U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigations Report 2009-5116

Topographic Change Detection at 

Select Archeological Sites in 

Grand Canyon National Park, 

Arizona, 2006–2007
Front Cover: U.S. Geological Survey researchers collecting 

high-resolution topographic terrestrial lidar data near an 

archeological site in Grand Canyon National Park.
Topographic Change Detection at Select 

Archeological Sites in Grand Canyon 

National Park, Arizona, 2006–2007

Brian D. Collins, Diane Minasian, and Robert Kayen

Scientific Investigations Report 2009-5116

U.S. Department of the Interior

U.S. Geological Survey
ii

U.S. Department of the Interior

KEN SALAZAR, Secretary

U.S. Geological Survey

Suzette M. Kimball, Acting Director

U.S. Geological Survey, Reston, Virginia: 2009

This report and any updates to it are available at:

http://pubs.usgs.gov/sir/2009/5116/

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Suggested citation:

Collins, B.D., Minasian, D., and Kayen, R., 2009, Topographic Change Detection at Select Archeological Sites in Grand 

Canyon National Park, Arizona, 2006-2007: U.S. Geological Survey Scientific Investigations Report 2009-5116, 58 p.

[http://pubs.usgs.gov/sir/2009/5116/]. 
 iii

Contents

Abstract...........................................................................................................................................................1

Introduction.....................................................................................................................................................1

Logistics...........................................................................................................................................................4

Methods...........................................................................................................................................................4

Data Collection......................................................................................................................................4

Data Processing....................................................................................................................................6

Error Analysis ........................................................................................................................................7

Surface Model Comparison ................................................................................................................8

Results .............................................................................................................................................................9

Site AZ:C:13:006...................................................................................................................................10

Site AZ:C:13:336...................................................................................................................................18

Site AZ:C:13:099...................................................................................................................................22

Site AZ:C:13:099 Playa Area ..............................................................................................................26

Site AZ:C:13:348...................................................................................................................................29

Site AZ:G:03:041...................................................................................................................................32

Site AZ:G:03:002...................................................................................................................................36

Site AZ:G:03:072 US.............................................................................................................................40

Site AZ:G:03:072 DS.............................................................................................................................50

Discussion.....................................................................................................................................................55

Conclusions...................................................................................................................................................56

Acknowledgments.......................................................................................................................................56

References....................................................................................................................................................56

Figures

1. Gullying of an archeological site in Grand Canyon National Park and excavation of 

a site when erosion threatens resources..........................................................................................2

2. Regional map of northern Arizona and Grand Canyon National Park...........................................3

3. Site map showing general location of sites included in this investigation and 

referenced by archeological identification number (ArchID)........................................................5

4. Terrestrial lidar data collection in Grand Canyon National Park....................................................6

5. Site AZ:C:13:006 showing main gullies, general downhill flow direction, and 

laser scan and laser control point locations...................................................................................10

6. Site AZ:C:13:006 area showing gully locations................................................................................11

7. Site AZ:C:13:006—5-cm triangulated irregular network (TIN) output showing 

relative magnitude of surface comparison from May 2006 to September 2007........................12

8. Site AZ:C:13:006—10-cm gridded output showing erosion and deposition

from May 2006 to September 2007 and approximate gully locations..........................................13

9. Site AZ:C:13:006—10-cm gridded output showing erosion and deposition 

from May 2006 to May 2007 and approximate gully locations .....................................................14

10. Site AZ:C:13:006—10-cm gridded output showing erosion and deposition 

from May 2007 to September 2007 and approximate gully locations...........................................15
iv

11. Site AZ:C:13:006 overview images showing area of as much as 30 cm 

deposition measured between May 2006 and September 2007. ..................................................16

12. Site AZ:C:13:006 overview images showing locations of erosion ................................................17

13. Site AZ:C:13:336 and site AZ:C:13:099 playa areas showing main gullies, 

general downhill flow direction, and laser scan and laser control point locations..................18

14. Site AZ:C:13:336 showing confluence of two drainages and rock check dam 

structures in the upper area of the site. ...........................................................................................19

15. Site AZ:C:13:336—5-cm triangulated irregular network (TIN) output showing relative 

magnitude of surface comparison from May 2006 to September 2007 .......................................20

16. Site AZ:C:13:336—10-cm gridded output showing erosion and deposition 

from May 2006 to September 2007 and approximate gully locations...........................................20

17. Site AZ:C:13:336—Photos of G2 depositional area in September 2007 .......................................21

18. Site AZ:C:13:099 showing main gullies, general downhill flow direction, 

and laser scan and laser control point locations............................................................................22

19. Site AZ:C:13:099 showing confluence of two smaller drainages into 

the main gully system...........................................................................................................................23

20. Site AZ:C:13:099—5-cm triangulated irregular network (TIN) output showing relative 

magnitude of surface comparison from May 2006 to September 2007 .......................................23

21. Site AZ:C:13:099—10-cm gridded output showing erosion and deposition 

from May 2006 to September 2007 and approximate gully locations...........................................24

22. Site AZ:C:13:099—Site overview images showing locations of as much 

as 20 cm measured erosion and location of gullies........................................................................25

23. Site AZ:C:13:099 playa area showing location of main gully .........................................................26

24. Site AZ:C:13:099 playa area—5-cm triangulated irregular network (TIN) 

output showing location and relative magnitude of surface comparison 

from May 2006 to September 2007.....................................................................................................26

25. Site AZ:C:13:099 playa area—10-cm gridded output showing erosion and deposition, 

positive) from May 2006 to September 2007 and approximate gully location ............................27

26. Site AZ:C:13:099 playa area—Image and inset showing area of as much as 

12 cm measured erosion and location of major gully.....................................................................28

27. Site AZ:C:13:348 area showing main gullies, general downhill flow direction, 

and laser scan and laser control point locations............................................................................29

28. Site AZ:C:13:348 area showing gully locations ................................................................................30

29. Site AZ:C:13:348—5-cm triangulated irregular network (TIN) output showing relative 

magnitude of surface comparison from May 2007 to September 2007 .......................................30

30. Site AZ:C:13:348—10-cm gridded output showing erosion and deposition 

from May 2007 to September 2007 and approximate gully locations...........................................31

31. Site AZ:C:13:348—Images of gully G1 and gully G2 from September 2007 

showing possible locations of minor erosion. .................................................................................32

33. Site AZ:G:03:041 area showing gully locations................................................................................33

32. Site AZ:G:03:041 area showing main gullies, general downhill flow direction, 

and laser scan and laser control point locations............................................................................33

34. Site AZ:G:03:041—5-cm triangulated irregular network (TIN) output showing relative 

magnitude of surface comparison from May 2006 to September 2007 .......................................34

35. Site AZ:G:03:041—10-cm gridded output showing erosion and deposition 

from May 2006 to September 2007 and approximate gully locations...........................................34

36. Site AZ:G:03:041—Images of gully G2 bottom slope area from May 2006 

and September 2007.............................................................................................................................35
 v

37. Site AZ:G:03:002 showing main gullies, general downhill flow direction, and laser scan 

crosses) and laser control point locations.......................................................................................36

38. Site AZ:G:03:002 area showing gully locations upper G1 and G2 and lower G1 ........................37

39. Site AZ:G:03:002—5-cm triangulated irregular network (TIN) output 

showing location and relative magnitude of surface comparison from May 2006 to 

September 2007.....................................................................................................................................37

40. Site AZ:G:03:002—10-cm gridded output showing erosion and deposition 

from May 2006 to September 2007.....................................................................................................38

41. Site AZ:G:03:002—Cross-section analysis of lower G1 area from 

manual filtered point data, and image showing cross-section location.....................................39

42. Site AZ:G:03:072 showing main gullies, general downhill flow direction, 

and laser scan and control point locations for both upstream and downstream sites............40

43. Site AZ:G:03:072 US area showing gully locations..........................................................................41

44. Site AZ:G:03:072 US—5-cm triangulated irregular network (TIN) output showing 

location and relative magnitude of surface comparison from May 2006 to May 2007 .............42

45. Site AZ:G:03:072 US—10-cm gridded output showing erosion and 

deposition from May 2006 to May 2007 and approximate gully locations...................................43

46. Site AZ:G:03:072 US—Photo comparison of G3 erosional area between 

May 2006 and May 2007.......................................................................................................................44

47. Site AZ:G:03:072 US—10-cm contour map comparison of G3 erosional area 

between May 2006 and May 2007......................................................................................................44

48. Site AZ:G:03:072 US— 5-cm triangulated irregular network (TIN) output 

showing location and relative magnitude of surface comparison from 

May 2007 to September 2007 ..............................................................................................................45

49. Site AZ:G:03:072 US—10-cm gridded output showing erosion and 

deposition from May 2007 to September 2007 and approximate gully locations.......................46

50. Site AZ:G:03:072 US—Photo of G1 erosional area in September 2007........................................47

51. Site AZ:G:03:072 US—Photo comparison of G2 erosional area between 

May 2007 looking updrainage and September 2007 looking downdrainage ..............................48

52. Site AZ:G:03:072 US—Photo of G2 slope erosional area in September 2007. ............................48

53. Site AZ:G:03:072 US—Photo of G1 dune erosional area in September 2007..............................49

54. Site AZ:G:03:072 US—Photo comparison of G3 erosional area between 

May 2007 looking downdrainage and September 2007 looking updrainage ..............................49

55. Site AZ:G:03:072 US—10-cm contour map comparison of G3 erosional area 

between May 2007 and September 2007..........................................................................................50

56. Site AZ:G:03:072 DS area showing gully locations in May 2006 and May 2007..........................51

57. Site AZ:G:03:072 DS—5-cm triangulated irregular network (TIN) output 

showing location and relative magnitude of surface comparison from 

May 2006 to May 2007..........................................................................................................................51

58. Site AZ:G:03:072 DS—10-cm gridded output showing erosion and 

deposition from May 2006 to May 2007 and approximate gully locations...................................52

59. Site AZ:G:03:072 DS—5-cm triangulated irregular network (TIN) output 

showing location and relative magnitude of surface comparison from 

May 2007 to September 2007 ..............................................................................................................53

60. Site AZ:G:03:072 DS—10-cm gridded output showing erosion and 

deposition from May 2007 to September 2007 and approximate gully locations.......................54
vi

Datum Information

Vertical coordinate information is referenced to the North American Datum of 1983

(NAD83) ellipsoid height, expressed in meters.

Horizontal coordinate information was collected referenced to the North American Datum of 

1983 (NAD83) and projected to Arizona Central Zone 0202 State Plane coordinates expressed 

in meters. For the purpose of protecting the sensitive nature of the archeological sites, all 

coordinates have been reoriented about a fictitious origin, still expressed in meters.

Elevation, as used in this report, refers to distance above the vertical datum.

Metadata for the products described in this report are available at:

http://walrus.wr.usgs.gov/infobank/l/lg106gc/html/l-g1-06-gc.meta.html

http://walrus.wr.usgs.gov/infobank/l/lg107gc/html/l-g1-07-gc.meta.html 

http://walrus.wr.usgs.gov/infobank/l/lg207gc/html/l-g2-07-gc.meta.html.

Tables

1. Lidar data collection at archeological sites in Grand Canyon National Park ................................4

2. Summary of data collection and surface modeling at each archeologic site ...............................9

3. Summary of net topographic change between May 2006 and September 2007 .........................55
Introduction 1

Topographic Change Detection at Select 

Archeological Sites in Grand Canyon 

National Park, Arizona, 2006–2007

By Brian D. Collins1, Diane Minasian2, and Robert Kayen2

Abstract

Topographic change of archeological sites within the Colorado River corridor of Grand Canyon National Park (GCNP) is 

a subject of interest to National Park Service managers and other 

stakeholders in the Glen Canyon Dam Adaptive Management 

Program. Although long-term topographic change resulting from 

a variety of natural processes is typical in the Grand Canyon 

region, a continuing debate exists on whether and how controlled 

releases from Glen Canyon Dam, located immediately upstream 

of GCNP, are impacting rates of site erosion, artifact transport, 

and the preservation of archeological resources. Continued 

erosion of archeological sites threatens both the archeological 

resources and our future ability to study evidence of past cultural 

habitation. Understanding the causes and effects of archaeological site erosion requires a knowledge of several factors including the location and magnitude of the changes occurring in 

relation to archeological resources, the rate of the changes, and 

the relative contribution of several potential causes, including 

sediment depletion associated with managed flows from Glen 

Canyon Dam, site-specific weather patterns, visitor impacts, and 

long-term climate change. To obtain this information, highly 

accurate, spatially specific data are needed from sites undergoing change. Using terrestrial lidar data collection techniques and 

novel TIN- and GRID-based change-detection post-processing 

methods, we analyzed topographic data for nine archeological 

sites. The data were collected using three separate data collection efforts spanning 16 months (May 2006 to September 2007). 

