized, generally the models did not yield results accurate 

enough to suggest their use in discerning sediment-supply limitation, likely partly owing to the limited range of wind velocities 

measured during the experiment. Subsequent high-resolution 

tests in the dune field at Malgosa (river mile 57.9, fig. 1) provided a greater range of wind velocities, but the physically more 

complex setting (canyon walls, vegetation, steeply sloping dune 

face) were such that the data were not obtained under simple, 

supply-unlimited conditions, as at the Dumont Dunes. Thus, the 

use of eolian-sediment-transport models to discern sedimentsupply limitation needs further study; multiple avenues of environmental management could benefit from such deterministic 

models, through which the effects of sediment-supply limitation 

could be quantified.

Eolian-Sediment-Transport Models

Measurement and prediction of eolian sediment transport is a primary focus of many geologic and agricultural 

studies. An accurate understanding of the movement of sand 

and dust by wind has widespread practical implications for 

predicting landform evolution and erosion in agricultural 

areas and for guiding environmental management of coastal 

and desert regions. Numerous studies, beginning with that by 

Bagnold (1941), have devised empirical relations between 

wind conditions and resulting sediment motion; Bagnold’s 

and other transport equations have been applied and tested in 

wind-tunnel and field settings with the goal of being utilized 

as predictive models. 

Many comparative studies have indicated, however, that 

the application of commonly cited eolian-sediment-transport 

models in the field is problematic and that measured sand 

flux may deviate substantially from that predicted by models 

(Hunter and others, 1983; Berg, 1983; Sarre, 1988, 1989; 

Bauer and others, 1990, 1996; Goldsmith and others, 1990; 

Sherman and Hotta, 1990; Sherman and others, 1998; Craig, 

2000). Assessment of the discrepancies between predicted and 

measured sand fluxes prompted Chapman (1990) and Bauer 

and others (1996) to suggest that field-based eolian-sedimenttransport investigations involve serious uncertainties owing 

to the large number of physical factors affecting such complex systems relative to the number of variables represented 

in existing transport equations. Studies of sand transport on 

coastal dunes have identified such complexities as vegetative 

cover, soil moisture, topographic slope, variations in sediment 

composition and grain size, presence of salt crystals in sand, 

and variations in sand-source area due to tidal fluctuations and 

runnel formation. As a result, testing of eolian-sediment-transAppendix 2. Evaluating the Predictive Power of 

Eolian-Sediment-Transport Models—Can SedimentSupply Limitation Be Discerned?

Appendix 2
56 The role of Eolian Sediment in the Preservation of Archeologic Sites Along the Colorado River Corridor

port models in coastal-dune settings is inherently complicated 

by spatiotemporal factors in such a setting (Baas and Sherman, 

2006).

One approach to field studies in a discipline prone to serious uncertainties, as proposed by Bauer and others (1996), is 

to minimize uncertainty by focusing on maximally simplified 

systems. By minimizing or eliminating the variables that are 

known to exacerbate uncertainties in eolian-sediment-transport 

investigations, the predictive power of standard transport 

equations can be evaluated more accurately. Recognizing that 

sources of uncertainty probably cannot be entirely eliminated, 

we tested eight eolian-sediment-transport models in a desert 

sand-sheet environment where the above-mentioned complexities are minimal or absent. In so doing, we evaluated whether 

the predictive power of these models is sufficient to discern 

sediment-supply limitation.

Sediment-Supply Limitation

Existing transport equations were developed under the 

assumption that sand flux is limited by wind conditions (wind 

velocity and, therefore, bed shear stress required to mobilize 

sediment). Eolian sediment transport and erosion are commonly affected by sediment-supply limitations; however, this 

factor is not incorporated into current models (Leys, 1999). As 

a result, (1) the predictive power of current eolian-sedimenttransport models will decrease as a given sand source is 

diminished by erosion over time, (2) discrepancies between 

predicted and measured sand flux may in some places be 

attributable to limited availability of sediment for transport, 

and (3) identification and quantification of sediment-supply 

limitation may be possible from analyzing those discrepancies. 

This investigation was particularly motivated by implications 

2 and 3. By first evaluating the predictive power of existing 

eolian-sediment-transport models in a supply-unlimited desert 

setting unaffected by variables that can influence sand fluxes 

measured elsewhere, we evaluated the usefulness of these 

models for discerning sediment-supply limitation.

Model Testing

Most of the commonly used eolian-sediment-transport 

models incorporate a shear velocity term, u* , which is defined 

as a function of shear stress [ , where is the 

boundary shear stress and is the fluid density]. Shear velocities are typically calculated from wind profiles by using the 

Karman-Prandtl equation, or “law of the wall”:

 (2)

where u(z) is the wind velocity (in meters per second) at 

height z, κ is von Karman’s constant (taken to be 0.4), and z0

is the roughness length (in meters) of the sand surface. Shear 

velocity is considered relative to a critical threshold of motion 

or threshold shear velocity u*t , given by Bagnold (1941) as

 (3)

where At is a dimensionless constant equal to 0.1 for the 

initiation of saltation (Bagnold’s fluid threshold), ρs and ρ are 

the densities of quartz sediment and air (2,650 and 1.2 kg/m3, 

respectively), g is the gravitational acceleration (9.8 m/s2), and 

d is the sediment grain size (in meters).

The eight eolian-sediment-transport models tested in this 

study are listed in table 4. The empirical models of Bagnold 

(1941) and Zingg (1953), based on wind-tunnel experiments, 

are of the same form but differ in the dimensionless constant 

and exponent. Kawamura’s (1951) model, also based on 

wind-tunnel experiments, first incorporated the threshold shear 

velocity 

� 

u*t into an eolian-sediment-transport model. Lettau 

and Lettau’s (1977) and White’s (1979) models, as well as 

Sørensen’s (1991) equation, the derivation of which incorporates sand-grain trajectories and grain-bed collision processes, 

also use threshold shear-velocity terms. Except for Lettau and 

Lettau’s (1977) models, equations of this form do not require 

a separate term for grain size because 

� 

u*t is itself a function 

of particle diameter. Hsu (1971, 1973) used a modified Froude 

number (of the form u/(gd)n) to express eolian-sedimenttransport rate. Among these eight models, Williams’ (1964) 

model alone describes sand flux, q, as a linear function of u*

. Several models exist that do not depend on shear velocity, 

for example, Kadib’s (1965) model, which uses a normally 

distributed transport-intensity function, and O’Brien and Rindlaub’s (1936) model, which does not include a grain-size term 

but depends solely on the cube of wind velocity measured at 

1.52-m height. We restricted our analysis to the models listed 

in table 4 because Kadib’s (1965) model has been found to 

be less reliable than equations that rely on u* , particularly at 

high wind velocities (Sarre, 1988; Sherman and others, 1998), 

and because u* represents flow characteristics (that is, shear 

affecting the bed, which determines sediment motion) independent of the height of measurement. 

