National Park Service

U.S. Department of the Interior

Natural Resource Stewardship and Science

Chaco Culture National Historical Park

Geologic Resources Inventory Report

Natural Resource Report NPS/NRSS/GRD/NRR—2015/1045
ON THE COVER: Photograph of Pueblo Bonito in Chaco Culture National Historical Park. Pueblo Bonito is a massive 

stone building, referred to as a “great house,” in Chaco Canyon. The Chacoan cultural complex, which encompassed 

these great houses, covered much of the present-day Southwest, including the San Juan Basin in northwestern New 

Mexico. National Park Service photograph. 

THIS PAGE: Photograph of Casa Rinconada in Chaco Culture National Historical Park. The blocks of Cliff House 

Sandstone used in construction were once part of a barrier island off the west coast of the Western Interior Seaway. 

The seaway inundated New Mexico about 96 million years ago. This time-lapse photograph shows star trails. The 

park’s natural nighttime darkness, commitment to reducing light pollution, and ongoing public outreach have led 

to its certification as an International Dark Sky Park by the International Dark-Sky Association. National Park Service 

photograph.
Chaco Culture National Historical Park

Geologic Resources Inventory Report

Natural Resource Report NPS/NRSS/GRD/NRR—2015/1045

Katie KellerLynn 

Colorado State University Research Associate

National Park Service Geologic Resources Division

Geologic Resources Inventory

PO Box 25287

Denver, CO 80225

September 2015

U.S. Department of the Interior

National Park Service

Natural Resource Stewardship and Science 

Fort Collins, Colorado
ii

The National Park Service, Natural Resource Stewardship and Science office in Fort Collins, Colorado, publishes a 

range of reports that address natural resource topics. These reports are of interest and applicability to a broad audience 

in the National Park Service and others in natural resource management, including scientists, conservation and 

environmental constituencies, and the public. 

The Natural Resource Report Series is used to disseminate comprehensive information and analysis about natural 

resources and related topics concerning lands managed by the National Park Service. The series supports the 

advancement of science, informed decision-making, and the achievement of the National Park Service mission. The 

series also provides a forum for presenting more lengthy results that may not be accepted by publications with page 

limitations.

All manuscripts in the series receive the appropriate level of peer review to ensure that the information is scientifically 

credible, technically accurate, appropriately written for the intended audience, and designed and published in a 

professional manner. This report received informal peer review by subject-matter experts who were not directly 

involved in the collection, analysis, or reporting of the data.

Views, statements, findings, conclusions, recommendations, and data in this report do not necessarily reflect views and 

policies of the National Park Service, U.S. Department of the Interior. Mention of trade names or commercial products 

does not constitute endorsement or recommendation for use by the U.S. Government. 

This report is available from the Geologic Resources Inventory website (http://go.nps.gov/gripubs), and the Natural 

Resource Publications Management website (http://www.nature.nps.gov/publications/nrpm/). To receive this report in 

a format optimized for screen readers, please email irma@nps.gov.

Please cite this publication as:

KellerLynn, K. 2015. Chaco Culture National Historical Park: Geologic resources inventory report. Natural Resource 

Report NPS/NRSS/GRD/NRR—2015/1045. National Park Service, Fort Collins, Colorado.

NPS 310/129981, September 2015
iii

Contents

Page

Figures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . v

Tables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vi

Executive Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vii

Products and Acknowledgments . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xi

GRI Products . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xi

Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xi

Geologic Setting and Significance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Geologic Features and Processes . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Upper Cretaceous Rocks and Fossils . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Quaternary Fossils . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

Chaco Canyon . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

Chaco Arroyo . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

Dynamic Sedimentation and Arroyo Development . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

Alluvial Fill . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

Sheetwash Alluvium and Slope-Wash Deposits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

Eolian Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

Tinajas and Charcos . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

Badlands . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

Cave Shelters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

Geologic Resource Management Issues . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

Oil and Gas Development . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

Coal Resources and Mining . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

Uranium Production . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

Abandoned Mineral Lands . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36

Disturbed Lands Restoration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

Rockfall . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38

Paleontological Resource Inventory and Monitoring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43

Piping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44

Seismicity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46

Eolian Processes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47

Efflorescence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47

Geologic History . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49

Late Cretaceous Period: Western Interior Seaway . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49

Close of the Cretaceous Period: San Juan Basin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49

Pleistocene Epoch: Chaco Canyon . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50

Pleistocene and Holocene Epochs: Dynamic Sedimentation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50

Holocene Epoch: Cut-and-Fill Cycles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51

Holocene Epoch: Chaco Arroyo and Active Inner Channel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53

Holocene Epoch: Human Populations in Chaco Canyon . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54

Holocene Epoch: Geoarcheology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54

Geologic Map Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55

Source Maps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55

GRI GIS Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56

GRI Map Poster . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57

Map Unit Properties Table . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57

Use Constraints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
iv

Contents (continued)

Glossary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59

Literature Cited . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65

Additional References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75

Geology of National Park Service Areas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75

NPS Resource Management Guidance and Documents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75

Climate Change Resources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75

Geological Surveys and Societies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75

US Geological Survey Reference Tools . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75

Appendix A: Scoping Participants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77

2007 Scoping Meeting Participants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77

2014 Conference Call Participants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77

2014 Oil and Gas Issues Conference Call Participants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77

Appendix B: Geologic Resource Laws, Regulations, and Policies . . . . . . . . . . . . . . . . . . . . . . . . . 79

Page

GRI Poster . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .in pocket

Map Unit Properties Table . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .in pocket
v

Figure 1. Regional map showing the location of Chaco Culture National Historical Park, great houses, and prehistoric roads . . . . . . . . . . . 1

Figure 2. Geologic time scale . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Figure 3. Paleogeographic map of the Western Interior Seaway. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Figure 4. Cross section of the San Juan Basin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Figure 5. Photograph of Fajada Butte . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Figure 6. Graphic representation of San Juan Basin stratigraphy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Figure 7. Photograph of badlands . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Figure 8. Photograph of fossil tree stump . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Figure 9. Photograph of ceratopsian (?) fossil . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Figure 10. Photograph of side-neck turtle fossi . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Figure 11. Photograph of turtle remains . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

Figure 12. Photograph of crocodile fossil . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

Figure 13. Photograph of Menefee Formation concretions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

Figure 14. Photograph of cross-bedding in Cliff House Sandstone . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

Figure 15. Cross section of Chaco Canyon . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

Figure 16. Schematic diagram of barrier-island complex. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

Figure 17. Photograph of tidal “bundles” in Cliff House Sandstone . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

Figure 18. Photograph of storm deposit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

Figure 19. Photograph of bivalve fossil . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

Figure 20. Photograph of gastropod fossil . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

Figure 21. Photograph of ammonite cast . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

Figure 22. Photograph of fossil burrows and bioturbation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

Figure 23. Photograph of fossil burrows . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

Figure 24. Photograph of petrified log . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

Figure 25. Photograph of shark teeth fossils . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

Figure 26. Photograph of mosasaur fossil . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

Figure 27. Photograph of plesiosaur fossil . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

Figure 28. Photograph of concretion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

Figure 29. Photograph of iron-cemented burrows . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

Figure 30. Photograph of honeycomb weathering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

Figure 31. Photograph of Lewis Shale . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

Figure 32. Photograph of Chetro Ketl. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

Figure 33. Schematic diagram of geomorphic features of Chaco Canyon . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

Figure 34. Schematic diagram of Chaco Canyon without an arroyo . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

Figure 35. Schematic diagram of Chaco Canyon with an arroyo . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

Figure 36. Photograph of broken concretions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

Figure 37. Photograph of Menefee badlands . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

Figure 38. Photograph of cave shelter. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

Figure 39. Map of surface ownership . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

Figure 40. Map of coal fields in the San Juan Basin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

Figure 41. Map of Grants uranium district . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35

Figure 42. Photograph of talus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

Figure 43. Photograph of Threatening Rock . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

Figure 44. Satellite imagery of Pueblo Bonito . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40

Figure 45. Schematic illustration of slope movements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41

Figure 46. Photograph of rockfall hazard areas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42

Figure 47. Photograph of rockfall at Chaco Culture National Historical Park . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43

Figure 48. Photograph of piping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45

Figures

Page

Plate 1. Map of Chaco Culture National Historical Park . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . in pocket
vi

Figures (continued)

Figure 49. Photograph of Pueblo del Arroyo . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45

Figure 50. Map of earthquake probability. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46

Figure 51. Photograph of efflorescence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48

Figure 52. Satellite imagery of erosion surfaces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51

Figure 53. Diagram of Chaco Canyon through time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52

Figure 54. Schematic illustration of Chaco Canyon . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53

Tables

Page

Table 1. Upper Cretaceous stratigraphy of the San Juan Basin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

Table 2. GRI GIS data for Chaco Culture National Historical Park . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57

Page
vii

Executive Summary

The Geologic Resources Inventory (GRI) is one of 12 inventories funded by the National Park Service 

(NPS) Inventory and Monitoring Program. The Geologic Resources Division of the NPS Natural 

Resource Stewardship and Science Directorate administers the GRI. This report synthesizes discussions 

from a scoping meeting for Chaco Culture National Historical Park (New Mexico) on 14 February 

2007 and follow-up conference calls on 13 February 2014 and 15 April 2014, which were held by 

the Geologic Resources Division to identify geologic resources of significance and geologic resource 

management issues, as well as determine the status of geologic mapping. It is a companion document to 

previously completed GRI GIS data.

Chaco Culture National Historical Park encompasses 

13,744 ha (33,960 ac) in four park units—the main 

Chaco Canyon unit and three smaller outliers (Kin 

Bineola, Pueblo Pintado, and Kin Ya’a). The park’s main 

geomorphic feature is Chaco Canyon, which contains 

13 primary prehistoric sites and hundreds of smaller 

ones. A major Chacoan building phase produced 

multistoried great houses and large kivas (underground 

or partly underground chambers) between 850 to 1150 

CE (common era). 

Most of the Chacoan great houses were built along the 

northern side of Chaco Canyon, under vertical cliffs of 

towering Cliff House Sandstone. This sandstone and the 

other bedrock units in the park were deposited during 

the Late Cretaceous Period between about 100 million 

and 70 million years ago when a vast sea, called the 

“Western Interior Seaway,” inundated the central part 

of North America, splitting the continent into two land 

masses. The site of Chaco Culture National Historical 

Park was on the western shoreline of this seaway.

The ancestral Chaco River cut down though Upper 

Cretaceous bedrock, exposing former deposits of 

the Western Interior Seaway in the walls of Chaco 

Canyon. The exact timing of incision of Chaco Canyon 

is unknown but estimated to have initiated less than 2 

million years ago. At least seven preserved Pleistocene 

gravel deposits, three of which are in the park, reflect an 

erosional episode related to changes in the grade of the 

Chaco River or the San Juan River. 

Once the canyon was incised, more 30 m (100 ft) of 

alluvium (silt, sand, and gravel in stream channels), 

eolian (windblown) sand, and slope-wash material (clay, 

silt, and rock fragments distributed by overland flow) 

began to fill it. These sediments serve as a record of past 

events, but dynamic sedimentation continues to the 

present. 

Throughout its history, the floor of Chaco Canyon 

has alternated between being deeply gullied by arroyo 

channels, as it is today, and having no arroyo. Integrated 

analysis using both geologic and archeologic methods 

(i.e., geoarcheology) shows that ancient occupants of 

the canyon experienced these changes. 

This GRI report was written for resource managers to 

support science-informed decision making at Chaco 

Culture National Historical Park. It may also be useful 

for interpretation. The report was prepared using 

available geologic information, and the NPS Geologic 

Resources Division (GRD) did not conduct any new 

fieldwork in association with this report. Chapters of 

the report discuss distinctive geologic features and 

processes within the park, highlight geologic issues 

facing resource managers, describe the geologic history 

leading to the present-day landscape, and provide 

information about the GRI geographical information 

system (GIS) data. A poster (in pocket) illustrates these 

data. In addition, the Map Unit Properties Table (in 

pocket) summarizes report content for each map unit 

within Chaco Culture National Historical Park. 

Geologic features and processes at Chaco Culture 

National Historical Park include the following:

● Upper Cretaceous Rocks and Fossils. The 

Western Interior Seaway inundated the area about 

96 million years ago, and advanced and retreated 

for 30 million years, depositing sediments in 

marine, coastal, and continental settings. The 

shoreline migrated as a result of changes in sea 

level, sedimentation, and subsidence of the ocean 

basin. The five primary bedrock units at Chaco 

Culture National Historical Park—Crevasse 

Canyon Formation, Menefee Formation, Cliff 

House Sandstone, Lewis Shale, and Pictured Cliffs 

Sandstone—record these changes and the life-forms 

that lived in these ancient environments.
viii

● Quaternary Fossils. Chaco Culture National 

Historical Park is a prolific source of packrat 

(Neotoma spp.) middens, which contain collections 

of plant material, food waste, coprolites (fossil 

dung), and bones from the last 2.6 million years 

(Pleistocene and Holocene epochs). Additionally, 

Pleistocene gravels may yield ice-age vertebrate 

fossils. 

● Chaco Canyon. Chaco Canyon cuts through the 

main unit of Chaco Culture National Historical 

Park. The canyon is 32 km (20 mi) long. The 

asymmetry of the north and south sides, sheer 

walls of Cliff House Sandstone, and an alluvial floor 

currently cut by an arroyo are distinctive features of 

the canyon. 

● Chaco Arroyo. Multiple episodes of arroyo cutting 

and filling are recorded in Chaco Canyon. Chaco 

Arroyo is the most recent. Historical observations 

indicate that an intermittent channel or succession 

of pools had developed by 1849, and incision of 

Chaco Arroyo began before 1877. Photographs 

and channel measurements beginning in 1896 

show an incising arroyo with little vegetation and 

a flat bottom until the early 1930s. The active inner 

channel developed after 1934. 

● Dynamic Sedimentation and Arroyo 

Development. About 11 m (36 ft) of alluvial fill, as 

well as slope-wash and eolian deposits, are exposed 

in the walls of Chaco Arroyo. Arroyos existed on 

at least seven separate occasions throughout the 

development of Chaco Canyon. 

● Alluvial Fill. As shown on source maps and in the 

GRI GIS data, the floor of Chaco Canyon is covered 

by Naha alluvium (map unit Qn) and undivided 

Naha and Tsegi Alluviums (Qnt), which were 

originally described by Hack (1941) in “Navajo 

Country” of Arizona and later used in Chaco 

Canyon. Hall (1977, 2010) and other investigators 

showed that the alluvial fill exposed on the floor of 

Chaco Canyon and in the walls of Chaco Arroyo 

has a distinctive stratigraphy, as indicated by color, 

grain size, and sedimentary structures, as well as 

the presence of archeological sites of different 

ages. Hall (1977, 2010) dated and divided the 

alluvial fill of Chaco Canyon into four units, using 

nomenclature from local geographic features: (1) 

pre-Gallo (undated), (2) Gallo (6,700–2,800 years 

BP), (3) Chaco (2,100–1,000 years BP), and (4) 

Bonito (800–100 years BP). 

● Sheetwash Alluvium and Slope-Wash Deposits. 

Part of the sedimentary fill of Chaco Canyon 

consists of sheetwash alluvium and slope-wash 

deposits, which also covers mesa tops. These units 

were deposited via overland flow, which is not 

concentrated in a channel and moves downslope as 

a thin, continuous sheet of water. 

● Eolian Features. Investigators have mapped and 

described eolian features, such as sand dunes and 

sand sheets, throughout Chaco Culture National 

Historical Park. These windblown deposits occur 

on cliff tops and at the mouth of Chaco Canyon, as 

well as in tributary canyons. The idea that a sand 

dune dammed Chaco Wash and created “Lake 

Chaco” has become part of the scientific and 

popular literature about the park. Geomorphic 

and stratigraphic evidence does not support the 

occurrence of such a lake, however.

● Tinajas and Charcos. In the 1920s, Kirk Bryan—

the well-known geoarcheologist whose work 

in Chaco Canyon led the way for decades of 

research—was one of the first scientists to study 

tinajas (potholes) in the US Southwest. He also 

studied charcos (mud holes) on the alluvial floor of 

Chaco Canyon. These features are valuable geologic 

(and ecologic) resources at Chaco Culture National 

Historical Park, providing an ephemeral but 

significant source of surface water and habitat for 

wildlife and microorganisms. A thorough inventory 

of these features has not been conducted at the 

park. 

● Badlands. Badlands are a distinctive and scenic 

feature of natural landscapes in the western United 

States. The badlands topography at Chaco Culture 

National Historical Park develops in areas of 

the Menefee Formation, in particular the Juans 

Lake Beds of Miller (1984) (Kmfaj). Results of 

an ongoing paleontological inventory in the park 

indicate that badlands topography, especially in the 

Juans Lake Beds, is highly fossiliferous.

● Cave Shelters. In Chaco Culture National 

Historical Park, cave shelters form along the 

shale-sandstone contact between the Menefee 

Formation and Cliff House Sandstone. These 

shelters provided temporary and permanent living 

areas for prehistoric peoples, and are noteworthy 

for the resources they contain, including packrat 

(Neotoma spp.) middens and some of the earliest 

datable, cultural material such as corn and basketry. 

As a result of investigation of packrat middens, 
ix

the location of most cave shelters in the park are 

known, and could be plotted in the park’s GIS for 

use in management.

Geologic resource management issues identified during 

the 2007 GRI scoping meeting and 2014 follow-up 

conference calls include the following:

● Oil and Gas Development. Perhaps the most 

pressing issue for park managers is the development 

of oil and gas resources in the San Juan Basin. 

Improvements in horizontal drilling and hydraulic 

fracturing have spurred renewed industry interest 

in the Mancos Shale and Gallup Sandstone. The 

location of Chaco Culture National Historical 

Park near the center of this highly productive 

basin makes it vulnerable to oil and gas exploration 

and development on federal (Bureau of Land 

Management) lands, tribal lands, and allotments 

held by individual tribal members. Oil and gas 

exploration and development could impact the 

park’s cultural resources, paleontological resources, 

air quality, visual resources, night skies, natural 

and cultural soundscapes, water resources, and 

wilderness characteristics. 

● Coal Resources and Mining. The Crevasse 

Canyon Formation, Menefee Formation, and 

Kirtland Shale–Fruitland Formation are known 

for coal in the San Juan Basin. The Gibson Coal 

Member of the Crevasse Canyon Formation (Kcg) 

in the vicinity of the Kin Ya’a unit of the park, and 

the Allison Member coal zone of the Menefee 

Formation (Kmfa), which crops out on West Mesa 

and along the Chaco River west of the confluence 

of Chaco and Escavada washes, contain coal 

resources. Although coal mining could occur on 

any of the eight allotments within the administrative 

boundaries of the park, participants at the scoping 

meeting thought this was unlikely. If an owner 

chose to pursue his or her right, however, park 

managers, with the assistance of the NPS Geologic 

Resources Division, would work with an owner 

to ensure that NPS resources and values were not 

adversely impacted.

● Uranium Production. Uranium has been 

produced from the 156 million–147 million-yearold (Jurassic Period) Morrison Formation in the 

Grants uranium district, which encompasses Chaco 

Culture National Historical Park. At present, no 

uranium production is occurring, but the district 

has the potential to become an important future 

global source of uranium, adding to its historical 

significance.

● Abandoned Mineral Lands. The National Park 

Service mined sand and gravel at Chaco Culture 

National Historical Park for administrative uses 

until the late 1980s. Three abandoned coal mines 

are known to occur within the Chaco Canyon unit 

of the park. The Kin Ya’a unit contains 73 drill sites 

from past uranium exploration. The New Mexico 

Mines Database documents nine sites with past 

activity associated with uranium exploration in the 

vicinity of the Chaco Canyon and Kin Ya’a units. 

These sites and features have not yet been recorded 

in the NPS servicewide Abandoned Mineral Lands 

(AML) database.

● Disturbed Lands Restoration. Past disturbances 

at Chaco Culture National Historical Park include 

a legacy of grazing during the late 1800s and 

early 1900s. In 1947, the National Park Service 

fenced the park area to exclude grazing, which has 

resulted in the return of native grasses, shrubs, and 

wildlife. Grazing is still allowed and could occur 

on allotments within the administrative boundary 

of the park, however. Disturbances associated with 

work by the Civilian Conservation Corps (CCC) in 

the 1930s include berms constructed on the floor 

of Chaco Canyon for erosion control and a CCC 

camp in Marcia’s Rincon. From the 1950s to the 

early 1990s, the National Park Service disposed of 

solid waste in trenches on the eastern side of South 

Gap. Except for arsenic, all contaminants tested 

were below a standard safety threshold, and arsenic 

was lower than background mean concentrations 

for New Mexico. Park managers are looking for 

funding options to remove the site. An earth dam 

(Qaf1), surrounding a flowing well, occurs in the 

Kin Ya’a unit of the park. Earth dams also occur in 

the Kin Bineola unit. In some places, these earth 

dams have totally altered normal drainage and 

sediment deposition along the Kim-me-ni-oli Wash. 

The National Park Service has no plans to remove 

these dams at present.

● Rockfall. The stratigraphic arrangement of more 

resistant sandstone (Cliff House Sandstone) 

over more rapidly eroding mudstone (Menefee 

Formation) at Chaco Culture National Historical 

Park creates rockfall hazards. The park housing 

area and Gallo Campground, which are at the base 

of highly jointed cliffs of sandstone, are of greatest 

concern because they are frequently occupied by 
x

people. As a result of a technical assistance request 

by park managers in 2013, GRD staff provided 

rockfall-monitoring guidance and a risk assessment 

of these areas.

● Paleontological Resource Inventory and 

Monitoring. An inventory of the Upper Cretaceous 

rocks at Chaco Culture National Historical Park, 

which started in 2005 and is ongoing, revealed 

abundant and widespread paleontological 

resources, primarily in the Menefee Formation 

and Cliff House Sandstone. In 2009, investigators 

provided an inventory and monitoring report for 

paleontological resources in the Southern Colorado 

Plateau Network, including Chaco Culture National 

Historical Park. In 2014, NPS representatives 

from Chaco Culture National Historical Park 

and the Geologic Resources Division met with 

representatives of 28 American Indian tribes to 

discuss fossils. Discussions illuminated the cultural 

significance of these resources at the park and 

provided impetus for park planning. Also in 2014, 

a meeting with professional paleontologists took 

place in order to develop a strategy for future 

paleontological research and resource management 

at the park. 

● Piping. Piping is a type of subsurface erosion 

that forms conduits, tunnels, or “pipes” through 

which soluble or granular soil material is removed. 

Piping is a management concern at Chaco Culture 

National Historical Park because it infringes on and 

endangers archeological sites and threatens roads. 

Piping can occur in “fill soils” used in reburial (a 

conservation strategy) of archeological sites such 

as Chetro Ketl in the park. Piping also creates bat 

habitat.

● Seismicity. Earth movements (“seismicity”) may 

be caused by earthquakes (movement along a 

fault), landslides, blasting, drilling, road building, 

or vehicular traffic. The primary concern at Chaco 

Culture National Historical Park is that ground 

shaking could damage archeological structures. It 

also may induce rockfalls. A seismic and vibrationhazard investigation at the park provided guidelines 

for construction and traffic on park roads. Activities 

associated with coal mining are considered too 

far away to cause damage, but oil and gas activities 

adjacent to the park could cause mild shaking. The 

probability of a moderate earthquake (>magnitude 

5.0) shaking the Chaco Canyon unit over the next 

100 years is between 0.04 and 0.10 (4% to 10% 

“chance”). The probability increases to the east 

toward Los Alamos and Santa Fe.

● Eolian Processes. Historically, eolian processes 

have buried archeological sites at Chaco Culture 

National Historical Park with windblown silt 

and sand. Winds can cause walls of archeological 

structures to sway, initiating seismic vibrations. 

The bracing of walls, particularly using modern 

materials, generally increases the natural 

frequencies of these structures, which can make 

them more susceptible to wind-induced vibrations. 

Eolian processes cause dust storms, impairing 

visibility. Before the park road was rerouted to its 

present location, eolian processes transported 

sand across the road, which required regular 

maintenance. The removal of sediment, between a 

cliff face and loose rock, by eolian processes may 

aid rockfall hazards.

● Efflorescence. Efflorescence—also called “salt 

weathering”—appears as a whitish, fluffy, or 

crystalline powder on stone surfaces. Scoping 

participants suggested that efflorescence may 

accelerate the deterioration of stone and mortar 

in structures at Chaco Culture National Historical 

Park and accelerate the deterioration of roof 

surfaces in natural cave shelters. Not all salt 

behaviors result in deterioration, however, and 

efflorescence may cause only minor surface 

damage. Park managers use the presence of 

efflorescence as an indicator of water penetration, 

drainage problems, and stone deterioration. 

Also, efflorescence is evidence that replacement 

mortars used in preservation are less permeable 

than the original fabric, thus indicating the need to 

reevaluate mortar mixes.
xi

Products and Acknowledgments

The NPS Geologic Resources Division partners with institutions such as Colorado State University, 

the US Geological Survey, state geological surveys, local museums, and universities to develop GRI 

products. This chapter describes those products and acknowledges contributors to this report.

GRI Products

The objective of the Geologic Resources Inventory is 

to provide geologic map data and pertinent geologic 

information to support resource management and 

science-informed decision making in more than 

270 natural resource parks throughout the National 

Park System. To realize this objective, the GRI team 

undertakes three tasks for each natural resource park: 

(1) conduct a scoping meeting and provide a summary 

document, (2) provide digital geologic map data in a 

geographic information system (GIS) format, and (3) 

provide a GRI report (this document). These products 

are designed and written for nongeoscientists.

Scoping meetings bring together park staff and geologic 

experts to review and assess available geologic maps, 

develop a geologic mapping plan, and discuss geologic 

features, processes, and resource management issues 

that should be addressed in the GRI report. Following 

the scoping meeting, the GRI map team converts the 

geologic maps identified in the mapping plan to digital 

geologic map data in accordance with the GRI data 

model. After the map is completed, the GRI report team 

uses these data, as well as the scoping summary and 

additional research, to prepare the GRI report. 

The compilation and use of natural resource 

information by park managers is called for in the 1998 

National Parks Omnibus Management Act (section 

204), 2006 National Park Service Management 

Policies, and the Natural Resources Inventory and 

Monitoring Guideline (NPS-75). The “Additional 

References” chapter and Appendix B provide links to 

these and other resource management documents and 

information.

Additional information regarding the GRI, including 

contact information, is available at http://go.nps.gov/gri. 

The current status and projected completion dates of 

products are available at http://go.nps.gov/gri_status.

Acknowledgments

The GRI team thanks Phil Varela (Chaco Culture 

National Historical Park, paleontology technician) 

for tracking down information, finding photographs, 

and reviewing this report. His unyielding assistance 

was most appreciated! Jim Von Haden and Dabney 

Ford (Chaco Culture National Historical Park, natural 

resource program manager and cultural resources 

chief, respectively) provided substantial information 

that improved the report. Also, thanks to David W. 