Our results documented positive evidence of erosion, deposition, or both at six of the nine sites investigated during this time 

interval. In addition, we observed possible signs of change at two 

of the other sites. Erosion was concentrated in established gully 

drainages and averaged 12 cm to 17 cm in depth with maximum 

depths of 50 cm. Deposition was concentrated at specific locations outside of drainages but generally was spread over larger 

areas (tens to hundreds of square meters). Maximum depths 

of deposition averaged 12 cm to 15 cm and reached as much 

as 35 cm. Overall, we found that the spatial distribution and 

magnitudes of surface change are specific to each site and that 

1U.S. Geological Survey, Western Earth Surface Processes Team, Menlo Park, California

2U.S. Geological Survey, Western Coastal and Marine Geology Team, Menlo Park, California

a thorough understanding of the geomorphology, weather, and 

sand supply is requisite for a complete understanding of the data. 

Additional work in combining these results with site-specific 

weather, hydrology, and geomorphology data will assist in the 

development of working models for determining the causes of 

the documented topographic changes

Introduction

Topographic change of archeological sites within the Colorado River corridor of Grand Canyon National Park (GCNP) 

is a subject of interest to National Park Service (NPS) managers and other stakeholders in the Glen Canyon Dam Adaptive 

Management Program. Although long-term topographic change 

resulting from a variety of natural processes is typical in the 

Grand Canyon region, a continuing debate exists on whether 

and how controlled releases from Glen Canyon Dam, located 

immediately upstream of GCNP, are affecting rates of site erosion, artifact transport, and the preservation of archeological 

resources. Archeological sites in Grand Canyon represent an 

irreplaceable cultural and scientific resource. Studies of these 

sites have shown that human occupation in Grand Canyon dates 

to 11,000 years before the present (Fairley, 2005). Continued 

erosion of archeological sites threatens both the archeological 

resources and our future ability to study evidence of past cultural habitation (fig. 1). Many sites are located in alluvial terrace 

deposits that are prone to erosion (Hereford, 1996; Hereford and 

others, 1993, 1998). Among the potential causes of continued 

site erosion may be a lack of renewed sandbars at river level 

which are thought to replenish sediment covering many archeological sites in the river corridor through aeolian transport. 

Wright and others (2005, 2008) provide reviews of post-dam 

sediment budgets balancing the amount of sand supplied by 

tributaries downstream of the dam and the capacity of the river 

to transport the input. Without replenishment, gullying in the 

form of new and increasingly incised drainage channels leads to 

the potential loss of artifacts to the river system and loss of the 

archeological sites’ overall physical integrity. This hypothesis 

was first suggested by Hereford and others (1991, 1993); recent 
2 Topographic Change Detection at Select Archeological Sites in Grand Canyon National Park, Arizona, 2006–2007

Figure 1. A, Gullying of an archeological site in Grand Canyon National Park and B, excavation of a site when erosion threatens 

resources. The area in B was previously buried by aeolian deposition and emerged as precipitation runoff and wind deflation exposed 

small features of the habitation site.

follow up studies by Draut and Rubin (2008), for example, 

have begun to quantitatively evaluate these linkages.

Studies documenting the erosion of archeological sites 

were first performed by Hereford and others (1991, 1993) 

using comparative photography following the 1983 flood 

release from Glen Canyon Dam. Additional studies by Fairley 

and others (1994) on an inventory of approximately 475 

sites located throughout the Colorado River corridor (fig. 2) 

showed that a variety of erosion-related impacts were occurring to these sites including surface deflation, gullying, bank 

slumpage, and animal- and human-caused erosion due to 

trailing (that is, the creation and repeated use of trails) and 

bioturbation. Following passage of the Grand Canyon Protection Act in 1992, the NPS initiated a monitoring program using 

conventional total station surveying at more than 70 sites to systematically document potential erosion-induced changes to site 

topography affecting archeological sites in the river corridor (for 

example, Leap and others, 1996, 1997). For a variety of reasons, 

this effort was halted before a change-detection study could be 

completed (Leap and others, 2000). From 2001 to 2003, both 

low-altitude photogrammetry (1:1600 scale) and conventional 

total station surveying were used by Pederson and others (2003, 

2006) in a study focused on evaluating the evolution of drainage channels (gullies) through nine archeological sites in the 

river corridor and to monitor the effectiveness of check dams 

for stabilizing gully erosion at these sites. During this time, 

NPS resource managers became increasingly concerned that 

research and monitoring activities using total station surveying 

may be having a detrimental impact, through trailing-induced 

erosion, on the resources that researchers are trying to protect. 

Partly in response to these concerns, remote-sensing survey 

techniques were investigated (Davis, 2004) in the hopes that 

their use would prevent potentially damaging site effects caused 

by repeated direct access at the sites required by conventional 

methods. A variety of techniques were investigated, including 

the use of airborne light detection and ranging (aerial lidar) for 

remote collection of topographic data. In both the Pederson and 

others (2003, 2006) and Davis (2004) studies, it was determined 

that the lower-than-desired accuracy of the remotely sensed 

data (that is, photogrammetry and aerial lidar), coupled with its 

high cost, limited its applicability as a site-specific, long-term 

monitoring tool.

In response to these studies, researchers from the U.S. 

Geological Survey (USGS) Grand Canyon Monitoring and 

Research Center (GCMRC), in collaboration with the NPS, 

initiated a project to explore other remote sensing technologies 

that potentially would be more efficient, more accurate, and less 

intrusive for monitoring geomorphic change (Fairley and others, 

2007). One of these—terrestrial lidar—was selected for testing 

because of its recent proven track record for documenting site 

conditions with high resolution (hundreds of points per square 

meter) and accuracy (centimeter level) in a variety of applications (for example, Bellian and others, 2005; Collins and Sitar, 

2002, 2008; Doneus and Neubauer, 2005; Kayen and Collins, 
Introduction 3

2005; Labourdette and Jones, 2007; Nagihara and others, 2004; 

Wawrzyniec and others, 2007). Although terrestrial lidar had 

been used in previous studies in GCNP and other NPS units 

to document existing conditions of archeological structures 

and resources (for example, Hough and Brennan, 2008), data 

collection was limited to single temporal data sets of archeological structures rather than being focused on collecting multiple, temporally distinct data sets for centimeter-scale change 

detection of geomorphic features. Thus, use of terrestrial lidar 

as a change detection tool at archeological sites had not been 

previously tested, nor had its utility as a monitoring tool applied 

to resources within the logistically challenging confines of the 

inner Grand Canyon been previously evaluated.

The use of terrestrial lidar as a remote-sensing survey 

technique for geomorphologic studies in the Colorado River 

corridor was first investigated by Collins and Kayen (2006) 

during the 2004 high- flow experiment from Glen Canyon 

Dam. They collected high-resolution survey data of hydrologic, biologic, and archeologic features and sites, several 

thousands of square meters in size, and created three-dimensional models of the topography for future change detection studies. Unfortunately, owing to excessive rain and fog 

creating false returns from water droplets in the atmosphere, 

they were unable to prove its effectiveness for archeological 

site topographic change detection monitoring at that time and 

suggested that its future use required additional evaluation. 

As a result, the GCMRC Sociocultural Program initiated a 

study in 2006 to assess the applicability of terrestrial lidar 

for monitoring physical change at archeological sites and to 

compare its use to total station surveying (Collins and others, 

2008). One focus of this study was to compare site impacts 

of the two techniques, measured in terms of survey time and 

foot step counts within archeological site boundaries. The 

results showed that whereas the two techniques were quantitatively approximately the same, they were spatially different, 

with terrestrial lidar able to collect data from a much larger 

area at each site with approximately the same level of field 

effort. The main component of the study focused on the ability of each method to collect accurate long profile sections 

of drainage gullies that cross archeological sites. The study 

showed that although terrestrial lidar could remotely model an 

accurate gully long profile, in this particular application it was 

no more accurate than total station data, required additional 

post-processing effort, and was limited in its ability to identify 

Figure 2. Regional map of northern Arizona and Grand Canyon National Park.
4 Topographic Change Detection at Select Archeological Sites in Grand Canyon National Park, Arizona, 2006–2007

centimeter-scale, field-visible features such as small knickpoints in the thalweg. However, the study also showed that terrestrial lidar could efficiently collect accurate topographic data 

of whole site areas rather than just localized feature topography such as small-scale drainage systems—a capability that 

would permit researchers to monitor sediment aggradation and 

deflation over much broader areas of sites with highly precise, 

densely spaced data points that simply could not be collected 

efficiently using total station methods.

Thus, the Collins and others (2008) study showed 

promising results for high-accuracy (subdecimeter) change 

detection over the entire area of an archeological site. Coincidentally, a data review panel independently reviewing cultural 

monitoring legacy data at the GCMRC also recommended that 

terrestrial lidar be pursued for temporal change monitoring 

of archeological sites (Kintigh and others, 2007). As a result 

of these initial results and recommendations, the GCMRC 

Sociocultural Program continued the study in 2007 with a 

specific focus on the potential utility of terrestrial lidar for 

whole site change detection monitoring of archeological sites 

within Grand Canyon. This report presents the results of that 

study and compares the terrestrial lidar data sets collected in 

2006 with those collected in 2007. Data for a total of nine sites 

situated throughout the length of the Colorado River corridor 

are presented and compared for three data sets collected in 

May 2006, May 2007, and September 2007. We present a full 

description of terrestrial lidar methods in this report because 

the technique is relatively new and because post-processing 

methods are still in their infancy. The results indicate areas 

of both erosion and deposition at specific archeological sites. 

Although we present interpretations of the likely geomorphologic processes causing these changes, this report does not try 

to relate them either directly or indirectly to the controlled flow 

regime from Glen Canyon Dam. Instead, we focus on presenting the highest resolution topographic change detection data yet 

available for monitoring the geomorphic controls at archeological sites in GCNP, with the intention that these data may then be 

used for future dam- and river-process related studies.

Logistics

Three data collection efforts were made in Grand Canyon 

National Park between 2006 and 2007 (table 1). For simplicity, 

we refer to each effort as either the May 2006, May 2007, or September 2007 surveys. During the surveys, data were collected at 

nine localities (fig. 3), each encompassing an archeological area 

of interest where erosion has been identified as having a potential 

impact on site resources. To protect the sensitive nature of the 

sites, specific site location information is omitted, and the GCNP 

archeological site identification number is used for reference. At 

each site, data collection was focused on the terrain surrounding 

and including one or more drainage systems, colloquially termed 

“gullies,” that are referred to in this report as G1, G2, and so on, 

and numbered sequentially moving from upstream to downstream along the river corridor or contributing side drainage.

Each survey effort consisted of two GCMRC-supported 

motor rafts carrying all personnel and equipment for trips lasting from 16 to 18 days. Equipment consisted of camping gear 

and food supplies, a battery charging system for all electronics, 

and survey equipment, including the USGS Coastal and Marine 

Geology (CMG) Program’s terrestrial lidar unit, GCMRC’s 

total station unit, and CMG’s pair of differential GPS receivers. 

Personnel consisted of researchers from the USGS in Menlo 

Park, California, and researchers and staff from the GCMRC 

in Flagstaff, Arizona. Assistance in mobilization of equipment 

was provided by a team from Utah State University performing concurrent geomorphologic assessments of the same sites. 

Additional trip personnel included archeologists from NPS and 

the Zuni Tribe and raft pilots (boatmen).

Methods

Data Collection

The terrestrial lidar technique (three-dimensional, or 3-D, 

laser scanning) consists of sending and receiving laser pulses to 

build a point file of 3-D coordinates of virtually any surface. A 

laser scanning device is set up at a fixed location with an open 

field of view and aimed at the ground surface. The time of travel 

and/or phase-shift for a single laser pulse reflection is measured 

along a known trajectory such that the distance from the laser 

scanner, and consequently the location of a point of interest, 

is computed. In the present study, a Riegl Z210 laser scanner 

was used as a tripod-mounted survey instrument (fig. 4). The 

Riegl Z210 uses a Class 1 (eye safe under normal operating 

conditions), near-infrared (900 nm), pulsed laser diode with 

beam divergence of 0.172° (approximately 3 cm at 10 m range). 

Typical maximum range for natural targets with 10 percent and 

80 percent reflectivity is 150 m and 350 m, respectively, with 

25 mm accuracy. The laser system consumes relatively low 

Table 1. Lidar data collection at archeological sites in Grand 

Canyon National Park.

Site name May 2006 May 2007 Sept. 2007

C:13:006 5/6/2006 4/28/2007 9/15/2007

C:13:336 5/7/2006 4/29/2007 9/16/2007

C:13:099 5/8/2006 4/29/2007 9/16/2007

C:13:099 playa area 5/7/2006 4/29/2007 9/16/2007

C:13:348 5/8/2006 4/30/2007 9/17/2007

G:03:041 5/14/2006 5/7/2007 9/24/2007

G:03:002 5/15/2006 5/8/2007 9/25/2007

G:03:072 US

(upstream site) 5/17/2006 5/9/2007 9/26/2007

G:03:072 DS 

(downstream site) 5/16/2006 5/10/2007 9/26/2007
Methods 5

power (typically 35 W) compared to similar laser systems, using 

12-volt, sealed, gel-cell, lead-acid batteries.