Experimental Methods

We conducted an experiment in the Dumont Dunes at the 

south end of Death Valley in the Mojave Desert, Calif., in late 

February 2004. The dune field occupies an area of about 20 

km2

 and contains central star dunes, >100 m tall, with lower 

barchan and linear dunes at its margins (McDonald, 1970; 

Nielson and Kocurek, 1987). A sand sheet at its north edge 

provided an ideal site to collect sand-transport data in an area 

unaffected by vegetation or other bed-roughness elements 

(other than wind ripples, footprints, and vehicle tracks, all 

u z

u z

z

( ) ln , * = κ 0

, 
57

<10 cm high). Instruments were deployed in a relatively flat 

area to minimize the effect of surface slope on wind velocity. 

Soil moisture was not detected in the surface sediment and is 

generally negligible in this arid environment.

The experiment at the Dumont Dunes was conducted 

during a 16-hour interval. Wind velocity was measured by 

using three spinning-cup anemometers mounted on an instrument tripod at heights of 2.0, 1.0, and 0.3 m and connected 

to a datalogger (fig. 35). Mean wind velocity, maximum gust 

velocity, and mean wind direction were measured at a 1-Hz 

sampling interval and recorded as 10-s averages. This sampling strategy used the shortest averaging interval over which 

the statistical reliability of shear-velocity measurements can be 

retained (Namikas and others, 2003; see Anderson and others, 

1991). 

An array of sand traps was set up 5 m from the anemometer tripod to collect windblown sand (see Zobeck and others, 

2003). Four “big spring number eight” (BSNE) sand traps 

(Fryrear, 1986) were mounted on a vertical pole; these sand 

traps are equipped with vanes to turn them into the wind. Sand 

traps were deployed with their orifice bases at heights of 1.0, 

0.7, 0.4, and 0.1 m (fig. 35). Air temperature was measured at 

heights of 2.0 and 0.3 m to evaluate local atmospheric instabilities caused by insolation heating, which may affect windvelocity profiles (Rasmussen and others, 1985; Lancaster and 

others, 1991; Frank and Kocurek, 1994). The measured temperature gradient was minor because thick cloud cover limited 

direct solar heating during the experiment. Because vertical 

motion of air due to solar instabilities is negligible relative to 

lateral motion at wind speeds high enough to generate sand 

transport (G. Kocurek, written commun., 2004; N. Lancaster, 

written commun., 2004), this factor is not considered further 

here.

The total sand mass collected from each trap during the 

experiment was weighed, and sand-transport rates were calculated by integrating a curve fitted to the mass-versus-height 

Reference Equation for calculating sand 

flux (q)

u*

(m/s)

Bagnold (1941) 0.6–1.8 

Kawamura (1951) N/A 

Zingg (1953) 0.35–1.06 

Williams (1964) 0.4–1.35 

Hsu (1971) 0.05–0.8 

Lettau and Lettau (1977) <0.32 

White (1979) 0.9–1.7 

Sørensen (1991) 0.2–0.6 

Table 4. Eolian-sediment-transport models tested in the Dumont Dunes in Death Valley, Calif., and the dune field at Malgosa 

at Grand Canyon National Park, Ariz. (fig. 1). 

[u*, shear velocity for which the equations were derived. d, grain size (in meters); D, reference grain size (in meters); for 250 μm-diameter sand; u*t

 , threshold 

shear velocity for motion of grain size considered; s and , densities of quartz sediment and air, respectively (taken to be 2,650 and 1.2 kg/m3

; g, gravitational 

acceleration (9.8 m/s2

). In Williams’ (1964) model, the constant is represented as the multiple of two constants obtained for 330 μm-diameter sand, slightly 

coarser than the 306 μm-diameter sand in this study. q value is expressed in all models as a mass of sand passing through a unit width in unit time (in kilograms 

per meter per second). For comparison with field data, q values were adjusted to reflect the 10-s averaging interval of wind data, and the 0.02-m width of the 

sand traps used. Bagnold’s (1941) model was based on wind-tunnel data and tested in desert dunes. Kawamura’s (1951), Zingg’s (1953), Williams’ (1964), and 

White’s (1979) models were based on wind-tunnel data. Hsu’s (1971) and Lettau and Lettau’s (1977) models were based on field studies. Sørensen’s (1991) model 

was analytically derived and tested in wind-tunnel experiments]

Appendix 2
58 The role of Eolian Sediment in the Preservation of Archeologic Sites Along the Colorado River Corridor

data. The curve-fitting procedure used a five-parameter combined power-law and exponential function, which has been 

shown to model vertical sand flux more accurately than either 

power-law or exponential fits alone (Sterk and Raats, 1996). 

Grain-size analysis of surface sand at the Dumont Dunes on a 

Coulter LS100Q laser diffraction particle-size analyzer yielded 

a d50 value of 305.8 μm (average of six analyses), which (from 

eq. 3) gives 

� 

u*t =0.257.

In May 2004, we conducted a similar experiment during 

2 days of high winds on the dune field at Malgosa (river mile 

57.9, fig. 1). One of the weather stations deployed at that 

site (Mal U; Draut and Rubin, 2005, 2006) was refitted to 

match the configuration used in the experiment at the Dumont 

Dunes, with anemometers at heights of 2.0, 1.0, and 0.3 m, 

BSNE sand traps at 1.0, 0.7, 0.4, and 0.1 m, and the datalogger 

recording with a 1-Hz sampling interval and a 10-s averaging 

interval (as opposed to the 4-minute averaging interval used 

during normal operation of that weather station). Two tests 

were performed at Malgosa, on May 11 and 12, 2004; sand 

traps were emptied at the end of each test. Sand in the dune 

field at Malgosa has a d50 value of 312.9 μm (average of four 

analyses), and the 

� 

u*t value is calculated to be 0.260. Using 

� 

u*t values, cumulative sand fluxes at the Dumont Dunes 

and Malgosa were predicted from wind data, using the eight 

models listed in table 4, and then compared with the sand 

fluxes measured at both study sites.

Results

The sand fluxes measured in the experiment at the 

Dumont Dunes and in both tests at Malgosa are compared with 

those predicted by each of the eight eolian-sediment-transport 

models (table 4) in table 5. In the 16-hour experiment at the 

Dumont Dunes, the mean sustained wind velocities recorded 

at 2.0-m height (averaged over 10-s intervals) were 3.6±1.6 

m/s, with gusts of ≤10.8 m/s. At those wind velocities, the 

efficiency range of BSNE sand traps is 105–115 percent 

Figure 35. Study site at the Dumont Dunes in the Mojave Desert, southern Calif., showing location of experiment in 

late February 2004. At left is a tripod on which three anemometers (at heights of 2.0, 1.0, and 0.3 m) and a datalogger were mounted; at right are four sand traps (at heights 1.0, 0.7, 0.4, and 0.1 m). Surrounding sand sheet was free 

of vegetation and nonerodible obstacles, such as rocks, and had little slope for tens of meters in any direction. Tire 

tracks and footprints created surface-roughness elements <10 cm high.
59

(Goossens and others, 2000). In the first test at Malgosa, 

which lasted 7 hours, mean sustained wind velocities recorded 

at 2.0-m height were 5.8±3.2 m/s, with gusts of ≤20.8 m/s; 

in the second test at Malgosa, which lasted 14.5 hours, mean 

sustained wind velocities at 2.0-m height were 3.1±1.9 m/s 

with gusts of ≤13.7 m/s. BSNE sand trap efficiency during 

both high-resolution experiments at Malgosa was considered 

to span an efficiency range of 95–115 percent (Goossens and 

others, 2000). Histograms of the u* values calculated for the 

duration of each experiment are shown in figure 36. 