Love (New Mexico Bureau of Geology and Mineral 

Resources, geologist) for attending the scoping meeting 

in 2007 and for providing references, information, 

and photographs for use in this report. Thanks to 

other staff members at the New Mexico Bureau of 

Geology and Mineral Resources, including Ron 

Broadhead (principal senior petroleum geologist), 

Gretchen Hoffman (senior coal geologist), and Ginger 

McLemore (senior economic geologist), for their 

guidance and information about mining and energy 

development in the San Juan Basin. Additionally, 

thanks to Larry Martin (NPS Water Resources 

Division, hydrogeologist) for his input on potential 

contamination of the park’s water-supply well, and to 

Stephen Monroe (NPS Southern Colorado Plateau 

Network, hydrologist) for his input about water-related 

topics. Thanks to NPS Geologic Resources Division 

staff Jeremiah Kimbell (petroleum geologist) and 

Julia Brunner (policy and regulatory specialist) for 

their comments on the oil and gas development and 

rockfall sections, respectively. Finally, thanks to Trista 

Thornberry-Ehrlich (Colorado State University), who 

created many graphics used in this report.

Review

Jason Kenworthy (NPS Geologic Resources Division)

Stephen Monroe (NPS Southern Colorado Plateau 

Network)

Dale Pate (NPS Geologic Resources Division)

Vincent Santucci (NPS Geologic Resources Division)

Phil Varela (Chaco Culture National Historical Park)

Jack Wood (NPS Geologic Resources Division)
xii

Editing

Rebecca Port (NPS Geologic Resources Division)

Report Formatting and Distribution

Jason Kenworthy (NPS Geologic Resources Division)

Rebecca Port (NPS Geologic Resources Division)

Source Maps

US Geological Survey

Berge Exploration Inc.

Dames & Moore

GRI GIS Data Production

Heather Stanton (Colorado State University)

Stephanie O’Meara (Colorado State University)

Derek Witt (Colorado State University)

Georgia Hybels (Colorado State University)

James Winter (Colorado State University)

Kari Lanphier (Colorado State University)

Elaine Jacobs (Colorado State University)

Jason Isherwood (Colorado State University)

Tim Cleland (Colorado State University)

Christopher Kizer (Colorado State University)

Jim Chappell (Colorado State University)

Cory Karpilo (Colorado State University)

John Detring (Colorado State University)

Melissa Copfer (Colorado State University)

GRI Poster Design

James Winter (Colorado State University)

Georgia Hybels (Colorado State University)

GRI Poster Editing

Georgia Hybels (Colorado State University)

Rebecca Port (NPS Geologic Resources Division)

Jason Kenworthy (NPS Geologic Resources Division)
1

Geologic Setting and Significance

This chapter describes the regional geologic setting of Chaco Culture National Historical Park and 

summarizes connections among geologic resources, other park resources, and park stories.

Originally proclaimed as Chaco 

Canyon National Monument in 1907 

to preserve sites of the prehistoric 

Chacoan culture, the monument was 

expanded and designated Chaco 

Culture National Historical Park in 

1980. The park now encompasses 

13,740 ha (33,960 ac) and consists of 

four units—the main Chaco Canyon 

unit (plate 1, in pocket) and three 

smaller outliers: Kin Bineola, which is 

west of the main unit, Pueblo Pintado 

to the east, and Kin Ya’a to the south 

(see poster, in pocket). The park is 

both nationally and internationally 

significant. It is listed in the National 

Register of Historic Places and is part 

of a World Heritage Site that includes 

Aztec Ruins National Monument in 

the National Park System and five 

smaller Chacoan sites managed by the 

Bureau of Land Management.

Chaco Canyon was a major center of 

trade, political activity, and spiritual 

ceremonies in a vast cultural complex 

that dominated the region in the 

mid-ninth to early 13th centuries (fig. 

1). Planned in stages, this ancient 

cultural complex was unlike anything 

constructed before or since. It is 

remarkable for its monumental public 

buildings and distinctive multistory “great houses,” 

which demonstrate a sophisticated understanding of 

astronomical phenomena. The Chacoan great houses, 

including those in Chaco Canyon and the ones at Aztec 

Ruins National Monument to the north, were linked 

by an elaborate system of carefully engineered and 

constructed roads (UNESCO 2014; fig. 1). 

The Chacoan cultural complex covered much of 

the present-day Southwest, including the San Juan 

Basin of New Mexico and Colorado (National Park 

Service 2006). The San Juan Basin developed during 

three phases of tectonic subsidence at the end of the 

Laramide Orogeny—the mountain-building event 

that created the Rocky Mountains (Cather 2003). At 

that time, additional, mostly continental and coastal, 

sediments accumulated atop sediments previously 

deposited in the Western Interior Seaway. These 

“previously deposited” sediments comprise the cliffs 

and mesa tops of the park and record sea level rise 

and fall between 100 million and 70 million years ago 

(i.e., during the Late Cretaceous Period; fig. 2). At that 

time, the park was situated on the western shoreline 

of the Western Interior Seaway, which bisected the 

North American continent and stretched from the 

Arctic Ocean to the Gulf of Mexico (fig. 3). As sea water 

Figure 1. Regional map showing the location of Chaco Culture National 

Historical Park (detail map is plate 1, in pocket), great houses, and prehistoric 

roads. By 1050 CE, Chaco had become the ceremonial, administrative, and 

economic center of the San Juan Basin. Its sphere of influence was extensive. 

Dozens of great houses in Chaco Canyon were connected by roads to more 

than 150 great houses throughout the region. National Park Service graphic.
2

Formation of the Earth

Eon Era Period Epoch MYA Phanerozoic Proterozoic Archean Hadean Cenozoic (CZ) Mesozoic (MZ) Paleozoic (PZ)

Quaternary

(Q)

Neogene

(N)

Cretaceous (K)

Jurassic (J)

Triassic (TR)

Permian (P)

Pennsylvanian (PN)

Mississippian (M)

Devonian (D)

Silurian (S)

Ordovician (O)

Cambrian (C)

Precambrian (PC, X, Y, Z)

Holocene (H)

Pleistocene (PE)

Pliocene (PL)

Miocene (MI)

Oligocene (OL)

Eocene (E)

Paleocene (EP)

2.6

5.3

23.0

33.9

56.0

145.0

201.3

298.9

323.2

358.9

419.2

443.8

485.4

2500

4000

4600

66.0

541.0

Age of Mammals Age of Reptiles Age of Amphibians Fishes Marine Invertebrates

Modern humans 

Spread of grassy

 ecosystems

Extinction of large

 mammals and birds 

Early primates 

Placental mammals 

Early flowering plants 

Dinosaurs diverse and

 abundant

First dinosaurs; first mammals

Flying reptiles

Sharks abundant

First reptiles

Mass extinction

First amphibians

First forests (evergreens)

First land plants

Mass extinction

Primitive fish

Trilobite maximum

Rise of corals

Complex multicelled organisms 

Simple multicelled organisms 

Early bacteria and algae

 (stromatolites)

Origin of life

0.01

Mass extinction

Paleogene

(PG)

Tertiary (T)

Basin and Range extension (W)

Elko Orogeny (W)

Breakup of Pangaea begins

Sonoma Orogeny (W)

Supercontinent Pangaea intact

Ouachita Orogeny (S)

Ancestral Rocky Mountains (W)

Antler Orogeny (W)

Acadian Orogeny (E-NE)

Taconic Orogeny (E-NE)

Extensive oceans cover most of 

 proto-North America (Laurentia)

First iron deposits

Abundant carbonate rocks

Formation of Earth’s crust

Oldest known Earth rocks

Formation of early supercontinent

Grenville Orogeny (E)

Cascade volcanoes (W)

Ice age glaciations;

 glacial outburst floods

Columbia River Basalt eruptions (NW)

Linking of North and South 

 America (Isthmus of Panama)

Laramide Orogeny ends (W)

Nevadan Orogeny (W)

Sevier Orogeny (W)

Laramide Orogeny (W)

Alleghany (Appalachian)

 Orogeny (E)

Supercontinent rifted apart

Western Interior Seaway (W)

Early shelled organisms

252.2 Mass extinction

 Life Forms North American Events 

Mass extinction

Coal-forming swamps
3

Figure 2 (facing page). Geologic time scale. The divisions of the geologic time scale are organized stratigraphically, 

with the oldest divisions at the bottom and the youngest at the top. GRI GIS abbreviations for each time division are in 

parentheses. Compass directions in parentheses indicate the regional locations of events. Boundary ages are millions of 

years ago (MYA). Upper Cretaceous rocks and Pleistocene deposits and unconsolidated deposits document the geologic 

story at Chaco Culture National Historical Park, which includes inundation by the Western Interior Seaway during the 

Cretaceous Period (K; fig. 3), creation of the San Juan Basin as a result of tectonic forces during the Laramide Orogeny 

in the Cretaceous (K) and Paleogene (PG) periods, development of Chaco Canyon during the Quaternary Period (Q), 

and dynamic sedimentation and deposition of alluvium during the Pleistocene (PE) and Holocene (H) epochs. National 

Park Service graphic using dates from the International Commission on Stratigraphy (http://www.stratigraphy.org/

index.php/ics-chart-timescale; accessed 27 August 2015).

repeatedly advanced and retreated, 

sediments were deposited in variety 

of marine and coastal environments 

such as barrier islands, lagoons, tidal 

inlets, stream deltas, estuaries, and 

swamps. Changes in sea level, sediment 

supply, and subsidence caused multiple 

northeast–southwest shifts in shoreline 

position (Love 2010). 

Encompassing more than 67,000 km2

(26,000 mi2), the San Juan Basin is 

the dominant structural and physical 

feature in northwestern New Mexico. 

It is a nearly circular depression 

containing a thick sequence of 

sedimentary rocks, ranging in age 

from Pennsylvanian to Pliocene (300 

million to 2 million years ago; fig. 2). 

These sedimentary units are underlain 

by Precambrian (1.7 billion to 1.4 

billion years ago) crystalline rocks 

(Price 2010). The sedimentary layers 

of the San Juan Basin form a bull’s 

eye in map view, and resemble nested 

mixing bowls in cross section (fig. 4). 

As is the case of structural basins, the 

youngest strata are exposed near the 

center of the basin, where the thickest 

accumulations of sediments occur. 

Aztec Ruins National Monument 

sits on these younger sediments (see 

GRI report by KellerLynn in review). 

Progressively older strata are exposed 

toward the edges of the basin, where 

Precambrian rocks were uplifted and 

crop out in mountain ranges such as 

the Nacimiento and Zuni mountains 

in New Mexico and the San Juan 

Mountains in Colorado. Chaco 

Figure 3. Paleogeographic map of the Western Interior Seaway. During the 

Cretaceous Period, an expansive seaway spread across the North American 

continent. The seaway inundated New Mexico about 96 million years 

ago. This map represents the maximum extent of the seaway at about 85 

million years ago. The red star indicates the approximate location of Chaco 

Culture National Historical Park. Base paleogeographic map by Ron Blakey 

(Colorado Plateau Geosystems, Inc.), available at http://cpgeosystems.com/

index.html (accessed 7 July 2014).
4

Culture National Historical Park is about 72 km (45 

mi) southwest of the center of the basin where folded 

sedimentary layers of Upper Cretaceous rocks crop out 

at the surface (fig. 4). 

In Chaco Culture National Historical Park, the Chaco 

River and its tributaries have incised deeply into 

Upper Cretaceous bedrock, producing excellent 

three-dimensional exposures (Donselaar 1989). Above 

the mouth of the canyon, which is marked by the 

confluence of the Chaco and Escavada washes, the river 

is referred to as “Chaco Wash.” Below the mouth of 

the canyon, Chaco Wash joins Escavada Wash, and the 

“Chaco River” moves out of its presently entrenched 

channel and becomes a broad meandering alluvial 

stream between 200 and 450 m (660 and 1,480 ft) wide 

(Love 1977; Simon, Li & Associates, Inc. 1982a). The 

river then continues southwest, west, and north to join 

the San Juan River at Shiprock, New Mexico. 

Throughout most of the year, the Chaco River’s sandy 

bed is dry, but its considerable length and the violence 

Figure 4. Cross section of the San Juan Basin. Before subsidence during the Laramide Orogeny, the San Juan Basin 

occupied a small area on the western edge of the Western Interior Seaway where sediments were deposited in 

marine, coastal, and continental settings and include the Crevasse Canyon Formation, Cliff House Sandstone, Menefee 

Formation, Lewis Shale, and Pictured Cliffs Sandstone in Chaco Culture National Historical Park. Late in the Cretaceous 

Period, the basin began to subside and thousands of feet of additional terrestrial sediment accumulated (shown as 

Tertiary rocks in orange). The thickest accumulation of sediments is close to the center of the basin. This figure shows 

the locations of the park’s drinking-water well and coal and uranium mining areas in the vicinity of the park. The 

Gallup Sandstone and Mancos Shale are the current target formation for oil and gas production, as illustrated by 

the brown droplets on the figure. Graphic by Trista Thornberry-Ehrlich (Colorado State University) after Brister and 

Hoffman (2002, figure 3) and Martin (2005, figure 9). 
5

of its floods dignify the name “river” (Bryan 1954). It is 

more than 220 km (140 mi) long and drains an 11,500-

km2- (4,400-mi2-) area of semiarid lands. 

At the headwaters on the Continental Divide, 40 km 

(25 mi) east of the park, the river is not entrenched. 

The dominant landforms in the upper catchment basin 

are gently sloping erosional surfaces called pediments. 

These are capped by Quaternary sediments, including 

alluvium and eolian deposits, and dissected by badlands 

composed of Fruitland Formation (Kf; see poster in 

pocket) and Kirtland Shale (Kk). The Kirtland Shale and 

Fruitland Formation crop out northeast of the Chaco 

Canyon unit of the park and represent post–Western 

Interior Seaway swamp, river, lake, and floodplain 

deposits laid down landward and on top of the Pictured 

Cliff Sandstone (Kpc; Fassett 1974). Tributaries draining 

the badlands flow into the ephemeral Chaco Wash 

(Simon, Li & Associates, Inc. 1982a). 

The dominant landforms in the lower catchment basin 

are canyons, in particular Chaco Canyon, but also 

tributary side canyons such as Mockingbird and Clys 

canyons on the north, and South Gap on the south. 

Gallo Wash joins Chaco Wash from the north; Fajada 

Wash joins Chaco Wash from the south. Commonly, 

Chaco Wash and Fajada Wash do not flow at the same 

time, and local runoff that reaches the main canyon 

from the sides tends to precede the floods from the 

headwaters. As a result, discharge does not increase 

through the canyon, and sediments brought into the 

canyon from the headwaters or from the local canyon 

sides are not immediately transported out of the 

canyon, downstream to the San Juan River (Love 1977).

Other features in the lower catchment basin include 

Fajada Butte, Chacra Mesa, and other mesas and buttes 

along the course of the river. These were created by 

erosion. Depositional features include talus slopes 

(Qc) and sheetwash alluvium (Qsw) below cliff faces, 

and alluvial fans (Qf) that spread onto the floor of 

Chaco Canyon from the mouths of tributary canyons. 

Additionally, sand dunes are common on the tops of 

mesas and in some tributary canyons.

The attraction of Chaco Canyon for researchers 

started more than 150 years ago and continues to 

this day. Geoarcheologists apply geological concepts 

and methods to archeological problems and vice 

versa. Studies at Chaco Canyon incorporated some 

of the earliest applications of tree-ring dating and 

biogeochemistry, palynology, physical and chemical 

anthropology, remote sensing, archeological 

stratigraphy, and millennial-scale environmental 

reconstructions using packrat (Neotoma spp.) middens.

The history of geoarcheology at Chaco Canyon includes 

the following:

● 1849—James Hervey Simpson and Richard 

H. Kern described Chaco Canyon and its sites 

and speculated about environmental changes 

during occupation of the great houses and other 

structures. Simpson (1850) documented the 

Washington Expedition—a military reconnaissance 

that surveyed the “Navajo Country” and reported 

on the ancestral Puebloan and Navajo cultural 

sites now associated with Chaco Culture National 

Historical Park.

● 1877—William Henry Jackson drew Pueblo del 

Arroyo and methodically described the filled-in 

gully at this site. He also found and described 

prehistoric human remains, including a cranium.

● 1878—Walter James Hoffman, the physician who 

examined the prehistoric cranium collected by 

Jackson in 1877, was the first to speculate about 

environmental degradation as a result of human 

activities.

● 1903—Richard E. Dodge made one of the first 

attempts to correlate geologic data with the 

results of archeological work, in a study entitled 

“An Interesting Landslide of Chaco Cañon, New 

Mexico” (Dodge 1903).

● 1920s—Kirk Bryan spent parts of the summers 

of 1924 and 1925 in Chaco Canyon developing 

an alluvial chronology and geomorphic models 

for interpreting behavior of ephemeral streams 

in the semiarid Southwest. He also provided 

interpretations about the paleochannel now known 

as the “Bonito channel.” His work was published 

posthumously in 1954. 

● 1950s and 1960—Sponsored by the National 

Geographic Society, Neil Judd systematically 

studied and excavated Pueblo Bonito and Pueblo 

del Arroyo. He applied geologic data in his analyses 

and interpretations (see Judd 1954, 1959, 1964).

● 1960s—Yi-Fu Tuan reviewed and summarized 

previous ideas concerning arroyo behavior in 

New Mexico (e.g., Tuan 1966). He pointed out the 

paucity of critical data for determining the timing of 

inception of Chaco Arroyo and the timing of cut-
6

and-fill sequences of buried channels, such as the 

Bonito channel. His critical review was published in 

1966.

● 1970s and 1980s—In 1969, the National Park 

Service and the University of New Mexico 

instituted a long-term interdisciplinary research 

program, called the Chaco Project. This effort 

attracted researchers from a variety of fields. The 

resulting publications between 1970 and 1980 were 

20 times more voluminous than those generated 

over the previous 100 years (Greening 1995).

● 2010s—As part of the Chaco Project, Steven H. Hall 

and David W. Love studied and mapped exposures 

of Chaco Canyon alluvium, including charcoal 

and pollen, and extended interpretations of 

environmental changes over several thousand years. 

More recent studies include new interpretations 

of alluvial and paleovegetation records from the 

canyon by Hall (2010) and analysis and applications 

of geomorphology, hydrology, and alluvial 

stratigraphy in lower Chaco Canyon by Love et al. 

(2011).

A thorough bibliography is listed at the Chaco Research 

Archive (http://www.chacoarchive.org/cra/chacoresources/bibliography/; accessed 27 August 2015).
7

Geologic Features and Processes

This chapter describes noteworthy geologic features and processes in Chaco Culture National 

Historical Park.

During the 2007 scoping meeting and 2014 

conference calls, participants (see Appendix A) 

identified the following geologic features and 

processes:

● Upper Cretaceous Rocks and Fossils

● Quaternary Fossils

● Chaco Canyon 

● Chaco Arroyo

● Dynamic Sedimentation and Arroyo 

Development

● Alluvial Fill

● Sheetwash Alluvium and Slope-Wash Deposits

● Eolian Features

● Tinajas and Charcos

● Badlands

● Cave Shelters

Upper Cretaceous Rocks and Fossils

The majority of strata exposed in Chaco Culture 

National Historical Park belong to a suite of rocks 

known as the Mesaverde Group for exposures in Mesa 

Verde National Park (see GRI report for Mesa Verde 

National Park by Graham 2006). The Mesaverde Group 

was deposited during the Late Cretaceous Period (100 

million–66 million years ago). Conforming to standard 

use in geologic writing, this report uses “Late” in 

describing geologic time and “Upper” in describing the 

position of rocks. Collier (1919) divided the Mesaverde 

Group into three formations (from oldest to youngest): 

Point Lookout Sandstone (not exposed in Chaco 

Culture National Historical Park), Menefee Formation, 

and Cliff House Sandstone. In the process of naming, 

Collier (1919) joined the two words, “Mesa Verde” to 

become “Mesaverde.” Attempts to return the spelling 

to its two-word origins have not succeeded (Fasset et al. 

2010). The oldest rock unit in Chaco Culture National 

Historical Park is the Upper Cretaceous Crevasse 

Canyon Formation, which was added to the Mesaverde 

Group in 1954 (Allen and Balk 1954). This bedrock 

(map units Kcg and Kcda) appears in the Kin Ya’a unit of 

the park only (see poster, in pocket). 

The Menefee Formation and Cliff House Sandstone 

are the most prevalent rock units in Chaco Canyon. 

The Menefee Formation is part of West, South, and 

Chacra mesas, as well as Fajada Butte, where the 

contact between the underlying Menefee Formation 

and overlying Cliff House Sandstone is readily visible 

(fig. 5). The Menefee Formation is the primary bedrock 

unit in the Kin Bineola unit of the park (see poster, in 

pocket). The Cliff House Sandstone makes up the walls 

on both sides of Chaco Canyon, but forms particularly 

impressive cliffs on the northern side. It also caps the 

West, South, and Chacra mesas on the southern side of 

Chaco Canyon and underlies the southwestern corner 

of the Pueblo Pintado unit. 

The towering cliffs of Cliff House Sandstone provided 

people of the Chaco Culture with ample building stone 

(National Park Service 2006). Most of the rock used at 

the height of Chacoan construction was quarried from a 

layer of dense, dark Cliff House Sandstone that capped 

the canyon cliffs. Once quarried, stone blocks were 

probably dropped to the floor of Chaco Canyon where 

Figure 5. Photograph of Fajada Butte. Fajada Butte is an 

impressive landmark in Chaco Canyon. This view is from the 

Fajada Butte Overlook. The name Fajada means “striped, 

belted, or banded” in Spanish and describes the black coal 

seams and other sedimentary layers that run across the butte. 

Within Chaco Canyon, investigators have subdivided and 

named the various beds of Cliff House Sandstone (“Kch” 

units; see Map Unit Properties Table and poster, in pocket). 

The Menefee Formation (“Kmf” units) intertongues with 

these beds. US Geological Survey photograph available at 

http://3dparks.wr.usgs.gov/chcu/html2/chaco044.htm (accessed 

6 May 2014).
8

they were shaped and dressed (put the finishing touches 

on the stone) (Strutin 1994). 

Stone for later buildings (early 12th century) was 

probably quarried from the softer sandstone near the 

base of the cliffs (Strutin 1994). Some archeologists 

believe that by the last quarter of the 11th century, the 

dense stone used in classic Chacoan buildings had been 

almost completely stripped from the rim of the cliffs. 

This resource shortage may have caused changes in the 

style of later buildings, though new architectural ideas 

and approaches were being adapted at Chaco and other 

regions at the time (Strutin 1994).

Ironstone concretions, which occur in the Menefee 

Formation and Cliff House Sandstone, were used 

to decorate floors in kivas and may have possessed 

a particular Chacoan “value” or source of power. 

Coal seams in the Crevasse Canyon and Menefee 

formations are clearly visible throughout the park and 

were probably used by Indian inhabitants prior to 

exploration by European Americans (Nickelson 1988).

In addition to the Cliff House Sandstone and Menefee 

Formation, two other rock units occur in the park but 

are not part of the Mesaverde Group—Lewis Shale 

and Pictured Cliffs Sandstone. These too are Late 

Cretaceous in age but younger than the Mesaverde 

Group. Lewis Shale covers the eastern part and 

northeastern corner of the Pueblo Pintado and Chaco 

Canyon units of the park, respectively. The Pictured 

Cliffs Sandstone crops out in the northeastern corner of 

the Chaco Canyon unit.

The bedrock at Chaco Culture National Historical 

Park was deposited following inundation by the 

Western Interior Seaway across the North American 

continent. Seawater began to cover the land area 

that is now New Mexico about 96 million years ago. 

The seaway was oriented northwest–southeast, and 

the park was on the western shoreline (fig. 3). As the 

shoreline migrated back and forth for 30 million years, 

Table 1. Upper Cretaceous stratigraphy of the San Juan Basin

Upper Cretaceous Rocks

(Map Unit Symbol) Event Environmental Setting Energy Resources

Kirtland Shale (Kk) Post–Western Interior Seaway Swamp, river, lake, and 

floodplain Coal

Fruitland Formation (primarily shale) (Kf) Post–Western Interior Seaway Swamp, river, lake, and 

floodplain

Coal, coal-bed 

methane

Western Interior Seaway

Pictured Cliffs Sandstone (Kpc) Final retreat of seaway from San 

Juan Basin area

Coastal delta front, beach, 

and stream channel Oil, gas

Lewis Shale (Kl)

Marine deposition between a major 

transgressive (advance)–regressive 

(retreat) cycle

Offshore marine (deep water) Gas

Mesaverde 

Group

Cliff House Sandstone

(Kch, Kchu, Kchwu Kchwl, 

Kchm, Kchi, and Kchl)

Marine transgression Barrier island Oil, gas

Menefee Formation (primarily 

shale)

(Kmf, Kmft Kmfa, Kmfaj, and 

Kmfal)

Continental deposition between 

a major marine regressive–

transgressive cycle

Lowland swamp, lagoon, and 

stream channel

Coal, coal-bed 

methane, gas

Point Lookout Sandstone Marine regression/retreat Nearshore marine (littoral/

intertidal zone) Oil, gas

Crevasse Canyon Formation 

(primarily shale)

(Kcg and Kcda)

Marine regression Lagoon, estuary, and beach Coal

Gallup Sandstone Marine transgression Offshore marine to coastal 

(shoreface) Oil, gas

Mancos Shale Marine transgression Offshore marine Oil

Dakota Sandstone Initial advance of the Western 

Interior Seaway into New Mexico

Stream channel and 

floodplain grading into 

offshore marine

Oil, gas

Notes: Blue-shaded units occur within Chaco Culture National Historical Park. These rocks are between 100 million and 66 million years old (fig. 6). 

Source: Brister and Hoffman (2002).
9

and sandstone, shale, mudstone, coal, and limestone 

formed in continental, coastal, and marine settings 

(table 1). When sea level rose, a marine transgression 

took place, causing retreat of the western shoreline 

toward the southwest. When sea level fell, a marine 

regression took place, causing the western shoreline 

to advance toward the northeast (table 1). During the 

existence of the Western Interior Seaway, as many as 

five major transgression–regression episodes and many 

minor ones took place (Molenaar 1977). These cycles 

are recorded by the rock formations of the San Juan 

Basin of New Mexico and Colorado (figs. 4 and 6). Not 

all of these formations occur in Chaco Culture National 

Historical Park (table 1).

Sea level rise during the Late Cretaceous Period was 

primarily the result of changes in the rate of sediment 

delivery into the subsiding ocean basin (Fassett et 

al. 1990), rather than melting of continental ice caps 

like today. At least 2,000 m (6,500 ft) of sediment was 

deposited in the San Juan Basin while sea level was 

rising and/or the area was subsiding (Molenaar 1977). 