Most laser scanners operate using some combination of precisely aligned rotating polygonal mirrors and extremely smallstepping motors to guide the laser paths over the area of interest. 

With the Riegl Z210, laser pulses are reflected from a triangular 

mirror, rotating around the horizontal axis (with minimum angle 

step width of 0.072°), while the entire head of the scanner pans 

around the vertical axis of the laser diode origin (also with 

minimum angle step width of 0.072°). The technology, specifically developed for rapid topographic surveys, allows data to be 

collected at rates of thousands of points per second, generating 

a “point cloud” of 3-D coordinates. Acquisition of sufficiently 

dense point clouds (that is, point-to-point spacing on the order of 

5 cm or less) can, in most cases, fully describe site topography. 

The point files from data collection are transformed into 3-D 

surfaces for cross-section and volumetric analyses.

At each survey location, we transported the laser from the 

raft to the archeological site by backpack. We used an elevated 

tripod (to 2.3 m) to position the laser above each site to 

capture a wide range and more direct line of sight to the area 

topography. We collected multiple scans from different locations during each survey to fill in “shadow zones” of areas not 

directly in the line of sight of the laser and to expand the range 

and density of the point data. Data with the Riegl Z210 were 

collected at a rate of 8,000 points per second using a single, 

last return for each point and scanning over a 333° range in 

the horizontal direction and ±40° from the horizontal range in 

the vertical direction. This provided approximately 2.3 million 

points for each scan, although only a portion (about 50 percent) of those actually defined the site topography of interest.

The major challenge in the terrestrial lidar method is in 

combining the multiple scans collected into a single, georeferenced, point-cloud model. Although many methods exist, all 

rely on the accurate collection of georeferenced survey points 

on either the laser itself, a network of visible reflectors within 

the scans, or both (Collins and others, 2006). For each survey 

effort, we collected high accuracy (<1 cm RMS error) survey 

Figure 3. Site map showing general location of sites included in this investigation and referenced by archeological identification 

number (ArchID). Exact locations are not shown to protect the archeological resources of interest. Numbers in blue represent river mile 

measured downstream from Glen Canyon Dam.
6 Topographic Change Detection at Select Archeological Sites in Grand Canyon National Park, Arizona, 2006–2007

control on all scanner origins and a network of three to six 

control targets. Coordinates were determined by either locating 

the instrument over known survey benchmarks or by collecting 

either total station or global positioning system (GPS) positions 

on the laser and target locations. We note that the RMS survey 

control error represents a relative level of horizontal and vertical 

control in georeferenced space since the control points used in 

the survey are only known to a three-dimensional accuracy of 

5 cm to 8 cm (Grand Canyon Monitoring and Research Center, 2008). However, since identical control points were used 

throughout the study, this component of error is not included in 

the subsequently outlined error analysis.

In 2006, we collected georeferenced survey data for our 

laser instrument locations using a Topcon total station survey 

device. In 2007, we collected this data using a pair of surveygrade, real-time kinematic differential Topcon Hyper+ GPS 

receivers. Metadata for the data collection efforts are available at http://walrus.wr.usgs.gov/infobank/l/lg106gc/html/lg1-06-gc.meta.html, http://walrus.wr.usgs.gov/infobank/l/

lg107gc/html/l-g1-07-gc.meta.html, and http://walrus.wr.usgs.

gov/infobank/l/lg207gc/html/l-g2-07-gc.meta.html (U.S. Geological Survey, 2008a).

Data Processing

We processed the lidar data through an integrated suite 

of registration, georeferencing, filtering, and surface-model 

generation techniques specific to terrestrial lidar data. 

Because each scan contains data of only a part of each site, 

the data from all scans must be combined (registered) and 

spatially located (georeferenced) to a common geographic 

coordinate system. To obtain a continuous bare ground 

surface model of a site, the data must be filtered of extraneous data such as vegetation and atmospheric interference 

(birds, bugs, dust, and others), and then a surface is built 

from the remaining data. These steps involve the mathematical translation and rotation of the data from local coordinates 

centered about each scan origin to geographic coordinates 

specific to the survey data and also the categorization of 

points both within and outside of the bare earth (without 

vegetation) model. The scan and surface model files, which 

typically contain several million points each, require specific 

software to handle the large number of matrix transformation 

equations applied to the files. Among the several software 

programs available, we used I-SiTE Studio software (I-SiTE, 

2008) for all data filtering, registration, georeferencing, and 

initial surface-model building.

We used an integrated processing workflow that ensures 

that data quality and accuracy are maximized and that the data 

are properly archived following each major processing step. 

The workflow is outlined here for reference:

1. Raw Data Archiving—The data are archived in raw field 

format to ensure a backup copy.

Figure 4. Terrestrial lidar data collection in Grand Canyon National Park. The extendable tripod allows 

a larger area of data collection and less oblique laser returns from areas of flat topography. Differential 

global positioning system (GPS) with a fixed radio-linked base station is used to georeference the 

instrument location. Inset shows typical transportation of the equipment.
Methods 7

2. Survey Data Processing—The survey data provided by total 

station or GPS are processed to determine accurate georeferenced positions for the scanner and reflectors and to 

eliminate common field errors such as incorrectly recorded 

tripod or antenna heights.

3. Preliminary Scan Filtering—Extraneous points that define 

such items as people, equipment, dust, or birds are removed 

from the raw scan files. Distant points outside the overall 

study area are also removed.

4. Georeferencing—Each scan is located to geographic coordinates through a matrix transformation of the scan origin.

5. Registration—Each scan is rotated about its now fixed, georeferenced origin until the best fit of the scan to all neighboring scans is achieved. Best fit is measured by direct comparison and minimization of error between nearest-neighbor 

point pairs within each scan’s point cloud (that is “cloud-tocloud” registration). This requires the manual selection of the 

best overlapping data within each scans’ point cloud, such 

that poorly fitting data points (for example, vegetation) are 

deselected and well-fitting items (for example, bare ground, 

cliff faces, boulders) remain. Initial registration of a site is 

achieved by registering three scans with origins that form an 

approximately equilateral triangle on the ground, thus forming a plane with a single geometric solution. Additional scans 

are registered to this georeferenced group of point clouds. 

The order of the registration process of the scans is set by the 

triangular layout of the scan locations, which are carefully 

and specifically selected in the field. Control reflector points, 

located outside the archeological site areas, were also sometimes used to constrain the number of degrees of motion 

when cloud-to-cloud registration did not achieve the required 

registration accuracy.

6. Topographic Filtering—Points representing anything other 

than the ground surface are removed from each scan using 

a sequence of topographic filtering steps. Following a 

rough, manual removal of tall vegetation points, the lowest 

point within each 0.5-m-square grid cell is first selected. A 

surface is then constructed of these points. All points within 

10 cm of this surface are added back to the scan data. The 

lowest point within each 5-cm-square grid cell is then 

selected. These steps generally achieve a well-refined, highresolution ground point data file, although some additional 

manual manipulation of the data is sometimes required for 

particularly small and large vegetation.

7. Surface Model Generation—The final surface model is 

created using a triangulated irregular network (TIN). Minor 

filtering of the TIN is sometimes needed to remove obvious 

remaining extraneous high points from tall vegetation. In 

some cases, difficulties in manual filtering larger vegetation 

led to inconsistencies in the final surface models, for example, when a large boulder was mistaken as a similar-sized 

bush or tree. These instances are discussed on a case-by-case 

basis in the presentation of the data and results.

Error Analysis

Terrestrial lidar data, similar to any other survey data, are 

subject to errors originating from both the data collection and 

post-processing methodologies. We include a detailed analysis 

of the errors associated with the data to allow the objective 

presentation of limitations in detecting topographic change. 

Although terrestrial lidar data provide a three-dimensional 

basis for surface modeling, we focus our results on the calculation of erosion and depositional change in only the vertical 

dimension as this is the most obvious way to understand and 

interpret surface change. Thus, the following error analysis 

was developed over a framework that focuses on the vertical 

component of error, unless otherwise noted.

Error introduced to the final terrestrial lidar surface models 

Etotal, is a result of the summation of three independent errors: 

(1) the error associated with the position of the origin of the 

scanner (Esurvey), (2) error associated with the pulse and reflection of the laser beam (Elaser), and (3) error associated with the 

registration of the laser point data (Ereg). However, as previously 

discussed, registration occurs through the alignment of a generally equilateral triangle created by the origins of three individual 

scans—from one scan to the next, and from these two scans to 

the third, and the vertical component of registration error must 

be included twice—once each for each registration step. Calculation of TIN surface models technically can introduce a fourth 

source of error (Etin) through interpolation between the modeled 

surface and the true bare ground surface. This error is primarily 

dependent on the data density (point spacing) used in TIN generation and the relative change in slope (actual surface roughness) between data points. In this study, we assume negligible 

error from surface generation (that is, Etin ≈ 0) due to the close 

(5 cm) spacing of the points forming the TIN and observation 

that the majority of the areas investigated are of subtle topography (that is, few “sharp” edges within the site area). This error 

source is therefore not included in the subsequent calculations.

The sum of a series of independent errors are typically 

calculated as a root mean square error (RMSE):

E Esurvey

2 + Elaser2 + Ereg12 + Ereg22

total =

 

 (1)

In this study, we determined the origin of the scanner position by either total station surveying (May 2006) or 

differential GPS surveying (May and September 2007). For 

both statistical significance and mathematical simplicity, the 

vertical component of error in positioning was estimated as 

the average single standard deviation calculated from each 

group of vertical measurements. In May 2006, the vertical 

component of error from the total station data for 80 independent survey points at one standard deviation (1) was 5 mm. In 

2007, the vertical component of error (1) from the GPS data 

was 5 mm for 114 survey points in May and 4 mm for 117 

survey points in September. We therefore estimate the vertical 

survey position error Esurvey, of all models as the average value 

(4.6 mm). We note again that the final error budget will be 

that for a relative calculation in georeferenced space as errors 
8 Topographic Change Detection at Select Archeological Sites in Grand Canyon National Park, Arizona, 2006–2007

because of GPS benchmark location (typically between 5 cm 

and 8 cm positional accuracy; Grand Canyon Monitoring and 

Research Center, 2008) are not included in the analysis. In 

calculating differences between each data set, any additional 

benchmark-related error can be ignored, however, because the 

same identical benchmark control point locations were used 

for both total station and GPS base station positioning between 

the 2006 and 2007 survey efforts. Although this requires 

assumptions of maximum point stability and minimal differential tectonic movement between control point benchmarks 

and site areas, these are both valid for short duration surveys 

in Grand Canyon. 

Laser beam pulse and reflection error can be measured by 

either absolute (maximum possible) or empirical (actual measured) methods. For calculating the vertical component of error 

in the laser beam, we use the average results (Elaser = 7.2 mm) 

of two sophisticated, third-party empirical calibration tests performed on the Riegl Z210 laser system (4.1 mm by Lichti and 

others, 2002; 10.2 mm by Boehler and others, 2003). Both of 

these tests were performed at relatively close range, consistent 

with the data gathered in this study (typically less than 15 m).

The registration error is associated with the numerical 

alignment of the point clouds (scans). The scans are aligned 

with one another in such a way that the error between all 

points used in the registration of each cloud (typically between 

100,000 and 1,000,000 points) is minimized. The following 

equation presents this calculation in terms of the horizontal 

(x, y) and vertical (z) dimensions for two positions, 1 and 2, calculated for N pairs of points, each delineated between i and N:

(2a)

In general, our data processing resulted in a maximum, threedimensional (x, y, and z), point-matching error not greater 

than 5 cm. For simplicity, we assume that errors are evenly 

distributed between the three dimensions due to the threedimensional nature and equivalent point spacing of the data. 

However, this should be noted as a conservative error estimate because most of the sites are not very steep (<45°) in 

slope, and it is only at a 45° inclination that the errors can be 

assumed evenly distributed. For increasingly flat surfaces, the 

error associated with the z dimension diminishes to zero.

Using the evenly distributed error assumption, the vertical error component can be simplified as only a portion of the 

point-matching error and we can equate the x, y, and z error 

components:

 (2b)

Calculating through the sum, and simplifying, we solve for the 

vertical component of error of a single registration between 

two point clouds (Δz = Ereg1 = Ereg2) as:

 (2c)

Solving for Δz, the error estimate is 29 mm each for Ereg1 and 

Ereg2.

RMSE3D = − + − + −

=

∑

1

1 2

2

1 2

2

1 2

2

1

N x x y y z z i i i

i

N

( ) ( ) ( )

1

1

5 cm = N [3 (z1

− z2)

2

] i

i

N

=

∑

5 3 cm = ∆z

From equation 1, the total vertical error estimate in a 

single constructed model surface is: 

(3)

Note that the meaning of Etotal is that all points on the final 

surface are within 41.9 mm of their true position in relative 

georeferenced space. When calculating vertical distances 

between two surfaces, the error estimate must be accounted for 

in each case, because each surface could potentially be in error 

by Etotal. Although the errors could be treated independently, 

as it is highly unlikely that the errors between two surfaces 

are exactly opposite of one another, we used an error bound 

of 83.8 mm (≈ 8 cm) that is double the single surface error. 