Kawamura’s (1951) model predicted a cumulative sand 

flux that most closely approximates the measured sand flux 

in the experiment at the Dumont Dunes. Three other models 

overpredicted the sand flux: Bagnold’s (1941) model by a 

Sand flux (kg/m per second)

Dumont Dunes Measured 105-pct trap 

efficiency

115-pct trap 

efficiency

Measured transported sand (g) 61.8 58.9 53.7

Ratio of predicted to measured 

sand flux

Bagnold (1941) 1.47 1.54 1.69

Kawamura (1951) 0.856 0.898 0.985

Zingg (1953) 0.712 0.747 0.819

Williams (1964) 34.9 36.6 40.2

Hsu (1971) 2.29 2.41 2.64

Lettau and Lettau (1977) 0.430 0.452 0.495

White (1979) 0.406 0.426 0.467

Sørensen (1991) 0.241 0.253 0.277

Malgosa, test 1 Measured 95-pct trap 

efficiency

115-pct trap 

efficiency

Measured transported sand (g) 2,770 2,910 2,400

Ratio of predicted to measured 

sand flux

Bagnold (1941) 1.82 1.73 2.09

Kawamura (1951) 2.58 2.45 2.96

Zingg (1953) 0.880 0.840 1.01

Williams (1964) 17.3 16.4 19.8

Hsu (1971) 2.85 2.70 3.27

Lettau and Lettau (1977) 1.99 1.89 2.29

White (1979) 1.38 1.31 1.59

Sørensen (1991) 0.620 0.590 0.710

Table 5. Comparison of predicted sand flux with sand flux measured by using sand 

traps during experiments in the Dumont Dunes and the dune field at Malgosa. 

[Measured sand flux is given for each test as an integrated value for a height of 0 to 1 m, along with sand flux 

predicted from wind data measured at 10-s intervals. Modeled sand fluxes have been adjusted to account for 

the 10-s interval and 0.02-m width of sand trap orifices. Values are indicated for the possible range of measured 

sand fluxes, given the efficiency range of the sand traps used (105–115 percent during the study experiment in 

the Dumont Dunes and 95–115 percent for the tests in the dune field at Malgosa, Goossens and others, 2000)]

Appendix 2

Malgosa, test 2 Measured 95-pct trap 

efficiency

115-pct trap 

efficiency

Measured transported sand (g) 183 193 160.0

Ratio of predicted to measured 

sand flux

Bagnold (1941) 48.6 46.2 55.9

Kawamura (1951) 63.0 59.8 72.4

Zingg (1953) 23.6 22.4 87.5

Williams (1964) 603 574 694

Hsu (1971) 76.1 72.3 87.5

Lettau and Lettau (1977) 42.6 40.5 49.0

White (1979) 32.0 30.4 36.8

Sørensen (1991) 16.3 15.5 18.7
60 The role of Eolian Sediment in the Preservation of Archeologic Sites Along the Colorado River Corridor

factor of about 1.5 to 1.7 (given the sand-trap-efficiency 

range), Hsu’s (1971) model (which uses a modified Froude 

number) by a factor of >2, and Williams’ (1964) model by 

a factor of >30; and four other models underpredicted the 

observed sediment flux: Zingg’s (1953) model by about 18–25 

percent, both Lettau and Lettau’s (1977) and White’s (1979) 

models by 50–57 percent, and Sørensen’s (1991) model by 

72–75 percent.

In the first test at Malgosa, during which the total sand 

transport was nearly two orders of magnitude greater than in 

the experiment at the Dumont Dunes, all the models generally performed similarly, though with a greater tendency to 

overprediction (table 5). The model that most closely approximated the measured sand flux in the first test at Malgosa was 

Zingg’s (1953), which predicted about 84–101 percent of the 

measured value, given a sand-trap efficiency of 95–115 per0 0.2 0.4 0.6 0.8 1.0 1.2 1.4

500

0 0.2 0.4 0.6 0.8 1.0 1.2 1.4

200

400

600

800

1,000

1,200

1,400

1,600

0 0.2 0.4 0.6 0.8 1.0 1.2 1.4

200

400

600

800

1,000

1,200

1,400

1,600

FREQUENCY

FREQUENCY

FREQUENCY

SHEAR VELOCITY, IN METERS PER SECOND

A

B C

SHEAR VELOCITY, IN METERS PER SECOND

3,000

2,500

2,000

1,500

1,000

Figure 36. Histograms of shear velocity (u

*

) measured during experiment at the Dumont Dunes in the Mojave Desert, southern Calif., and two 

tests at Malgosa along the Colorado River corridor in Grand Canyon National Park, Ariz. (fig. 1). A, Shear velocity during 16-hour experiment at 

the Dumont Dunes from February 29 to March 1, 2004, in which mean sustained wind velocities recorded at 2.0-m height (averaged over 10-s 

intervals) were 3.6±1.6 m/s (1), with gusts to 10.8 m/s. Shear velocity was calculated by using equation 2. B, Shear velocity during first test at 

Malgosa, which lasted for 7 hours on May 11, 2004. Mean sustained wind velocities recorded at 2.0-m height were 5.8±3.2 m/s with gusts to 20.8 

m/s. C, Shear velocity during second test at Malgosa, which lasted 14.5 hours on May 12, 2004. Mean sustained wind velocities recorded at 2.0-

m height were 3.1±1.9 m/s with gusts to 13.7 m/s.
61

cent. Kawamura’s (1951) model, which had best predicted the 

measured sand flux in the experiment at the Dumont Dunes, 

overpredicted the measured value in the first test at Malgosa 

by a factor of 2.5 to 3. In the second test at Malgosa, during 

which the cumulative sand flux was intermediate between the 

values measured in the experiment at the Dumont Dunes and 

in the first test at Malgosa (about 100 g), all the models greatly 

overpredicted the measured value. 

Discussion

Potential Sources of Error

Calibration of sand-trap efficiency plays an important 

role in measuring sand transport and can be a substantial source of error in field studies if not well established 

(McEwan and Willets, 1993; Sherman and others, 1998). The 

BSNE sand-trap design used in this study (Fryrear, 1986; 

Stout and Fryrear, 1989) is one of the most widely applied in 

agricultural and sedimentologic studies (Zobeck and others, 

2003). Its efficiency has been determined by multiple windtunnel and field studies over wide ranges of sediment grain 

size and wind velocity (Fryrear, 1986; Shao and others, 1993; 

Goossens and Offer, 2000; Goossens and others, 2000, 2001). 

The widespread use of this design also allows comparison 

between studies. BSNE sand traps were chosen for this study 

because existing calibrations suggest that an efficiency range 

of 95–115 percent for the grain sizes and wind velocities in 

our experiments can be reasonably assumed. 