Characteristic of their marine history, Upper 

Cretaceous rocks are known to be fossiliferous (Siemers 

and King 1974). The remains of organisms (organic 

matter) deposited along with sediment would later be 

converted to hydrocarbons as the basin subsided during 

the Laramide Orogeny (approximately 75 million–40 

million years ago), and more sediment accumulated 

atop these Cretaceous strata (fig. 4). Oil and gas was 

ultimately developed in the Upper Cretaceous rocks as 

a result of increasing burial depth that caused increased 

temperature. By the end of the Laramide Orogeny, 

these rocks had reached a maximum depth of burial. 

Following the orogeny, regional heating of deeply 

Figure 6. Graphic representation of San Juan Basin stratigraphy. The stratigraphic record at Chaco Culture National 

Historical Park includes the Crevasse Canyon Formation, Menefee Formation, Cliff House Sandstone, Lewis Shale, and 

Pictured Cliffs Sandstone, which were deposited during the Late Cretaceous Period (100 million–66 million years ago). 

The scale on the right breaks the Late Cretaceous Period into stages. The map unit symbols are from the GRI GIS data. 

Graphic by Trista Thornberry-Ehrlich (Colorado State University) after Donselaar (1989, figure 2).
10

buried organic matter resulted in the generation of 

hydrocarbons.

The following discussion highlights the rocks and fossils 

that were deposited in the Western Interior Seaway 

in what is now Chaco Culture National Historical 

Park. Tweet et al. (2009) provided a detailed list of 

fossils documented from rocks that occur in the park. 

Varela (2013a, 2013b) presented preliminary results of 

an ongoing field-based inventory of paleontological 

resources within the park (see “Paleontological 

Resource Inventory and Monitoring” section). 

Crevasse Canyon Formation

The oldest bedrock at Chaco Culture National 

Historical Park is the Crevasse Canyon Formation, 

which marks a marine regression (retreat) after 

deposition of the marine Mancos Shale (table 1). The 

Crevasse Canyon Formation crops out in the Kin Ya’a 

unit of the park, where Robertson (1986, 1992) mapped 

the Gibson Coal (map unit Kcg) and Dalton Sandstone 

(Kcda) members. The Gibson Coal Member, which 

overlies the Dalton Sandstone Member, is composed 

of carbonaceous shale, siltstone, and claystone, as well 

as sandstone. It was deposited in estuarine, fluvialchannel, distributary-channel, and floodplain-splay 

settings. The unit locally intertongues (grades laterally 

into) tidal-channel and marine-beach and bar deposits 

(Robertson 1986, 1992). Some beds are bioturbated, 

indicating animal activity (Robertson 1986). The Gibson 

Coal Member has yielded pollen, spores, coal (Tschudy 

1976), plant debris, petrified wood, leaf impressions 

(Kirk and Zech 1977), and a few fragments of dinosaurs 

(Lucas et al. 2000), including a partial lower jaw from a 

duckbilled dinosaur (Williamson 2000).

The Dalton Sandstone was deposited during a marine 

regression (Kirk and Zech 1977). As the shoreline 

migrated seaward, a succession of settings—lagoon, 

tidal or estuarine channel, and shore or beach—

developed (Robertson 1986, 1992). A variety of lifeforms inhabited these paleoenvironments. Abundant 

plant life lived in lagoons. Some plant fossils retained 

probable root structures. Animals burrowed into 

lagoonal sediments, leaving trace fossils. Sediments 

in tidal or estuarine channels also are bioturbated 

(churned up by organisms) and contain trace fossils 

such as Ophiomorpha (burrows presumably made 

by marine crustaceans), Thalassinoides (cylindrical, 

horizontal branched burrows), and Skolithos (tubelike, 

vertical burrows). Foreshore sediments contain fish 

teeth, broken shell fragments, and a few fossil burrows. 

Upper shoreface sediments locally contain Skolithos, 

Ophiomorpha, and Thalassinoides burrows. Lower 

shoreface sediments contain a few trace fossils such 

as Ophiomorpha and Skolithos (Robertson 1992). 

The Dalton Sandstone has yielded internal casts of 

ammonites (steinkerns), coprolites of cartilaginous fish, 

and body fossils of turtles, mosasaurs, crocodilians, 

dinosaurs, and cartilaginous and bony fish (Johnson 

and Lucas 2003).

Menefee Formation

The dark shale of the Menefee Formation forms 

slopes at the base of the steep northern walls of Chaco 

Canyon. Locally as much as 50 m (160 ft) of the 

uppermost part of the Menefee Formation is exposed 

(Siemers and King 1974). On the southern side of the 

canyon, the regional dip of the rocks to the north and 

east brings the shale to the surface, where erosion 

has produced irregular ledges rather than continuous 

cliffs (Bryan 1928). The Menefee Formation also forms 

badlands (fig. 7).

The Menefee Formation crops out in the Chaco 

Canyon and Kin Bineola units of the park. The main 

formation (Kmf) and tongues (Kmft) occur in the 

Figure 7. Photograph of badlands. Areas of badlands 

topography occur in Chaco Culture National Historical 

Park, including near Kin Klizhin, shown here. They form 

from the Menefee Formation (shale). National Park 

Service photograph available at http://www.nps.gov/

chcu/photosmultimedia/photogallery.htm (accessed 17 

April 2014).
11

Chaco Canyon unit. Tongues extend and thin into the 

Cliff House Sandstone northward from the main body 

of the Menefee Formation. Investigators mapped the 

Allison Member (Kmfa), the lower part of the Allison 

Member (Kmfal), and Juans Lake Beds of the Allison 

Member (Kmfaj) in the Kin Bineola unit (see Map Unit 

Properties Table, in pocket).

With respect to its origin in the Western Interior Seaway, 

the Menefee Formation lies between the Point Lookout 

Sandstone (not mapped in the park; see table 1), 

which was deposited during a marine regression to the 

northeast, and the Cliff House Sandstone (Kch), which 

was deposited during a marine transgression to the 

southwest (Fassett 1974). 

The Menefee Formation preserves abundant evidence 

of its origins as lowland swamps, streams, and lagoons, 

which became coal seams, sandstone ledges, and 

mudstone with abundant plant and animal fossils. The 

Juans Lake Beds (mudstone; Kmfaj) are particularly 

fossiliferous, especially in badlands terrain at the park 

(Varela 2013b; see “Badlands” section). Typical fossils 

are petrified wood, including several in situ stumps, 

some of which are still upright (fig. 8). Investigators 

found rare fossilized in-filled termite burrows in the 

Figure 8. Photograph of fossil tree stump. Petrified 

wood occurs in the Menefee Formation at Chaco 

Culture National Historical Park. Investigators discovered 

several preserved in situ stumps, some of which are still 

upright. Compass atop stump for scale. National Park 

Service photograph (Chaco Culture National Historical 

Park, CHCU 109791, Coll 0200/007-#116738) by Tom 

Lyttle (taken in 2006).

Figure 9. Photograph of ceratopsian (?) fossil. One 

of the vertebrate fossils discovered during the 

paleontological inventory at Chaco Culture National 

Historical Park is a possible ceratopsian vertebra in the 

Menefee Formation. Ceratopsians were herbivorous, 

beaked dinosaurs that thrived during the Cretaceous 

Period. Ancestral forms lived earlier, in the Jurassic 

Period (see fig. 2). National Park Service photograph 

(Chaco Culture National Historical Park, CHCU 109791, 

Coll 0200/007-#109333) by Phil Varela (taken in 2011).

Figure 10. Photograph of side-neck turtle fossil. 

Testudines palomeusidea lived during the Late 

Cretaceous Period. Investigators found this specimen 

in the Menefee Formation during the paleontological 

resource inventory. Paintbrush for scale. National Park 

Service photograph (Chaco Culture National Historical 

Park) by Tom Lyttle (taken in 2007).
12

wood and casts of palm leaves and bark impressions 

(Varela 2013b). During the paleontological resource 

inventory, investigators documented fragmentary 

dinosaur bones, including hadrosaur and theropod, 

and a possible ceratopsian vertebra (fig. 9). Additionally, 

investigators found a carapace of a rare, extinct 

pelomedusid (side-necked turtle) (fig. 10), as well as 

other fragmentary turtle specimens such as a trionychid 

turtle (fig. 11). A pelomedusid turtle specimen, which is 

the first of its kind known from the Menefee Formation 

(Tom Lyttle, Chaco Culture National Historical Park, 

volunteer, personal communication in Tweet et al. 2009, 

p. 66), was prepared by curators at Petrified Forest 

National Park and is now housed at the Hibben Center 

at the University of New Mexico in Albuquerque 

(Phil Varela, Chaco Culture National Historical Park, 

paleontology technician, written communication, 31 

October 2014). The Menefee Formation also yielded 

possible crocodilian remains, including limb elements, 

scute fragments, and a possible skull/snout element (fig. 

12).

Concretions

In addition to fossils, large calcareous (calcium 

carbonate [CaCO3]–rich) concretions characterize 

the Juans Lake Beds of the Allison Member (Kmfaj) 

(fig. 13). Calcareous, as well as siderite (iron carbonate 

[FeCO3]–rich), concretions are hard masses of Figure 11. Photograph of turtle remains. Trionychid 

turtles lived in coastal lowland swamps, streams, and 

lagoons where the Menefee Formation was deposited. 

National Park Service photograph (Chaco Culture 

National Historical Park, CHCU 109791, Coll 0200/007-

#109950) by Phil Varela (taken in 2012).

Figure 12. Photograph of crocodile fossil. During the 

paleontological resource inventory, investigators found 

this possible skull/snout element of an Upper Cretaceous 

crocodilian specimen in the Menefee Formation. Other 

fragmentary evidence includes several limb and scute 

fragments. National Park Service photograph (Chaco 

Culture National Historical Park, CHCU 109791, Coll 

0200/007-#112183) by Phil Varela (taken in 2012).

Figure 13. Photograph of Menefee Formation 

concretions. The Juans Lake Beds of the Menefee 

Formation are characterized by large calcareous 

concretions (hard masses of cemented sandstone) and 

small ironstone (siderite) concretions. As groundwater 

flowed through sedimentary strata, concretions formed 

within previously deposited layers. Concretionary 

“cement” makes the concretions harder and more 

resistant to weathering than the host stratum. The 

outcrop is approximately 5 m (15 ft) high. National Park 

Service photograph (Chaco Culture National Historical 

Park).
13

cemented sandstone. Concretions are typically oval 

or round, though irregular shapes occur. They form 

as a result of the precipitation of mineral cements 

within the spaces between sediment grains. Commonly 

concretions form around some kind of nucleus such 

as organic matter (leaf) or fossil fragment (piece of 

shell), which enhances chemical reactions, altering local 

chemistry to precipitate iron or calcite in a uniform 

(spherical) manner (Chan and Parry 2002). 

As groundwater flows through sedimentary strata, 

concretions form within previously deposited layers, 

usually early in the burial history of the sediment 

before the rest of the sediment is hardened into rock. 

Concretionary “cement” makes the concretions harder 

and more resistant to weathering than the host stratum, 

thus preserving these early sedimentary structures 

(Mozley 1995). Concretions may preserve features of 

the original sediment such as sedimentary layering, 

burrows, or fossils. For this reason, fossil collectors are 

attracted to concretions, breaking them open in their 

search for plant and animal remains.

The presence of calcareous concretions distinguishes 

the Juans Lake Beds (Kmfaj) from the lower part of 

Allison Member (Kmfal), which it overlies. The Juans 

Lake Beds also contain small ironstone (siderite) 

concretions scattered along individual horizons or 

coalescing into thin beds. The base of the Juans Lake 

Beds is defined as the lowest occurrence of calcareous 

concretions. No calcareous concretions and few siderite 

concretions occur in the lower part of Allison Member.

Cliff House Sandstone

The Cliff House Sandstone overlies the Menefee 

Formation and forms vertical cliffs and intervening 

slopes within Chaco Canyon and its tributaries (see 

Map Unit Properties Table, in pocket). Cross-bedding 

(fig. 14), laminations, fossils including burrows, and 

cross-canyon changes within the sandstone show that 

these alternating cliffs and slopes are the vertically 

stacked remnants of barrier islands (fig. 15). The 

Menefee Formation represents shoreward lagoons, and 

the Lewis Shale represents offshore marine mud (fig. 

16). The barrier islands built upward and prograded 

seaward as sediment accumulated (David W. Love, New 

Mexico Bureau of Geology and Mineral Resources, 

geologist, written communication, 15 May 2007). 

Figure 14. Photograph of cross-bedding in Cliff 

House Sandstone. Packages of cross-bedding suggest 

deposition in water, in this case along the western 

shoreline of the Western Interior Seaway. National Park 

Service photograph available at http://www.nps.gov/

chcu/photosmultimedia/photogallery.htm (accessed 17 

April 2014).

Figure 15. Cross section of Chaco Canyon. This generalized southwest–northeast cross section shows the bedrock across 

Chaco Canyon. Note the levels of Cliff House Sandstone, which represent past barrier-island complexes. Graphic by 

Trista Thornberry-Ehrlich (Colorado State University) after Love (2010, page 69). 
14

Island position shifted back and forth during sediment 

accumulation so that cliffs now vary in height and 

record different depositional environments across the 

canyon and adjacent mesas (Love 2010). Each barrierisland sand deposit is about 5 km (3 mi) wide and as 

much as 20 m (70 ft) thick.

By analyzing the outcrops of Cliff House Sandstone 

in Chaco Culture National Historical Park, Donselaar 

(1989) was able to reconstruct the development of 

the western shoreline of the Western Interior Seaway. 

Donselaar (1989) identified notable examples of tidalchannel deposits in Gallo Canyon. These deposits show 

Figure 16. Schematic diagram of barrier-island complex. Upper Cretaceous rocks in Chaco Culture National Historical 

Park record deep marine water (Lewis Shale); barrier islands (Cliff House Sandstone); and lagoon, swamp, and coastal 

plain settings (Menefee Formation) along the western shoreline of the Western Interior Seaway. Graphic by Trista 

Thornberry-Ehrlich (Colorado State University) after Love (2010, page 71).

Figure 17. Photograph of tidal “bundles” in Cliff 

House Sandstone. Tidal channels exposed in Gallo 

Canyon record lunar/tidal cycles in a barrier-island 

system of the Western Interior Seaway. This 10-

m- (32-ft-) thick package of sandstone shows an 

ebb-tidal delta and tidal channel sequence with 

a sharp, flat base resting on the distal part of the 

ebb-tidal delta, which consists of interbedded sandy 

shale and very fine-grained, parallel laminated sand. 

These “bundles” of sand once moved with flooding 

(landward) and ebbing (seaward) of tides. New 

Mexico Bureau of Geology and Mineral Resources 

photograph by David W. Love, as discussed and 

annotated in Donselaar (1989). 
15

where seawater alternately flooded landward across a 

barrier island with the rising tide and ebbed seaward 

with the falling tide, depositing flood-tidal and ebb-tidal 

deltas, respectively. This coastal process is preserved in 

the rock record as lunar “bundles” of sand (fig. 17). In 

addition, Donselaar (1989) documented many finescale features of barrier islands such as hummocky 

cross stratification in beach deposits and storm deposits 

composed of concentrated shell fragments (fig. 18). 

Paleontologists commonly refer to these storm deposits 

as “invertebrate hash” horizons.

Cliff House Sandstone preserves past sea life such 

as bivalves (fig. 19), gastropods (fig. 20), and rare 

ammonite casts (Placenticeras sp. [fig. 21] and Baculites

sp.), which are associated with invertebrate hash 

horizons (i.e., storm deposits). Because of their sheer 

numbers, shrimp (Callianasa) burrows are noteworthy 

in the sandstone; the fossil burrows themselves are 

called Ophiomorpha nodosa (figs. 22 and 23). Fossil 

wood is less common in the Cliff House Sandstone than 

the Menefee Formation, but several in situ logs protrude 

from cliffs (fig. 24).

Figure 18. Photograph of storm deposit. Sometimes 

referred to as “invertebrate hash,” deposits of shell 

fragments record storm events in the Western Interior 

Seaway, shown here in the Cliff House Sandstone. 

New Mexico Bureau of Geology and Mineral Resources 

photograph by David W. Love.

Figure 19. Photograph of bivalve fossil. Bivalve fossils 

are exposed on ledges that cap the lower and upper 

sandstones of the Cliff House Sandstone. National Park 

Service photograph (Chaco Culture National Historical 

Park, CHCU 109791, Coll 0200/007-#116295) by Tom 

Lyttle (taken in 2006).

Figure 20. Photograph of gastropod fossil. Indicative 

of life in the Western Interior Seaway, gastropods 

are preserved in the Cliff House Sandstone at Chaco 

Culture National Historical Park. National Park Service 

photograph (Chaco Culture National Historical Park, 

CHCU 109791, Coll 0200/007-#116292) by Tom Lyttle 

(taken in 2006).

Figure 21. Photograph of ammonite cast. Placenticeras

sp. from the lower sandstone of the Cliff House 

Sandstone was a rare find during the paleontological 

resource inventory at Chaco Culture National Historical 

Park. Ammonites are an extinct group of marine 

mollusks related to living octopus and squid. National 

Park Service photograph (Chaco Culture National 

Historical Park, CHCU 109791, Coll 0200/007-#116499) by 

Phil Varela (taken in 2011).
16

Although vertebrate fossils are not abundant in the Cliff 

House Sandstone, the lower sandstone (Kchl) contains 

shark teeth (fig. 25). Significant horizons of shark teeth, 

fish vertebrae, and fragmentary bone material occur 

in the upper sandstone (Kchu). Particularly notable 

vertebrate fossils from the Cliff House Sandstone 

include a fragment of a mosasaur dentary (jaw) (fig. 

26) and a plesiosaur humerus (fig. 27). During the 

paleontological resource inventory, investigators also 

found fragmentary bone material throughout the 

sandstone. Other specimens of interest are a possible 

plesiosaur vertebra and a single tyrannosaurid tooth 

fragment found among many shark teeth (Varela 

2013b).

Concretions

Like the Menefee Formation, the Cliff House 

Sandstone contains concretions (fig. 28). Study of 

concretions provides a means for understanding 

diagenetic (post-depositional) processes and events, 

Figure 22. Photograph of fossil burrows and 

bioturbation. Animal activity burrowed and churned 

up barrier-island sand, creating interesting features in 

the Cliff House Sandstone. For example, fossil shrimp 

(Callianasa) created trace fossil burrows (Ophiomorpha), 

which are abundant in the sandstone in the park. 

National Park Service photograph (Chaco Culture 

National Historical Park, CHCU 109791, Coll 0200/007-

#116300) by Tom Lyttle (taken in 2006).

Figure 23. Photograph of fossil burrows. These 

Skolithos (vertical) burrows are trace fossils in the Cliff 

House Sandstone. National Park Service photograph 

available at http://www.nps.gov/chcu/photosmultimedia/

photogallery.htm (accessed 17 April 2014).

Figure 24. Photograph of petrified log. Petrified wood is 

common in the Menefee Formation, but the Cliff House 

Sandstone (shown here) also contains Upper Cretaceous 

tree specimens. National Park Service photograph 

(Chaco Culture National Historical Park, CHCU 109791, 

Coll 0200/007-#116325) by Tom Lyttle (taken in 2008).

Figure 25. Photograph of shark teeth fossils. Although 

vertebrate fossils are uncommon in the Cliff House 

Sandstone, shark teeth occur in horizons in the lower 

sandstone. National Park Service photograph available 

at http://www.nps.gov/chcu/photosmultimedia/

photogallery.htm (accessed 17 April 2014).
17

including the timing, flow direction, and geochemistry 

of groundwater over long time scales (McBride et 

al. 2003). Many of the spheroidal concretions likely 

formed in a deltaic groundwater system where reduced 

iron was able to mobilize for relatively early diagenetic 

precipitation of cements in the concretions. Based 

on the complex relationships and internal structure 

of some of the concretions, multiple episodes of iron 

mobility and precipitation occurred (Roberts and Chan 

2010). 

Hematite-Cemented Trace Fossils

Hematite-cemented trace fossils such as Ophiomorpha

are a distinctive feature of Cliff House Sandstone 

(fig. 29). The organic matter in the fecal pellets of the 

burrowing organisms may have provided the right 

mixture of reducing and oxidizing waters to precipitate 

the iron. Some of the concentrated iron in the burrows 

may actually be iron that was disseminated and 

Figure 26. Photograph of mosasaur fossil. During the 

paleontological resource inventory at Chaco Culture 

National Historical Park, investigators documented a 

fragment of a mosasaur dentary (jaw) from the lower 

sandstone of the Cliff House Sandstone. Mosasaurs 

are an extinct marine reptile. With the extinction of 

ichthyosaurs and decline of plesiosaurs at the end of 

the Cretaceous Period, mosasaurs became the dominant 

marine predators. National Park Service photograph 

from Varela (2013b, figure 8).

Figure 27. Photograph of plesiosaur fossil. Notable 

vertebrate fossils from the Cliff House Sandstone 

include a plesiosaur humerus from the upper sandstone. 

Plesiosaurs were large, marine reptiles that swam in 

the Western Interior Seaway. National Park Service 

photograph (Chaco Culture National Historical Park, 

CHCU 109791, Coll 0200/007-#109583) by Phil Varela 

(taken in 2012).

Figure 28. Photograph of concretion. Concretions are 

typically round, possibly forming around a nucleus 

of organic matter or other material that enhanced 

chemical reactions and precipitation. This concretion 

formed in the Cliff House Sandstone at Chaco Culture 

National Historical Park. National Park Service 

photograph (taken in 2009).

Figure 29. Photograph of iron-cemented burrows. 

Ancient burrows made by shrimplike organisms were 

later cemented by iron oxides, including hematite. 

Organic matter related to the burrowing organisms 

provided a locally reducing environment that mobilized 

the iron. The width of an individual burrow is an 

estimated 5 cm (2 in) across. National Park Service 

photograph available at http://www.nps.gov/chcu/

photosmultimedia/photogallery.htm (accessed 17 April 

2014).
18

distributed in the original shoreline sands (Chan and 

Parry 2002). The cemented trace fossils are intriguing 

because of the preferential iron-oxide cementation in 

the burrows and the implication that organics from 

the original burrow helped enhance iron cementation 

(Roberts and Chan 2010). 

Honeycomb Weathering

Honeycomb weathering—also known as tafoni, stone 

lattice, stone lace, fretting, or alveolar weathering 

(Grisez 1960; Mustoe 1982; Neuendorf et al. 2005)—

is another interesting feature of the Cliff House 

Sandstone. This irregular surface phenomenon 

consists of numerous small pits a few millimeters or 

centimeters wide and deep that coalesce to create a 

network resembling honeycomb (fig. 30). Honeycomb 

weathering occurs in a variety of rock types and a 

range of built and natural settings. It shapes ocean 

cliffs, deserts rocks, and Arctic landscapes (RodriguezNavarro et al. 1999). Honeycomb weathering may 

also help alter rocks on other planets, such as Mars 

(Rodriguez-Navarro 1998).

Charles Darwin (1839) made the first documented 

observation of honeycomb weathering on the 

voyage of the HMS Beagle, and Kirk Bryan made the 

first documented observations in Chaco Canyon 

(Bryan 1928). Despite long-standing interest of 

this geomorphic “curiosity,” however, the origin of 

honeycomb weathering is poorly understood. Suggested 

mechanisms include wind erosion (Futterer 1899), 

mechanical disintegration induced by expansive 

chemical changes and associated agents of removal 

of debris (e.g., wind) (Blackwelder 1929), freezethaw (Cailleux 1953), thermal changes (Klaer 1956), 

erosion of large clasts (Schattner 1961), variation in 

moisture content in clay-rich rocks (Dragovich 1969), 

salt weathering (Evans 1970; Bradley et al. 1978; 

Mustoe 1982), chemical weathering (Gill et al. 1981; 

Mottershead and Pye 1994), erosion of the core stone 

or “core softening” (Conca and Rossman 1985), and 

a dynamic balance between salt weathering and the 

protective effects of endolithic (growing within rock) 

microbes (Mustoe 2010). In many cases, identifying 

and isolating a single mechanism responsible for the 

development of honeycomb has been difficult (Martini 

1978). Moreover, a dearth of laboratory experiments 

that test the many hypotheses for the development of 

honeycomb weathering has added to the ambiguity of 

its genesis (Rodriguez-Navarro et al. 1999). 

Researchers at the Getty Conservation Institute in Los 

Angeles, California, were the first to experimentally 

reproduce honeycomb weathering (Rodriguez-Navarro 

et al. 1999). They showed that heterogeneous wind flow 

over a homogeneous limestone surface is important 

in the development of honeycomb weathering. Wind 

promotes evaporative salt growth between grains on a 

stone surface (see “Efflorescence” section), resulting in 

the development of small, randomly distributed cavities. 

A reduction in air pressure within the cavities resulted 

in increased wind speed and rapid evaporation. A high 

evaporation rate and evaporative cooling of the saline 

solution in the cavity led to more rapid and greater 

granular disintegration than in the surrounding areas. 

Apparently, local supersaturation and subsequent 

buildup of salt crystallization pressure ultimately 

resulted in the formation of this weathering pattern. 

These findings demonstrated the close relationship 

between salts, wind, and honeycomb weathering, and 

offered new ways to understand the genesis of this 

interesting and sometimes harmful (to building stone) 

feature. Better understanding of honeycomb weathering 

has important implications for geomorphology and 

environmental geology, as well as stone conservation 

(Goudie and Viles 1997).

Figure 30. Photograph of honeycomb weathering. 

In the 1920s, Kirk Bryan made the first documented 

observations of honeycomb weathering in the Cliff 

House Sandstone of Chaco Canyon. This surfaceweathering feature appears in all types of rocks and 

climates but is particularly notable in arid and semiarid 

environments. National Park Service photograph (taken 

in 2014).
19

Lewis Shale

The Lewis Shale (Kl; fig. 31)—which consists of 

thin-bedded siltstone, sandy shale, and shale, with 

some sandstone beds, as well as sandy concretionary 

limestone—represents marine deposition in deeper 

water, farther offshore during an advance of the 

Western Interior Seaway to the southwest. The Lewis 

Shale reached its maximum thickness of 745 m (2,400 

ft) on the northeastern side of the San Juan Basin 

(Molenaar 1983). It is only about 30 m (100 ft) thick 

in the Chaco area. North of Chaco Canyon, the Lewis 

Shale forms a broad, soil-covered slope. On the mesas 

south of the canyon, the Lewis Shale and the upper few 

meters of the Cliff House Sandstone have been removed 

by erosion (Siemers and King 1974).

Limestone beds in the Lewis Shale in the park are 

fossiliferous (Mytton and Schneider 1987). Trace fossils, 

a tooth, bone, and shell fragments are known from the 

Pueblo Pintado unit (Tweet et al. 2009). Plant material 

including petrified wood has been found on Lewis 

Shale surfaces at the park, but may have eroded from 

the overlying Pictured Cliff Sandstone (Tom Lyttle, 

Chaco Culture National Historical Park, volunteer, 

personal communication in Tweet et al. 2009, p. 69). 