This error limit serves as the distinguishing bound between 

areas of actual measured change and that potentially caused by 

data collection and processing errors. However, in the absence 

of any errors in the data collection and processing, smaller 

scale changes may have occurred at some sites. Thus, it can 

be considered conservative in the context of detection of only 

significant topographic change; that is, vertical change that has 

the potential for greater impact on archeological sites.

Surface Model Comparison

For each site, three surface models were created—one 

each for the May 2006, May 2007, and September 2007 field 

efforts. We analyzed the surface models methodically, first 

comparing the May 2006 and September 2007 surfaces. If 

no change was detected outside the survey error bounds, no 

additional analysis was undertaken. If change was detected, 

we compared the shorter surface change intervals from May 

2006 to May 2007 and May to September 2007 to identify the 

time period in which the change occurred. However, because 

of this analysis method, the possibility exists that cycles of 

erosion and deposition may have occurred within a single time 

period and gone undetected. Given the relatively short time 

period between data collection (between 3 and 12 months), 

it is probable that only one additional cycle of erosion and 

deposition may have occurred (between May 2006 and May 

2007). Regardless, the results still present measurements of 

actual measured change and provide definitive results for the 

time period in which monitoring occurred.

We note here the use of the generalized terms “erosion” 

and “deposition” to indicate surface lowering and surface 

rising, respectively. Thus, these may, at times, capture such 

processes as surface compaction and aeolian dune inflation, 

which are technically neither erosion nor depositional processes. When a more specific geomorphic process is known, 

we identify this within the results for each site.

Two types of surface change maps were used to detect 

vertical change—a three-dimensional TIN surface change map 

and a two-dimensional grid of the surface change. The threedimensional surface change map was constructed by coloring the 

more recent surface by the elevation difference with the previous surface (with orange equaling negative change representing 

Etotal = 4 6 7 2 29 29 41.9mm + + + = 2 2 2 2 . .
Results 9

erosion; and blue equaling positive change representing deposition). In the results, the number of points reported for each 

surface construction indicates the number of points used in TIN 

model construction—the actual number of points collected is 

typically an order of magnitude greater but were removed as per 

the filtering and post-processing methodologies previously outlined. The three-dimensional TIN allowed in-depth analysis of 

both the statistics and locations of the change. A histogram of the 

differences between every TIN triangle to the previous complementary surface provided the distribution of the change over the 

maximum range of expected change (± 50cm). The histogram 

was normally distributed in all cases and we therefore calculated 

the average, standard deviation, and 2s (95.4 percent confidence 

interval) differences between each pair of compared surfaces. All 

TINs were retriangulated using a consistent triangle-edge size 

(5cm) so that the area of the histogram outside the error limits 

(±8 cm) could be calculated. Further, when confirmed change 

was detected, we calculated the two-dimensional area of affected 

ground. When available, we used and present photographs of the 

sites to confirm and highlight the exact location and extent of 

each area of positively detected change.

Two-dimensional grid maps were constructed from the 

5-cm surface-change TIN data using Surfer software (Golden 

Software, 2008) to perform regular kriging on a 10-cm-square 

grid. Kriging technically introduces a new error term, the error 

associated with gridding (Egrid) to the analysis, but because 

of the close spacing of the TIN (5 cm) and grid (10 cm), we 

found these errors to be negligible for the change detection 

presented here. Comparisons of a subset of the data for sites 

where the greatest site change occurred show an average TINgrid mean surface difference of only 3.7 mm.

Using the grid data, vertical change was contoured 

and colored according to the same orange (erosion) to blue 

(deposition) gradient scheme. The grid provided us with direct 

maps of the magnitude of the recorded change throughout 

the surface. We colored areas within the ±8 cm error bounds 

gray as a way to highlight those areas outside this range where 

change did occur. In some cases, the maps indicated change 

that was due to difficult-to-filter vegetation or poor overlap 

between consecutive surfaces. These areas are indicated as 

such in the figures presented with the results.

When change was significant at a site, we performed 

more detailed volumetric and cross-sectional analyses using 

the TIN data. This provided additional pertinent data for those 

sites, such as the exact vertical magnitude of the change (as 

opposed to the range of change from the grid map), the spatial 

location of those changes, and the volume of material mobilized either into or out of the site.

Results

The results for each of the nine sites are presented separately and include brief descriptions of the topography, geomorphology, hydrology, archeology, and general vegetation 

ecology at each site. Additional details for some of the sites 

have also been summarized by Pederson and others (2003). 

Base maps were developed from the USGS GCMRC Internet 

Map Server (U.S. Geological Survey, 2008b) but to protect the 

sensitivity of each site they do not contain georeferenced identifiable features. Change detection results highlight areas of 

significant erosion and deposition measured between the three 

surface models of the 2006–2007 data sets. Where no change 

was detected between the earliest (May 2006) and latest 

(September 2007) data sets, no further discussion is included 

for the mid-range (May 2007) data set. As a reference, table2 

Site Number Number of 

scan locations 

Approximate 

surface area of 

data collection

(m2

)

Number of points used 

in each surface model

Approximate surface 

area modeled for 

change detection

(m2)

AZ:C:13:006 6 2,730 600,000 1,280

AZ:C:13:336 5 to 6 3,120 450,000 1,250

AZ:C:13:099 4 1,700 400,000 770

AZ:C:13:099 playa area 4 to 7 6,900 1,400,000 3,300

AZ:C:13:3481 4 to 14 3,210 to 6,110 300,000 to 1,000,000 920 to 3,020

AZ:G:03:0412 9 to 16 1,000 to 1,380 195,000 to 290,000 600 to 800

AZ:G:03:002 11 to 13 3,470 380,000 1,020

AZ:G:03:072 US3 8 to 13 1,090 to 1,490 290,000 to 440,000 870 to 1,210

AZ:G:03:072 DS4 6 to 7 1,100 150,000 450 to 460

1

 In May 2006 data from only four scan locations of a smaller area were collected.

2

 In May 2007 the digital data from six scans were corrupt and only a smaller area could be modeled.

3

 Following the May 2006 data collection, the number of scan locations was increased.

4

 The modeled surface region represents a neighboring but slightly different area between the May 2006 to May 2007 and 

the May 2007 to Sept. 2007 comparisons.

Table 2. Summary of data collection and surface modeling at each archeologic site.
Figure 5. Site AZ:C:13:006 showing main gullies (dashed lines), general downhill flow direction (blue arrows), 

and laser scan (red crosses) and laser control point (blue triangles) locations.

10 Topographic Change Detection at Select Archeological Sites in Grand Canyon National Park, Arizona, 2006–2007

provides a summary of the number of scan locations and 

measured area where data were collected and area and number 

of points used in the creation of each surface model for the 

presented results. The collected and modeled surface areas are 

different in size because of the lack of overlap between some 

data, the inability to accurately analyze change at the boundaries of the site area or in areas of dense vegetation, and the 

effort to avoid analyzing outside the area of interest.

Site AZ:C:13:006

Site AZ:C:13:006 consists of a raised alluvial terrace that 

overlooks the confluence of a deeply incised arroyo with the 

Colorado River (fig. 5). The area is composed of overwash 

cliff deposits and aeolian dune sands stabilized with biological 

soil crust and is of increasingly convex profile moving down 

in elevation towards the arroyo and the river. Four small, 

shallow drainages (G1a, G1b, G2, and G3) traverse the site 

(fig. 6), and all but G3 appear to be nearing a state of incipient entrenchment. The remaining drainage (G3) has already 

formed an approximately 10-cm-deep incised gully. Vegetation cover consists of a mix of bunch grasses and small cacti, 

chiefly prickly pear (for example, Opuntia polyacantha var. 

erinacea), generally averaging less than 20 cm in height with a 

few larger mesquite trees (Prosopis glandulosa var. torreyana)

near the boundaries of the site (fig. 6). The site is archeologically important as an area of Puebloan II (about A.D. 900 to 

1100) habitation (Fairley and others, 1994). Although there 
Figure 6. Site AZ:C:13:006 area showing gully locations (dashed lines).

Results 11

are no visible habitation structures, the types and varieties of 

artifacts visible on the site surface suggest that structures may 

be buried beneath the dune sands in this area (H. Fairley, pers. 

comm., 2006)

Surface comparison between May 2006 and September 

2007 shows both areas of deposition and erosion throughout 

the site (fig. 7). The average distance between the two modeled surfaces is 3.3 cm with a standard deviation of 6.4 cm. 

Given that the surface change is normally distributed (fig. 

7C), the 2s confidence intervals (about 95 percent) can be 

calculated (-9.5 cm and 16.1 cm) which are greater than the 

vertical error bound estimates (±8 cm). Likewise, the histogram distribution identifies a total of 21.4 percent of the data 

outside the range of the error bounds (that is, indicating actual 

topographic change) with 2.7 percent (35 m2) of the site showing erosion and 18.7 percent (240 m2

) showing deposition. 

The largest identifiable change within the site boundary is a deposition area located between gullies G2 and G3 

(fig. 6). Here, we calculated deposition as great as 30 cm in 

isolated areas, averaging between 8 cm and 15 cm over an 

area encompassing approximately 160 m2 (fig. 8). Overall, 

a total of 26.9 m3 of sediment was transported to this area. 

Additional analysis was performed using surface comparisons between May 2006 and May 2007, and May 2007 

and September 2007. The results show that all deposition 

occurred between May 2006 and May 2007, over a slightly 

larger area (260 m2) and with greater depth (fig. 9). Between 

May 2007 and September 2007, erosion on the order of 8 cm 

to 15 cm occurred throughout a large part (220 m2

) of the 

area (fig. 10). Analysis of photographs taken in May 2006 

and September 2007 (fig. 11) shows that this area aggraded 

due to aeolian deposition. Partial to complete burial of 

prickly pear cacti and grasses is shown in the September 

2007 images (fig. 11B).

The detailed comparison also shows two positively 

identifiable areas of erosion. The first is located in the lower 

portion of Gully 1, below the confluence of Gully 1a and 1b 

(fig. 9). Here, isolated erosion of as much as 30 cm in depth 

and 0.2 m3 in volume has affected a small (<2 m2) area of the 

drainage (fig. 12). Although surface water runoff may be the 

cause of this erosion, we note that this drainage also serves 

as an unofficial access trail leading up to the site; thus, an 

anthropogenic source for this topographic change cannot be 

ruled out.

We also found statistically significant erosion along a 

10-m length (over an approximately 10 m2 area) of the upper 

portion of G3 (figs. 10 and 12) totaling 0.5 m3 in volume. 

Although the calculated surface change is on the order of 10 

cm to 30 cm in places, we suspect that vegetation that is difficult to filter (that is, small prickly pear cacti) is responsible for 

at least a part of the measured change. However, an erosion 

signature is present for a majority of the drainage in this area, 

and therefore we conclude that the gully is actively eroding, 

albeit at the lower end of the detected change (on the order of 

10 cm). Our observations indicate that channelized overland 

flow is responsible for this erosion.
12 Topographic Change Detection at Select Archeological Sites in Grand Canyon National Park, Arizona, 2006–2007

Figure 7. Site AZ:C:13:006—5-cm triangulated irregular network (TIN) output showing relative magnitude of surface comparison from 

May 2006 to September 2007. Laser scan and control point locations coincide with figure 5. Identified change is outlined by polygon 

areas. A, plan view; B, oblique view; and C, vertical change histogram distribution and color scale.
Results 13

Figure 8. Site AZ:C:13:006—10-cm gridded output showing erosion (red, negative) and deposition (blue, positive) from May 2006 to 

September 2007 and approximate gully locations (dashed lines). Identified change is outlined by polygons.
14 Topographic Change Detection at Select Archeological Sites in Grand Canyon National Park, Arizona, 2006–2007

Figure 9. Site AZ:C:13:006—10-cm gridded output showing erosion (red, negative) and deposition (blue, positive) from May 2006 to May 

2007 and approximate gully locations (dashed lines). Identified change is outlined by polygons.
Results 15

Figure 10. Site AZ:C:13:006—10-cm gridded output showing erosion (red, negative) and deposition (blue, positive) from May 2007 to 

September 2007 and approximate gully locations (dashed lines). Identified change is outlined by polygons.
16 Topographic Change Detection at Select Archeological Sites in Grand Canyon National Park, Arizona, 2006–2007

Figure 11. Site AZ:C:13:006 overview images showing area of as much as 30 cm deposition (polygons) measured between (A) May 2006 

and (B) September 2007. Note grasses in A are buried in B.
Results 17

Figure 12. Site AZ:C:13:006 overview images showing locations of erosion (oval and polygon). The majority of change in A occurred 

between May 2006 and May 2007, whereas the majority of change in B occurred between May 2007 and September 2007.
18 Topographic Change Detection at Select Archeological Sites in Grand Canyon National Park, Arizona, 2006–2007

Site AZ:C:13:336

In the Palisades region, we investigated three separate 

areas for topographic change. This area consists of a pre-Glen 

Canyon Dam flood level alluvial terrace (that is, an alluvial 

terrace formed from high-flows of the Colorado River prior 

to impoundment of the river by Glen Canyon Dam in the 

early 1960’s) that has been subject to aeolian deposition and 

subsequent erosion by channelized flows. Drainages with 

channel widths ranging from less than a decimeter to more 

than a meter traverse the site, with the largest of these causing 

significant incision and headward retreat. This area hosts a 

major concentration of prehistoric habitation sites, agricultural 

areas, and artifacts, generally related to middle Puebloan II 

(about A.D. 1050 to 1100) occupation (Fairley and others, 

1994). Several major archeological sites have been identified 

in the area. We performed topographic change detection data 

collection and analysis at two of them.