The accuracy of shear-velocity estimates is affected by 

the number of anemometers used to generate wind velocity 

profiles. In this experiment, u* values at each 10-s data point 

were generated from three measurements of wind velocity. Although increasing the number of anemometers would 

decrease the uncertainty associated with calculations of u* , 

the accuracy of results would not necessarily increase (Namikas and others, 2003; see comparison of four- versus eightanemometer u* estimates by Namikas, 1999).

Bed-roughness elements are not believed to have affected 

data collection significantly during the experiment at the 

Dumont Dunes. Location of the instrument tripod at the study 

site was selected on the basis of absence of vegetation, large 

bedforms, or pebbles on the sand surface. Values of the roughness length, z0, obtained from wind-velocity profiles, generally are within an order of magnitude of twice the Nikuradse 

roughness for the grain size at the study site (2d50/30), and 

their departure from this value is attributable to the influence of saltation and/or ripple development. The low apparent roughnesses obtained at the Dumont Dunes indicate that 

form drag on the bed was negligible during the experiment. 

With unobstructed sand on an approximately flat surface for 

distances of >20 m around the instrument tripod and sand traps 

in all directions, we are reasonably confident that eolian sand 

transport measured at the Dumont Dunes reached equilibrium 

conditions (Anderson and Haff, 1988; Anderson and others, 

1991; Raupach and others, 1993; King and others, 2005; R.S. 

Anderson, written commun., 2006).

In contrast to the Dumont Dunes, bed-roughness elements 

in the dune field at Malgosa are problematic. Even though 

Malgosa has among the sparsest vegetation of any Grand 

Canyon eolian deposit, vegetation and, possibly, a nearby talus 

slope generated measurably more roughness than in the Dumont 

Dunes; the wind data obtained at Malgosa yielded z0

 values 

five to six orders of magnitude above the Nikuradse roughness. 

Sand transport measured at Malgosa also was probably affected 

by variations in wind velocity caused by the approximate 20° 

slope of the stoss side of the dune on which the weather station 

was located (see Lancaster, 1985; Mulligan, 1988). Previous 

studies have shown that wind-velocity profiles on the stoss sides 

of dunes are not log-linear as on flat surfaces, such as the sand 

sheet in our experiment at the Dumont dunes, complicating the 

use of the Karman-Prandtl equation (2) to calculate shear velocity (Frank and Kocurek, 1996; Lancaster and others, 1996). The 

height of the lowermost anemometer used in our study (0.3 m) 

also was likely not low enough to measure wind velocity in the 

part of the boundary layer where much of the sand transport 

occurred (Lancaster and others, 1996). 

Using spinning-cup anemometers under conditions of 

abundant windblown sand introduces an additional source of 

error because sand can clog the instruments and interfere with 

movement of the cups. Lower anemometers in a vertical array 

are preferentially affected by this problem, causing the wind 

velocities recorded to be erroneously low. If the lower anemometers are preferentially slowed by windblown sand, wind 

velocity profiles appear artificially steep, and the values 

calculated from them will lead to artificially high predictions 

of sand flux q. This condition can be a source of significant 

error in experiments of this type where anemometers are used 

for an extended time, and was probably the reason why all the 

models greatly overpredicted sand flux in the second test at 

Malgosa (table 5), which was conducted after the anemometers had been subjected to sustained high winds and abundant 

sand transport for several days. Although the anemometers 

were cleaned between the two high-resolution tests at Malgosa 

(and during every maintenance visit throughout the 2-year 

Grand Canyon study), windblown sand continued to slow the 

function of the lower anemometer there (and at the Forster 

study site at river mile 123.0, fig. 1, where the lower anemometer was eventually disabled by windblown sand). This same 

problem probably affected the first test at Malgosa, especially 

to the end of the 7-hour interval, possibly explaining why all 

the eolian-sediment-transport models tended more to overprediction in the first test at Malgosa relative to the experiment 

at the Dumont Dunes (table 5). The anemometers used at the 

Dumont Dunes had never been deployed in the field before, 

suggesting that sand clogging was only a minimal factor there, 

whereas those at Malgosa had been in use (with regular cleaning and maintenance) for 6 months before the two high-resolution tests in May 2004.

u*

Appendix 2
62 The role of Eolian Sediment in the Preservation of Archeologic Sites Along the Colorado River Corridor

Performance of Tested Models

Predicted sand flux is plotted against shear velocity in 

figure 37. Differences in the performance of the eight eoliansediment-transport models become much more apparent at 

higher shear velocities (higher wind velocities) than those 

measured in either the experiment at the Dumont Dunes or the 

two tests at Malgosa. Values of u* represented in our datasets (fig. 36) were <0.5 m/s at the Dumont Dunes (clustering 

around 0.1 m/s) and <1 m/s at Malgosa (clustering around 0.3 

m/s). Wind velocities during the field studies were low enough 

that the models being tested would not necessarily show 

significant differences in predicted sand fluxes, except for the 

linear Williams (1964) model, because most of the divergence 

in their predicted sand fluxes occurs at u* >1 m/s (fig. 37).

Several of the models tested in this study showed 

somewhat greater predictive power in the simplified desert 

setting at the Dumont Dunes than had been indicated in previous studies conducted in coastal-dune environments, where 

some transport rates are commonly overpredicted and others 

0 0.5 1.0 1.5

0

0.5

1.0

1.5

1

2

3

4

5

6

7

8

1, Lettau and Lettau (1977)

2, Hsu (1971)

3, Kawamura (1951)

4, White (1979)

5, Bagnold (1941)

6, Zingg (1953)

7, Williams (1964)

8, Sorensen (1991)

0 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45 0.50

10 -4

10 -3

10 -2

10-1

10 0

A

B

1 2

3 4

5

6

7

8

8

1

2 5

5

6

6

4

4

3

3

SAND FLUX, IN KILOGRAMS PER METER-SECOND

SHEAR VELOCITY, IN METERS PER SECOND

EXPLANATION

Figure 37. Sand flux (q) predicted for various shear velocities (u

* ) by eight 

eolian-sediment-transport models. Most divergence in predicted sand flux occurs 

when u

* >1.0, such that predicted shear velocities substantially exceed those 

calculated from wind-velocity data obtained in this study.
63

underpredicted. Using Lettau and Lettau’s (1977) model, 

Bauer and others (1996) reported that predicted transport rates 

exceeded those measured by factors of 1.9 to 5.6 on a sparsely 

vegetated foredune beach. Hunter and others (1983) reported 

that Bagnold’s (1941) model overpredicted the transport 

rates measured from bedform migration of coastal dunes by 

a factor of 3.6. Overprediction factors of 5 and about 50 were 

obtained by Goldsmith and others (1990) and Bauer and others 

(1990), respectively, in applying Bagnold’s (1941) equation 

to wind and sand-transport data on coastal beaches. Sherman 

and others (1998) reported overprediction of sand transport 

on a beach by factors of ≥2 when using Bagnold’s (1941), 

Kawamura’s (1951), and Lettau and Lettau’s (1977) models, 

whereas Zingg’s (1953) model underpredicted sand transport. 