Pictured Cliffs Sandstone

Pictured Cliffs Sandstone (Kpc) is present in the main 

Chaco Canyon unit of the park where it forms low 

bluffs and has a total thickness of about 18 m (60 ft). 

The coastally deposited sandstone represents the final 

retreat of the Western Interior Seaway from the San 

Juan Basin area. The sea retreated to the northeast and 

deposited delta front, beach barrier, and distributary 

channel sediments (Erpenbeck and Flores 1979; Flores 

1979; Dam et al. 1990). Fossils are not common in the 

Pictured Cliffs Sandstone at the park, except for the 

trace fossil Ophiomorpha (Mytton and Schneider 1987). 

Mostly north of the park, this massively bedded unit 

is resistant to erosion and forms sandstone cliffs. The 

unit was named in 1875 during the Hayden Survey for 

the exposures of sandstone in cliffs along the San Juan 

River in northwestern New Mexico (Holmes 1877). The 

Pictured Cliffs rise stratigraphically some 380 m (1,250 

ft) across the San Juan Basin (Fassett and Hinds 1971).

Quaternary Fossils

Tweet et al. (2012, p. 359) identified Chaco Culture 

National Historical Park as “a prolific source of [packrat 

(Neotoma spp.)] middens,” which contain collections 

of plant material, food waste, coprolites (fossil dung), 

bones, and other biological materials. The majority 

of the middens at the park are younger than 5,550 

radiocarbon years before present (BP, where “present” 

is 1950 CE) (Betancourt and Van Devender 1981). 

The oldest dated middens are 10,600 ± 200 years 

BP and 10,500 ± 250 years BP (Betancourt and Van 

Devender 1981). Middens are an important tool for 

the reconstruction of late Pleistocene and Holocene 

paleoecology and climate in western North America 

because they document evidence of the builder’s 

foraging range. Commonly, they are well preserved 

in arid, protected settings, such as alcoves and rock 

shelters (see “Cave Shelters” section). 

A database maintained by the US Geological Survey 

(USGS) and National Oceanographic and Atmospheric 

Administration (NOAA) records 55 middens from 

nine sites at Chaco Culture National Historical Park. 

Betancourt (1990) identified more than 300 middens in 

Chaco Canyon that contain needles of the now much 

less abundant Colorado pinyon (Pinus edulis). These 

midden sites are at elevations of 1,860 to 2,020 m (6,100 

to 6,630 ft) between Chacra Mesa and the mouth of 

Chaco Canyon. 

Studies of packrat middens at the park led to the 

discovery of an extinct species of rabbitbrush 

(Chrysothamnus pulchelloides) by Anderson (1980). 

Figure 31. Photograph of Lewis Shale. Lewis Shale was 

deposited in deep, marine waters during an advance 

of the Western Interior Seaway. National Park Service 

photograph available at http://www.nps.gov/chcu/

photosmultimedia/photogallery.htm (accessed 17 April 

2014).
20

The type material came from a midden in Mockingbird 

Canyon radiocarbon dated at 1,910 ± 90 years BP. 

This species records the only known Holocene plant 

extinction in the Southwest; its extinction may be 

related to human activities (Anderson 1980).

In addition to park rat middens and Upper Cretaceous 

rocks, scoping participants noted that Pleistocene 

gravels are known to yield vertebrate fossils (KellerLynn 

2007). None have been found in the park, to date, 

however.

Chaco Canyon

Chaco Canyon is the primary geomorphic feature at 

Chaco Culture National Historical Park. It is 32 km (20 

mi) long, 500 to 1,000 m (1,600 to 3,200 ft) wide, and 

traverses the main unit of the park from the southeast 

to the northwest. The canyon has incised into Upper 

Cretaceous rocks by as much as 180 m (590 ft) (Love 

1983). The floor is covered by alluvium (see “Alluvial 

Fill” section).

A striking feature of the canyon is the asymmetry of its 

walls (King et al. 1985). Because the bedrock dips gently 

(2°–3°) northeastward, the elevation on the south side 

of the canyon is higher than the north side. Moreover, 

the canyon walls on the south side are sloped. Fanlike 

deposits of broken, eroded rock spill onto the canyon 

floor from crumbling walls (fig. 32). The south side also 

is more deeply dissected by tributary canyons than the 

north side.

Small villages, some predating the great houses but most 

concurrent with them, lie at the base of the southern 

slopes and are now buried by centuries of sheetwash 

alluvium (Qsw) and eolian (windblown) sand (Qes) 

(Strutin 1994). By contrast, the Chacoans built great 

houses, including the immense D-shaped Pueblo 

Bonito (see front cover), under the sheer, buff-colored 

cliffs on the north side of the canyon.

Chaco Arroyo

The alluvial-covered floor of Chaco Canyon is presently 

cut by Chaco Arroyo, which in turn is cut by an active 

inner channel (fig. 33). Throughout its history, the floor 

of Chaco Canyon has experienced repeated cut-and-fill 

cycles (see “Alluvial Fill” section), alternating between 

deeply gullied with arroyo channels, as it is currently, 

and having no gullies (Love 2010). With respect to the 

most recent cycle, Simpson (1850) reported observing 

that an intermittent channel or succession of pools 

had developed by 1849. Incision apparently began 

Figure 32. Photograph of Chetro Ketl. The northern and southern sides of Chaco Canyon are distinctly different. Fans 

of debris on the southern side of canyon, as shown in the background, spill onto the canyon floor from crumbling 

walls. Cliffs of vertical sandstone mark the northern walls of the canyon. National Park Service photograph available at 

http://www.nps.gov/chcu/photosmultimedia/photogallery.htm (accessed 17 April 2014).
21

Figure 33. Schematic diagram of geomorphic features of Chaco Canyon. Chaco Canyon is the primary landscape 

feature in Chaco Culture National Historical Park. Chaco Arroyo cut into the canyon floor before 1877. The active inner 

channel cut into the floor of Chaco Arroyo after 1934. The lowest point of the active inner channel is the thalweg. 

Graphic by Trista Thornberry-Ehrlich (Colorado State University) after Love (1980, figure 17).
22

before 1877 when Jackson (1878) reported a channel 

more than 4 m (13 ft) deep. Photographs and channel 

measurements beginning in 1896 describe an incising 

arroyo with little vegetation and a flat bottom until 

the early 1930s (Love 1980). The active inner channel 

developed after 1934 (see “Geologic History” chapter). 

The walls of Chaco Arroyo are between 3 and 11 m (10 

and 36 ft) high and exhibit various stages of erosion, 

from freshly broken vertical walls to eroded, badlandslike slopes. The floor of the arroyo averages 65 m (200 

ft) wide (Love 1977). The walls of the active inner 

channel are between 1 and 3 m (3 and 10 ft) high, and 

the width of the channel is between 3 and 10 m (10 and 

30 ft) across. Ephemeral waters in Chaco Wash flow 

within the active inner channel and sometimes onto the 

floor (floodplain) of Chaco Arroyo during floods (fig. 

33).

Geomorphic features in Chaco Arroyo include, from 

roughly top to bottom, windblown sand, natural levees, 

oxbows, active and inactive point bars, and the thalweg 

(lowest point of the active inner channel) (Love 1980). 

Additionally, a terrace or bench of alluvium is 1.5 to 3 m 

(5 to 10 ft) below the top of the arroyo’s walls (fig. 33).

Dynamic Sedimentation and Arroyo 

Development

Chaco Canyon has 30 m (100 ft) of alluvial fill; 11 

m (36 ft) of this fill is exposed in the walls of Chaco 

Arroyo (Love 1983). Color, clay mineralogy, and 

sedimentary structures distinguish these sediments as 

eolian, side canyon, arroyo channel, or bank deposits 

(Love 1977). The fill consists of both locally derived 

and headwater derived sediments (Siemers and King 

1974). Locally derived Cliff House Sandstone sediments 

are “sandy” yellowish kaolinite (clay), whereas 

sediments derived from upstream areas in the Menefee 

Formation are “clayey” brownish gray or grayish brown 

montmorillonite (clay) (Love 1977; Hall 2010). 

Love (1977) proposed that when no arroyo is 

present, sediments from the headwaters dominate the 

sedimentary record, spreading across the canyon floor 

and interfingering with locally derived deposits along 

the canyon margins (fig. 34). When an arroyo is present, 

local sediments dominate the sedimentary record 

because headwater sediments are confined to an arroyo 

(fig. 35).

Figure 34. Schematic diagram of Chaco Canyon without 

an arroyo. Without an entrenched channel (arroyo), 

sediments from the headwaters (gray arrows) spread 

across the canyon floor (light stipple) during a flood 

and interfinger with locally derived sediments (brown 

deposits) along the canyon margins. Headwater 

sediments also may be transported by overland flow 

or in a single shallow channel or numerous shallow 

braided channels. Some sediment from the headwaters 

may be windblown onto the canyon margins (black 

arrow on right). Side channels may be flooded (brown 

arrows). Graphic by Trista Thornberry-Ehrlich (Colorado 

State University) after Love (1977, figure 10).

Figure 35. Schematic diagram of Chaco Canyon with 

an arroyo. When sediments from the headwaters are 

confined to an arroyo, sediments from the canyon 

margins (brown arrow) and reworked sediments on the 

canyon floor dominate deposition. Local side drainages 

also may be confined to channels. Graphic by Trista 

Thornberry-Ehrlich (Colorado State University) after 

from Love (1977, figure 9).
23

Alluvial Fill

As shown on the source maps and in the GRI GIS 

data, the floor of Chaco Canyon is covered by 

undifferentiated Naha and Tsegi Alluviums (Qnt) or 

Naha Alluvium (Qn) (see poster, in pocket). The terms 

“Naha” and “Tsegi” come from work by Hack (1941) 

in Arizona’s “Navajo Country.” Hack’s system of 

alluvium, in ascending order (oldest to youngest), is 

Jeddito, Tsegi, and Naha. According to Hack (1941), the 

Jeddito Alluvium contains proboscidian remains, the 

Tsegi Alluvium contains evidence of human occupation 

deposited before the 13th century, and the Naha 

Alluvium contains Pueblo IV pottery (i.e., older than 

1300 CE). Investigators in the Chaco Canyon area, 

including Weide et al. (1980), Scott et al. (1984), and 

Mytton and Schneider (1987), used this nomenclature 

introduced by Hack (1941). 

By contrast, Miller et al. (1991) used less formal 

names, which according to that study, seemed easier to 

understand and better fit the surficial geology in La Vida 

Mission quadrangle, including the Kin Bineola unit of 

the park. Some parts of the areas mapped as soil cover 

(Qsl and Qss) and as alluvium (Qal) in La Vida Mission 

quadrangle may include surficial deposits of the type 

designated as Naha by other investigators. 

In the Kin Ya’a unit of the park, Robertson (1986, 

1992) mapped two alluvial deposits of different ages. 

The older unit—unit 2 (Qa2)—was deposited during 

the Holocene Epoch before the latest cycle of arroyo 

cutting. Robertson (1986, 1992) cited Bryan (1954) for 

the timing of arroyo cutting, beginning about 1850. The 

younger unit—unit 1 (Qa1)—is upper Holocene in age. 

Robertson (1986, 1992) noted that this unit has been 

incised by recent arroyos, starting about 1850 (Bryan 

1954). 

The youngest unit of alluvium (Qal) occurs in the 

Chaco Canyon and Kin Bineola units of the park. It 

was mapped by Weide et al. (1980), Scott et al. (1984), 

Mytton and Schneider (1987), and Miller (1991) and 

consists of stream-deposited clay, silt, sand, and gravel 

along major drainages. This unit fills the lowest channels 

cut into the floodplains of ephemeral streams, including 

Chaco Wash.

Hall (1990, 2010) questioned the use of Hack’s 

terminology in Chaco Canyon because the timing 

of deposition of these alluviums is unclear, and a 

correlation between the type localities in Arizona 

and Chaco Canyon in New Mexico has not been 

established. During geologic mapping at Chaco Canyon 

in the 1980s, investigators chose to use and apply 

Hack’s terminology rather than Chaco-specific work 

by Bryan (1954), Hall (1977), and Love (1977), which 

showed that the exposed alluvial fill is neither uniformly 

the same over the canyon floor as indicated by color, 

grain size, and sedimentary structures, nor the same 

age, as indicated by the presence of archeological sites 

of different ages. Hall (1977, 2010) found that at any 

one place on the canyon floor, alluvium could be one 

of four types: (1) pre-Gallo (not dated, but estimated 

at late Pleistocene or early Holocene age), (2) Gallo 

(6,700–2,800 years BP), (3) Chaco (2,100–1,000 years 

BP), or (4) Bonito (800–100 years BP) (see “Geologic 

History” chapter). 

Sheetwash Alluvium and Slope-Wash 

Deposits

Overland flow is runoff that moves over the land 

surface, ultimately on its way to a stream channel. 

In contrast to streamflow, overland flow is not 

concentrated in a channel, but moves downslope as a 

thin, continuous sheet of water. 

Source maps included two map units of overland flow: 

sheetwash alluvium (Qsw) in the Chaco Canyon unit 

of the park, and slope-wash deposits (Qswd) in the Kin 

Bineola unit of the park. Scott et al. (1984) and Mytton 

and Schneider (1987) mapped sheetwash alluvium 

(Qsw) on the tops of mesas north and south of Chaco 

Canyon and along the canyon’s margins. This material 

accumulated when rain fell and moved fine sediments 

downslope where they grade into stream-deposited 

alluvium. Most of this material originated from the 

underlying Menefee Formation, but was deposited 

during the Holocene Epoch, and is still accumulating. 

Some small areas of gravel with a sheetwash origin 

along Fajada Wash are older (Pleistocene Epoch). 

These deposits correlate with the Jeddito Alluvium of 

Hack (1941), which is exposed in a gravel pit 0.8 km 

(0.5 mi) southwest of park headquarters, and may be 

equivalent to the “Fajada gravel” of Hall (1977, 2010) 

(see “Geologic History” chapter).

Miller et al. (1991) mapped slope-wash deposits 

(Qswd) in the Kin Bineola unit of the park. Many large 

and small areas in the La Vida Mission quadrangle, 

where Kin Bineola is located, consist of gently sloping, 

almost smooth surfaces that have been formed by 
24

“sheetflood” erosion. Sheetfloods usually occur before 

runoff is sufficient to promote channel flow, or after 

a period of sudden and heavy rainfall (Neuendorf et 

al. 2005). Slope-wash deposits developed most readily 

where mudstone of the Menefee Formation weathered 

to form an easily eroded mantle. Some of the slopewash surfaces consist of mud left behind by a flood, 

but some are paved with sand or rock fragments from 

nearby weathered beds of sandstone in the Menefee 

Formation. Still others have a veneer of angular chips of 

ironstone derived from the disintegration of ironstone 

concretions (fig. 36), which occur in the Juans Lake 

Beds (Kmfaj). Margins of the slope-wash areas are 

commonly irregular and interfinger with stabilized 

eolian sand or soil (Miller et al. 1991).

Eolian Features

Eolian processes refer to windblown erosion, 

transportation, and deposition of sediments (Lancaster 

2009). The broad, continuous channel of Escavada 

Wash–Chaco River, at the mouth of Chaco Canyon, is 

a source of abundant loose sand available for eolian 

transport (Love et al. 2011). Exposed bedrock, such 

as the Cliff House and Pictured Cliffs sandstones, is 

another source of eolian material (Weide et al. 1980; 

Scott et al. 1984). Southwest–northeast-prevailing winds 

have eroded and transported sand from channels of 

major washes and sandstone bedrock to create eolian 

features since the Pleistocene Epoch (Weide et al. 1980).

Three types of eolian deposits occur in the GRI GIS 

data for Chaco Culture National Historical Park. These 

deposits range in age from Pleistocene to Holocene. 

From oldest to youngest they are (1) older eolian 

deposits (Qoe), (2) eolian sand (Qes), and (3) alluvium 

and eolian deposits (Qae) (see Map Unit Properties 

Table, in pocket). 

In the Chaco Canyon unit of the park, investigators 

mapped eolian sand (Qes) on mesa tops, at the mouth 

of Chaco Canyon, in Weritos Rincon (southern side of 

Chaco Canyon), and surrounding Tsin Kletsin. Much 

of the surface of the Kin Ya’a unit is covered by older 

eolian deposits (Qoe) of Holocene and Pleistocene age. 

A mixture of alluvium and eolian deposits (Qae) covers 

parts of the Kin Bineola unit. Investigators did not map 

any eolian units at the Pueblo Pintado unit, but deposits 

occur nearby.

In addition, Soil Survey of Chaco Culture National 

Historical Park, New Mexico (Zschetzsche and Clark 

2004) mapped eolian soils in the park. In the Chaco 

area, eolian soils can be very deep and located in large 

dune fields or they can occur as a shallow mantle over 

bedrock-controlled surfaces. The Razito series is found 

on dunes.

Sand dunes at Chaco Culture National Historical Park 

include the following types:

● Barchan—crescent-shaped dunes perpendicular 

to the direction of the prevailing winds, composed 

of younger eolian sand (Qes) in the Chaco Canyon 

unit (Scott et al. 1984). 

● Climbing—dunes formed by the piling-up of sand 

against a cliff, composed of younger eolian sand 

(Qes) in the Chaco Canyon unit (Scott et al. 1984).

● Coppice—small dunes forming on the lee side of 

vegetation, mostly above the cliffs in Chaco Canyon 

and along mesa tops (Love 1980).

● Parabolic—U-shaped dunes with arms pointing 

upwind, associated with large alluvial fans at the 

mouths of tributary canyons (Love 1980).

● Transverse—elongated, asymmetrical dunes 

perpendicular to the direction of prevailing winds. 

According to Zschetzsche and Clark (2004), most 

dunes in the Chaco area are relatively small, mostly 

stable transverse dunes; vegetation that restricts 

their activity has been established. Transverse dunes 

are associated with the Chaco River and Escavada 

Figure 36. Photograph of broken concretions. The 

formation of concretions takes place underground, but 

where exposed at the surface can become broken into 

fragments. This debris is from the Menefee Formation 

south of Chaco Culture National Historical Park. 

Photograph by David W. Love (New Mexico Bureau of 

Geology and Mineral Resources). 
25

Wash near the mouth of Chaco Canyon; these 

dunes are up to 4 m (13 ft) high (Love 1980). 

● Seif (meaning “sword”)—elongated dunes parallel 

to the prevailing winds. Robertson (1992) mapped 

large-scale seif dunes (Qoesd; see GRI GIS data), 

some combined with barchan dunes, near Kin Ya’a, 

but not within the park. Seif dunes rise 1–6 m (3–20 

ft) above older eolian deposits.

Zschetzsche and Clark (2004) noted that dunes may be 

a component of most of the other landforms. Dunes 

also occur within tributary canyons; for example, the 

dune in Weritos Rincon is more than 30 m (100 ft) 

high and 500 m (1,640 ft) long (Love 1980). Scoping 

participants mentioned this dune, as well as large dunes 

in the vicinity of Pueblo Pintado (KellerLynn 2007).

The general locations of the eolian deposits in and 

around the park remain consistent. Their forms change 

over time, however, as does the amount of stabilizing 

vegetation. Love et al. (2011) compared 1935 and 2009 

aerial photographs of the mouth of Chaco Canyon that 

showed that active oblique transverse dunes in 1935 had 

shifted north and east and became blowouts (eroded 

hollows in a preexisting dune) and parabolic dunes 

with long, partially stabilized arms. In addition, thick 

accumulations of eolian sand along the lower cliffs on 

the northeastern side of the Chaco Canyon had shifted 

slightly east, and blowouts exposed lower cliffs that had 

been buried by eolian sand in 1935.

“Lake Chaco”

The idea that a sand dune dammed Chaco Wash and 

created a lake at the mouth of the canyon is part of the 

scientific and popular literature about Chaco Culture 

National Historical Park (see Force et al. 2002 and Force 

2004). Creation of so-called “Lake Chaco” is proposed 

to have taken place on several occasions and has been 

associated with a prehistoric wall, which apparently 

Chacoan people built to actively manage the “dune 

dam.” Scoping participants were skeptical of this idea, 

particularly because the existence of a lake had not 

been verified; also, the age of the dune had not been 

established (see KellerLynn 2007). 

Since the 2007 scoping meeting, Love et al. (2011) 

published findings that provided several lines of 

evidence that nullify the hypothesis that a sand dune 

dammed Chaco Wash during Pueblo II occupation 

(900–1150 CE). Lines of evidence include the dynamic 

geomorphology of the sand dunes at the confluence 

of Chaco and Escavada washes and the floor of Chaco 

Arroyo, the shape of the bedrock outcrops at the 

confluence that influences wind currents and dune 

locations, the hydrology of Chaco Wash, and detailed 

stratigraphic mapping and analysis of the locality where 

lake beds were thought to exist. Descriptive details of 

the modern geomorphology and dynamic nature of 

the confluence of Chaco and Escavada washes and the 

sand dunes near the mouth of Chaco Canyon indicate 

that the dunes could not have formed a resistant dam 

for the discharges of Chaco Wash. Based on observed 

geomorphology and stratigraphy, Love et al. (2011) 

saw no evidence, actual or theoretical, of lacustrine 

depositional environments in lower Chaco Canyon.

Tinajas and Charcos

In 2007, GRI scoping participants identified tinajas as 

a potentially valuable geologic (and ecologic) resource 

in need of study at Chaco Culture National Historical 

Park. Participants suggested that these natural potholes 

may have been and may continue to be a significant 

source of surface water within the park, providing 

seasonal habitat for wildlife and microorganisms. Kirk 

Bryan (see “Geologic Setting and Significance” chapter) 

was one of the first scientists to study tinajas in the US 

Southwest. Bryan referred to these features as “rock 

tanks,” though noted the name “tinajas,” meaning bowl 

or jar in Spanish. Bryan (1920, p. 188) recognized the 

importance of these features in arid regions, where 

small water supplies made possible “a journey which 

otherwise could not be undertaken.” Bryan saw these 

features as “an interesting geologic problem” and noted 

that regional physiography controlled their distribution. 

He also observed that the bases of these depressions 

are covered by “an effective seal composed of the slime 

from decayed organic matter and dust” (Bryan 1923, p. 

301).

A primary characteristic of tinajas is that they form 

in bedrock, which in the Colorado Plateau region 

is usually characterized by flat, exposed surfaces of 

porous sandstone (Chan et al. 2005, 2006). Another 

characteristic of tinajas is that they form naturally, 

although their origin continues to be a scientific enigma. 

Early attempts to explain their formation included 

unequal weathering of rock surfaces by glaciers, 

streams, dissolution, and even sea urchins (Elston 

1917, 1918; Bryan 1920; Ross 1923; Alexander 1932). 

Recent investigations indicate that the formation of 

tinajas may be linked to biology. Organisms adapt and 
26

flourish within tinajas despite extreme seasonal and 

daily fluctuations in moisture, temperature, and pH 

(Chan et al. 2001). Many species become dormant when 

these features dry, and must endure intense heat, UV 

radiation, desiccation, and freezing, but flourish again 

upon rehydration. These life-forms appear as a black 

biofilm within tinajas, which may dissolve the cement 

between sandstone grains, causing enlargement, as 

well as sealing the tinajas, enabling them to retain water 

longer than the surrounding sandstone (Chan et al. 

2001). 

Most tinajas are passive water sources, as opposed 

to active water sources such as springs. They require 

recharge by direct precipitation (Brown and Johnson 

1983). Factors that affect the presence or longevity of 

water in a tinaja include the amount of protection or 

shade, the size of the adjacent bedrock catchment area, 

the amount of sediment infilling, and the permeability 

of the bedrock (Brown and Johnson 1983; Pate and 

Filippone 2006).

Charcos, meaning pond or small lake in Spanish, 

are another surface water feature at Chaco Culture 

National Historical Park. They are mud holes or 

watering holes that form in depressions in an alluvial 

plain or ephemeral stream bed, filling with water after 

rains or floods. Surface water collects in such pools 

at the confluence of the Chaco and Escavada washes 

(Mathien 2005). Bryan (1920, 1954) studied these 

features in Chaco Canyon and observed that they were 

a water supply during the growing season and, although 

limited, probably provided favorable conditions for 

farming in the canyon.

Badlands

The term “badlands” was first applied to an area in 

South Dakota by early French fur traders who found 

the lands difficult for traveling (“mauvaises terres 

du traverser”) (see the GRI report about Badlands 

National Park by Graham 2008). Other connotations 

of “badlands” imply areas of sparse vegetation, not 

suitable for agriculture. Badlands in the western 

United States today, however, are commonly viewed 

as “charming features of the natural landscape” 

(Love 2002, p. 26). These features are abundant in 

northwestern New Mexico, forming 30%–40% of the 

area (Love 2002). Some of the most extensive badlands 

occur in coal-bearing rocks such as the Menefee 

Formation, which is mapped throughout the park, and 

the Fruitland-Kirtland formations, which occur in the 

Chaco River headwaters east of the park. Badlands are 

notable in the southwestern part of the park, south of 

West Mesa (fig. 37).

Cave Shelters

In Chaco Culture National Historical Park, cavelike 

features form as a result of differential weathering along 

the shale-sandstone contact between the Menefee 

Formation and Cliff House Sandstone (fig. 38). Usually 

referred to as “shelters,” these features are notable for 

the resources they contain, such as packrat (Neotoma

spp.) middens (see “Quaternary Fossils” section). 

Figure 37. Photograph of Menefee 

badlands. Once identified by negative 

attributes—difficult for travel and 

unsuitable for farming—visitors 

today view and enjoy badlands as 

a distinctive feature of the natural 

landscape. Badlands are a characteristic 

of the Menefee Formation in Chaco 

Culture National Historical Park. 

National Park Service photograph 

available at http://www.nps.gov/chcu/

photosmultimedia/photogallery.htm

(accessed 17 April 2014).
27

As a result of the investigation of packrat middens, the 

locations of many cave shelters in the park are known, 

and could possibly be plotted in the park’s GIS (Dabney 

Ford, Chaco Culture National Historical Park, chief, 

Cultural Resources, conference call, 15 April 2014). 

An estimated 100 to 150 of these features occur in the 

park. In addition, an estimated 100 or so shelters were 

built under or attached to large talus boulders, and 

are essentially detached cliff shelters (Dabney Ford, 

Chaco Culture National Historical Park, chief, Cultural 

Resources, email correspondence, 13 August 2014). A 

thorough cave inventory of these features has not been 

conducted.

Cave shelters provided temporary and permanent living 

areas for prehistoric peoples. Excavations in some of the 

larger cave shelters at the park have provided significant 

information on older cultures that date back to preClovis times, 11,000 years ago and older (Dale Pate, 

NPS Geologic Resources Division, National Cave and 

Karst Program, coordinator, written communication, 22 

May 2014). Cave shelters preserve some of the earliest 

datable cultural material such as corn and basketry, 

which elsewhere readily biodegrade (KellerLynn 2007).