The first, site AZ:C:13:336, consists of an area of low 

relief situated among several vegetation-stabilized coppice 

mounds (fig. 13). A single gully crosses this area but bifurcates in the middle of the site (fig. 14). Each fork of the gully 

Figure 13. Site AZ:C:13:336 and site AZ:C:13:099 playa areas showing main gullies (dashed lines), general 

downhill flow direction (blue arrows), and laser scan (red crosses) and laser control point (blue triangles) 

locations.
Results 19

transitions into an area of very flat topography immediately 

adjacent to but topographically divided from the AZ:C:13:099 

playa area (discussed subsequently). The gully has been the 

subject of an erosion mitigation study (Pederson and others, 2003), and both vegetation and rock-type check dams 

have been installed in various portions of the main channel. 

Although the main gully area is not heavily vegetated, the flatter upper portion of the drainage contains irregularly spaced 

grasses, shrubs, and prickly pear cacti (for example, Opuntia 

polyacantha var. erinacea), with mesquite trees (Prosopis 

glandulosa var. torreyana) several meters in height located at 

the edges of the site. All vegetation within the site is generally no larger than 0.5 m in diameter and 0.5 m in height, and 

individuals are separated from one another by several meters.

Surface comparison between May 2006 and September 

2007 indicates that one area of statistically significant deposition occurred at this site (figs. 15 and 16). However, the 

overall statistics show that the majority of the site remained 

unchanged. The average distance between the two modeled 

surfaces is 0.6 cm with a standard deviation of 2.9 cm. The 

2s  confidence intervals (about 95 percent) are -5.2 cm and 

6.4 cm and are both within the vertical error bound estimates 

(±8cm). The histogram distribution (fig. 15C) identifies a total 

of 1.8 percent of the data outside the range of the error bounds 

with 0.5 percent (6 m2

) of the site showing erosion and 1.3 

percent (16 m2) showing deposition. With the exception of the 

noted deposition, we correlated each of these areas to processing difficulties with vegetation.

Within gully G2 and below the confluence of the two 

upper branches, we identified a 3.3-m-length of the gully 

with up to 15 cm of deposition between May 2006 and 

September 2007 (fig. 17). Analysis of the May 2007 surface shows that deposition of this magnitude began along a 

1.8-m-length of the gully between May 2006 and May 2007 

and expanded an additional 1.5 m updrainage between May 

2007 and September 2007. The total volume change (0.1 

m3

) occurred over a 0.9-m2 area located immediately above 

a brush check dam built to mitigate continued erosion of 

the site. The deposit is composed mainly of sandy material 

and infilled the brush check dam nearly to its crest. Because 

similar deposition did not occur outside the gully banks, we 

propose that the sand was transported and deposited by surface water rather than wind. However, because an upstream 

erosion source could not be positively identified, an aeolian 

deposition mode cannot be ruled out—aeolian transport 

could have infilled an isolated section of the gully.

Figure 14. Site AZ:C:13:336 showing confluence of two drainages (dashed lines, G1 and G2) and rock check dam structures in the upper 

area of the site.
20 Topographic Change Detection at Select Archeological Sites in Grand Canyon National Park, Arizona, 2006–2007

Figure 15. Site AZ:C:13:336—5-cm triangulated irregular network (TIN) output showing relative magnitude of surface comparison from 

May 2006 to September 2007. Laser scan and control point locations coincide with figure 13. One area of deposition in gully G2 was 

identified (ovals). A, plan view; B, oblique view; and C, vertical change histogram distribution and color scale.

Figure 16. Site AZ:C:13:336—10-cm gridded output showing erosion (red, negative) and deposition (blue, positive) from May 2006 to 

September 2007 and approximate gully locations (dashed lines). One area of deposition (oval) in G2 was identified.
Results 21

Figure 17. Site AZ:C:13:336—Photos of G2 depositional area (rectangle) in September 2007. Note brush check dam 

located immediately below area of deposition.
22 Topographic Change Detection at Select Archeological Sites in Grand Canyon National Park, Arizona, 2006–2007

Site AZ:C:13:099

The second major archeological site investigated in the 

Palisades region (site AZ:C:13:099) is located north of site 

AZ:C:13:336, in and around an incised gully system (fig. 18). 

The drainage system begins to the east of the site as a series of 

very shallow channels near the “playa” area, which forms the 

third site investigated in the Palisades region (discussed subsequently). As the shallow channels converge, they form ever 

deepening gullies until two channels located north and south 

of the site join to form a single larger drainage in the main portion of the site (fig. 19). Artifacts, including several varieties 

of sherds of middle Pueblo II origin, have been exposed by 

gully sidewall erosion near this area (H. Fairley, pers. comm.). 

Below this point, the gully passes through existing aeolian and 

alluvial terrace deposits, forming an approximately 1-m-deep 

channel, until draining into the Colorado River. This particular 

drainage and the associated archeological remains have been 

the focus of intensive research by archeologists and geomorphologists for more than two decades (Hereford and others 

1991, 1993; Hereford 1996; Leap and others, 2000; Draut and 

others, 2005; Yeatts, 1996; Hazel and others, 2008).

Vegetation occurs throughout the site, consisting mainly 

of small diameter (about 0.5 m) shrubs, grasses, and several 

Figure 18. Site AZ:C:13:099 showing main gullies (dashed lines), general downhill flow direction (blue 

arrows), and laser scan (red crosses) and laser control point (blue triangles) locations.
Figure 19. Site AZ:C:13:099 showing confluence of two smaller drainages (dashed lines, G1 and G2) into the main gully system

Figure 20. Site AZ:C:13:099—5-cm triangulated irregular network (TIN) output showing relative magnitude of surface comparison from 

May 2006 to September 2007. Laser scan and control point locations coincide with figure 18. Identified change is outlined by ovals and 

polygons. A, plan view; B, oblique view; and C, vertical change histogram distribution and color scale.

Results 23
Figure 21. Site AZ:C:13:099—10-cm gridded output showing erosion (red, negative) and deposition (blue, positive) from May 2006 

to September 2007 and approximate gully locations (dashed lines). Identified change is outlined by ovals and polygon. Orange areas 

identified as vegetation occurred because of inconsistent filtering of the point-cloud data.

24 Topographic Change Detection at Select Archeological Sites in Grand Canyon National Park, Arizona, 2006–2007

larger (several meters in canopy diameter) mesquite trees 

(Prosopis glandulosa var. torreyana). In addition, small 

woody debris is scattered throughout the site, and check dams 

have been constructed to slow erosion in the most susceptible 

gully locations.

The surface comparison between May 2006 and September 2007 shows that several areas of the site have either 

eroded or been subject to deposition (fig. 20). The average 

distance between the two modeled surfaces is 0.4 cm with 

a standard deviation of 4.6 cm. The 2s confidence intervals (about 95 percent) are -8.8 cm and 9.6 cm and are both 

greater than the vertical error bound estimates (±8 cm). Thus, 

at least 5 percent of the modeled surface shows evidence of 

change above the error bounds. The histogram distribution 

(fig. 20C) identifies a total of 6.5 percent of the data outside 

the range of the error bounds with 4.0 percent (31 m2) of 

the site showing erosion and 2.5 percent (19 m2) showing 

deposition.

We positively identified two areas of erosion that 

encompass 1.4 percent of the total surface area (fig. 21, 

ovals) and show changes as great as 20 cm. One area is 

located in a section of the south fork of the drainage above 
Figure 22. Site AZ:C:13:099—Site overview images showing locations of as much as 20 cm measured erosion (arrows) and location of 

gullies (G1 and G2).

Results 25

the confluence with the main gully (fig. 22). At this location, 

channel sidewall stabilization has been attempted with rock 

armoring, thus this area is of particular importance. Analysis of the May 2007 data indicates that 0.3 m3

 of sediment 

eroded from this area between May and September 2007; 

the change is not visible when the May 2006 and May 2007 

surfaces are compared. The other erosion area is located 

immediately adjacent to the north gully (G1) within aeolian 

sediments (fig. 22). As such, it is a likely area for potential 

change. Our analysis of the May 2006 to May 2007 surfaces 

shows that the area experienced the most erosion during 

that time, although the change continued to become more 

pronounced by September 2007, for a total of 0.5 m3 of sediment removed. The remaining 2.6 percent of denudation (of 

the total site) could not be positively associated with erosion 

processes. Although we identified a part (1.0 percent) of the 

area related to errors associated with difficult-to-remove, 

unfiltered vegetation in the bare-ground model, the remaining 1.6 percent of the total area associated with erosion could 

not be linked to any one source.

We found that the 2.5 percent (19 m2

) of the total area 

of measured deposition is attributed to infilling of the bottom of the channel of the north fork of the drainage and the 

confluence below the site (figs. 20 and 21). Here, deposition 

is as great as 15 cm and totals 2.3 m3. Although some areas 

of erosion are visible immediately adjacent to the areas of 

deposition, they are of small (<10 cm) magnitude and area 

(about 1 m2), and it is therefore not possible to conclude 

whether the deposition is due to aeolian infilling or gully 

bank slumpage.
26 Topographic Change Detection at Select Archeological Sites in Grand Canyon National Park, Arizona, 2006–2007

Site AZ:C:13:099 Playa Area

The playa area near site AZ:C:13:099 is the third study 

site in the Palisades region that we investigated for topographic change (fig. 13). This area is named because it resembles a dry lakebed. Although the playa area does not constitute 

an archeological site in itself, its close proximity to adjacent 

sites of Puebloan age, and the incipient state of the existing 

drainages that could propagate into these archeological areas, 

makes this an important target site for topographic monitoring.

Of the three sites investigated in the Palisades region, this 

area is located farthest from the Colorado River. The site consists of a formerly ponded area of sand, silt, and clays with very 

flat topography, backed immediately by talus slopes formed 

from canyon wall rockfall (fig. 23). Rockfall events have deposited boulders approximately 1 to 2 m in diameter sporadically 

throughout the site. Site soils consist mainly of abiotic cruststabilized sands, although cryptobiotic soils are also present; 

the hard crust has most likely formed due to precipitation of 

cementing agents from evaporation of surface water caught in 

Figure 23. Site AZ:C:13:099 playa area showing location of main gully (dashed line, G1).

Figure 24. Site AZ:C:13:099 playa area—5-cm triangulated irregular network (TIN) output showing location and relative magnitude of 

surface comparison from May 2006 to September 2007. Laser scan and control point locations coincide with figure 13. Identified erosion 

is outlined by dashed area. A, plan view; B, oblique view; and C, vertical change histogram distribution and color scale.
Results 27

Figure 25. Site AZ:C:13:099 playa area—10-cm gridded output showing erosion (red, negative) and deposition (blue, 

positive) from May 2006 to September 2007 and approximate gully location (dashed line). Rectangle shows area of 

identified erosion. Inset is shown with 4 X magnification.
G1

28 Topographic Change Detection at Select Archeological Sites in Grand Canyon National Park, Arizona, 2006–2007

the area. A major concern at this site is that large rainfall events 

may lead to surface water flow that will break through the overlying crust and cause massive gullying of the underlying sands. 

With the exception of a few larger mesquite trees (Prosopis 

glandulosa var. torreyana) around the periphery of the “playa” 

and a few small bushes in the central and northern areas, the 

site is relatively bare of vegetation. A single primary drainage 

traverses the site (G1), but has incised less than 10 cm into the 

underlying soils thus far. Many other smaller channels form a 

dendritic pattern stemming from the primary channel such that 

maximum drainage distances for the transition from initial overland flow to channelized flow are only about 15 meters.

Our comparison of the topography at this site between 

May 2006 and September 2007 shows only one minor area 

(about 0.4 m2) of change (erosion) within the modeled site 

boundary (figs. 24 and 25). The average distance between 

the two modeled surfaces is 0.1 cm with a standard deviation 

of 3.8cm. The 2s confidence intervals (-7.5 cm and 7.7 cm), 

representing 95 percent of the data, are within the error range 

(±8 cm). According to the histogram distribution (fig. 24C), 1.5 

percent of the total surface area (about 50 m2

) underwent more 

than 8 cm of vertical erosion and 0.9 percent (about 30 m2) 

underwent more than 8 cm of vertical deposition. However, on 

additional investigation of the May 2007 model data, we attributed nearly all of these areas either to edge boundary effects of 

the models or poor data density caused by a single faulty scan 

from May 2006. The single area of erosion that was identified 

(about 0.4 m2) represents only 0.01 percent of the entire surface, 

but is located immediately in the main drainage of the site (fig. 