Coastal studies by Sarre (1988) indicated that the predictive 

value of most tested equations can vary with shear velocity, 

with Bagnold’s (1941) equation overpredicting sand transport at shear velocities comparable to those calculated in this 

study ( 5.0 u* < m/s). Sarre (1989) reported that White’s (1979) 

model substantially overpredicted sand transport on foredunes 

in an intertidal zone.

The improvement in the predictive power of transport 

equations in a highly simplified field setting, such as the 

Dumont Dunes, would be expected (for example, Sherman 

and Hotta, 1990). Eolian sediment transport in coastal or other 

more complex sand systems can be influenced by multiple 

factors that did not affect the Dumont Dunes: vegetation 

(Olson, 1958; Bressolier and Thomas, 1977; Ash and Wasson, 

1983; Wasson and Nanninga, 1986; Buckley, 1987; Bauer and 

others, 1996; King and others, 2005), soil moisture (Svasek 

and Terwindt, 1974; Sarre, 1988, 1989; McKenna Neuman 

and Nickling, 1989; Namikas and Sherman, 1995; Selah and 

Fryrear, 1995; Wiggs and others, 2004; Baas and Sherman, 

2006), salt encrustation on sediment (Nickling, 1984; Sarre, 

1989), fetch limitation due to nearby dune crests (Bauer 

and others, 1990) and tidal fluctuations (Sarre, 1988; Nordstrom and Jackson, 1992), trapping of sand by runnels and 

tidal channels (Bauer and others, 1996), nonerodible surface 

objects such as rocks (Gillette and Stockton, 1989; Raupach 

and others, 1993; King and others, 2005), biologic soil crusts 

(Leys and Eldridge, 1998; Belnap, 2003; Goossens, 2004), and 

perturbation of the wind-velocity profile by waves breaking 

near shore (Bauer and others, 1996). 

Kawamura’s (1951) model, one of the four listed in table 4 

that incorporates threshold shear velocity into its expression for 

sand-transport rate, most closely represented the measured sand 

flux at the Dumont Dunes. Although the actual transport was 

slightly underpredicted, the range of values obtained indicates 

that Kawamura’s model might have predicted up to 98.5 percent 

of the actual transport if the BSNE sand traps had performed 

at the upper limit of their known efficiency range for this grain 

size. The efficiency range for which Kawamura’s (1951) model 

most closely approximates the measured sand flux occurs for 

BSNE sand traps collecting medium sand at wind velocities less 

than approximately 7 m/s(Goossens and others, 2000). Kawamura’s (1951) model overpredicted the sand flux in the first test 

at Malgosa by a factor of 2.5 to 3; however, the performance of 

the models at the Dumont Dunes is considered a more accurate 

reflection of their predictive value, given that the second and, 

possibly, also the first test at Malgosa were apparently affected 

by sand-clogged lower anemometers, leading to erroneously 

high shear-velocity estimates. 

The other three tested models that incorporate a threshold 

shear velocity yielded less accurate predictions of the sand flux 

at the Dumont Dunes. Lettau and Lettau’s (1977) and White’s 

(1979) models predicted 40–50 percent of the measured sand 

fluxes, whereas Sørensen’s (1991) model predicted just over 25 

percent of the measured value. 

In his study of eolian sediment transport on coastal dunes 

in an intertidal zone, Sarre (1988) reported a close agreement 

between measured sand flux and that predicted by Kawamura’s (1951) model, although the agreement improved when 

a constant of 2.4 was used in place of Kawamura’s value of 

2.78. Sarre (1988) reported that, in general, equations using 

the cube of u* and a 

� 

u*t term provided the closest approximation to the measured sand flux, with White’s (1979) model 

performing best. Svasek and Terwindt (1974) attributed the 

poor performance of Bagnold’s (1941) and Kawamura’s (1951) 

models when tested on a beach to capillary forces of moisture 

in the beach sand. Sherman and others (1998), studying coastal 

dunes in Ireland, reported that Kawamura’s (1951) model 

overpredicted sand flux by a factor of 2 to 3 after corrections 

for soil moisture and surface slope. Lettau and Lettau’s (1977) 

model yielded ratios of predicted to measured sand flux that 

ranged from 1.0 to 1.2 after such corrections in one coastal area 

(Sherman and others, 1998), and from 1.9 to nearly 6 in another 

coastal area (Bauer and others, 1996). Hsu’s (1971) model 

overpredicted sand flux in this study by a factor of >2. This 

behavior is similar to that reported by Sarre (1988), in which 

Hsu’s (1971) model overpredicted sand flux at low to moderate 

u* values, much like Bagnold’s model.

Arguably the most commonly used eolian-sediment-transport model, that of Bagnold (1941), which depends on the cube 

of u* , overpredicted sand flux in this study by a factor of ≥1.5, 

comparable to the result of Sarre’s (1988) study, which showed 

the overpredictive behavior of Bagnold’s model for shear velocities in the range measured during this study (<0.5 m/s, generally <0.4 m/s). Bagnold’s model yielded a closer fit to our data 

when the constant in this transport equation was decreased from 

1.8 to 1.2. Zingg’s (1953) model, which is of the same form as 

Bagnold’s but differs in its constant and exponent, predicted 

about 75−82 percent of the measured sand flux at the Dumont 

Dunes, similar to the upper end of this model’s predictive value 

as evaluated by Sherman and others (1998) after corrections 

to remove the effects of soil moisture and slope. Sarre (1988) 

also reported that Zingg’s (1953) model reasonably predicted 

sand flux within the range of shear velocities considered here, 

although at higher u* values Zingg’s model underpredicted 

sand flux.

Williams’ (1964) model, the only one tested in this study 

that considers sand-transport rate to be a linear function of shear 

velocity, performed poorly. Williams’ model overpredicted sand 

Appendix 2
64 The role of Eolian Sediment in the Preservation of Archeologic Sites Along the Colorado River Corridor

flux in the experiment at the Dumont Dunes by more than an 

order of magnitude; his model also overpredicted the sand flux 

in both tests at Malgosa to a much greater degree than did the 

other models (table 5). A direct comparison between this study 

and the wind-tunnel experiments on which Williams’ model is 

based may not be possible, however, because the constant terms 

in his equation apply to a specific grain size (330 μm), slightly 

coarser than that of the sand collected at the Dumont Dunes. 

Furthermore, using sand of a similar grain size to that required 

by Williams’ model, Sarre (1988) obtained sand-transport rates 

that differed substantially from those predicted by Williams’ 

model.