Figure 38. Photograph of cave shelter. Cave shelters, which prehistoric people used as temporary and permanent 

dwellings, such as the Gallo cliff dwelling shown here, form along the contact between the Menefee Formation (shale) 

and Cliff House Sandstone. This opening is 70 m (230 ft) wide, 8 m (26 ft) deep, and 5 m (15 ft) high at its highest 

point. National Park Service photograph (taken in 2006).

29

Geologic Resource Management Issues

This chapter describes geologic features, processes, or human activities that may require management 

for visitor safety, protection of infrastructure, and preservation of natural and cultural resources in 

Chaco Culture National Historical Park. The NPS Geologic Resources Division provides technical and 

policy assistance for these issues.

During the 2007 scoping meeting (see KellerLynn 

2007) and 2014 conference calls, participants (see 

Appendix A) identified the following geologic resource 

management issues:

● Oil and Gas Development

● Coal Resources and Mining

● Uranium Production

● Abandoned Mineral Lands

● Disturbed Lands Restoration

● Rockfall

● Paleontological Resource Inventory and 

Monitoring

● Piping

● Seismicity

● Eolian Processes

● Efflorescence

Resource managers may find Geological Monitoring

(Young and Norby 2009) useful for addressing some 

of these geologic resource management issues. 

The manual provides guidance for monitoring 

vital signs—measurable parameters of the overall 

condition of natural resources. Each chapter covers 

a different geologic resource and includes detailed 

recommendations for resource managers and 

suggested methods of monitoring. An online version of 

Geological Monitoring is available at http://go.nps.gov/

geomonitoring (accessed 27 August 2015).

As this report was in final review, the foundation 

document was completed for Chaco Culture National 

Historical Park (National Park Service 2015). 

The foundation document lists the following as 

“fundamental” resources or values:

● Core canyon communities and associated 

architectural features (great houses, great kivas, 

earthen mounds, community/habitation sites, 

prehistoric roads, stairways, shrines, signaling 

stations, rock art, and water control features)

● Chaco regional system (cultural landscape)

● Museum collections

● Ongoing cultural connections

● Unique visitor experience

Fundamental resources or values warrant primary 

consideration during planning and management 

processes because they are essential to achieving the 

purpose of the park and maintaining its significance.

Paleontological resources (fossils) are considered 

“important” resources or values. Important resources 

are not fundamental to the purpose of the park and 

may be unrelated to its significance, but are important 

to consider in planning processes. Geologic features 

and processes and some of the resource management 

issues described in this chapter affect these values and 

resources highlighted in the foundation document.

Oil and Gas Development

Oil and gas development and associated impacts are a 

potential threat to four of the five fundamental values 

(the fifth being museum collections) identified in the 

park’s foundation document (National Park Service 

2015). Oil and gas development is therefore a “key 

issue” for park managers and additional information 

on threats posed by hydraulic fracturing (“fracking”) 

is a medium priority data need (National Park Service 

2015).

At present, the Mancos Shale (oil) and Gallup 

Sandstone (oil and gas) are the primary targets 

for oil and gas development in the San Juan Basin. 

Improvements in horizontal drilling and hydraulic 

fracturing, commonly called “fracking,” have spurred 

renewed industry interest in these rocks (National Park 

Service 2014b). The potential role of this technology in 

the San Juan Basin cannot be overemphasized (Engler et 

al. 2001), and the size and scale of horizontally drilled, 

hydraulically fractured wells will likely dwarf anything 

seen in the area previously (National Park Service 

2014b).
30

In conventional vertical wells, production of oil and 

gas in the Mancos Shale and Gallup Sandstone is 

limited by natural fracturing, which was induced as 

a result of deformation that occurred during basin 

formation. Horizontal drilling can enhance production 

by first drilling vertically to or near the top of the target 

formation and then turning the drill bit horizontally into 

the target formation. This maneuver intersects a series 

of vertical fractures, exposing more of the production 

zone to the well bore. Recent technological innovations 

in drilling and steering the bit to stay within the target 

formation have increased the success rate of this 

process (Just et al. 2013).

Production is further enhanced by fracking of the 

rock to concentrate pressures and increase subsequent 

fracture length (Just et al. 2013). Fracturing rock in this 

way is accomplished using a technique in which a liquid, 

typically water, is mixed with sand and chemicals, and 

then injected at high pressure into a well bore to create 

artificial fractures, along which gas and oil can migrate. 

After hydraulic pressure is removed from the well, small 

grains of sand or aluminum oxide, called “proppant,” 

hold these fractures open.

Fracking of the Gallup Sandstone is a particular concern 

for park managers because the park’s drinking water 

well is developed in this sandstone. The risk is related 

to potential contamination from the introduction of 

fracking fluids in the production well development 

process (Stephen Monroe, NPS Southern Colorado 

Plateau Network, hydrologist, written communication, 

30 October 2014). If large-scale development of natural 

gas from the Mancos Shale were occurring close to 

the park, it could be cause for concern about the 

potential for contamination of the fresh groundwater 

resource in the Gallup Sandstone (Larry Martin, 

NPS Water Resources Division, hydrogeologist, email 

communication, 5 September 2014).

Other effects of horizontal drilling and hydraulic 

fracturing may include the following:

● Water contamination related to drilling and 

disposal of drilling fluids;

● Reductions in streamflow and groundwater levels 

from operational water requirements;

● Air quality degradation from internal combustion 

engines on drill rigs and trucks;

● Excess dust from equipment transportation;

● Disruption of solitude and night skies from 

operational lights or flaring;

● Impacts to cultural resources, including 

archeological structures, as a result of vibrations 

from transportation and drilling (see “Seismicity” 

section); and

● Safety concerns and impacts to wildlife associated 

with the necessary transportation to support 

drilling operations (National Park Service 2013, 

2014b). 

A concern of park managers at Chaco Culture National 

Historical Park is the uncertainty of how many wells 

will be drilled. Estimates depend on current technology, 

as well as interest and investment by oil and gas 

companies. For example, Engler et al. (2001) discussed 

reasonable foreseeable development in the New 

Mexico portion of the San Juan Basin and predicted 

the completion of 16,615 wells over a 20-year period 

(2002–2022). These investigators estimated a significant 

reduction (25%) in this number (to 12,461) as a result 

of opportunities for commingling (producing oil and 

gas from two or more reservoirs at different depths) and 

dual completion (a single well that produces from two 

separate formations at the same time), equating to a rate 

of 623 wells completed per year. In actuality, 1,519 wells 

were completed in the San Juan Basin with an average of 

190 wells per year between January 2006 and December 

2013 (Ron Broadhead, New Mexico Bureau of Geology 

and Mineral Resources, principal senior petroleum 

geologist, email communication, 2 May 2014). Thus the 

actual outcome at that time was noticeably lower than 

those anticipated by Engler et al. (2001) because that 

report was prepared before the advent of horizontal 

drilling and was based on the assumption that all 

wells would be conventional vertical wells, which 

are less costly. A substantial increase in the number 

of completed wells (greater than 190) is anticipated 

based on the interest and investment of the three most 

involved companies—Encana Corporation, WPX 

Energy, and Logos Resources, LLC. If these companies 

can define the most productive parts of the play, and 

if production is substantial enough, then drilling will 

probably increase year-to-year over the next few years 

(Ron Broadhead, New Mexico Bureau of Geology 

and Mineral Resources, principal senior petroleum 

geologist, email communication, 2 May 2014). 

The New Mexico Oil Conservation Division provides 

data and statistics about wells drilled in the state, 
31

including a weekly activity report on intentions to 

drill at https://wwwapps.emnrd.state.nm.us/ocd/

ocdpermitting//Reporting/Activity/WeeklyActivity.aspx

(accessed 24 August 2015). This information may help 

park managers anticipate future activity near the park’s 

boundary. This website provides the county and land 

type (federal, state, or private) of each well.

Another concern for park managers is the location of 

future drilling activities and wells. The majority (82%) 

of adjacent land to Chaco Culture National Historical 

Park is tribally owned by the Navajo Nation or is Navajo 

allotted lands, some of which are available for leasing 

(fig. 39). In addition, eight allotments occur within the 

administrative boundaries of the park. Allotments are 

not held by the tribal government but have been given 

to individual tribal members by the federal government. 

Most allotees inherited the land from their parents, 

grandparents, or great-grandparents. The incentive for 

allotees to develop their mineral rights is potentially 

high. Many allotment owners in northwestern New 

Figure 39. Map of surface ownership. Chaco Culture National Historical Park is surrounded by the Navajo Nation, 

individual allotments, and Bureau of Land Management lands. Some of these lands are available for oil and gas 

leasing. Surface ownership data compiled by the Bureau of Land Management and available online: http://www.blm.

gov/nm/st/en/prog/more/geographic_sciences/spatial_data_metadata.html (accessed 28 September 2015). Map by Jason 

Kenworthy (NPS Geologic Resources Division). 
32

Mexico are economically disadvantaged, and the 

dramatic increase of oil and gas production in the San 

Juan Basin would provide royalties for individual Indian 

families, as well as encourage economic growth and job 

creation on Indian lands (Bureau of Indian Affairs 2013; 

Montoya Bryan 2014).

In the event that an owner of one of the eight allotments 

wanted to explore or develop his/her mineral rights, 

the National Park Service would require that the owner 

follow the Code of Federal Regulations 36, Part 9, 

Subpart B (see Appendix B of this report). With respect 

to horizontal drilling, an allotment owner would not 

have the right to drill horizontally under NPS lands 

through “federal minerals”; the owner would have to 

stay within the allotment. Additionally, the allotment 

owner would need a New Mexico state permit to drill 

an exploration well. The National Park Service would 

work with the state, owner, and the operator to reduce 

or eliminate impacts to park resources (Kerry Moss, 

NPS Geologic Resources Division, External Energy and 

Minerals Program coordinator, email communication, 2 

May 2014).

Federal acquisition of these private inholdings 

and all outstanding mineral rights would eliminate 

concern over future energy development within the 

boundaries of the park. The 1980 enabling legislation 

for Chaco Culture National Historical Park directed 

the National Park Service to acquire all lands within 

its administrative boundary, including these eight 

allotments, through exchange or purchase. The 

National Park Service is working with the Bureau of 

Indian Affairs and the Bureau of Land Management 

to identify acquisition opportunities (Jim Von 

Haden, Chaco Culture National Historical Park, 

Natural Resources Program manager, telephone 

communication, 4 September 2014).

With respect to oil and gas development, the National 

Park Service formally consults with the Navajo Nation 

at a government-to-government level. The NPS 

Geologic Resources Division can provide technical 

assistance to park managers to strive to reduce or 

eliminate impacts to NPS resources and values. 

The mutual concern of the National Park Service 

and Navajo Nation in protecting sensitive cultural 

resources is a point of agreement for conversations and 

consultation about oil and gas development within or 

near the park (Jim Von Haden, Chaco Culture National 

Historical Park, Natural Resources Program Manager, 

telephone communication, 15 April 2014). 

About 18% of the land surrounding Chaco Culture 

National Historical Park is federally owned and 

managed by the Bureau of Land Management (BLM). 

In August 2014, the National Park Service and Bureau 

of Land Management signed a memorandum of 

understanding that formally included the National Park 

Service as a cooperating agency in planning to address 

issues relating to oil and gas in the Mancos Shale and 

Gallup Sandstone (Jim Von Haden, Chaco Culture 

National Historical Park, Natural Resources Program 

Manager, telephone communication, 4 September 2014; 

see Bureau of Land Management 2014).

Coal Resources and Mining

Geologic setting determines whether coal is present and 

determines whether coal beds are thick and flat-lying 

enough to be mined with available technology. Other 

factors that affect the potential for mining include 

coal quality (sulfur content and heating value), ash 

content, proximity to available transportation networks, 

market competition, and land-use restrictions such as 

ownership and access (Hoffman 2002; Hoffman and 

Jones 2011).

Coal-bearing units in the San Juan Basin formed in peat 

swamps contemporaneous with the Western Interior 

Seaway. Most of the San Juan Basin coals that are thick 

enough to have economic potential developed as the 

seaway retreated to the northeast. Slow, uneven retreat 

of the seaway allowed for substantial buildup of organic 

material in swamps, which became preserved as coal in 

the rock record (Broadhead and Hoffman 2002). 

The Crevasse Canyon, Menefee, and Fruitland 

formations are the major coal-bearing rocks in the 

San Juan Basin. Within Chaco Culture National 

Historical Park, the Crevasse Canyon Formation (Kcg) 

and Menefee Formation (Kmf, Kmft, Kmfa, Kmfaj, 

and Kmfal) contain coal (see poster, in pocket). The 

GRI GIS data include coal resource occurrence and 

development source maps by Berge Exploration Inc. 

and Dames & Moore (see “Geologic Map Data” 

chapter). Linear geologic units in the data mark coal 

beds.

At present, coal seams in the Crevasse Canyon 

Formation are not being mined in the San Juan 

Basin. The Menefee Formation has two coal-bearing 
33

Figure 40. Map of coal fields in the San Juan Basin. Upper Cretaceous rocks in the San Juan Basin contain coal 

resources. The Standing Rock field is currently the primary area for coal extraction near Chaco Culture National 

Historical Park. The Lee Ranch and El Segundo mines produce coal in this field. The Cleary Coal Member of the 

Menefee Formation is mined. Graphic by Trista Thornberry-Ehrlich after Hoffman (2002, figure 2). Base map by Tom 

Patterson (National Park Service).
34

sequences: the Cleary Coal Member (Kmfc; see GRI 

GIS data) at the base, and the upper coal member at the 

top. The Cleary Coal Member is actively being mined 

in the Standing Rock field (see description below). The 

Fruitland Formation is actively being mined west of 

Farmington (Hoffman 2002).

In the 1970s, coal beds in southern Chaco Canyon and 

the La Vida Mission areas were of interest for mining 

(Shomaker et al. 1971). Coal in these areas was probably 

used by Indian inhabitants prior to exploration by 

European Americans (Nickelson 1988). Two mines are 

mentioned in the literature: (1) Blake mine in the La 

Vida Mission area and (2) Pueblo Bonito mine on the 

southern wall of Chaco Canyon (Nickelson 1988). In 

the La Vida Mission area, 907 million–1.7 billion kg 

(1–1.9 million tons) of strippable coal was extracted 

(Shomaker et al. 1971). The extent of production at the 

Pueblo Bonito mine is unknown (Shomaker et al. 1971).

At present, the primary area for coal extraction near 

Chaco Culture National Historical Park is in the 

Standing Rock field (fig. 40), which targets the Cleary 

Coal Member of the Menefee Formation (Hoffman 

and Jones 2011). The Lee Ranch Mine in the Standing 

Rock field, which is now owned by Peabody Energy, 

began operation in 1985. In 2008, the El Segundo Mine 

opened; this mine, also owned by Peabody Energy, is 

adjacent to the Lee Ranch Mine. These mines have 

access to rail transportation and ship coal to power 

plants. The El Segundo Mine is the most productive 

US mine outside of Wyoming’s Powder River Basin. 

In 2013, it supplied 7.6 billion kg (8.4 million tons) of 

coal to the Arizona Public Service Company, Tucson 

Electric Power, and Arizona Electric Power Cooperative 

and Western Fuels Association (Peabody Energy 2014). 

These mining operations are 23 km (14 mi) east of the 

Kin Ya’a unit of the park. Notably, mining is restricted 

in the entire 1⁄4 section (T17N R12W S28, McKinley 

County, New Mexico) in which the Kin Ya’a unit lies 

(Hoffman and Jones 2011).

Present-day owners of eight allotments within the park 

have the authority to extract resources such as coal 

on their lands. Scoping meeting participants thought 

this was unlikely, however, because the parcels of land 

are small and no one lives on them to use the coal for 

“personal consumption” (i.e., heating or cooking) 

(KellerLynn 2007). 

The National Park Service has the legal authority to 

provide input during permitting of mining activities 

within a park’s viewsheds, or if a federal action may in 

any way impact or impair park resources of values. The 

Surface Mining Control and Reclamation Act of 1977 

controls surface coal mining and reclamation activities 

on both federal and nonfederal lands (see Appendix B). 

Surface coal mining includes activities conducted on 

the land surface in connection with a surface coal mine 

or surface operations and impacts associated with an 

underground mine. Section 522(e) of this act contains 

provisions that protect “publicly owned parks” from 

adverse impacts of surface coal mining.

The NPS Geologic Resources Division works with 

adjacent land managers and other permitting entities 

to help ensure that NPS resources and values are 

not adversely impacted by mineral exploration and 

development. Potential impacts include groundwater 

and surface water contamination, erosion and siltation, 

introduction of exotic plant species, reduction of 

wildlife habitat, impairment of viewsheds and night 

skies, excessive noise, and diminished air quality. Visitor 

safety and overall degradation of the visitor experience 

are particular concerns. The NPS Geologic Resources 

Division website, http://go.nps.gov/grd_energyminerals

(accessed 27 August 2015), provides additional 

information about energy development and mineral 

extraction.

Uranium Production 

For nearly three decades (1951–1980), the Grants 

uranium district in the San Juan Basin of northwestern 

New Mexico produced more uranium than any other 

district in the United States (McLemore 2007). The 

Grants district extends from east of Laguna to west 

of Gallup and encompasses parts of Chaco Culture 

National Historical Park. The Chaco Canyon unit of the 

park is in the Chaco Canyon subdistrict; the Kin Ya’a 

unit is in the Church Rock–Crownpoint subdistrict (fig. 

41). The exploration of uranium resulted in abandoned 

mineral lands (AML) sites within and near the park. 

These sites are discussed in the “Abandoned Mineral 

Lands” section.

To date, the closest mining operation to the park to 

have produced uranium was the Crownpoint Mine, 

which is about 4 km (3 mi) west of the Kin Ya’a unit 

(see GRI GIS data, mine point feature). In addition, the 

Mobil Oil Company had an in situ leaching (ISL) pilot 
35

project in the Church Rock–Crownpoint subdistrict. In 

situ leaching, also known as solution mining, involves 

leaving the ore in the ground, and recovering the 

minerals from it by dissolving them and pumping the 

enriched solution to the surface where the minerals can 

be recovered.

The most important uranium deposits in the Grants 

uranium district are within the Upper Jurassic 

Morrison Formation (sandstone). Most of the 

uranium production in New Mexico has come from 

these deposits (McLemore 1983). Humates (organicrich deposits) also have produced uranium (Ginger 

McLemore, New Mexico Bureau of Geology and 

Figure 41. Map of Grants uranium district. The historically significant Grants uranium district of northwestern New 

Mexico encompasses parts of Chaco Culture National Historical Park. Black outlines and labels delineate uranium 

subdistricts. Units of the park are indicated with green boxes and/or labels. The Chaco Canyon unit of the park is in 

the Chaco Canyon subdistrict. The Kin Ya’a unit of the park is in the Church Rock–Crownpoint subdistrict. Although 

no production is occurring within the Grants uranium district today, the Morrison Formation (sandstone) retains rich 

uranium reserves. Graphic by Trista Thornberry-Ehrlich (Colorado State University) after McLemore (2007, figure 1). 

Base map by Tom Patterson (National Park Service).
36

Mineral Resources, senior economic geologist, written 

communication, 2 September 2015). Following 

deposition, groundwater transported uranium into the 

sandstone and humates.

In the 1970s and 1980s, park managers were concerned 

that groundwater pumping at uranium mines might 

eventually affect the supply of water from the park’s 

well. Uranium mining operations in the Crownpoint 

and Ambrosia Lake areas required pumping large 

volumes of groundwater to dewater the underground 

workings at these mines. The source of the park’s 

drinking water is the Gallup Sandstone aquifer. The 

Gallup Sandstone, however, is separated from the 

uranium-rich Morrison Formation by thousands 

of feet of low-permeability Mancos Shale (fig. 4). 

Monitoring has shown that the Mancos Shale is an 

effective confining unit and severely restricts movement 

of groundwater between the Morrison Formation and 

Gallup Sandstone aquifers (fig. 4; Martin 2005). The 

source of the park’s drinking water is thus protected 

from uranium contamination by virtue of stratigraphy 

and geologic conditions (Martin 2005). Furthermore, 

fracking of the Mancos Shale would not provide a 

pathway for uranium to move from the Morrison 

Formation into the Gallup Sandstone (Larry Martin, 

NPS Water Resources Division, hydrogeologist, email 

communication, 8 September 2014; see “Oil and Gas 

Development” section). 

The effect of wastewater discharge upon ephemeral 

streams is a potential management concern resulting 

from uranium mining. Discharge could cause gullying, 

piping, or headward erosion in tributaries, or the 

reverse effect—the accumulation of sediment as a 

result of vegetation growth stimulated by an increased 

water supply (Simons, Li & Associates, Inc. 1982a). The 

greatest impacts of erosion and sedimentation would 

occur in tributaries adjacent to mines and mill sites. 

Although the Grants district has no mines producing 

uranium today, energy companies have acquired 

uranium properties and plan to explore and develop 

deposits in the district (McLemore 2014). Before 

uranium could be produced again from the Grants 

uranium district and elsewhere in New Mexico, 

however, several challenges would need to be overcome:

● No conventional mills remain in New Mexico to 

process the ore, adding to the cost of producing 

uranium in the state;

● Permitting for new in situ leaching, especially for 

conventional mines and mills, will take years to 

complete;

● Closure plans, including reclamation, must be 

developed before mining or leaching begins, and 

modern regulatory costs will add to the cost of 

producing uranium in the United States;

● Some communities do not view development of 

uranium properties as favorable; for example, the 

Navajo Nation—which was severely impacted 

in 1979 by the Church Rock uranium mill when 

radioactive waste and contaminated water spilled 

into an arroyo that emptied into the Puerco River—

has declared that no uranium production will occur 

on its tribal lands; and 

● High-grade, low-cost uranium deposits in Canada 

and Australia and the large, low-grade deposits 

in Kazakhstan are sufficient to meet current 

international demands (McLemore 2007).

As low-cost technologies, such as in situ leaching 

techniques improve, and as global demand for uranium 

increases, the Grants uranium district has the potential 

to become an important future source, adding to its 

historical significance (McLemore 2014).

Abandoned Mineral Lands

Abandoned mineral lands (AML) are lands, waters, 

and surrounding watersheds that contain facilities, 

structures, improvements, and disturbances associated 

with past mineral exploration, extraction, processing, 

and transportation, including oil and gas features 

and operations. The National Park Service takes 

action under various authorities (see Appendix B) to 

mitigate, reclaim, or restore AML features in order to 

reduce hazards and impacts to resources. Resource 

management of AML features requires an accurate 

inventory and reporting. The NPS Geologic Resources 

Division maintains a servicewide AML database, and 

can provide assistance to park managers in recording 

AML features. An accurate inventory identifies human 

safety hazards and contamination issues, and facilitates 

closure, reclamation, and restoration of AML features. 

An accurate inventory also may identify opportunities 

for interpretation of AML features as cultural resources. 

Burghardt et al. (2014) and the NPS AML website, 

http://go.nps.gov/grd_aml (accessed 30 June 2015), 

provide more information.
37

The following is a discussion of known AML features 

within and near the boundaries of Chaco Culture 

National Historical Park. These features have not yet 

been documented in the servicewide AML database.

The National Park Service mined sand and gravel in the 

park for administrative uses until the late 1980s. The 

source of sand and gravel was Pleistocene terraces: one 

mining site was about 1.6 km (1 mi) south of the visitor 

center; the other was in Clys Canyon (for sand only). 

Moreover, building stone for the park housing area was 

extracted from the northern wall of Gallo Canyon.

In January 2015, park staff identified and field checked 

three abandoned coal mines in the park: (1) “Wetherill 

Mine” (also known as “Pueblo Bonita Mine”) in 

Rafael’s Rincon, (2) “CCC Mine” on the east side of 

South Mesa, and (3) “Hidden Mine” on the southwest 

side of West Mesa. Hayes (1981) mentioned a fourth 

mine, apparently at the foot of Chacra Mesa, but this 

mine could not be relocated in January 2015 (Phil 

Varela, Chaco Culture National Historical Park, 

paleontology technician, email communication, 5 

January 2015). 

With respect to past uranium exploration, a 1984 

inventory identified two abandoned uranium test drill 

holes and associated access routes and drill pads in the 

park (Marks 1989). The locations of these particular 

features are unknown (John Burghardt, NPS Geologic 

Resources Division, geologist, email communication, 

13 March 2007). The Kin Ya’a unit contains 73 drill 

holes. Hurley (1978) recorded these features, which 

were test wells drilled in 1977 and 1978 by the Mobil 

Oil Company, Uranium Exploration Division. Most of 

these drill holes are fairly evenly scattered throughout 

the southern part of the northeast quarter of section 28 

(T17N, R12W) (Phil Varela, Chaco Culture National 

Historical Park, paleontology technician, email 

communication, 26 August 2015). The National Park 

Service acquired these features as a result of the 1980 

boundary expansion. A primary concern associated 

with uranium exploration is accelerated erosion 

along access roads and at drilling sites (Simons, Li & 

Associates, Inc. 1982a).

The New Mexico Mines Database, which is maintained 

by the New Mexico Bureau of Geology and Mineral 

Resources, documents nine sites of past uranium 

exploration in the vicinity of the park: five separate 

drill holes, one quarry at Pueblo Alto, one pit in the 

Star Lake quadrangle, one prospect in the Kimbeto 

quadrangle, and a series of drill holes associated with 

an ISL pilot project in the Heart Rock quadrangle 

(see “Uranium Production” section). None of these 

sites produced any uranium, and future uranium 

production is unlikely because the mineralized layers 

are thin and too deep to mine economically (Ginger 

McLemore, New Mexico Bureau of Geology and 

Mineral Resources, senior economic geologist, written 

communication, 2 September 2015).

Disturbed Lands Restoration

Disturbed lands are those park lands where the natural 

conditions and processes have been directly impacted 

by development, including facilities, roads, dams, and 

abandoned campgrounds; agricultural activities such 

as farming, grazing, timber harvest, and abandoned 

irrigation ditches; overuse; or inappropriate use. Some 

of these features may be of historical significance, 

but most are not in keeping with the mandates of the 

National Park Service. Usually, lands disturbed by 

natural phenomena such as landslides, earthquakes, 

floods, and fires are not considered for restoration 

unless influenced by human activities. Restoration 

activities return a site, watershed, or landscape to some 

previous condition, commonly some desirable historic 

baseline. Park managers are encouraged to contact the 

NPS Geologic Resources Division for assistance with 

restoration of disturbed lands. 

During the 2007 scoping meeting and 2014 conference 

calls, participants (see Appendix A) identified the 

following disturbances at Chaco Culture National 

Historical Park:

Grazing

In the late 1800s and early 1900s, ranchers moved 

large herds of sheep and cattle from Chama, New 

Mexico, into the Chaco Canyon area for winter grazing 

(Western National Park Association, publication date 

unknown). In 1947 the National Park Service fenced 

Chaco Canyon National Monument to exclude grazing; 

as a result native grasses, shrubs, and wildlife have 

returned (KellerLynn 2007). Grazing is still allowed on 

allotments within the administrative boundary of the 

park, however, and could occur in these areas in the 

future.