26). Our comparisons of the three surfaces identify that the 

change occurred between May 2006 and May 2007. Though the 

change detection values show possible change that is as much as 

20 cm, additional analysis shows that a majority of this change 

is within the (±8 cm) error bounds. We conclude, therefore, that 

statistically significant erosion of as much as 12 cm occurred 

in this location. On the basis of the relative location and shape 

of the eroded area within the channel, we also propose that the 

change is likely due to channel widening rather than deepening.

Figure 26. Site AZ:C:13:099 playa area—Image and inset showing area of as much as 12 cm measured erosion (arrows) and 

location of major gully (G1).
Results 29

Site AZ:C:13:348

Site AZ:C:13:348 consists of a broad alluvial fan of slope 

wash deposits grading into an alluvial terrace that adjoins a 

former flood plain of the Colorado River. Sand dunes several 

meters in height are located immediately downstream from 

the area, providing a potential source for aeolian transport 

to the site. Three small gullies traverse the site (G1, G2, and 

G3); G1 is composed of two smaller drainages (G1a, G1b) 

that join together at the top of the terrace and gullies G2 and 

G3 are separated from one another by a large coppice mound/

sand dune as they descend from the terrace to river level (fig. 

27). All the gullies appear to be actively downcutting through 

the slope wash deposits as they move across this steeper 

slope. Vegetation consists of irregularly spaced, small desert 

seepweed bushes (Suaeda moquinii) and larger mesquite trees 

(Prosopis glandulosa var. torreyana), which in some cases are 

sufficiently dense to partially obscure the gullies from overhead observation (fig. 28).

This area is archeologically important as an area of 

Puebloan II habitation; first occupation has been generally 

constrained to approximately A.D. 1100 (Fairley and others, 

1994). Two separate archeological sites are located here but 

are similar in age and setting. They consist of the remains 

of jacal-type structures, built by planting wood posts in the 

ground, weaving sticks between the posts, and plastering the 

Figure 27. Site AZ:C:13:348 area showing main gullies (dashed lines), general downhill flow direction (blue 

arrows), and laser scan (red crosses) and laser control point (blue triangles) locations.
Figure 28. Site AZ:C:13:348 area showing gully locations (dashed lines): A, G1 and G2; B, G3.

Figure 29. Site AZ:C:13:348— 5-cm triangulated irregular network (TIN) output showing relative magnitude of surface comparison from 

May 2007 to September 2007. Laser scan and control point locations coincide with figure 27. Two small areas of possible erosion were 

identified in gullies G1 and G2 (ovals). A, plan view; B, oblique view; and C, vertical change histogram distribution and color scale.

30 Topographic Change Detection at Select Archeological Sites in Grand Canyon National Park, Arizona, 2006–2007

wooden framework with mud. Given the surface proximity 

of the structural remains, it is thought that some structures 

extend below the current ground level. The area is also dense 

with surface artifacts, consisting mainly of sherds, although 

complete arrowheads have also been found.

Because of data collection (software) problems in May 

2006, surface comparisons between May 2006 and May 2007 

were performed on only a smaller area of the site (920 m2; 

table 2) containing a single gully (G3). The May 2007 to September 2007 surface comparison was performed on a larger 

area (3,020 m2) containing all three gullies.

The surface comparison between May 2006 and May 

2007 shows that no identifiable change occurred throughout the site. The average distance between the two modeled 

surfaces is 0.4 cm with a standard deviation of 3.3 cm. The 2s

confidence intervals (about 95 percent) are therefore -6.2cm 

and 7.0 cm and are both within the vertical error bound 

estimates (±8 cm). Analysis of the surface change histogram 

distribution (not shown) identified only 2.1 percent of the data 

outside these error bounds; we associated this entirely with 

lack of overlapping data due to vegetation shadows.

The surface comparison between May 2007 and September 2007 identifies two small areas associated with gullies 

G1 and G2 that may have eroded during this time (figs. 29 

and 30). The majority of the site was unchanged. The average 

distance between the two modeled surfaces is -0.9 cm with 

a standard deviation of 2.5 cm. The 2s confidence intervals 

(about 95 percent) are -5.9 cm and 4.1 cm, both well within 
Results 31

the vertical error bound estimates (±8 cm). From the histogram 

distribution (fig. 29C) only 0.7 percent of the area is outside 

the range of error bounds. Analysis of these areas shows that 

with the exception of two small areas, the majority of the 

presumed detected change areas was due to difficult-to-filter 

vegetation.

The two areas of erosion are each very small (about 

0.2m2) and near the detectable change limits (± 8 cm) of this 

study. Although comparative photos from May 2007 are not 

Figure 30. Site AZ:C:13:348—10-cm gridded output showing erosion (red, negative) and deposition (blue, positive) from May 2007 to 

September 2007 and approximate gully locations (dashed lines). Two small areas of possible erosion (ovals) were identified in gullies G1 

and G2.

available, photos from September 2007 indicate the likelihood 

of erosion in these areas (fig. 31). However, given the small 

footprint of the areas and the proximity of the detected change 

to the error bound estimates, we were not able to definitely 

identify these as erosion areas. We identify them here as possible locations for future monitoring. If erosion is occurring, 

we propose it is caused either by surface-water sediment transport or trailing from the use of these gullies as access routes 

by archeologists and geomorphologists.
Figure 31. Site AZ:C:13:348—Images of (A) gully G1 and (B) gully G2 from September 2007 showing possible locations (arrows) of 

minor (about 8 cm) erosion.

32 Topographic Change Detection at Select Archeological Sites in Grand Canyon National Park, Arizona, 2006–2007

Site AZ:G:03:041

Site AZ:G:03:041 is located in an area of slope wash 

deposits covered by aeolian sands. The site contains evidence of 

prehistoric habitation and includes roasting pit features, associated fire-cracked rock, and sparse but identifiable lithic objects. 

Roasting pits are more generally found in the lower, western portion of Grand Canyon and are often associated with protohistoric 

and prehistoric occupations (about A.D. 1500 to 1850) although 

this site has not been precisely dated (Fairley and others, 1994).

A large arroyo, several meters in width with bank height 

of about 1 to 2 m, is located immediately downstream from 

this site and forms the main geomorphic feature of the area. In 

general, the site is flatter at its upper end, increasing in gradient as it drops down towards the Colorado River (fig. 32). Four 

small gullies (fig. 33) traverse the site, parallel in flow direction 

to the larger arroyo, and drain directly to the Colorado River. The 

gullies begin directly in the aeolian sediments (G1 and G2) or 

in the upper slope wash deposits (G3a and G3b) and cut directly 

through some of the roasting features at the site. A check dam has 

been built on one of the gullies (G1) to mitigate against further 

erosion. Pederson and others (2003) performed detailed geomorphic studies in this area to evaluate the erosion control effort.

Vegetation cover consists of a mix of both small grasses and 

shrubs and larger ocotillo (Fouquieria splendens), sagebrush (Artemisia species), cholla (Cylindropuntia acanthocarpa), and mesquite 

(Prosopis glandulosa var. torreyana). Overall, very few open, 

unvegetated areas are present, and in some cases the gullies themselves traverse the site through and under dense shrubs and trees.

Although comparison of the entire site (1,380 m2

) was possible using the May 2006 and September 2007 data, only a smaller 

area (1,000 m2; table 2) could be used for topographic change 

detection with the May 2007 data because of corrupt digital data 

files from six scan locations. This reduced the size of the final 

model for this survey effort by about 25 percent (table 2) and only 

topography for the two gullies farthest upstream (G1 and G2) 

could be analyzed with the May 2007 data.

Overall, little change occurred at this site except for an 

area of sand sheet deposition at the bottom of G2 (fig. 34). 

The statistics of the May 2006 to September 2007 surface 

comparison show an average distance between the two modeled surfaces of 2.6 cm with a standard deviation of 3.4 cm. 

The 2s confidence interval range, representing 95 percent 

of the data, is -4.2 cm to 9.4 cm. Thus, only change associated with deposition is outside the error bound range (±8 

cm). According to the histogram distribution (fig. 34C), 5.0 

percent (about 40 m2

) of the area underwent more than 8 cm 

of vertical deposition and 0.5 percent (about 4 m2

) of the area 

underwent more than 8 cm of erosion. Our analyses attribute 

all measured erosion to processing difficulties with removal 

of vegetation.

Observations and measurements indicate that the deposition occurred as a result of aeolian sand transport and covered an 

area of approximately 38 m2

 at the bottom of G2 (fig. 35). Thus, 

this area accounts for nearly all the identified deposition from the 

histogram analysis. Volume calculations using the model surfaces indicate that 3.5 m3

 of material was deposited in this region 

between May 2006 and September 2007. Additional analysis of 

all surfaces, along with photo interpretation (fig. 36), show that the 

deposition began between May 2006 and May 2007 to a maximum depth of 5 cm and then continued between May 2007 and 

September 2007 to a total average depth of 12 cm.
Figure 32. Site AZ:G:03:041 area showing main gullies (dashed lines), general downhill flow direction 

(blue arrows), and laser scan (red crosses) and laser control point (blue triangles) locations.

Figure 33. Site AZ:G:03:041 area showing gully locations (dashed lines): A, G3b, G3a, and G2;B, G2 and G1.

Results 33
Figure 34. Site AZ:G:03:041—5-cm triangulated irregular network (TIN) output showing relative magnitude of surface comparison from 

May 2006 to September 2007. Laser scan and control point locations coincide with figure 32. One area of deposition at the base of G2 

was identified (ovals). A, plan view; B, oblique view; and C, vertical change histogram distribution and color scale.

Figure 35. Site AZ:G:03:041—10-cm gridded output showing erosion (red, negative) and deposition (blue, positive) from May 2006 to 

September 2007 and approximate gully locations (dashed lines). One area of deposition at the base of gully G2 (oval) was identified.

34 Topographic Change Detection at Select Archeological Sites in Grand Canyon National Park, Arizona, 2006–2007
Figure 36. Site AZ:G:03:041—Images of gully G2 bottom slope area from (A) May 2006 and (B) September 

2007 showing area of as much as 15 cm deposition (ovals).

Results 35
Figure 37. Site AZ:G:03:002 showing main gullies (dashed lines), general downhill flow direction (blue 

arrows), and laser scan (red crosses) and laser control point (blue triangles) locations.

36 Topographic Change Detection at Select Archeological Sites in Grand Canyon National Park, Arizona, 2006–2007

Site AZ:G:03:002

Site AZ:G:03:002 is located on a gently sloping alluvial 

terrace overlain with semistabilized aeolian sand deposits, as 

indicated by grasses and shallow (several centimeters) soil 

development (fig. 37). The terrace is located in a transition 

area between looser, fine-grained aeolian and alluvial deposits 

nearer to the river and coarser-grained slope wash derived 

from the canyon walls. The area contains evidence of protohistoric (A.D. 1500 to mid-1800) occupation by ancestors of 

Hualapai and Southern Paiute peoples. The occupation areas 

have been recorded by archeologists as two separate sites, 

although the division between the two sites is not distinct 

(Fairley and others, 1994). Archeological remains include 

several large roasting pit features in which charcoal and firecracked rocks are abundant.

One main gully (G1) traverses the site and is joined in 

its upper section by a smaller side drainage (G2). The main 

gully is of relatively low gradient until reaching the border 

of the site and the intersection with much looser dune sands 

(fig. 38A). Here, the gully plunges two meters through the 

sands (fig. 38B), forming a sizeable knickpoint before continuing its course towards the river. With the knickpoint possibly 

progressing towards areas of archeologic sensitivity, the 

drainage channel has been lined with rock to help stop erosion. 

Vegetation cover on the upper terrace consists of large (several meters) diameter and relatively well spaced shrubs and 

mesquite trees (Prosopis glandulosa var. torreyana) with only 
Figure 39. Site AZ:G:03:002—5-cm triangulated irregular network (TIN) output showing location and relative magnitude of surface 

comparison from May 2006 to September 2007 for the upper area. Laser scan and control point locations coincide with fig. 37. No significant 

topographic change was identified. A, plan view; B, oblique view; and C, vertical change histogram distribution and color scale.

Results 37

minor smaller cacti. During the spring, grasses cover much of 

the site. Below the upper terrace and within the well-incised 

gully, vegetation becomes much denser and more riparian. In 

some places, it is not possible to walk between trees.

Although all three survey efforts allowed generation of 

detailed site topography models, the dense vegetation and 

narrow dimensions of the lower section of G1 prevented 

construction of complete surface models of this lower area. 

In many places, the lower gully is only 1.5 m wide, less than 

the 2-m minimum range required by the lidar unit. Vegetation grows very close to the edges of the gully, preventing the 

location of scan positions from farther away. As a result, the 

surface models we present here only examine topographic 

changes in the upper part of the site (scan locations 1 through 

5; fig. 37). In the lower section (scan locations 6 through 13), 

we investigated changes by comparing only a smaller selection 

of manually filtered points that we could positively correlate 

with ground topography.