Relevance for Investigation of SedimentSupply-Limited Systems

Testing of the eight eolian-sediment-transport models 

(table 4) at the Dumont Dunes, where sediment supply is nearly 

unlimited, indicates that Kawamura’s (1951) model appears to 

be the most potentially useful for discerning sediment-supply 

limitation, considering the limited range of wind velocities 

available in the experiment at the Dumont Dunes and the more 

divergent performance of the models at higher shear velocities 

(fig. 37). To be useful for discerning sediment-supply limitation, an eolian-sediment-transport model would need to predict 

sand flux to within 5–10 percent in a sediment-supply-unlimited setting. Kawamura’s (1951) model predictions fall within 

this boundary for the upper end of the sand-trap-efficiency 

range. Given that BSNE sand-trap efficiency decreases with 

increasing wind velocity, this result suggests that Kawamura’s 

model is most applicable at lower wind velocities, where sand 

fluxes are low. This suggestion is consistent with the result of 

Sarre’s (1988) study, in which Kawamura’s model predicted 

sand flux most closely at the lowest shear velocities considered 

(<0.35 m/s); Sarre’s (1988) field data also agreed well with 

Lettau and Lettau’s (1977) and White’s (1979) models. The 

wide variation in model applicability among different field 

areas and at different shear velocities indicates that the use of 

this or any other eolian-sediment-transport model to discern 

sediment-supply limitation warrants caution; therefore, we did 

not pursue similar model applications extensively as a means 

of discerning sediment-supply limitation in Grand Canyon 

dune fields, which are much more complex environments than 

that in our highly simplified experiment at the Dumont Dunes. 

More research is needed to determine the reliability of such 

models in sediment-supply-unlimited areas with, for example, 

different grain sizes, variation in sorting, and higher wind 

velocities than those represented here. 

Although construction of a new eolian-sediment-transport 

model specifically for sediment-supply-limited systems is 

beyond the scope of this report, the practical applications of 

such a model would be extensive (Leys, 1999). Quantification 

of agricultural erosion processes would benefit from modeling 

capabilities that include adjustment for diminished sediment 

supply as erosion proceeds. Environmental-management problems that concern sediment availability could be more fully 

addressed if it were possible to determine the degree to which a 

system undergoing eolian sediment transport is supply limited. 

Examples include sediment mobilization on subaerial sandbars 

in dam-controlled rivers, such as the Colorado River in Grand 

Canyon, and the condition of beaches used for recreation on 

eroding coastlines. We recommend the construction of eoliansediment-transport models that can be used for such purposes 

as a future research direction.

Conclusions

Testing of eight eolian sediment-transport models in a 

desert setting considered to have an unlimited sediment supply 

indicates that Kawamura’s (1951) model most closely predicted the cumulative sand flux measured during a 16-hour 

experiment at the Dumont Dunes in Death Valley, Calif. This 

model appears to be the most potentially useful for discerning 

sediment-supply limitation, although at higher wind velocities 

than were measured during this study the predictive value of 

the tested models could vary substantially. Additional testing 

of this and other eolian-sediment-transport models in supplyunlimited settings is advisable as a future direction of research, 

as is construction of an eolian-sediment-transport model that 

could quantify the expected reduction in sand flux as sediment 

supply becomes progressively more limited. The ability to 

quantify the influence of sediment-supply limitation on eolian 

erosion, transport, and deposition would be advantageous for 

many environmental-management initiatives.
65

This appendix catalogs our effort to evaluate changes in 

the availability of sand involved in eolian-sediment-transport 

systems within the Colorado River corridor on decadal scales. 

For this purpose, we used a geographic information system 

(GIS) database compiled by the Fluvial Geomorphology Laboratory of the Department of Watershed Sciences at the Utah 

State University (USU) that is based on aerial photographs 

taken from 1935 to 1996 between Glen Canyon Dam and the 

Unkar area (river mile 73, fig. 1). The aerial photographs and 

GIS resources discussed below were part of the dataset used 

by Schmidt and others (2004) to document decreased fine 

sediment in the river corridor between the dam and Bright 

Angel Creek (river mile 88). For the purposes of this study, 

although site-by-site changes are apparent, widespread decadal 

trends in eolian deposits and sand-source areas were not readily apparent. We believe that this observation is partly due to 

the great differences in riverflow represented in early aerial 

photographs relative to those taken in the 1990s, when all 

aerial photographic missions were flown during a steady 226-

m3

/s riverflow. The absence of regional decadal trends likely is 

also due to difficulties of interpreting sedimentary features on 

the land surface by using only aerial photographs without the 

benefit of supplemental information, such as oblique photographs and direct field observations. 

Aerial Photographs Incorporated into 

a GIS Database Compiled by the Utah 

State University

Aerial photographs of five river reaches between Glen 

Canyon Dam and approximately river mile 73 (fig. 1) were 

studied by a team of Fluvial Geomorphology Laboratory 

scientists led by J.C. Schmidt of USU’s Department of Watershed Sciences. USU scientists interpreted the geomorphology shown in multiple sets of aerial photographs taken from 

1935 to 1996, identified geomorphic units and mapped their 

boundaries as polygons, and stored the layers of polygons as 

shapefiles in a GIS database. 

By using the polygons in those shapefiles that represent 

previously interpreted geomorphic units, the total area of 

sedimentary deposits considered relevant to eolian-sedimenttransport systems was summed for each river reach in each 

set of available aerial photographs. Geomorphic features (for 

example, debris fans, channel-margin sand deposits, eolian 

deposits, and eddy sandbars) interpreted by USU scientists 

were not reinterpreted during this study, but representative 

areas were checked by independently studying the original 

aerial photographs from which the features had been mapped. 

The river reaches for which USU scientists compiled shapefiles of geomorphic features, and the dates of available aerial 

photographs used for each reach, are listed in table 6; and the 

dates of aerial photographs included in the USU GIS database, 

and the available mapped river reaches in each set of aerial 

photographs, are listed in table 7.

Categories of geomorphic features that together indicate eolian deposits were grouped together and their areas 

summed for each river reach and set of aerial photographs. 

Polygons designated as “eolian sand” in the GIS database 

were those that USU scientists interpreted to be “fine-grained 

sand deposits, often with dunelike features visible, commonly 

found on high terrace deposits and large, high-relief gravelbars. Reworking of a deposit between times of photography 

was considered to be good evidence of eolian sand if the 

deposit was topographically higher than any level reached 

by riverflows during the intervening years” (description 

excerpted from USU laboratory-procedure notes). In numerous polygons, the exact geomorphic feature was not identified 

exclusively but was listed under a combined heading, such as 

“eolian sand/channel margin” deposit, or “eolian sand/gravel.” 

Predam sedimentary deposits formed above the 2,700-m3

/s

flood stage (reached by the postdam flood of 1983) were 

assigned categories of “upper terrace” or “high terrace” deposits. Also summed for this exercise were areas of polygons 

representing fluvial sand deposits in eddies: separation bars, 

reattachment bars, and, where the distinction between separation and reattachment bars could not be made, simply eddy 

bars (Rubin and others, 1990; Schmidt, 1990). 