Logging

No commercial logging has occurred in the 
38

park, although timber was collected for personal 

consumption on Chacra Mesa until the 1960s. 

Earth Dams

Using 1975 aerial photographs, Robertson (1992) 

mapped an earth dam (Qaf1) in the Kin Ya’a unit of 

the park (see poster, in pocket). This dam surrounds a 

flowing well. Additionally, Miller et al. (1991) identified 

earth dams in the La Vida Mission quadrangle, 

including the Kin Bineola unit of the park, and included 

them as part of the alluvium map unit (Qal). According 

to Miller et al. (1991), earth dams were built across 

many washes in the La Vida Mission quadrangle to 

catch and retain storm water for irrigation and livestock. 

Dams across broader washes may be as long as 0.6 km 

(0.4 mi). In some places, these earth dams have altered 

normal drainage and sediment deposition along the 

Kim-me-ni-oli Wash. The effect of these dams has been 

deposition of silt and mud along with fine-grained sand. 

When Miller et al. (1991) were conducting fieldwork, 

during the summer and fall months, no water was 

retained by any earth dam in the quadrangle. Many of 

the shorter dams do occasionally channel storm water 

into scooped-out ponds, which provide some water for 

sheep, goats, cattle, and a few horses that live on the 

range. A few scooped-out hollows are fed by water from 

nearby wells pumped by windmills (Miller et al. 1991). 

At present, earth dams remain in place, and the 

National Park Service has no plans to remove them 

(Phil Varela, Chaco Culture National Historical Park, 

paleontology technician, written communication, 31 

October 2014).

Solid Waste Disposal

From the 1950s to the early 1990s, the National Park 

Service disposed of solid waste in wide trenches, 

which were cut with backhoes on the eastern side of 

South Gap. At the time of scoping, park managers were 

planning to have these dumps tested for toxicity and 

mobility of waste (KellerLynn 2007). Since scoping, 

the dump sites were tested for a range of contaminants. 

All tested contaminants except arsenic were below 

the standard safety threshold, and arsenic levels at 

the dump site were lower than at control test points. 

No further testing is planned, but park staff is looking 

at funding options to remove the dump (Phil Varela, 

Chaco Culture National Historical Park, paleontology 

technician, written communication, 31 October 2014).

Erosion Control

In 1934, the National Park Service, Soil Conservation 

Service, and Civilian Conservation Corps (CCC) 

undertook an extensive program of erosion control that 

included planting 94,000 seedlings of willow, tamarisk, 

wild plum, and cottonwood in Chaco Arroyo (Hall 

2010). GRI scoping participants noted that planting of 

exotic species has affected stream-channel morphology. 

Park staff is now controlling tamarisk in certain areas 

where spreading is extensive, channel morphology 

is changing, and cultural resources are affected 

(KellerLynn 2007). Other past erosion-control efforts 

included planting native grasses; building revetments, 

jetties, gabions, and fences in arroyos; plowing 

parts of the alluvial canyon floor and building dikes; 

exterminating rodents to preserve dikes; and artificially 

straightening the inner channel (National Park Service 

1988).

During an erosion control study by Simons, Li & 

Associates (1982a), 58 cross sections were surveyed 

along Chaco Wash. These cross sections, however, were 

not well documented and park staff could not relocate 

them in the late 1990s. In 1999, with assistance from 

the NPS Water Resources Division (WRD), park staff 

established 13 well-documented and benchmarked 

transects throughout the park for the purpose of 

monitoring channel morphology. In 2005, WRD staff 

resurveyed these transects, and the Southern Colorado 

Plateau Network resurveyed them in 2008 and 2012. 

The network’s plan is to repeat these surveys at 

approximately five-year intervals (Stephen Monroe, 

NPS Southern Colorado Plateau Network, hydrologist, 

written communication, 30 October 2014).

Rockfall

The stratigraphic arrangement of rocks—mudstone 

under sandstone—sets the stage for rockfall at Chaco 

Culture National Historical Park. Mudstone (Menefee 

Formation) erodes from beneath sandstone (Cliff 

House Sandstone). The unsupported sandstone then 

breaks away in blocks or slabs along a joint or local 

weakness in the rock. The movement of a block or slab 

away from a cliff allows other joints to open up some 

distance back (Bryan 1954). This stepwise erosion 

produces the prominent cliff faces in Chaco Canyon 

and the slopes of debris, called talus, at their bases (fig. 

42).
39

Where erosive processes encroach from several 

directions, a landform may become segmented, 

producing a large singular rock mass. Fajada Butte 

formed in this manner over the last 10,000 years 

(National Park Service 2014a). In May 2012, a large 

rockfall occurred at Fajada Butte, illustrating the 

ongoing nature of this process in Chaco Canyon 

(Bilderback and Pranger 2013).

Threatening Rock

Since occupation of Chaco Canyon, rockfall has been 

a hazard. When ancient builders were constructing 

Pueblo Bonito, an immense slab of sandstone stood 

precariously behind the site (fig. 43). Apparently aware 

of the danger, ancient builders propped up the cliff with 

slanted pine posts embedded in rubble; the rubble was 

weather-proofed by masonry. An enormous buttress 

supported the masonry (Keur 1933; Judd 1959, 1964).

The slab was first described in 1901 and referred to as 

the “Elephant.” The Navajos called it “Braced-up Cliff,” 

and the National Park Service coined “Threatening 

Rock” (National Park Service 2014a). 

On 22 January 1941, Threatening Rock fell, destroying 

60 rooms in Pueblo Bonito (fig. 44). This event 

constitutes one of the most dramatic examples 

of rockfall in the National Park System. It was an 

extraordinary instance when the geologic processes that 

shaped the canyon over millennia were observed by 

people in historic times (National Park Service 2014a). 

In an attempt to predict the fall of Threatening Rock 

and document movement, the National Park Service 

began monthly monitoring in 1935. Schumm and 

Chorley (1964), who investigated and reported on 

the fall, used data gathered by NPS personnel in 

Figure 42. Photograph of talus. Snow covers the talus 

slope next to the parking area at the visitor center in 

Chaco Culture National Historical Park. The talus deposit 

is composed of the lower sandstone (Kchl) of Cliff 

House Sandstone, which broke away from the upper 

cliff face shown in the figure. The base of the cliff 

consists of sandstone, shale, and coal of the Menefee 

Formation (Kmf). US Geological Survey photograph 

available at http://3dparks.wr.usgs.gov/chcu/html2/

chaco429.html (accessed 13 January 2014).

Figure 43. Photograph of Threatening Rock. Schumm 

and Chorley (1964) investigated and reported on the 

fall of Threatening Rock. They estimated that original 

movement began in 550 CE. In the last five years 

that Threatening Rock stood over Pueblo Bonito, the 

National Park Service monitored its movement monthly. 

The rate of movement increased steadily until it fell, 

with 25 cm (10 in) of outward movement occurring in 

the final month. NPS staff measured/monitored the 

hazard on the day it fell, 22 January 1941. Note the 

wall of Pueblo Bonito on the lower, left side of the 

photograph. National Park Service photograph by 

George Grant (taken in 1929).
40

their analysis. These data yielded information about 

the type, rate, and approximate timing of original 

movement, which Schumm and Chorley (1964) 

estimated as beginning in 550 CE. In the last five years 

that Threatening Rock stood over Pueblo Bonito, 

the rock monolith moved 56 cm (22 in). The rate 

of movement increased steadily until it fell, with 25 

cm (10 in) of outward movement in the final month. 

Monthly measurements indicated that the rock was 

periodically stationary for several months, but would 

show movements, relatively rapid or slow, during other 

periods. Notably, the periods of rapid movement always 

occurred in winter, when snow had collected behind 

the rock. This may have been an important factor in its 

eventual failure. 

On the day the rock fell, which happened to be a day 

of monitoring, NPS staff heard the rock popping and 

cracking. The rock moved outward 0.08 cm (1/32 in) 

during measuring. According to eyewitness accounts, 

the rock fell in a combination of tilting and sliding (fig. 

45). It initially appeared to settle and move (en masse) 

away from the cliff and subsequently tilted, probably 

due to a shift in its center of gravity beyond the 

underlying shale support (Schumm and Chorley 1964). 

Present-Day Hazards and Monitoring

Rockfall continues in the park, with events in developed 

areas occurring several times per year (KellerLynn 

2007). The foundation document identified rockfall as 

a threat to the core canyon communities and associated 

architectural features (considered fundamental 

resources) in the park (National Park Service 2015). 

The two areas of greatest concern for rockfall are 

the housing area and Gallo Campground, which are 

commonly occupied by people and are located below 

highly jointed cliffs of sandstone (fig. 46). The Menefee 

Formation is exposed to a much greater extent in the 

housing area than other areas of the park, adding to the 

Figure 44. Satellite imagery of Pueblo Bonito. Pueblo Bonito, meaning “pretty village” in Spanish, is a distinctive 

D-shaped great house in Chaco Canyon. Its Navajo name—tse biyaa anii’ahi—means “leaning rock gap” and refers 

to a monolith of rock that separated from the cliff wall behind the pueblo. On 22 January 1941, the rock known as 

“Threatening Rock” in English fell and crushed the northeastern part of Pueblo Bonito. Landsat image (taken 24 June 

2014) accessed via Google Earth.
41

Figure 45. Schematic illustration of slope movements. Different categories of slope movement are defined by material 

type, nature of the movement, rate of movement, and moisture content. The fall of Threatening Rock involved falling, 

toppling, and some sliding movements. Graphic by Trista Thornberry-Ehrlich (Colorado State University) after Varnes 

(1978, figure 4.33 and information therein).
42

hazard at this location (Bilderback and Pranger 2013). 

Environmental weathering factors, which weaken 

the rock, and mechanisms that trigger rockfall (e.g., 

earthquakes, unusually wet periods, an abundance of 

freeze-thaw cycles, or construction vibrations) are the 

same at the housing area and campground. Conditions 

governing rockfall runout at the Gallo Campground, 

however, are different from those of the housing area. 

At about 15 m (50 ft) above the campground, the cliffs 

are not as high as those above the housing area, and the 

Menefee Formation only crops out at the base of these 

cliffs. The slope below the Menefee Formation serves 

as a ramp between the rockfall source area (Cliff House 

Sandstone) and the canyon floor, reducing potential 

impacts. Several constructed tent pads are very close 

to the cliff face, however, and are within the fall zone 

of even a small volume rockfall event (Bilderback and 

Pranger 2013). 

Based on a rockfall hazard assessment by Wachter 

(1985), park staff established monitoring sites on the 

cliffs above the housing area. Depending on adequate 

staffing, however, monitoring has been sporadic over 

the years (Bilderback and Pranger 2013). Since 2011, 

the sites have been monitored quarterly (Phil Varela, 

Chaco Culture National Historical Park, paleontology 

technician, written communication, 31 October 2014). 

In 2000, one of the hazardous rocks that had been 

monitored above the housing area fell, fractured, and 

came to rest less than 9 m (30 ft) from a residence 

(Bilderback and Pranger 2013). These rocks included 

four fragments weighing 140–230 kg (300 to 500 lbs), 

and one boulder weighing an estimated 180,000 kg 

(400,000 lbs or 200 tons) (fig. 47).

In 2012, monitoring indicated that a hazardous rock 

above the campground had moved 3 cm (1.2 in). 

Although this measurement was later determined to 

be incorrect, concern resulted in the submission of a 

technical assistance request by park managers to the 

NPS Geologic Resources Division (GRD). Investigation 

Figure 46. Photograph of rockfall hazard areas. The “fall line” (red line on the figure) indicates the best fit angle 

(30°) that defines a runout zone for a rockfall from the cliffs at the housing area. The line was generated using 

the CONEFALL model (Jaboyedoff and Labiouse 2003, 2011), a USGS digital elevation model of the area, and field 

measurements of outlying boulders (see Bilderback and Pranger 2013). The fall line is subject to some variability and 

serves as a guide rather than a definitive border. The yellow oval on the figure marks the resting locations of rocks 

that detached from monitoring station 6 on the Cliff House Sandstone cliff above the housing area in 2000 (see fig. 

47). National Park Service graphic from Bilderback and Pranger (2013).
43

during a site visit on 19–21 August 2013 determined the 

monitoring error, but also resulted in improvements 

to the procedure, including inscribed metal site labels, 

site photos, and precise GPS locations. GRD staff 

recommended that park staff continue monitoring 

at the established sites on a quarterly basis. Clearly 

labeled monitoring pins at precisely recorded locations 

should allow for quicker and more accurate monitoring 

(Bilderback and Pranger 2013).

Information about monitoring rockfall hazards is 

provided by Wieczorek and Snyder (2009) in Geological 

Monitoring (Young and Norby 2009). Moreover, during 

the 2007 scoping meeting, participants suggested 

that sheet joints parallel to cliff faces could be used 

as indicators of rockfall hazards not currently fitted 

with monitoring devices (KellerLynn 2007). Although 

geologic source maps, and thus the GRI GIS data, do 

not include these features, scoping meeting participants 

thought that this information could be retrieved from 

aerial photos and incorporated into the park’s GIS. 

Such a project has the potential to be funded through 

the Geoscientists-In-the-Parks Program (see 

http://go.nps.gov/gip; accessed 18 July 2014).

GRD staff also completed a risk assessment of rockfall 

hazards in the housing area in 2013. This assessment 

places the risk in a societal context. Park staff members 

are encouraged to contact the NPS Geologic Resources 

Division with questions about this assessment. A 

rockfall hazard plan is a medium priority planning need 

identified in the foundation document (National Park 

Service 2015).

Paleontological Resource Inventory and 

Monitoring

Paleontological resources are an important resource 

in Chaco Culture National Historical Park as defined 

by the foundation document (National Park Service 

2015). All paleontological resources are non-renewable 

and subject to science-informed inventory, monitoring, 

protection, and interpretation as outlined by the 

2009 Paleontological Resources Preservation Act (see 

Appendix B). Department of Interior regulations 

associated with the act are under development. A 

variety of publications and resources provide parkspecific or servicewide information and guidance. For 

example, in Geological Monitoring, Santucci et al. (2009) 

described five methods and vital signs for monitoring 

in situ paleontological resources: (1) erosion (geologic 

factors), (2) erosion (climatic factors), (3) catastrophic 

geohazards, (4) hydrology/bathymetry, and (5) human 

access/public use. 

Tweet et al. (2009) provided an inventory and 

monitoring report about paleontological resources in 

Figure 47. Photograph of rockfall at Chaco Culture National Historical Park. In 2000, a block detached from a nearly 

vertical cliff composed of Cliff House Sandstone and fractured upon impact with the underlying, sloping outcrop of 

Menefee Formation. The event left a trail of debris on the slope. The main block and possibly several smaller pieces 

continued down the slope, skipping or rolling over an older significant rockfall deposit. This event shows the large 

blocks present in the talus deposit do not necessarily provide protection from future rockfall and should not be viewed 

as a rockfall barrier. Outlying boulders came to rest in and just outside the enclosed yard of one of the park residences 

(yellow oval on fig. 46). This event provides a baseline from which to evaluate the risk from future rockfall along this 

section of the Chaco Canyon wall. National Park Service graphic from Bilderback and Pranger (2013).
44

the Southern Colorado Plateau Network, including 

Chaco Culture National Historical Park. This report 

included background information about the park; 

preliminary recommendations for management 

of paleontological resources within the park; and 

discussions about in situ fossils in Upper Cretaceous 

rocks and Quaternary deposits, fossil specimens in 

park collections, and records of fossils found in cultural 

resource contexts. 

An ongoing field inventory, starting in 2005, of the 

Upper Cretaceous rocks at the park has revealed 

abundant and widespread paleontological resources, 

shedding light on the potential scientific significance of 

the fossil-bearing strata in the area (Varela 2013b). The 

two most fossiliferous rock units within the park are 

the Menefee Formation and the Cliff House Sandstone 

(see “Upper Cretaceous Rocks and Fossils” section). 

As of the end of the 2013 field season, investigators had 

identified and mapped more than 300 fossil localities 

within the park, including 148 plant, 95 vertebrate, 49 

invertebrate, and 10 localities with a combination of 

plant, vertebrate, and invertebrate fossils (Varela 2013a). 

Very little research has been done on these resources, 

but preliminary results from the inventory indicate 

that the potential for new and scientifically significant 

material is very high, especially in the Menefee 

Formation (Varela 2013b). Findings thus far show 

that the paleoflora and paleofauna at Chaco Culture 

National Historical Park are much more diverse that 

previously suspected, with promising areas for potential 

future investigations, especially the Menefee Formation, 

which is poorly studied in the region (Varela 2013b). 

In 2013, managers at Chaco Culture National Historical 

Park submitted a technical assistance request to the 

NPS Geologic Resources Division for development of 

a paleontological resource management plan, which 

would cover fossils in a geologic context within park 

strata and fossils that occur in a cultural resource 

context. A principal focus of the plan is to evaluate 

the variables associated with management of park 

fossils at archeological sites. An objective is to develop 

strategies for enabling scientific research and education 

without placing archeological resources at risk (Vincent 

Santucci, NPS Geologic Resources Division, senior 

geologist/paleontologist/Washington liaison, email 

communication, 25 June 2014). Completion of this 

initial inventory is considered a medium priority data 

need for the park (National Park Service 2015).

In April 2014, NPS staff from Chaco Culture National 

Historical Park and the Geologic Resources Division 

met with representatives of 28 American Indian tribes. 

The meeting at Chaco Culture National Historical 

Park may have been the first of its kind for the 

National Park Service, and perhaps any Department 

of Interior bureau (Vincent Santucci, NPS Geologic 

Resources Division, senior geologist/paleontologist/

Washington liaison, email communication, 25 June 

2014). During the meeting, the National Park Service 

presented information about the paleontological 

resources in the park and discussed the development 

of a paleontological resource management plan. The 

presentation prompted an engaged discussion among 

NPS and tribal participants related to Chaco Culture’s 

fossils. The tribal participants provided insight on 

their perspectives of fossils and the relationship of 

fossils to their cultural origins and history. As a result 

of this meeting, tribal representatives requested further 

targeted meetings with the National Park Service 

regarding fossils.

In November 2014, park managers hosted a meeting 

with professional paleontologists to develop a strategy 

for future paleontological research and resource 

management at Chaco Culture National Historical Park 

(Phil Varela, Chaco Culture National Historical Park, 

paleontology technician, written communication, 31 

October 2014). Recommendations from this meeting 

will be incorporated into the paleontological resource 

management plan (Vincent Santucci, NPS Geologic 

Resources Division, senior geologist/paleontologist/

Washington liaison, email communication, 25 June 

2014).

Piping

Piping is a type of subsurface erosion that is infringing 

on and endangering archeological sites at Chaco 

Culture National Historical Park (Simons, Li & 

Associates, Inc. 1982a). It is also threatening park roads 

(Zschetzsche and Clark 2004). In addition, piping has 

affected fill soils at archeological sites such as Chetro 

Ketl, where reburial using fill is a conservation strategy 

(Ford et al. 2004). Scoping participants also noted that 

piping creates bat habitat (KellerLynn 2007).

Simons, Li & Associates, Inc. (1982a) described the 

sequential development of pipes (narrow conduits, 

tunnels, or “pipes” through which soil or sediment 

is removed) at Chaco Culture National Historical 
45

Park. Materials subject to piping include alluvium and 

colluvium that contain clay, silt, and fine sand; shale 

that contains montmorillonite and bentonite clays; and 

loess (Simons, Li & Associates, Inc. 1982a). In semiarid 

areas like Chaco Canyon where long dry periods are 

interspersed with intense rainfall, the drying out of soil 

(particularly those containing montmorillonite) and 

subsequent cracking determine vertical flow routes 

(Simons, Li & Associates, Inc. 1982a).

Notably, Chaco Arroyo did not form via piping; it 

incised along a meandering stream (Love 1980). Hodges 

(1975) found that piping has a pronounced effect on 

tributary-arroyo development but plays an insignificant 

role in the main wash. Pronounced bank collapse of the 

arroyo walls, however, may be associated with piping 

(Simons, Li & Associates, Inc. 1982a). 

Piping is one of several processes by which tributary 

arroyos form (Love 1980). As pipes enlarge over time, 

overlying material collapses into a subsurface void and 

a small side ravine to the main arroyo forms (fig. 48). 

Some pipes extend hundreds of feet. Many, but not all, 

have an outlet in the walls of Chaco Arroyo. Whether 

or not a soil pipe connects to Chaco Arroyo appears 

to be a function of depth of the desiccation cracks and 

the lateral and vertical distribution of permeable layers 

interspersed with impermeable layers above the arroyo 

(i.e., water flows along the impermeable layers). Where 

outlets do exist, most are in walls of Chaco Arroyo, 

that is, below the floor of Chaco Canyon and above the 

active inner channel and floodplain (KellerLynn 2007). 

Ebert and Brown (1981; scale 1:1,200) mapped piping 

at the park and identified some of the more prominent 

areas as Wijiji Ruins, Bradley site, northeastern side of 

Gallo Wash (northwest of the visitor center), western 

side of Fajada Wash near the confluence of Gallo Wash 

and Mockingbird Canyon, north of Casa Rinconda 

along the wash, and Pueblo del Arroyo. Additionally, 

Simons, Li & Associates, Inc. (1982b) completed a soil 

piping study in the vicinity of Pueblo Bonito, which 

analyzed drainage patterns and provided site-specific 

improvement plans for Chetro Ketl, Pueblo Bonito, 

Pueblo del Arroyo, and Kin Kletso. Of these four major 

sites, only one—Pueblo del Arroyo (fig. 49)—was 

directly threatened by erosion due to piping (Simons, Li 

& Associates, Inc. 1982b).

During a soils scoping session at Chaco Culture 

National Historical Park, participants addressed the 

issue of piping. The NPS Soils Program worked with 

park staff to identify problem areas. Park staff is referred 

to Soil Survey of Chaco Culture National Historical Park, 

New Mexico (Zschetzsche and Clark 2004). Piping is a 

Figure 48. Photograph of piping. Subsurface erosion, 

called “piping,” is one of several processes by which 

tributary arroyos form. It also creates bat habitat. 

Natural Resources Conservation Service photograph 

from Zschetzsche and Clark (2004, figure 4).

Figure 49. Photograph of Pueblo del Arroyo. Pueblo 

del Arroyo, meaning “town by the arroyo” in Spanish, 

is a classic D-shaped great house located next to Chaco 

Wash about 275 m (900 ft) west of Pueblo Bonito. It 

differs from other great houses in the canyon because 

it was not built near the northern cliff face and is 

oriented to the east rather than to the south. Due to 

its location, the site has been threatened in the past by 

erosion caused by floodwaters in the wash. Its soils are 

also subject to piping. National Park Service photograph 

available at http://www.nps.gov/chcu/photosmultimedia/

photogallery.htm (accessed 12 May 2014).
46

specific problem within the Notal and Battlerock soils 

at the park (Pete Biggam, NPS Geologic Resources 

Division, soil scientist, email communication, 23 

February 2007).

Seismicity

Seismicity—the phenomenon of earth movements—

includes all vibrations induced by natural processes 

and human activities. Vibrations may be caused by 

movement along a fault (earthquakes), landslides, 

blasting, drilling, road building, and vehicular traffic 

(King et al. 1985, 1991). The primary concern regarding 

seismicity at Chaco Culture National Historical Park 

is that ground shaking could damage archeological 

structures. It may also induce rockfall (see “Rockfall” 

section). 

King et al. (1985) analyzed the seismic risk to the larger 

archeological structures at the park. Based on normal 

blasting practices in the area, conventional rail traffic, 

use of road building equipment, and vehicular traffic 

patterns, the investigation recommended that structures 

be a minimum of 1.2 km (0.7 mi) from blasting, 0.5 km 

(0.3 mi) from railroad traffic, 45 m (150 ft) from road 

building, and 25 m (80 ft) from vehicular traffic. 

King et al. (1991) recommended that heavy vehicular 

traffic on a rough road be at least 30 m (100 ft) from a 

sensitive site. Moreover, that investigation found the 

Kin Kletso complex “exceptional” because parts of it 

rest on sandstone bedrock, and sandstone bedrock is 

also directly beneath the highway at this site. Bedrock is 

a concern because it attenuates the induced vibrations 

at a much lower rate than the sandy, unconsolidated 

sediments underlying other sites. Thus limiting heavy 

equipment on the road near Kin Kletso and keeping the 

road surface smooth are significant for preservation. 

King et al. (1991) also recommended that within 45 m 

(150 ft) of the structure, no heavy equipment be used, 

no parking lots be located, and traffic be controlled. 

As a result of these recommendations, in 1995 the 

National Park Service rerouted a segment of the park 

road to mitigate seismically induced damage to cultural 

sites. The route had passed within 15 m (50 ft) of Kin 

Kletso, Casa Chiquita, and Pueblo del Arroyo. This 

reroute closed State Road 57 from the park’s northern 

boundary, down Cly Canyon, to Pueblo del Arroyo 

(Dabney Ford, Chaco Culture National Historical Park, 

cultural resource manager, email communication, 19 

March 2007). 

Generally speaking, activities associated with coal 

production such as blasting, mining, and transportation 

have the potential to produce vibrations that could 

damage sensitive structures at the park. The nearest 

potential mining site is about 13 km (8 mi) north 

of Pueblo Bonito (King et al. 1985), and scoping 

participants surmised that such activities are not close 

Figure 50. Map of 

earthquake probability. 

The map shows the 

probability of an 

earthquake with 

magnitude >5.0 during 

the next 100 years. Star 

indicates the location of 

the Chaco Canyon unit of 

the park and is centered 

on Pueblo Bonito.

Map generated using the 

2009 US Geological Survey 

earthquake probability 

mapping program 

(https://geohazards.

usgs.gov/eqprob/2009/

index.php; accessed 22 

September 2015).
47

enough to cause damage to park structures (KellerLynn 

2007). Hydraulic fracturing, which is now occurring 

in the San Juan Basin (see “Oil and Gas Development” 

section), could cause mild shaking (conference call 

participants, telephone communication, 13 February 

2014).

The probability of a moderate earthquake (magnitude 

5) shaking the Chaco Canyon unit over the next 100 

years is relatively low, between 0.04 and 0.10 (4% to 

10% “chance”). However, the probability increases to 

between 0.50 and 0.60 (50% to 60% “chance”) east 

of the park near Valles caldera in the Los Alamos and 

Santa Fe area (fig. 50; see GRI report for Bandelier 

National Monument by KellerLynn 2015).

Eolian Processes

“In the late 1800s—before the advent of the first 

archeological protection laws—travelers, vandals, and 

pothunters repeatedly knocked massive holes into the 

back wall of Pueblo Bonito, removing the contents of 

the rooms this way, rather than digging into the rooms 

from above through many feet of windblown sand

[italics added]” (National Park Service 2006, stop 6). 

This description is an indication of the persistence of 

eolian processes—windblown erosion, transportation, 

and deposition of sediments (see Lancaster 2009)—

occurring at Chaco Culture National Historical Park. 