We found no statistically significant change in the upper 

gully area between May 2006 and September 2007 (fig. 39). 

Although the results indicate some minor, scattered erosion 

towards the boundary of the site (fig. 40), we attribute this to 

a coarser alignment of scan clouds caused by a lack of survey 

data for some scan locations during the May 2006 effort. 

Analysis of the May 2006 to May 2007 and May to September 2007 surfaces confirmed this analysis. The statistics of 

the May 2006 to September 2007 surface comparison calculate an average distance between the two modeled surfaces 

Figure 38. Site AZ:G:03:002 area showing gully locations (dashed lines): A, upper G1 and G2; t, lower G1.
Figure 40. Site AZ:G:03:002—10-cm gridded output showing erosion (red, negative) and deposition (blue, positive) from May 2006 to 

September 2007 and approximate gully locations (dashed lines). No significant topographic change was identified. “Erosion areas” 

were attributed to poor registration of some areas of the May 2006 data as indicated.

38 Topographic Change Detection at Select Archeological Sites in Grand Canyon National Park, Arizona, 2006–2007

of 0.1 cm with a standard deviation of 3.2 cm (fig. 39). The 

2s confidence interval range, representing 95 percent of the 

data, is -6.3 cm to 6.5 cm. Thus, the vast majority of the data 

is within the error bound range (±8 cm). According to the 

histogram distribution (fig. 39C), 0.5 percent (about 5 m2) of 

the area underwent more than 8 cm of vertical deposition and 

1.8 percent (18.4 m2) of the area underwent more than 8 cm of 

erosion. As discussed, our analyses indicate that none of this 

change is statistically significant.

Our analysis of the point data in the lower gully area yielded 

no statistically significant change with the exception of one minor 

area. However, given the difficulties associated with the data 

collection in this narrow area and our inability to model the entire 

lower area effectively, we do not include this measured change in 

our final site change results. We performed cross-section analysis 

on two sections of the drainage, one in the immediate vicinity 

of the major gully knickpoint and another in the lowest section 

as the gully transitions out of the loose sand deposits. One small 

(<0.5 m2) section in the knickpoint area appears to have undergone very minor channel sidewall slumping and related gully 

bottom deposition, with as much as 10 cm of erosion and related 

deposition at the gully bottom. Given poor registration of the May 

2007 data in this area, we were not able to determine whether this 

change occurred before or after this time. In the lower transition 

area, all measured change was within the error bounds (fig. 41). 

Given the difficulties associated with the data collection in such 

narrow confines, this area may not be well suited for whole-site 

monitoring using the presented terrestrial lidar methods. Instead, 

future surveys should focus on specific sections of the gully, with 

longer range scanner setup vantage points.
Figure 41. Site AZ:G:03:002—A, Cross-section analysis of lower G1 area from manual filtered point data. Average vertical distance 

between all sections is less than the error range (±8 cm). B, Image showing cross-section location and narrow confines of this area.

Results 39
40 Topographic Change Detection at Select Archeological Sites in Grand Canyon National Park, Arizona, 2006–2007

Site AZ:G:03:072 US

Site AZ:G:03:072 US (upstream) and site AZ:G:03:072 

DS (downstream) form a single archeological site but were 

divided into two study areas (sites) because of their large 

spatial extent. The entire area is important as a prehistoric and 

protohistoric habitation site containing evidence of numerous 

roasting pits (Fairley and others, 1994). The sites are divided 

by a prominent large boulder-chocked drainage, and three small 

but well-developed gullies traverse each area (fig. 42). The 

downstream gullies are steeper in maximum gradient but generally show signs of less geomorphic activity due to incision to 

bedrock and better-stabilized soils. However, in many places, 

the archeological features are in close or direct proximity to the 

gullies, highlighting their vulnerability to future erosion and the 

importance of tracking topographic change.

Our observations indicate that the upstream site 

(AZ:G:03:072 US) consists of both active and stabilized 

aeolian dune areas. The gradient is generally constant over 

most of the site with the exception of several well-developed 

drainage knickpoints. Of the three gullies that cross this site, 

two are located in areas of generally stabilized vegetated and 

cryptobiotic crust (fig. 43A, B), although drainage knickpoints through the crust are visible in places and are the sites 

Figure 42. Site AZ:G:03:072 showing main gullies (dashed lines), general downhill flow direction, and laser 

scan (red crosses) and control point (blue triangles) locations for both upstream and downstream sites.
Results 41

of apparent recent erosion. The third is located in an area of 

active aeolian dune sand (fig. 43C); this gully appears to be 

actively downcutting through the dune field. All three gullies drain directly to the Colorado River which borders the 

site. Vegetation consists of clumps of grasses, smaller bushes, 

and prickly pear cactus (Opuntia basilaris), along with taller 

groups of ocotillo (Fouquieria splendens), cholla (Cylindropuntia acanthocarpa), and larger creosote (Larrea tridentata

var. tridentata) and catclaw acacia (Acacia greggii) bushes 

several meters in height. Although vegetation generally 

clumps together, it is sufficiently dense to prevent line-ofsight visibility from one area to the next. Although individual 

gullies are sufficiently open to allow data collection, it is our 

opinion that this site is likely near maximum complexity for 

large-scale terrestrial lidar change detection studies.

Following the May 2006 data collection, we increased 

the number of scan locations and consequently the total area 

of scanning (table 2). During the subsequent May 2007 and 

September 2007 survey efforts, we saw visible change at identical locations within this site. As a result, we present separate 

change detection analyses for the May 2006 to May 2007 and 

May 2007 to September 2007 timeframes.

The May 2006 to May 2007 comparison shows only one 

area of significant topographic change linked to the headward 

erosion of G3 (figs. 44 and 45). The overall statistics indicate that the majority of the site did not undergo topographic 

change; the average distance between the two modeled 

surfaces is 1.1 cm with a standard deviation of 4.4 cm. The 

2s confidence interval range, representing 95 percent of the 

data, is therefore -7.7 cm to 9.9 cm. Thus, slightly more than 

Figure 43. Site AZ:G:03:072 US area showing gully locations 

(dashed lines): A, G1; B, G2; C, G3.
42 Topographic Change Detection at Select Archeological Sites in Grand Canyon National Park, Arizona, 2006–2007

5 percent of the data is outside the error bound range (±8cm). 

According to the histogram distribution (fig. 44C), 4.2 percent (about 37 m2

) of the area underwent more than 8 cm of 

vertical deposition, but we attribute nearly all this change to 

processing difficulties with vegetation (fig 45). In terms of net 

erosion, the histogram distribution shows 2.5 percent of the 

total surface area (about 22 m2

) underwent more than 8 cm of 

vertical erosion. Although some of this change is associated 

with processing difficulties with vegetation, the majority (13 

m2

) is linked to erosion and bank slumpage along an 11-m 

length of the drainage concentrated in and around gully G3 

(fig. 45). The change is visible in both photo (fig. 46) and contour map (fig. 47) comparative analysis. Additional volumetric 

analysis between a best fit of the two surfaces in this region 

indicates a net sediment loss of 2.0 m3

 from this area between 

May 2006 and May 2007.

The May 2007 to September 2007 comparison indicates 

that additional change occurred to this site and was distributed 

throughout the three gully areas. The overall surface comparison 

shows that the average difference between the two surfaces is 

-0.9 cm with a standard deviation of 5.0 cm. The 2s confidence 

interval range, representing 95 percent of the data, is therefore 

-10.9 cm to 9.1 cm. Thus more than 5 percent of the data is 

outside the error bound range (±8 cm). The histogram distribution (fig. 48C) shows that 1.8 percent (about 22 m2

) of the area 

underwent more than 8 cm of vertical deposition; however, we 

attribute nearly all of this change to processing difficulties with 

vegetation. In terms of net erosion, the histogram distribution 

(fig. 48C) shows 4.3 percent of the total surface area (about 

52m2) underwent more than 8 cm of vertical erosion. Although 

some of this change is associated with processing difficulties with vegetation, the majority (30 m2

) is linked to erosion 

throughout the site and along all three gullies (fig. 49).

Five areas of erosion were identified. The first is located 

in a small length (3.2 m) of G1. Here, we measured an average of as much as 15 cm of erosion over a total area of 1 m2

(fig. 50) with maximum erosion of 20 cm and total sediment 

volume of 0.1 m3

. In G2, we also measured an average of 

15 cm of erosion over a longer length (12.3 m) and greater 

area (2.5 m2

) with a total eroded sediment volume of 0.3 m3. 

Maximum erosion resulting in vertical lowering was about 

25cm (fig. 51). Two areas of erosion were identified outside of 

the gullies, one on a slope bordering G2 (fig. 52) and the other 

in an active sand dune area near G3 (fig. 53). At the slope near 

G2, a 3.2 m2

 area underwent as much as 15 cm of erosion for a 

total eroded volume of 0.2 m3

. At the G3 dune area, a 12.1-m2

area also underwent as much as 15 cm of erosion and a total 

eroded volume of 0.8 m3

. The final identified area of erosion 

was within the G3 channel (fig. 54), encompassing an 11.2 m2

area over a 28.4 m length of the drainage. Within this area, we 

measured maximum erosion depths of 50 cm, averaging 25 cm 

over a 14-m-long section of the gully and shown by contour 

analysis in figure 55. Additional volumetric analysis of the two 

surfaces in this region indicates a net sediment loss of 4.7 m3

from this area between May 2007 and September 2007.

Figure 44. Site AZ:G:03:072 US—5-cm triangulated irregular network (TIN) output showing location and relative magnitude of surface 

comparison from May 2006 to May 2007. Laser scan and control point locations coincide with figure 42. Only one area of erosion 

(polygons) associated with gully G3 could be positively identified. A, plan view; B, oblique view; and C, vertical change histogram 

distribution and color scale.
Results 43

Figure 45. Site AZ:G:03:072 US—10-cm gridded output showing erosion (red, negative) and deposition (blue, positive) from May 2006 

to May 2007 and approximate gully locations (dashed lines). Only one area of erosion (polygon) associated with gully G3 could be 

positively identified.
44 Topographic Change Detection at Select Archeological Sites in Grand Canyon National Park, Arizona, 2006–2007

Figure 46. Site AZ:G:03:072 US—Photo comparison of G3 erosional area between (A) May 2006 and (B) May 2007.

Figure 47. Site AZ:G:03:072 US—10-cm contour map comparison of G3 erosional area between (A) May 2006 and (B) May 2007. Dashed 

line is approximate gully thalweg over the length of detected change (about 11 m).
Results 45

Figure 48. Site AZ:G:03:072 US— 5-cm triangulated irregular network (TIN) output showing location and relative magnitude of surface 

comparison from May 2007 to September 2007. Laser scan and control point locations coincide with figure 42. Topographic change 

(ovals and polygons) was identified in all three gullies. A, plan view; B, oblique view; and C, vertical change histogram distribution and 

color scale. “Hole” in G3 represents area not imaged in September 2007 because of the mislocation of the scanner.
46 Topographic Change Detection at Select Archeological Sites in Grand Canyon National Park, Arizona, 2006–2007

Figure 49. Site AZ:G:03:072 US—10-cm gridded output showing erosion (red, negative) and deposition (blue, positive) from May 2007 to 

September 2007 and approximate gully locations (dashed lines). Erosion was identified at five locations (ovals and polygons), including in 

all three gullies. Data points of large boulder were filtered inconsistently between model surfaces and therefore show up as false erosion.
Results 47

Figure 50. Site AZ:G:03:072 US—Photo of G1 erosional area (oval) in September 2007. Additional erosion lower in the gully (arrows) 

likely occurred but was within the error bounds of the data (change less than 8 cm) and therefore not detected in the comparison.
48 Topographic Change Detection at Select Archeological Sites in Grand Canyon National Park, Arizona, 2006–2007

Figure 51. Site AZ:G:03:072 US—Photo comparison of G2 erosional area (parallel lines) between (A) May 2007 looking updrainage and 

(B and C) September 2007 looking downdrainage. Identical prickly pear cactus (hexagon) is highlighted in all photos for orientation.

Figure 52. Site AZ:G:03:072 US—Photo of G2 slope erosional area (oval) in September 2007.
Results 49

Figure 53. Site AZ:G:03:072 US—Photo of G1 dune erosional area (oval) in September 2007.

Figure 54. Site AZ:G:03:072 US—Photo comparison of G3 erosional area (parallel lines) between (A) May 2007 looking downdrainage 

and (B) September 2007 looking updrainage. Small creosote bush (hexagon) is highlighted in both photos for orientation.
50 Topographic Change Detection at Select Archeological Sites in Grand Canyon National Park, Arizona, 2006–2007

Site AZ:G:03:072 DS

Site AZ:G:03:072 DS forms a triangular shaped area 

bounded by large (several meters in width) drainages on two 

sides and a significant change in slope on the other (fig. 42). 