Results and Interpretation

Bar graphs of the summed areas of different types of 

sedimentary deposit, by year, for each of the five river reaches 

listed in table 6 are shown in figures 38 through 42. The total 

mapped areas occupied by various types of sand deposit vary 

substantially between sets of aerial photographs for each river 

reach. This variation is believed to be largely an artifact of the 

different riverflows represented in each set of aerial photoAppendix 3. Estimation of Historical Changes in 

Eolian Sand Sources

Introduction

Appendix 3
66 The role of Eolian Sediment in the Preservation of Archeologic Sites Along the Colorado River Corridor

graphs until it became customary, in the 1990s, to conduct 

overflights only during a steady 226-m3/s discharge. Differences in riverflow between sets of photographs should not 

have affected the mapped area of “upper terrace” or “high terrace” deposits, however, because those deposits lie above the 

stage of any riverflows that appear in aerial photographs, and 

largely represent the 2,700-m3/s flood stage reached in 1983. 

Schmidt and others (2004) used changes in the area of the 

eddy sandbars visible in these aerial photographs, in combination with oblique photography and site-specific field study, to 

estimate that the open sand area in the predam and postdam 

flood zone was 1–20 percent less in the 1990s than in predam 

time. Schmidt and others’ (2004) analysis did not distinguish 

between sand deposits that were strictly fluvial and those that 

had undergone (or were available for) wind reworking. From 

the aerial photographs, particularly in the upstream (GL and 

LF, table 6) reaches, eddy sandbar area apparently decreased 

as a result of the 1996 controlled flood, an observation consistent with the more widely documented pattern of accretion 

and growth of sandbars farther downstream in Grand Canyon 

at the expense of sandbars that had been eroded from Marble 

Canyon. This decrease in sandbar area was a primary reason 

why the 2004 controlled flood was designed to follow recent 

substantial input of sediment from the Paria River (Topping 

and others, 2006). (Note that because the Paria River joins 

the Colorado at Lees Ferry, sandbars in the Glen Canyon 

reach [GL, table 6] still could have been sediment starved and 

eroded during the 2004 flood.) 

River reach River miles (fig. 1) 

Glen Canyon (GL) 15.2(dam)–0 

Lees Ferry (LF) 0.4–8.3 

Redwall Gorge (RW) 29.2–35.3 

Point Hansbrough (PH) 42.3–48.9 

Little Colorado River (LCR) 60.0–72.8 

Table 6. Reaches of the Colorado River, with corresponding river 

miles, analyzed by using a GIS database compiled by the Utah State 

University. 

[River miles, which are those given by the U.S. Geological Survey’s Grand Canyon 

Monitoring and Research Center (URL http://www.gcmrc.gov/products/ims/ims.htm) are 

measured downstream from Lees Ferry (fig. 1), with negative values indicating distances 

upstream from Lees Ferry. The same river reaches were used in the aerial-photographic 

analyses by Leschin and Schmidt (1995) and Schmidt and others (2004)]

Table 7. Dates of and riverflow in aerial photographs included in the Utah State University’s GIS database, with available 

mapped river reaches in each aerial photograph.

[March and April 1996 sets of aerial photographs were taken before and after the first controlled-flood experiment (Webb and others, 1999a; Schmidt and 

others, 2001). Riverflow is based on instantaneous discharge measured at the Lees Ferry stream gage on date of photographs (Topping and others, 2003)] 

Date Riverflow (m3/s) Reaches (table 6) 

Mid-1930s Unknown; apparently about 142–

226 

LF, RW, PH, LCR (partial) 

1951 Unknown LF 

1952 252–380 on Sept. 24–25, about 175 

on Oct. 8. 

GL (Sept.), LF (Sept. Oct.), 

RW (Sept.), PH (Sept.) 

1954 119–156 LCR 

1958 186–201 LCR 

1965 680–792 LF, RW, PH, LCR 

1973 76–396 LF, RW, PH, LCR 

1984 144–226 GL, LF, RW, PH, LCR 

1990 142 GL, LF, RW, PH, LCR 

1992 226 GL, PH, LCR 

1996 (Mar.) 226 GL, LF, RW, PH, LCR 

1996 (Apr.) About 226 GL, LF, RW, PH, LCR 

1996 (Sept.) 226 LF, RW 

1997 (Aug.) 226 RW 
67

1952 1984 1990 1992

1984 1990 1992 Mar. 1952 1984 1990 1992

1996

A B

C

Apr.

1996

Mar.

1996

Apr.

1996

Mar.

1996

Apr.

1996

20

40

60

80

100

120

100

200

300

400

500

600

700

20

40

60

80

100

120

YEAR

YEAR

YEAR

AREA, IN THOUSANDS OF SQUARE METERS

AREA, IN THOUSANDS OF SQUARE METERS AREA, IN THOUSANDS OF SQUARE METERS

Figure 38. Total area of various types of sedimentary deposits mapped from aerial photographs in the Glen Canyon (GL, table 6) reach of the 

Colorado River corridor in Grand Canyon National Park, Ariz. (fig. 1). A, Total area of polygons mapped by Utah State University scientists 

as containing eolian sand, either alone or in combination with another geomorphic category. B, Total area of polygons containing sediment 

mapped as “upper terrace” or “high terrace” deposits (predam deposits formed above 2,700-m3/s flood stage). Though not transported by wind, 

“upper terrace” or “high terrace” deposits contain sediment available for remobilization by wind. C, Total area of polygons containing fluvial 

sand deposits in eddies, including “separation bars,” “reattachment bars,” and, when separation and reattachment bars were not distinguishable as separate categories, “eddy bars.” Fluvial sand deposits in eddies, where exposed subaerially, indicate source areas from which sand 

could be reworked and transported by wind. March and April 1996 sets of aerial photographs were taken just before and after first controlledflood release from Glen Canyon Dam (Schmidt and others, 2001). Note decrease in area of eddy sandbars in the Glen Canyon reach (between 

dam and Lees Ferry) during time of 1996 flood; sandbars downstream in Grand Canyon that accreted during 1996 flood were built by sand 

eroded from eddy bars upstream in Glen Canyon and adjacent reaches.

Appendix 3

The absence of apparent regional decadal trends in 

eolian deposits is partly due to difficulties of interpreting sedimentary features on the land surface by using only 

aerial photographs without the benefit of such supplemental 

information as oblique photographs and field groundtruthing (using sedimentary structures, for example, to determine 

more accurately the depositional history of sediment by 

examining it in three dimensions). Particularly in the earlier 

sets of aerial photographs, poor quality (commonly overexposure), shadows, and large scale also complicate detailed 

interpretation. Error is also introduced into geomorphic mapping methods by subjective decisions by the interpreter—

whether in one set of aerial photographs a sedimentary 

deposit should be considered to contain eolian sand, while 

in another set of aerial photographs the same sedimentary 

deposit may look ambiguous or appear to have no geomorphic features suggesting wind reworking of sediment. These 

complexities would be amplified substantially as more 

people become responsible for interpretation and polygon 

naming, but this source of error was reduced in the USU 

laboratory by having the same personnel interpret most or all 

of the sets of aerial photographs, and was determined to be 

minimal when the interpretations by different scientists were 

compared (Schmidt and others, 2004).
68 The role of Eolian Sediment in the Preservation of Archeologic Sites Along the Colorado River Corridor

1935 Sept .

1952

Oct. 1965 1973 1984 1990

1952

Mar.

1996

Apr.

1996

Sept .

1996

1935 1951 1965 1973 1984 1990

1935 1951 1965 1973 1984 1990

Sept .