It also illustrates the potential for windblown sand 

to serve as a preservation strategy via reburial of 

archeological sites (see Ford et al. 2004). 

Eolian processes are the cause of a variety of resource 

management issues at the park:

● Windstorms. During spring, the average wind 

speed at the park is 16 kph (10 mph) with velocities 

exceeding 40 kph (25 mph) about 1% of the time. 

Windstorms lasting one to two days with velocities 

of 60–80 kph (40–50 mph) are not unusual (King 

et al. 1985). Scoping participants noted that 

dust storms occur frequently at this time of year 

(KellerLynn 2007). During dust storms, even 

the most immediate visibility becomes impaired 

(Maruca 1982). 

● Blowing sand. Before the park road was rerouted, 

eolian transport and deposition of sand and the 

formation of dunes across the old entry road 

(north) into the park, was a maintenance issue 

(KellerLynn 2007). 

● Rockfall. Eolian processes may aid rockfall 

hazards by removing sediment between a 

loosened (protruding) rock and a cliff face (Phil 

Varela, Chaco Culture National Historical Park, 

paleontology technician, written communication, 

31 October 2014; see “Rockfall” section).

● Wind-induced vibrations. King et al. (1985) 

observed that winds impose a considerable force 

on exposed walls of archeological structures, 

initiating vibrations and swaying. Wind gusts cause 

movement on two-, three-, and four-story walls 

and are a factor in collapses (Dabney Ford, Chaco 

Culture National Historical Park, chief, Cultural 

Resources, email communication 13 August 2014). 

The bracing of the walls by large timbers and steel 

rods generally increases the natural frequencies of 

these structures. Higher natural frequencies may 

then approach the predominant frequencies of 

the winds in the canyon. King et al. (1985) warned 

that modern rebuilding methods using concrete 

will result in different structural engineering 

characteristics than those of the ancient adobestone methods. The newer construction methods 

may introduce a more rigid structure which could 

be more susceptible to the vibrations induced by 

wind.

● Wind erosion. Sandblasting is a minor concern 

associated with high winds, which carry sand 

particles. 

In the event that park managers choose to monitor 

eolian processes, Lancaster (2009)—the chapter 

in Geological Monitoring (Young and Norby 2009) 

about eolian features and processes—described the 

following methods and vital signs for monitoring: (1) 

frequency and magnitude of dust storms, (2) rate of 

dust deposition, (3) rate of sand transport, (4) wind 

erosion rate, (5) changes in total area occupied by sand 

dunes, (6) areas of stabilized and active dunes, (7) dune 

morphology and morphometry, (8) dune field sediment 

state (supply, availability, and mobility), (9) rates of dune 

migration, and (10) erosion and deposition patterns on 

dunes.

Efflorescence

The great houses and other built structures at Chaco 

Culture National Historical Park are more than 

1,000 years old. Like other historic buildings, they 

require constant and appropriate care. Wind, summer 

monsoonal rains, snow, and extreme daily freeze–
48

thaw cycles all take their toll on these architectural 

monuments (National Park Service 2014c). 

Although a discussion of preservation techniques is 

beyond the scope of this report, one natural process—

“efflorescence,” also called “salt crystallization” (Ford 

et al. 2004) or “salt weathering” (Doehne 2002)—is 

worthy of mention in a geologic resources inventory. 

Efflorescent minerals, that is, soluble salts such as 

gypsum and halite (Neuendorf et al. 2005), appear 

on building stone as a result of evaporation of water 

brought to the surface by capillary action (fig. 51). In 

arid regions, efflorescence commonly appears as a 

whitish, fluffy or crystalline powder, and is particularly 

prevalent at the bases of walls. Geologic factors in 

efflorescence are rock porosity, pore size and shape; 

colloidal effects (for clay and iron); and processes such 

as wind velocity and direction.

Erosion of stone and mortar by this process is a 

management concern at the park because it may 

contribute to the deterioration of archeological 

structures by accelerating stone and mortar erosion. 

Efflorescence also may accelerate the deterioration 

of roof surfaces in natural cave 

shelters (Phil Varela, Chaco Culture 

National Historical Park, paleontology 

technician, written communication, 

31 October 2014; see “Cave Shelters” 

section).

Typical damaging behaviors for salts can 

include surface scaling, deep cracking, 

expansion, granular disintegration, 

surface powdering, and microcracking 

(Doehne 2002). Not all salt behaviors 

result in deterioration, however. For 

example, efflorescence may be highly 

visible, but generally results in little 

damage (Doehne 2002). Likewise, salt 

creep can move salts over the surface 

of materials but, as the name implies, is 

a surficial process. Furthermore, salts 

such as magnesium sulfate can actually 

bind together (i.e., cement) previously 

fractured material (Doehne 2002). 

Managers at Chaco Culture National 

Historical Park use the presence of 

efflorescence as an indicator of water 

penetration, drainage problems, and 

stone deterioration. Also, efflorescence indicates that 

preservation efforts may be using (or have used in the 

past) replacement mortars that are less permeable than 

the original fabric, thus indicating the need to reevaluate 

mortar mixes. Park managers have tried to find 

alternatives to using mortar additives that add salts to 

the already high concentrations because of the corrosive 

damage to sandstone (Dabney Ford, Chaco Culture 

National Historical Park, chief, Cultural Resources, 

email communication, 13 August 2014). 

Doehne (2002) noted more than 1,800 references in the 

scientific literature (e.g., geomorphology, geochemistry, 

environmental science, geotechnical and material 

sciences, and architectural conservation) on the topic of 

salt weathering, and provided a review of recent work, 

focusing on articles about conservation. Doehne (2002) 

supplied an organizing framework for considering the 

complexity of salt weathering, which park managers 

may find useful in the prevention, mitigation, and 

treatment of salt weathering at Chaco Culture National 

Historical Park.

Figure 51. Photograph of efflorescence. Also called “salt crystallization” or 

“salt weathering,” efflorescence (white “powder” on the stone wall in the 

photograph) is a management concern at Chaco Culture National Historical 

Park because it may accelerate erosion of stone and mortar and thus 

contribute to the deterioration of archeological structures. National Park 

Service photograph (taken in 2014).
49

Geologic History

This chapter describes the chronology of geologic events that formed the present landscape of Chaco 

Culture National Historical Park.

The rocks and unconsolidated deposits at Chaco 

Culture National Historical Park record the following 

geologic events spanning 100 million years:

● Inundation by the Western Interior Seaway;

● Downwarping of the San Juan Basin during the 

Laramide Orogeny and filling of the basin with 

terrestrial sediment;

● Widespread erosion and development of present 

drainages, including Chaco Canyon;

● Dynamic sedimentation in Chaco Canyon;

● Development of Chaco Arroyo and incision of the 

active inner channel; and 

● Human activities as part of the geologic record.

Late Cretaceous Period: Western Interior 

Seaway

The oldest geologic event recorded in the rocks at 

Chaco Culture National Historical Park is sea level 

rise and inundation by a vast inland sea—the Western 

Interior Seaway. The seaway stretched across the 

North American continent and prevailed for 30 million 

years, from about 100 million to 70 million years ago, 

reaching its greatest extent about 90 million years ago. 

The seaway first moved into New Mexico about 96 

million years ago. The Dakota Sandstone records this 

initial transgression (advance) of marine waters (fig. 6 

and table 1). Dakota Sandstone is not exposed in the 

park, though it occurs in many places in northern New 

Mexico (Price 2010). 

The rock record at Chaco Culture National Historical 

Park preserves the western coastline of the Western 

Interior Seaway (fig. 3). Continental, coastal, and marine 

sediments are well exposed in canyon walls and on 

mesa tops, and include the following rock formations in 

ascending order (oldest to youngest):

● Crevasse Canyon Formation (map units Kcg

and Kcda; see poster, in pocket)—a succession 

of lagoon, tidal or estuarine channel, and beach 

sediments, which were deposited as the shoreline 

built outward into the sea (Kirk and Zech 1977; 

Robertson 1986, 1992).

● Menefee Formation (Kmf, Kmft, Kmfa, Kmfaj, and 

Kmfal)—lowland swamps, lagoons, and alluvial 

plains with stream channels that lay landward of the 

shoreline to the northeast (Scott et al. 1984).

● Cliff House Sandstone (Kch, Kchu, Kchwu, Kchwl, 

Kchm, Kchi, and Kchl)—multiple, separate barrierisland complexes that built upward and prograded 

seaward as sediment accumulated (Donselaar 1989; 

Love 2010).

● Lewis Shale (Kl)—marine sand and silt deposited 

in deep water during an advance of the Western 

Interior Seaway to the southwest (Scott et al. 1984; 

Mytton and Schneider 1987).

● Pictured Cliffs Sandstone (Kpc)—mostly coastal 

sand in delta front, beach, and stream channels, 

representing the final retreat of the Western Interior 

Seaway from the San Juan Basin (Scott et al. 1984; 

Mytton and Schneider 1987).

As the seaway retreated to the northeast, coal swamps 

and coastal plains covered the area. The Fruitland 

Formation (Kf) and Kirtland Shale (Kk) represent 

these settings. These rocks crop out in the Chaco River 

headwaters, east of the park. 

Close of the Cretaceous Period: San Juan 

Basin

As the Western Interior Seaway made its final 

retreat, the landscape of western North America was 

dramatically changed by the Laramide Orogeny. For 

more than 30 million years (approximately 75 million 

to 40 million years ago), compressive deformation 

associated with this massive mountain-building event 

uplifted areas, including the Rocky Mountains, caused 

episodes of volcanism in parts of New Mexico, and 

created many structural features, including the San Juan 

Basin. Erosion of highlands associated with Laramide 

uplift shed terrestrial sediments into the San Juan 

Basin atop previously deposited and subsequently 

downwarped Upper Cretaceous marine and coastal 

rocks. More than 900 m (3,000 ft) of Paleocene through 

Oligocene (65 million–25 million years ago; see fig. 

2) silt, sand, and gravel covered the site of Chaco 

Culture National Historical Park before erosive forces 
50

stripped them away. Although none of these terrestrial 

rocks remain in the park area today, the Nacimiento 

Formation in Aztec Ruins National Monument to the 

north is representative of these sedimentary deposits 

(see GRI report by KellerLynn in review).

Pleistocene Epoch: Chaco Canyon

After overlying sedimentary units were removed by 

widespread erosion, the Chaco River drainage most 

likely incised into the Fruitland-Kirtland interval, which 

consisted of more than 200 m (660 ft) of non-resistant 

shale, siltstone, sandstone, and coal (Love 1980). A 

possible scenario begins with a meandering ancestral 

stream flowing across a relatively low-relief, plain 

composed of the Fruitland Formation and Kirtland 

Shale, then incising the plain and breaching the Pictured 

Cliffs Sandstone as erosion proceeded. Erosion along 

strike of the Lewis Shale followed. Eventually, incision 

reached Cliff House Sandstone, and the ancestral Chaco 

River slipped down-dip to the northwest, cutting Chaco 

Canyon nearly parallel to strike of the Cliff House 

Sandstone (Love 1980).

Although investigation has not revealed an absolute 

age of the entrenchment of Chaco Canyon, the canyon 

probably incised to its present depth during the middle 

Pleistocene Epoch (about 780,000 to 126,000 years ago) 

(David W. Love, New Mexico Bureau of Geology and 

Mineral Resources, geologist, email communication, 

25 July 2014). The pattern of the Chaco drainage was 

superimposed onto bedrock early in the history of 

the drainage. Tributary drainages would have been 

established at about the same time (Love 1980). 

In the Chaco Canyon area, severe erosion continued 

through the late Pleistocene Epoch, and most of 

the early and middle Pleistocene stream deposits 

and stream-cut surfaces were removed. Deposits of 

Pleistocene gravelly sand (Qgs7, Qgs6, and Qgs5) 

remain as the only evidence of a former landscape 

(fig. 52). These deposits occur as sheets overlying 

pediment-like surfaces that cut across nonresistant 

bedrock and slope toward the Chaco River or other 

local major valleys. At least seven erosion surfaces and 

their associated gravelly sand deposits are recognized 

in the drainage basin of the Chaco River. Each reflects 

an erosional episode related to changes in the grade of 

the Chaco River or the San Juan River. These remnants 

show that the ancestral Chaco River and its tributaries 

were more powerful than modern streams, having 

transported gravel instead of only sand, silt, and clay. 

As mapped by Scott et al. (1984), these high-elevation 

erosion surfaces are all late Pleistocene in age (126,000–

11,700 years old). They are mapped as highest/oldest 

(Qgs1) to lowest/youngest (Qgs7) and are distinguished 

from one another by their height above the modern 

Chaco River and major tributaries. The three youngest 

levels (Qgs7, Qgs6, and Qgs5) are preserved in Chaco 

Culture National Historical Park, and are 18 to 60 m (60 

to 200 ft) above the local drainage (Scott et al. 1984). 

In addition, Mytton and Schneider (1987) mapped a 

gravel-covered surface (Qg) overlying the Cliff House 

Sandstone at the northern end of West Mesa. 

Pleistocene and Holocene Epochs: Dynamic 

Sedimentation

After incision of Chaco Canyon into bedrock, 

sediments began to fill it. As much as 38 m (125 ft) 

of alluvium, eolian sand, and sheetwash and slopewash sediments have flowed, blown, and washed 

over the canyon floor from mesas, tributary canyons, 

and the headwaters area. Dunes near the mouth of 

Chaco Wash at Escavada Wash probably have been 

present in some form since the end of the Pleistocene 

Epoch, approximately 11,700 years ago. They probably 

interfinger with alluvium from Chaco Wash (David W. 

Love, New Mexico Bureau of Geology and Mineral 

Resources, geologist, email communication, 25 July 

2014). The large climbing dunes in some of the tributary 

canyons, such as Weritos Rincon, are suspected to have 

existed for much longer and may have stratigraphic 

layers composed of developed soils (as an indication 

of age). The youngest sand cover on these dunes is 

probably upper Holocene, but much older eolian sand 

is likely in the subsurface (David W. Love, New Mexico 

Bureau of Geology and Mineral Resources, geologist, 

email communication, 25 July 2014). Dunes in the 

vicinity, though outside Chaco Canyon, are known 

to have developed during the Pleistocene Epoch (see 

Schultz 1983; McFadden et al. 1983).

The alluvial stratigraphy of Chaco Canyon spans 

the middle–late Pleistocene Epoch to the present 

(Hall 1977, 2010). The oldest documented deposit is 

middle–late Pleistocene gravel, which is best exposed 

in a quarry along Chaco Wash near the park’s visitor 

center (Hall 1983). Hall (1977, 2010) referred to this 

gravel deposit as “Fajada gravel” (figs. 52 and 53). Some 

investigators mapped this deposit as sheetwash alluvium 

(Qsw), but multiple cross-beds in the unit indicate 
51

swiftly flowing water and a fluvial origin (Hall 1983). 

Formation of the gravel deposit is probably related 

to inception of either the Bull Lake glaciation (more 

than 140,000 years ago) or Pinedale glaciation (80,000–

70,000 years ago) (see Pierce 2004). 

After the gravel was deposited, the canyon fill was 

eroded to the bedrock floor. Erosion of the gravel, 

deposition of colluvium and eolian sediments, and the 

formation of a reddish brown paleosol, referred to as 

the “Fajada paleosol” by Hall (1977, 2010), helped to 

build up the canyon floor since that time (approximately 

the past 70,000 years; Love 1980).

Holocene Epoch: Cut-and-Fill Cycles

Using radiocarbon dating, Hall (2010) provided ages 

of the fill exposed in Chaco Canyon since 7,600 years 

before present (BP, where “present” is 1950 CE), 

and separated the fill into four units: (1) pre-Gallo 

(undated), (2) Gallo (6,700–2,800 years BP), (3) Chaco 

(2,100–1,000 years BP), and (4) Bonito (800–100 years 

BP) (fig. 53).

Pre-Gallo Fill

The pre-Gallo fill is thin-bedded sand with abundant 

pine pollen; it is exposed as a small erosional remnant 

that may be late Pleistocene or early Holocene in age 

(Hall 2010). 

Gallo Fill

The hot, dry climate of the mid-Holocene Epoch 

and accompanying low streamflow resulted in the 

accumulation of sand in Chaco Canyon, forming Gallo 

fill. Yellowish-brown, locally derived sand (from Cliff 

House Sandstone) dominates this alluvial fill, although 

layers of grayish brown silt (from Fruitland Formation 

and Kirtland Shale at the headwaters) show that the 

canyon floor was periodically flooded (figs. 34 and 35). 

By 2,500 years ago, a shift to less arid conditions and 

increased streamflow flushed out much of the Gallo 

sand from the canyon. 

Chaco Fill

Between 2,100 and 1,000 years BP, greater streamflow 

throughout the drainage basin resulted in flooding 

across the canyon floor, forming Chaco fill. 

Sedimentation filled in the channel left by the erosion 

Figure 52. Satellite imagery of erosion surfaces. Above Chaco Canyon, gravelly sand (Qg7, Qg6, and Qg5) and gravel 

(Qg) associated with pediment-like erosion surfaces are evidence of a Pleistocene landscape when an ancestral river 

incised Chaco Canyon. At least seven erosion surfaces and their associated gravelly sand deposits are recognized in the 

Chaco River drainage basin. Each elevated surface reflects an erosional episode related to changes in the grade of the 

Chaco River or the San Juan River. Graphic by Trista Thornberry-Ehrlich (Colorado State University) using GRI GIS data 

for Chaco Culture National Historical Park. Base imagery by ESRI World Imagery.
52

Figure 53. Diagram of Chaco 

Canyon through time. Most 

of the sediment exposed in 

the walls of Chaco Arroyo is 

Holocene alluvium, although 

the sedimentary record also 

includes a terrace gravel deposit 

and an ancient soil, referred 

to as the “Fajada gravel” and 

“Fajada paleosol,” respectively. 

As described by Hall (1977, 2010), 

the alluvial fills in Chaco Canyon 

are pre-Gallo (not dated, but 

estimated as late Pleistocene or 

early Holocene age), Gallo (6,700–

2,800 years BP), Chaco (2,100–

1,000 years BP), and Bonito 

(800–100 years BP). Chaco Arroyo 

had incised into the floor of 

Chaco Canyon by 1877, and the 

active inner channel developed 

after 1934. Graphic by Trista 

Thornberry-Ehrlich (Colorado 

State University) after Hall (1977, 

figure 5).
53

and downcutting of Gallo fill. Chaco fill is mostly 

grayish-brown, headwater-dominated clay, which 

spread over the canyon floor in the absence of an arroyo 

channel (Hall 1983). Abundant freshwater snails in the 

clay suggest wet conditions during seasonal flooding. 

Accumulation of the Chaco unit ended about 1,000 

years BP with a shift in climate to dry conditions. The 

Bonito channel—an arroyo that existed between 800 

and 100 years BP—formed at that time (figs. 52 and 53). 

Bonito Fill

The Bonito channel was filling with clayey, grayishbrown, headwater-dominated material by 800 years 

BP, based on buried potsherds. Fewer freshwater 

gastropods occur in the Bonito fill than the Chaco fill, 

indicating less moist conditions 800–100 years ago 

than when the Chaco fill was deposited (Hall 2010). 

Deposition of the Bonito unit ended with incision of 

Chaco Arroyo (fig. 53). 

Holocene Epoch: Chaco Arroyo and Active 

Inner Channel

The dynamics of Chaco Canyon include the formation 

of channels (arroyos). The floor of Chaco Canyon has 

alternated between being deeply gullied with arroyo 

channels, as it is currently, and having no gullies (Love 

2010). At least seven arroyos have been present during 

the history of Chaco Canyon (fig. 54; Love 1977). 

The amount of time it takes for an arroyo channel to 

downcut and backfill may be no more than 200 years 

(Hall 1986, 1990).

Chaco Arroyo represents the most recent episode of 

arroyo cutting. The arroyo formed along a meandering 

channel that had not previously existed on the canyon 

Figure 54. Schematic illustration of Chaco Canyon. Chaco Canyon has at least 38 m (125 ft) of fill above the bedrock 

floor. The uppermost 11 m (36 ft) show a dynamic sequence of cut-and-fill cycles and canyon-wide alluviation. The 

canyon floor was inundated by sediments from the headwaters that are connected to filled-in entrenched channels, 

swales with laminated clay, and yazoo channels. Remnants of earlier fill occur along the margins of the canyon and 

are partially buried by modern alluvium. Chaco Canyon has been cut by arroyos (light blue on figure) at least seven 

times during its history. Each of these Chaco Canyon channels may have correlative channels (and fills) in tributaries 

(purple on figure). A—gravel reworked into later channel. B—broad swale filled by laminated clay derived from the 

headwaters, overlain by canyon floor deposits. C—swale filled with laminated clay associated with 3,700-year-old fill 

in buried channel to right. D—deeply buried laminated silty clay with soils developed on top of deposit. E—undated 

buried channel. F—pottery-bearing channel, 3–4 m (10–13 ft) deep filled to present surface of canyon floor. G—thin 

wedge-shaped headwater-derived deposits pinch out against deposits from the canyon margin. H—complex arroyo 

cut-and-fill deposit about 3,700 years old. Graphic by Trista Thornberry-Ehrlich (Colorado State University) after Love 

(1983, figure 4). Named fills (i.e., Fajada, Gallo, Chaco, and Bonito) are correlated from Hall (1977, 2010).
54

floor (Love 1977). Simpson (1850) reported that 

an intermittent channel or succession of pools had 

developed on the floor of Chaco Canyon by 1849. 

Incision apparently began before 1877, when Jackson 

(1878) reported a channel more than 4 m (13 ft) deep. 

Photographs and channel measurements beginning in 

1896 describe an incising arroyo with little vegetation 

and a flat bottom until the early 1930s (Love 1980).

After incision of Chaco Arroyo began, an alluvial terrace 

(fig. 34) developed as an inner floodplain and channel 

similar to the modern inner floodplain and channel 

(Love 1977). The abandoned floodplain and channel 

aggraded 3–4 m (10–13 ft). When it was within 1.5 m 

(5 ft) of overtopping the arroyo walls, chute cutoffs 

formed, floods swept gravel out of the channel, and the 

arroyo became re-entrenched.

Following re-entrenchment, Chaco Arroyo widened, 

eroding most of the terrace. The channel became 

braided from wall to wall. By 1934, the braided channel 

was no longer stable, and by 1939, the arroyo channel 

had changed from braided to a narrow inner channel 

between partially stabilized point bars and an inner 

floodplain; this is today’s active inner channel (Love 

1977).

Minor accretion on the active inner channel’s 

floodplain and minor shifts in the channel continue to 

take place, but the channel is more or less stable. The 

active inner channel and floodplain gradually disappear 

toward the head of Chaco Canyon. Above the canyon, 

the arroyo has a braided channel (Love 1977).

Holocene Epoch: Human Populations in Chaco 

Canyon

Prehistoric Indians were in the San Juan Basin by at 

least 13,000 years ago. The earliest abundant evidence 

of people in Chaco Canyon dates from the Archaic 

Period, which ranges from about 7,000 to 1,500 years 

ago. Beginning about 500 CE, people designated as 

Basketmakers raised crops in Chaco Canyon and built 

semi-subterranean structures known as pit houses. 

By 500 CE, Chaco Canyon looked similar to present 

geomorphic conditions, though the level of the canyon 

floor was slightly (1–3 m [3–10 ft]) lower, and the 

margins of the canyon were slightly different than today 

as a result of eolian processes, erosion, and rockfall 

yet to occur (Love 1980). Aboveground structures, in 

contrast to subterranean pit houses, gradually appeared 

and evolved into pueblos by 770 CE. Pit houses 

acquired ceremonial significance and evolved into kivas.

The major Chacoan building phase that included 

multistoried great houses and large kivas began about 

1050 CE; this phase ended sometime after 1127 CE. 

During that time, arroyos were present, notably when 

Pueblo Bonito was under construction. Moreover, 

Pueblo del Arroyo was built in the center of the canyon 

floor, apparently while a major channel, the “Bonito 

channel,” existed south of the pueblo (fig. 54). When 

the Bonito channel began to aggrade and flooding of 

the canyon floor occurred, occupants of Pueblo del 

Arroyo built a wall south of the site along the margin of 

the arroyo. Even later, the occupants piled stones in a 

shallow channel at the surface of the aggraded channel 

(Love 1980).

During a period of widespread flooding after the 

Bonito channel filled, vegetation was sparse and wind 

transported gray clay to the canyon margins. Sometime 

after the gray-clay layer (i.e., Bonito unit of Hall 2010) 

was deposited, a small arroyo (predating Chaco Arroyo) 

cut and filled in Chaco Canyon (F on fig. 54). Pottery 

found along the channel base is not diagnostic enough 

to date the channel, but it cuts deposits overlying the 

Bonito channel so is younger than 1250 CE (Love 1983). 

Chaco Canyon was occupied sporadically by Pueblo 

people and later by Navajo until the time of James 

Hervey Simpson’s visit in 1849 (Vivian and Mathews 

1964). 

Holocene Epoch: Geoarcheology

Since Simpson’s visit, scientists in the field of 

geoarcheology have studied the relationships between 

prehistoric humans and the environment at Chaco 

Canyon (see “Geologic Setting and Significance” 

chapter). As an interdisciplinary study, geoarcheology 

strives to understand archeological sites in their 

natural contexts, in particular, human response to a 

changing environment. At Chaco Culture National 

Historical Park and throughout the Southwest, 

small climate changes have noticeably altered the 

landscape and affected plant (at least one to extinction; 

see “Quaternary Fossils” section) and animal 

species (Malde 1964). Geoarcheologists use many 

“geologic” methods, including mapping of alluvial 

fill, to understand the life ways of ancient people. The 

attraction of Chaco Canyon for research has continued 

to the present day.
55

Geologic Map Data

This chapter summarizes the geologic map data available for Chaco Culture National Historical Park. 

A poster (in pocket) displays the GRI GIS data draped over imagery of the park and surrounding area. 

The Map Unit Properties Table (in pocket) summarizes this report’s content for each geologic map unit. 

Complete GIS data are available at the GRI publications website: http://go.nps.gov/gripubs.

Source Maps

Geologic maps facilitate an understanding of an area’s 

geologic framework and the evolution of its present 

landscape. The American Geosciences Institute website, 

http://www.agiweb.org/environment/publications/

mapping/index.html (accessed 27 August 2015), 

provides more information about geologic maps and 

their uses.

The GRI team digitizes paper geologic maps and 

converts digital geologic data to conform to the GRI GIS 

data model. GRI GIS data include essential elements 

of source maps such as map unit descriptions, geologic 

unit correlation tables, legends, cross sections, figures, 

and references. The GRI team used the following source 

maps to produce the GRI GIS data for Chaco Culture 

National Historical Park. These sources also provided 

information for this report.

Dillinger, J. K. 1990. Geologic map and structure contour 

maps of the Gallup 30’ × 60’ quadrangle, McKinley 

County, New Mexico (scale 1:100,000). Miscellaneous 

Investigations Series Map I-2009. US Geological Survey, 

Denver, Colorado. http://pubs.er.usgs.gov/publication/

i2009 (accessed 14 January 2014).