The area is generally of increasingly convex gradient with 

three gullies (G1, G2, G3) in various stages of development 

traversing the site (fig. 56). The gullies begin in an area of 

generally flat topography but dramatically increase in gradient as they reach the edge of the site. The gullies lead into the 

two larger bordering drainages which then converge and drain 

to the Colorado River, some 40 m downstream. Two gullies 

are being actively monitored for annual change caused by 

monsoon rains. The third (G3) has already incised to bedrock 

and does not exhibit significant change. Vegetation includes a 

broad mix of cacti, including prickly pear (Opuntia basilaris) 

and ocotillo (Fouquieria splendens), as well as several larger 

mesquite (Prosopis glandulosa var. torreyana) and catclaw 

acacia (Acacia greggii) trees. In the gullies, vegetation is 

generally absent. Site soils generally appear stabilized by both 

vegetation and cryptobiotic crust.

We focused our survey efforts on the G1 and G2 gully 

locations, so there is minimal data available for the G3 gully 

bottom. All three efforts were successful in allowing the generation of detailed site topography, but an experiment with new 

scan locations in September 2007 resulted in a lack of sufficient 

data in the primary study area to construct a full detailed model. 

As a result, we were only able to compare the original site area 

(460 m2

; table 2) between May 2006 and May 2007 (fig. 57). A 

somewhat different area (about 450 m2) was compared for the 

May 2007 and September 2007 data sets.

The May 2006 to May 2007 comparison shows that no 

statistically significant change occurred during this period 

(figs. 57 and 58). The average distance between the two 

modeled surfaces is -0.8 cm with a standard deviation of 

3.6 cm. The 2s confidence intervals (-8.0 cm and 6.4 cm), 

representing 95 percent of the data, are within the error range 

bounds (±8 cm). According to the histogram distribution 

(fig. 57C), 3.0 percent of the total surface area (about 14 m2

) 

underwent more than 8 cm of vertical erosion and 0.8 percent 

(about 4 m2) underwent more than 8 cm of vertical deposition. After additional investigation, we attributed the change 

in these areas to difficult-to-filter, tall vegetation in the case of 

the deposition and the dying off of grasses (figs. 56 and 58) in 

the case of the erosion.

The May 2007 to September 2007 comparison also 

showed no statistically significant topographic change, 

although it is not immediately apparent from the results (figs. 

59 and 60). Because of the different alignments of the scan 

positions, we found discrepancies with how the data was filtered to remove vegetation and other nonbare ground objects. 

Thus, several areas that show deposition were determined 

to represent difficult-to-interpret ground areas such as small 

bushes of prickly pear cacti and jumbled cobble-sized rocks 

(fig. 60). The average distance between the two modeled surfaces was 2.4 cm with a standard deviation of 4.2 cm. The 2s

confidence intervals (-6.0 cm and 10.8 cm), representing 95 

percent of the data, are just outside the error range of the data 

(±8 cm). According to the histogram distribution (fig. 59C), 

5.2 percent of the total surface area (about 23 m2

) underwent 

more than 8 cm of vertical deposition and 1.1 percent (about 

5 m2) underwent more than 8 cm of vertical erosion. The six 

areas highlighted in figure 60 represent approximately 75 

percent of the detected deposition; we assume the other 25 

percent to be related to similar difficulties with data collection 

and processing at this site. Similarly, the vegetation “erosion” 

area indicated in figure 60 also represents the majority of the 

detected change.

Figure 55. Site AZ:G:03:072 US—10-cm contour map comparison of G3 erosional area between (A) May 2007 and (B) September 2007. 

Dashed line is approximate gully thalweg over the total length of detected change (about 28 m).
Results 51

Figure 56. Site AZ:G:03:072 DS area showing gully locations (dashed lines) in (A) May 2006 and (B) May 2007. Note longer grasses 

present in the May 2006 image.

Figure 57. Site AZ:G:03:072 DS—5-cm triangulated irregular network (TIN) output showing location and relative magnitude of surface 

comparison from May 2006 to May 2007. Laser scan and control point locations coincide with figure 42. No significant topographic 

change was identified. A, plan view; B, oblique view; and C, vertical change histogram distribution and color scale.
52 Topographic Change Detection at Select Archeological Sites in Grand Canyon National Park, Arizona, 2006–2007

Figure 58. Site AZ:G:03:072 DS—10-cm gridded output showing erosion (red, negative) and deposition (blue, positive) from May 2006 to 

May 2007 and approximate gully locations (dashed lines). No significant change was detected during this time period.
Results 53

Figure 59. Site AZ:G:03:072 DS—5-cm triangulated irregular network (TIN) output showing location and relative magnitude of 

surface comparison from May 2007 to September 2007. Laser scan and control point locations coincide with figure 42. No significant 

topographic change was identified. A, plan view; B, oblique view; and C, vertical change histogram distribution and color scale.
54 Topographic Change Detection at Select Archeological Sites in Grand Canyon National Park, Arizona, 2006–2007

Figure 60. Site AZ:G:03:072 DS—10-cm gridded output showing erosion (red, negative) and deposition (blue, positive) from May 2007 to 

September 2007 and approximate gully locations (dashed lines). Despite indications of deposition, no significant change was detected 

during this time period.
Discussion 55

Discussion

This investigation provides new information about the 

amount and types of topographic changes that are currently 

affecting archeological sites within the Colorado River corridor in Grand Canyon National Park. We detected statistically 

significant change (greater than ±8 cm) at six of the nine sites 

investigated in this study (table 3) and possible change at two 

of the other sites. In general, change was detected on less than 

5 percent of the total surface area modeled for each site, with 

the exception of site AZ:C:13:006, which showed deposition over almost 20 percent of the site area. Where detected, 

maximum erosion depths were between 12 cm and 50 cm and 

averaged between 12 cm and 17 cm. Similarly, maximum 

deposition depths were between 15 cm and 35 cm and averaged between 12 cm and 15 cm. While reinforcing the utility 

of methods used for this investigation and providing the ability 

to perform highly specific topographic change modeling, the 

results also highlight several points to be considered for additional geomorphologic and monitoring studies.

When detected, erosion was typically associated with 

surface water processes concentrated in drainages, whereas 

deposition was typically associated with aeolian sand transport 

outside drainage channels. This confirms the importance of 

studying gully geomorphology to understand potential effects 

of erosion at archeological sites. The identified change at sites 

AZ:C:13:006 and AZ:G:03:072 US are stand-out examples. 

However, measurements of aeolian sand deposition at several 

sites (for example, AZ:C:13:006 and AZ:G:03:041) also provide 

important information on surface aggradation and the potential 

for gully infilling, and thus topographic monitoring in areas 

outside already developed gullies is also important. At site 

AZ:C:13:006, the large depositional area detected between G2 

and G3 may in fact be keeping erosion from occurring in this 

area. However, we also note that these processes may be competing and taking place concurrently over varying time spans. 

Regardless, we conclude that it is important to monitor for 

change not only in areas of present-day erosion but also in areas 

of either potential new erosion or deposition. At a minimum, 

monitoring should occur for baseline change detection purposes. 

Simple geomorphic drainage models that calculate the potential 

for concentrated stream flow could be used for initial assessment of these areas.

The importance of using highly regimented and accurate data collection and processing methods should also be 

emphasized. In general, we found it extremely important to 

maintain the same set-up geometry and “look” angles for the 

topography of interest, regardless of the type of terrain being 

investigated (for example, flat, steep, or hummocky ground). 

This resulted in similar data point density and, consequently, 

highly comparable surface models. One specific limitation 

of the data collection and processing methodologies was the 

sometimes poor or inconsistent filtering of vegetation from the 

point- cloud data. The remedy to this issue is not simple. In 

fact, vegetative filtering problems are common to all “lineof-sight” data collection methods, including both aerial and 

terrestrial lidar. Several automated methods are available, but 

we still propose that additional, rigorous manual checking 

of the data be performed, as was implemented in this study, 

to ensure that poor filtering does not lead to false positives 

of detected change. Because the false positives may take the 

form of either erosion (the more recent surface has been more 

Table 3. Summary of net topographic change between May 2006 and September 2007.

Site Number

Area w/ measured erosion

(m2

)

Area w/ measured deposition (m2

)

Total percent of site 

area modeled w/ 

topographic change

(percent)

Average, maximum height of 

erosion 

(cm)

Average, maximum height of 

deposition 

(cm)

Total site volume 

of erosion (-) and 

deposition (+)

(m3

)

AZ:C:13:006 12.0 260 21.3 15,30 15,35 -0.7/+26.9

AZ:C:13:336 0 0.9 0.1 0,0 12,15 0/+0.1

AZ:C:13:099 11.0 19 3.9 12,20 12,15 -0.8/+2.3

AZ:C:13:099 playa area 0.4 0 <0.1 12,12 0,0 -0.1/0

AZ:C:13:348 0 0 0 0,0 0,0 0/0

AZ:G:03:041 0 38 4.8 0,0 12,15 0/+3.5

AZ:G:03:002 0 0 0 0,0 0,0 0/0

AZ:G:03:072 US 32.0 0 2.7 17,50 0,0 -8.1/0

AZ:G:03:072 DS 0 0 0 0,0 0,0 0/0
56 Topographic Change Detection at Select Archeological Sites in Grand Canyon National Park, Arizona, 2006–2007

rigorously filtered) or deposition (the less recent surface has 

been more rigorously filtered), neither false positive can be 

ruled out—both must be investigated. In this study, quality 

control for both of these issues was obtained through the use 

of photographs taken of each site at the time of data collection. Despite the high accuracy of the lidar data, we still found 

photographs indispensable for positively verifying areas of 

topographic change. We therefore strongly recommend that 

this type of data be gathered concurrently with terrestrial lidar 

surveys. The latest generation of laser instruments with built in 

high-resolution digital cameras capable of point-cloud photo 

draping will likely prove highly worthwhile in this regard.

Finally, we recommend that additional geomorphic studies be performed to understand the role of alluvial and aeolian 

sediment transport for maintaining relative topographic conditions at archeological sites in the Colorado River corridor. The 

data presented here only partly address this question. We plan 

to use this data collaboratively with other researchers who 

have gathered information on weather and geomorphic variables to arrive at conclusions on the effects of river levels and 

long-term climate patterns on archeological site preservation.

Conclusions

The deterioration of archeological sites from gully erosion within the Colorado River corridor of Grand Canyon 

National Park poses an ongoing management problem. Several 

questions exist including the location and magnitude of the 

changes occurring in relation to archeological resources, the 

rate of the changes, and the relative contribution of several 

potential causes including sediment depletion associated with 

managed flows from Glen Canyon Dam, site-specific weather 

patterns, visitor impacts, and long-term climate change. To 

answer these questions, highly accurate, spatially specific data 

are needed from sites undergoing change. Previous survey 

technologies have not been able to efficiently and accurately 

collect this data. Using terrestrial lidar data collection techniques and new post-processing methods, we analyzed topographic data for nine archeological sites, collected using three 

separate data collection efforts spanning 16 months.

Our results indicate that six of the nine sites showed positive signs of either erosion, deposition, or both during this time 

interval. Two other sites also showed possible signs of change.

Erosion was concentrated in established gully drainages and 

averaged 12 cm to 17 cm in depth with maximum depths of 

50 cm. Deposition was also concentrated at specific locations 

outside of drainages, but generally was spread over larger areas. 

Maximum depths of deposition averaged 12 cm to 15 cm and 

reached up to 35 cm. Overall, we found that the spatial distribution and magnitudes of surface change are specific to each site, 

and a thorough understanding of the geomorphology, weather, 

and sand supply is requisite for a complete understanding of the 

data. Additional work in combining these results with site-specific weather, hydrology, and geomorphology data will assist in 

the development of working models for determining the causes 

of the documented topographic changes.

Acknowledgments

Funding for this research was provided by a cooperative 

work agreement between the USGS Grand Canyon Monitoring 

and Research Center and the USGS Geologic Division initiated 

by Helen Fairley, Sociocultural Program Manager at the GCMRC. 

We thank Ms. Fairley for her vision and continuing commitment 

to this project. Kristin Brown, formerly of the GCMRC, provided 

field survey support and logistical assistance with all three data 

collection efforts, and her assistance is gratefully acknowledged. 

We thank Kevin Schmidt (USGS) and two anonymous reviewers 

whose comments improved this report. The authors would also 

like to thank the following individuals for their assistance with 

the data collection efforts: Jennifer Dierker and Lisa Leap, Grand 

Canyon National Park; Joel Pederson, Gary O’Brien, Ben Dejong, 

Mike Keller, Chris Tressler, and Tim Andrews, Utah State University; Richard Jonasse, USGS volunteer; Brian Dierker, Humphrey 

Summit Support, and the many other Grand Canyon river guides 

who participated in the field trips.

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Produced in the Western Region, Menlo Park, California

Manuscript approved for publication, June 1, 2009

Edited by James W. Hendley II

Layout by David R. Jones
Collins and others—Topographic Change Detection at Select Archeological Sites in Grand Canyon National Park, Arizona, 2006–2007—Scientific Investigations Report 2009-5116