1952

Oct.

1952

Mar.

1996

Apr.

1996

Sept .

1996

Sept .

1952

Oct.

1952

Mar.

1996

Apr.

1996

Sept .

1996

A B

C

5

10

15

20

25

30

50

100

150

200

250

300

35 350

YEAR

YEAR

YEAR

50

100

150

200

AREA, IN THOUSANDS OF SQUARE METERS

AREA, IN THOUSANDS OF SQUARE METERS AREA, IN THOUSANDS OF SQUARE METERS

Figure 39. Total area of various types of sedimentary deposit mapped from aerial photographs of the Lees Ferry (LF, table 6) reach of the Colorado River corridor in Grand Canyon National Park, Ariz. (fig. 1). A, Total area of polygons mapped by Utah State University scientists as containing eolian sand, either alone or in combination with another geomorphic category. B, Total area of polygons containing sediment mapped as 

“upper terrace” or “high terrace” deposits (predam deposits formed above the 2,700-m3/s flood stage). Though not transported by wind, “upper 

terrace” and “high terrace” deposits contain sediment available for remobilization by wind. C, Total area of polygons containing fluvial sand 

deposits in eddies, including “separation bars,” “reattachment bars,” and, when separation and reattachment bars were not distinguishable 

as separate categories, “eddy bars.” Fluvial sand deposits in eddies, where exposed subaerially, indicate source areas from which sand could 

be reworked and transported by wind. March and April 1996 sets of aerial photographs were taken just before and after first controlled-flood 

release from Glen Canyon Dam (Schmidt and others, 2001). As in the Glen Canyon reach immediately upstream, area of eddy bars in the Lees 

Ferry reach appears to have decreased slightly between March and April 1996 as a result of controlled flood, and to have decreased farther 

between April and September 1996. Decrease in area of deposits containing eolian sand from March to April 1996 may have been related to 

loss of subaerial sandbars in eddies; if so, it is not known why area of deposits containing eolian sand apparently increased between April and 

September 1996, while area of eddy bars declined.
69

1935 1951 1965 1973 1984 1990 Mar.

1996

Apr.

1996

Sept .

1996

Aug.

1997

1935 1951 1965 1973 1984 1990 Mar.

1996

Apr.

1996

Sept .

1996

Aug.

1997

A B

YEAR YEAR

20

40

60

80

100

5

10

15

20

25

AREA, IN THOUSANDS OF SQUARE METERS

AREA, IN THOUSANDS OF SQUARE METERS

Figure 40. Total area of various types of sedimentary deposit mapped from aerial photographs in the Redwall Gorge (RW, table 6) reach of the 

Colorado River corridor in Grand Canyon National Park, Ariz. (fig. 1). A, Total area of polygons mapped by Utah State University scientists as 

containing “upper terrace” or “high terrace” deposits (predam deposits formed above the 2,700-m3

/s flood stage). Though not transported by 

wind, the “upper terrace” and “high terrace” deposits contain sediment available for remobilization by wind. B, Total area of polygons containing fluvial sand deposits in eddies, including “separation bars,” “reattachment bars,” and, when separation and reattachment bars were not 

distinguishable as separate categories, “eddy bars.” Fluvial sand deposits in eddies, where exposed subaerially, indicate source areas from 

which sand could be reworked and transported by wind. Eolian sediment was not mapped as a separate category for the Redwall Gorge reach, 

where eolian deposits are now rare and those that do occur are small relative to those in other river reaches. 

Appendix 3
70 The role of Eolian Sediment in the Preservation of Archeologic Sites Along the Colorado River Corridor

1965 1973 1984 1990 1992 Mar.

1996

Apr.

1996

1935 1952 1965 1973 1984 1990 1992 Mar.

1996

Apr.

1996

1935 1952 1965 1973 1984 1990 1992 Mar.

1996

Apr.

1996

A B

C

YEAR

YEAR

YEAR

5

10

15

20

25

20

40

60

80

100

120

140

50

100

150

200

250

AREA, IN THOUSANDS OF SQUARE METERS

AREA, IN THOUSANDS OF SQUARE METERS AREA, IN THOUSANDS OF SQUARE METERS

Figure 41. Total area of various types of sedimentary deposit mapped from aerial photographs of the Point Hansbrough (PH, table 6) reach of 

the Colorado River corridor in Grand Canyon National Park, Ariz. (fig. 1). A, Total area of polygons mapped by Utah State University scientists 

as containing eolian sand, either alone or in combination with another geomorphic category. Eolian deposits were not mapped as separate 

categories on 1935 or 1952 sets of aerial photographs for the PH reach. B, Total area of polygons containing sediment mapped as “upper terrace” or “high terrace” deposits (predam deposits formed above the 2,700-m3

/s flood stage). Though not transported by wind, “upper terrace” 

and “high terrace” deposits contain sediment available for remobilization by wind. C, Total area of polygons containing fluvial sand deposits in 

eddies, including “separation bars,” “reattachment bars,” and, when separation and reattachment bars were not distinguishable as separate 

categories, “eddy bars.” Fluvial sand deposits in eddies, where exposed subaerially, indicate source areas from which sand could be reworked 

and transported by wind. March and April 1996 sets of aerial photographs were taken just before and after first controlled-flood release from 

Glen Canyon Dam (Schmidt and others, 2001). Note decrease in area of eddy bars as a result of 1996 flood.
71

Mar.

1996

Apr.

1996

1935 1954 1958 1965 1973 1984 1990 1992 Mar.

1996

Apr.

1996

1935 1954 1958 1965 1973 1984 1990 1992

1935 1954 1958 1965 1973 1984 1990 1992 Mar.

1996

Apr.

1996

A B

C

YEAR

YEAR

YEAR

100

200

300

400

500

600

700

800

200

400

600

800

1,000

1,400

1,200

50

100

150

200

250

300

350

AREA, IN THOUSANDS OF SQUARE METERS

AREA, IN THOUSANDS OF SQUARE METERS

AREA, IN THOUSANDS OF SQUARE METERS

Figure 42. Total area of various types of sedimentary deposits mapped from aerial photographs of the Little Colorado River (LCR, table 6) reach 

of the Colorado River corridor in Grand Canyon National Park, Ariz. (fig. 1). A, Total area of polygons mapped by Utah State University scientists 

as containing eolian sand, either alone or in combination with another geomorphic category. B, Total area of polygons containing sediment 

mapped as “upper terrace” or “high terrace” deposits (predam deposits formed above 2,700-m3/s flood stage). Though not transported by wind, 

“upper terrace” and “high terrace” deposits contain sediment available for remobilization by wind. C, Total area of polygons containing fluvial 

sand deposits in eddies, including “separation bars,” “reattachment bars,” and, when separation and reattachment bars were not distinguishable as separate categories, “eddy bars.” Fluvial sand deposits in eddies, where exposed subaerially, indicate source areas from which sand 

could be reworked and transported by wind. March and April 1996 sets of aerial photographs were taken just before and after first controlledflood release from Glen Canyon Dam (Schmidt and others, 2001).

Appendix 3