Kover, A. N. 1960. Photogeologic map of the Chaco Canyon-2 

quadrangle, McKinley County, New Mexico (scale 

1:62,500). Miscellaneous Investigations Series Map I-315. 

US Geological Survey, Washington, DC. http://pubs.er.usgs.

gov/publication/i315 (accessed 21 January 2014).

Miller, R. L., M. A. Carey, and C. L. Thompson-Rizer. 1991. 

Geology of the La Vida Mission quadrangle, San Juan and 

McKinley counties, New Mexico (scale 1:24,000). Bulletin 

1940. US Geological Survey, Denver, Colorado. http://pubs.

er.usgs.gov/publication/b1940 (accessed 14 January 2014).

Mytton, J. W., and G. B. Schneider. 1987. Interpretive geology 

of the Chaco area, northwestern New Mexico (scale 

1:24,000). Miscellaneous Investigations Series Map I-1777. 

US Geological Survey, Denver, Colorado. http://pubs.

er.usgs.gov/publication/i1777 (accessed 14 January 2014).

O’Sullivan, R. B., G. R. Scott, and D. L. Weide. 1979. 

Preliminary geologic map of the Kin Klizhin Ruins 

quadrangle, San Juan and McKinley counties, New Mexico 

(scale 1:24,000). Miscellaneous Field Studies Map MF1094. US Geological Survey, Reston, Virginia.

http://pubs.er.usgs.gov/publication/mf1094 (accessed 15 

January). Note: Used for geologic contacts only.

Robertson, J. F. 1986. Geologic map of the Crownpoint 

quadrangle, McKinley County, New Mexico (scale 

1:24,000). Geologic Quadrangle Map GQ-1596. US 

Geological Survey, Reston, Virginia. http://pubs.er.usgs.gov/

publication/gq1596 (accessed 14 January 2014).

Robertson, J. F. 1992. Geologic map of the Heart Rock 

quadrangle, McKinley County, New Mexico (scale 

1:24,000). Geologic Quadrangle Map GQ-1697. US 

Geological Survey, Reston, Virginia. http://pubs.er.usgs.gov/

publication/gq1697 (accessed 14 January 2014).

Scott, G. R., R. B. O’Sullivan, and D. L. Weide. 1984. Geologic 

map of the Chaco Culture National Historical Park, 

northwestern New Mexico (scale 1:50,000). Miscellaneous 

Investigations Series Map I-1571. US Geological Survey, 

Denver, Colorado. http://pubs.er.usgs.gov/publication/

i1571 (accessed 14 January 14, 2014).

Weide, D. L., G. R. Scott, and J. W. Mytton. 1980. Geologic 

map of the Pueblo Pintado quadrangle, McKinley 

County, New Mexico (scale 1:24,000). Miscellaneous 

Field Investigations Map MF-1219. US Geological Survey, 

Reston, Virginia. http://pubs.er.usgs.gov/publication/

mf1219 (accessed 14 January 2014).

In addition, the following sources identified and 

mapped outcrops of coal beds, drill holes for oil and 

gas, and test holes for coal zones associated with the 

Crevasse Canyon and Menefee formations and the Cliff 

House Sandstone. This information is included in the 

GRI GIS data.

Berge Exploration Inc. 1979a. Federal coal resource 

occurrence and coal development potential maps of the 

Crownpoint 71⁄2-minute quadrangle, McKinley County, 

New Mexico (scale 1:24,000). Open-File Report OFR-79-

1125. US Geological Survey, Washington, DC. http://pubs.

er.usgs.gov/publication/ofr791125 (accessed 21 January 

2014).

Berge Exploration Inc. 1979b. Federal coal resource 

occurrence and coal development maps of the Heart Rock 

71⁄2-minute quadrangle, McKinley County, New Mexico 

(scale 1:24,000). Open-File Report OFR-79-642. US 

Geological Survey, Washington, DC. http://pubs.er.usgs.

gov/publication/ofr79642 (accessed 21 January 2014).
56

Berge Exploration Inc. 1979c. Federal coal resource 

occurrence and coal development maps of the Kin Klizhin 

Ruins 71⁄2-minute quadrangle, San Juan and McKinley 

counties, New Mexico (scale 1:24,000). Open-File Report 

OFR-79-1047. US Geological Survey, Washington, DC. 

http://pubs.er.usgs.gov/publication/ofr791047 (accessed 21 

January 2014).

Berge Exploration Inc. 1979d. Federal coal resource 

occurrence and coal development maps of the Milk Lake 

71⁄2-minute quadrangle, McKinley County, New Mexico 

(scale 1:24,000). Open-File Report OFR-79-1377. US 

Geological Survey, Washington, DC. http://pubs.er.usgs.

gov/publication/ofr791377 (accessed 21 January 2014).

Berge Exploration Inc. 1979e. Federal coal resource 

occurrence and coal development maps of the Nose Rock 

71⁄2-minute quadrangle, McKinley County, New Mexico 

(scale 1:24,000). Open-File Report OFR-79-641. US 

Geological Survey, Washington, DC. http://pubs.er.usgs.

gov/publication/ofr79641 (accessed 21 January 15, 2014).

Berge Exploration Inc. 1979f. Federal coal resource 

occurrence and coal development maps of the Seven 

Lakes NE 71⁄2-minute quadrangle, McKinley County, New 

Mexico (scale 1:24,000). Open-File Report OFR-79-638. 

US Geological Survey, Washington, DC. http://pubs.er.usgs.

gov/publication/ofr79638 (accessed 15 January 2014).

Berge Exploration Inc. 1979g. Federal coal resource 

occurrence and coal development maps of the Seven 

Lakes NW 71⁄2-minute quadrangle, McKinley County, New 

Mexico (scale 1:24,000). Open-File Report OFR-79-1123. 

US Geological Survey, Washington, DC. http://pubs.er.usgs.

gov/publication/ofr791123 (accessed 21 January 2014).

Berge Exploration Inc. 1979h. Federal coal resource 

occurrence and coal development maps of the La Vida 

Mission 71⁄2-minute quadrangle, San Juan and McKinley 

counties, New Mexico (scale 1:24,000). Open-File Report 

OFR-79-1378. US Geological Survey, Washington, DC. 

http://pubs.er.usgs.gov/publication/ofr791378 (accessed 21 

January 2014).

Dames & Moore. 1979a. Coal resource occurrence maps and 

coal development potential map of the Pueblo Pintado 

quadrangle, McKinley County, New Mexico (scale 

1:24,000). Open-File Report OFR-79-113. US Geological 

Survey, Washington, DC. http://pubs.er.usgs.gov/

publication/ofr79113 (accessed 21 January 2014).

Dames & Moore. 1979b. Coal resource occurrence maps of 

the Pueblo Bonito quadrangle, San Juan and McKinley 

counties, New Mexico (scale 1:24,000). Open-File Report 

OFR-79-156. US Geological Survey, Washington, DC. 

http://pubs.er.usgs.gov/publication/ofr79156 (accessed 21 

January 14, 2014).

Dames & Moore. 1979c. Coal resource occurrence maps of 

the Sargent Ranch quadrangle, San Juan and McKinley 

counties, New Mexico (scale 1:24,000). Open-File Report 

OFR-79-157. US Geological Survey, Washington, DC. 

http://pubs.er.usgs.gov/publication/ofr79157 (accessed 21 

January 2014).

GRI GIS Data

The GRI team implements a GIS data model that 

standardizes map deliverables. The data model is 

available at http://go.nps.gov/gridatamodel. This data 

model dictates GIS data structure, including layer 

architecture, feature attribution, and relationships 

within ESRI ArcGIS software. The GRI team digitized 

the data for Chaco Culture National Historical Park 

using data model version 2.2. The GRI Geologic Maps 

website, http://go.nps.gov/geomaps, provides more 

information about GRI map products. 

GRI digital geologic data are available through the NPS 

Integrated Resource Management Applications (IRMA) 

portal (https://irma.nps.gov/App/Portal/Home). Enter 

“GRI” as the search text and select a park.

The following components are part of the data set:

● A GIS readme file (chcu_gis_readme.pdf) 

that describes the GRI data formats, naming 

conventions, extraction instructions, use 

constraints, and contact information.

● Data in ESRI geodatabase GIS format;

● Layer files with feature symbology (table 2);

● Federal Geographic Data Committee–compliant 

metadata;

● An ancillary map information document (chcu_

geology.pdf) that contains information captured 

from source maps;

● An ESRI map document (chcu_geology.mxd) that 

displays the digital geologic data; and

● A KML/KMZ version of the data viewable in 

Google Earth (table 2).

The different component maps are aslo available 

separately and are identified by the following prefixes: 

● CCNH – Chaco Culture National Historical Park 

area map (Kin Klizhin Ruins and Sargent Ranch 

quadrangles, and northern third of the Pueblo 

Bonito quadrangle)

● CHC2– northern Chaco Culture-2 15’ quadrangle 

(Seven Lakes NE and Seven Lakes NW 

quadrangles)

● CHCO – Chaco Culture National Historical Park 

area coal resources map (all park quadrangles)

● CRWN – Crownpoint 7.5’ quadrangle
57

● GALL – northeast portion of the Gallup 30’ 

x 60’ quadrangle (Milk Lake and Nose Rock 

quadrangles)

● HERO – Heart Rock 7.5’ quadrangle

● LVMI – La Vide Mission 7.5’ quadrangle

● PUBO – portion of the Pueblo Bonito 7.5’ 

quadrangle (southern two-thirds)

● PUPI – Pueblo Pintado 7.5’ quadrangle.

GRI Map Poster

A poster showing GRI GIS data draped over a shaded 

relief image of Chaco Culture National Historical Park 

and surrounding area is included with this report. 

Not all GIS feature classes are included on the poster 

(table 2). Selected geographic features, including 

park features, have been added to the poster. Digital 

elevation data and added geographic information are 

not included in the GRI GIS data, but are available 

online from a variety of sources. Contact the NPS 

Geologic Resources Division for assistance locating 

these data.

Map Unit Properties Table

The Map Unit Properties Table (in pocket) lists 

the geologic time division, map unit symbol, and a 

simplified description for each of the geologic units 

mapped within Chaco Culture National Historical Park. 

The table also notes the park unit in which each map 

unit occurs. Following the structure of the report, the 

table summarizes the geologic features and processes, 

resource management issues, and geologic history 

associated with each map unit. 

Use Constraints

Graphic and written information provided in this 

report is not a substitute for site-specific investigations. 

Ground-disturbing activities should neither be 

permitted nor denied based on the information 

provided here. Please contact the NPS Geologic 

Resources Division with any questions.

Minor inaccuracies may exist regarding the locations 

of geologic features relative to other geologic or 

geographic features on the poster. Based on the source 

map scales and US National Map Accuracy Standards, 

geologic features represented in the GRI GIS data are 

horizontally within 12 m (40 ft) of their true locations 

on 1:24,000-scale maps, 32 m (104 ft) on 1:62,500-scale 

maps, 25 m (82 ft) on 1:50,000-scale maps, and 51 m 

(167 ft) on 1:100,000-scale maps.

Table 2. GRI GIS data for Chaco Culture National Historical Park

Data Layer On Poster? Google Earth Layer?

Geologic Cross Section Lines No No

Geologic Attitude Observation Localities No No

Geologic Measurement Localities (fault displacement amount) No No

Geologic Observation Localities (geologic photograph localities) No No

Mine Point Features No No

Structure Contour Lines, Base of the Dakota Sandstone (Kd) No No

Geologic Line Features (coal zones and beds) Yes Yes

Fault and Fold Symbology Yes No

Folds Yes Yes

Faults Yes Yes

Linear Geologic Units Yes Yes

Mine Area Feature Boundaries No No

Mine Area Features No Yes

Geologic Contacts Yes Yes

Geologic Units Yes Yes

59

Glossary

These are brief definitions of selected geologic terms relevant to this report. Definitions are based on 

those in the American Geosciences Institute Glossary of Geology (5th edition; 2005). Additional terms 

are defined at http://geomaps.wr.usgs.gov/parks/misc/glossarya.html.

adit. A horizontal passage into a mine from the surface.

aggradation. The building up of Earth’s surface by 

depositional processes.

alluvial fan. A low, relatively flat to gently sloping, fanshaped mass of loose rock material deposited by a stream, 

especially in a semiarid region, where a stream issues from 

a canyon onto a plain or broad valley floor.

alluvial terrace. A stream terrace composed of 

unconsolidated alluvium produced by a rejuvenated 

stream via renewed downcutting of the floodplain or 

valley floor, or by the covering of a terrace with alluvium.

alluvium. Stream-deposited sediment.

Altithermal. A dry postglacial interval (from about 8,000 to 

4,000 calendar years ago) during which temperatures were 

higher than at present.

ammonite. Any ammonoid belonging to the suborder 

Ammonitina, characterized by a thick, ornamental shell 

with sutures having finely divided lobes and saddles. 

Range: Jurassic to Cretaceous.

aquifer. A rock or sedimentary unit that is sufficiently 

porous to hold water, sufficiently permeable to allow 

water to move through it, and saturated to some level.

arroyo. A small, deep, flat-floored channel or gully of an 

ephemeral stream in the arid and semiarid regions of the 

southwestern United States.

artesian. Describes groundwater confined under hydrostatic 

pressure.

artesian well. A well that taps confined groundwater. Water 

in the well rises above the level of the top of the aquifer 

under artesian pressure.

badlands. Eroded topography characterized by steep slopes 

and surfaces with little or no vegetative cover; composed 

of unconsolidated or poorly cemented clays or silts.

backwater. A body of water that is parallel to a river but is 

stagnant or little affected by the river’s currents.

barchan dune. A crescent-shaped dune in which the arms or 

horns of the crescent point downwind; characteristic of 

inland desert regions. 

barrier island. A long, low, narrow island consisting of a 

basin (structural). A doubly plunging syncline in which 

rocks dip inward from all sides.

basin (sedimentary). Any depression, from continental to 

local scale, into which sediments are deposited.

bathymetry. The measurement of ocean or lake depths and 

the charting of the topography of the ocean or lake floor.

beach. The unconsolidated material at the shoreline that 

covers a gently sloping zone, typically with a concave 

profile, extending landward from the low-water line to 

the place where there is a definite change in material 

or physiographic form (e.g., a cliff), or to the line of 

permanent vegetation (usually the effective limit of the 

highest storm waves).

bed. The smallest sedimentary stratigraphic unit, commonly 

ranging in thickness from about 1 cm (0.4 in) to 1 to 2 m 

(40 to 80 in) and distinguishable from beds above and 

below.

bedding. Depositional layering or stratification of 

sediments.

bedrock. Solid rock that underlies unconsolidated 

sedimentary deposits and soil.

benthic. Pertaining to the ocean bottom or organisms living 

on or in substrate; also, referring to that environment.

bentonite. Soft clay or greasy claystone composed mostly 

of the clay mineral smectite, formed by the chemical 

alteration of glassy volcanic ash in contact with water.

bioturbation. The reworking of sediments by organisms.

bituminous. Describes rocks that contain (and sometimes 

rocks smell of) asphalt, tar, or petroleum.

bituminous coal. An organic sedimentary rock referred to 

as “soft coal,” resulting from deeper burial with rising 

pressures and temperatures, driving hydrogen and other 

volatiles and leaving a fixed carbon content of 50% to 

60%. 

bivalve. Having a shell composed of two distinct, but equal 

or nearly equal, movable valves, which open and shut.

blowout. A general term for a small saucer-, cup-, or troughshaped hollow or depression formed by wind erosion on 

a preexisting dune or other sand deposit, especially in 

an area of shifting sand or loose soil, or where protective 

vegetation is disturbed or destroyed. 

body fossil. Evidence of past organisms such as bones, teeth, 

shells, or leaf imprints. 

braided stream. A sediment-clogged stream that forms 

multiple channels that divide and rejoin.

burrow. A tubular or cylindrical hole or opening, made in 

originally soft or loose sediment by a mud-eating worm, 

mollusk, or other invertebrate; may be later filled with clay 

or sand and preserved.

calcareous. Describes a substance that contains calcium 

carbonate. When applied to a rock name it implies that as 

much as 50% of the rock is calcium carbonate.

calcium carbonate. CaCO3. A solid occurring in nature as 

primarily calcite and aragonite.
60

calcite. A carbonate (carbon + oxygen) mineral of calcium, 

CaCO3

; calcium carbonate. It is the most abundant cave 

mineral.

caliche. A hard layer of cemented calcium carbonate, 

commonly on or near the surface in arid and semiarid 

regions.

capillary action. The action by which a fluid, such as water, is 

drawn up in small interstices or tubes as a result of surface 

tension.

carbonaceous. Describes a rock or sediment with 

considerable carbon, especially organic material, 

hydrocarbon, or coal.

cement (sedimentary). Mineral material, usually chemically 

precipitated, that occurs in the spaces among the 

individual grains of a sedimentary rock, thus binding the 

grains together.

cementation. The process by which clastic sediments 

become lithified or consolidated into hard, compact 

rocks, usually through deposition or precipitation of 

minerals in the spaces among the individual grains of the 

sediment; may occur simultaneously with sedimentation 

or at a later time.

channel. The bed where a natural body of surface water 

flows or may flow. Also, a natural passageway or 

depression of perceptible extent containing continuously 

or periodically flowing water, or forming a connecting link 

between two bodies of water.

clast. An individual constituent, grain, or fragment of a rock 

or unconsolidated deposit, produced by the mechanical 

or chemical disintegration of a larger rock mass.

clay. Minerals and sedimentary fragments that are less than 

1/256 mm (0.00015 in) across.

clay mineral. Any mineral occurring in the clay-sized 

fraction with the understanding that size imposes physical 

and chemical characteristics. 

claystone (sedimentary). An indurated rock with more than 

67% clay-sized minerals.

climbing dune. A dune formed by aeolian piling-up of sand 

by wind against a cliff or mountain slope.

coal. An organic sedimentary rock consisting of carbon, 

hydrogen, and oxygen, with some sulfur and nitrogen. 

Formed by the destructive distillation of plant remains 

under anaerobic and progressively rising pressures and 

temperatures until coal with a very high fixed carbon 

content is attained. Differences in the kinds of plant 

materials (type), in degree of metamorphism (rank), and 

in the range of impurity (grade) are characteristic of coal 

and are used in classification.

coastal plain. Any lowland area bordering a sea or ocean, 

extending inland to the nearest elevated land, and sloping 

very gently seaward; may result from the accumulation of 

material along a coast.

colluvium. A loose, heterogeneous, and incoherent mass 

of rock fragments and soil material deposited via surface 

runoff or slow continuous downslope creep; usually 

collects at the base of a slope or hillside, but includes 

loose material covering hillsides.

concretion. A hard, compact aggregate of mineral matter, 

rounded to irregularly shaped; composition generally 

differs from that of the rock in which it occurs.

contact. The surface between two types or ages of rocks.

continental. Formed on land rather than in the sea. 

Continental deposits may be of lake, swamp, wind, 

stream, or volcanic origin.

creep. The slow, imperceptible downslope movement of 

mineral, rock, and soil particles under gravity.

cross-bed. A single bed, inclined at an angle to the main 

planes of stratification; the term is commonly restricted to 

a bed that is more than 1 cm (0.4 in) thick.

cross-bedding. Uniform to highly varied sets of inclined 

beds deposited by wind or water that indicate flow 

conditions such as direction and depth. 

cross section. A graphic interpretation of geology, structure, 

or stratigraphy based on mapped and measured geologic 

extents and attitudes, depicted in a vertical plane (i.e., a 

cut or profile view).

deformation. The process of folding, faulting, shearing, or 

fabric development in rocks as a result of Earth stresses.

delta. The low, nearly flat, alluvial tract of land at or near 

the mouth of a river, commonly forming a triangular or 

fan-shaped plain of considerable area; resulting from 

the accumulation of sediment supplied by the river in 

such quantities that it is not removed by tides, waves, and 

currents.

delta fan. A deposit formed by the merging of an alluvial fan 

with a delta.

depth zone. One of five oceanic environments, or ranges of 

oceanic depths: (1) littoral zone, between high and low 

tides; (2) neritic zone, between low-tide level and 200 

m (660 ft) above the continental shelf; (3) bathyal zone, 

between 200 and 3,500 m (660 and 11,500 ft); (4) abyssal 

zone, between 3,500 and 6,000 m (11,500 and 20,000 ft); 

and (5) hadal zone 6,000 m (20,000 ft) and deeper. 

dip. The angle between a bed or other geologic surface and 

the horizontal plane.

discharge. The rate of flow of surface water or groundwater 

at a given moment, expressed as volume per unit of time.

displacement. The relative movement of the two sides of a 

fault; also, the specific amount of such movement.

downcutting. Stream erosion in which cutting is directed 

primarily downward, as opposed to laterally.

downwarping. Subsidence of Earth’s crust on a regional 

scale as a result of crustal loading by ice, water, sediments, 

or lava flows. 

drainage. The manner in which the waters of an area flow 

off in surface streams or subsurface conduits; also, the 

processes of surface drainage of water from an area by 

streamflow and sheet flow, and the removal of excess 

water from soil by downward flow.

drainage basin. A region or area bounded by a drainage 

divide and occupied by a drainage system, specifically 

the tract of country that gathers water originating as 

precipitation and contributes it to a particular stream 

channel or system of channels, or to a lake, reservoir, or 

other body of water.

dune. A low mound or ridge of sediment, usually sand, 

deposited by the wind.
61

ebb-tidal delta. A tidal delta formed on the seaward side of a 

tidal inlet.

efflorescence. A whitish fluffy or crystalline powder 

produced as a surface encrustation on a rock or soil in 

an arid region by evaporation of water brought to the 

surface by capillary action; it may consist of one or several 

minerals, commonly soluble salts such as gypsum and 

halite. Also, the process by which an efflorescent salt or 

crust is formed.

entrenched stream. A stream, often meandering, that flows 

in a narrow canyon or valley (i.e., “trench”) cut into a 

plain or relatively level upland; specifically a stream that 

has inherited its course from a previous cycle of erosion 

and that cuts into bedrock with little modification of the 

original course. 

eolian. Describes materials formed, eroded, or deposited by 

or related to the action of wind. 

ephemeral lake. A short-lived lake.

ephemeral stream. A stream that flows briefly, only in direct 

response to precipitation, and whose channel is always 

above the water table. 

epicontinental. Describes a geologic feature on the 

continental shelf or interior. 

escarpment. A steep cliff or topographic step resulting from 

vertical displacement on a fault or as a result of slope 

movement or erosion. Synonymous with “scarp.”

facies (sedimentary). The depositional or environmental 

conditions reflected in the sedimentary structures, 

textures, mineralogy, fossils, and other components of a 

sedimentary rock.

fault. A break in rock characterized by displacement of one 

side relative to the other.

fine-grained. Describes sediment or sedimentary rock and 

texture in which the individual constituents are too small 

to distinguish with the unaided eye, specifically sediment 

or rock whose particles have an average diameter less 

than 1/16 mm (0.002 in), that is, silt-size particles and 

smaller. Also, describes a crystalline or glassy rock and 

texture in which the individual minerals are relatively 

small, specifically an igneous rock whose particles have an 

average diameter less than 1 mm (0.04 in). 

floodplain. The surface or strip of relatively smooth land 

composed of alluvium and adjacent to a river channel, 

constructed by the present river in its existing regimen 

and covered with water when the river overflows its 

banks. A river has one floodplain and may have one or 

more terraces representing abandoned floodplains.

floodplain splay. A small alluvial fan or other outspread 

deposit formed where an overloaded stream breaks 

through a levee (artificial or natural) and deposits its 

material (often coarse-grained) on the floodplain. 

Synonymous with “overbank splay,” “sand splay,” 

“channel splay,” or simply “splay.”

flood-tidal delta. A tidal delta formed on the landward side 

of a tidal inlet.

fluvial. Of or pertaining to a river or rivers.

fold. A curve or bend in an originally flat structure, such 

as a rock stratum, bedding plane, or foliation; usually a 

product of deformation.

formation. Fundamental rock-stratigraphic unit that is 

mappable, lithologically distinct from adjoining strata, 

and has definable upper and lower contacts.

fossil. A remain, trace, or imprint of a plant or animal that 

has been preserved in the Earth’s crust since some past 

geologic time; loosely, any evidence of past life.

fracture. The breaking of a mineral other than along planes 

of cleavage. Also, any break in a rock such as a crack, joint, 

or fault.

freeze-thaw. The mechanical weathering process caused 

by alternate or repeated cycles of freezing and thawing 

water in pores, cracks, and other openings of rock and 

unconsolidated deposits, usually at the surface. 

gastropod. Any mollusk belonging to the class Gastropoda, 

characterized by a distinct head with eyes and tentacles 

and, in most, by a single calcareous shell that is closed 

at the apex, sometimes spiraled, not chambered, and 

generally asymmetrical. Range: Upper Cambrian to 

Holocene. 

geoarcheology. The application of concepts and methods 

of the earth sciences to archaeological problems and 

vice versa. It provides evidence for the development, 

preservation, and destruction of archaeological sites, and 

for regional-scale environmental change and the evolution 

of the physical landscape, including the impact of human 

groups.

geodetic surveying. Surveying that takes into account 

the figure and size of Earth, with corrections made for 

curvature; used where the areas or distances involved are 

so great that the desired accuracy and precision cannot 

be obtained by plane (ordinary field and topographic) 

surveying.

geodesy. The science concerned with the determination of 

the size and shape of the Earth and the precise location of 

points on its surface.

geology. The study of Earth, including its origin, history, 

physical processes, components, and morphology.

geomorphology. The study of the general configuration of 

surface landforms and their relationships to underlying 

structures, and of the history of geologic changes as 

recorded by these surface features.

gradient. A degree of inclination (steepness of slope), or a 

rate of ascent or descent, of an inclined part of Earth’s 

surface with respect to the horizontal; expressed as a ratio 

(vertical to horizontal), a fraction (such as m/km or ft/

mi), a percentage (of horizontal distance), or an angle (in 

degrees).

gravel. An unconsolidated, natural accumulation of typically 

rounded rock fragments resulting from erosion; consists 

predominantly of particles larger than sand; that is, 

greater than 2 mm (1/12 in) across.

groundwater. That part of subsurface water that is in the 

zone of saturation, including underground streams.

gully. A small channel produced by running water in 

unconsolidated material.

gypsum. A sulfate (sulfur + oxygen) mineral of calcium and 

water, CaSO4

 • 2H2O.

halite. A halide (chlorine or fluorine) mineral composed of 

sodium and chloride, NaCl. Synonymous with “native 

salt,” “rock salt,” and “common salt.”
62

hematite. An oxide mineral composed of oxygen and iron, 

Fe2

O3.

hydrology. The study of liquid and solid water properties, 

circulation, and distribution, on and under the Earth’s 

surface and in the atmosphere.

incision. Downward erosion by a stream, resulting in a 

deepened channel and commonly a narrow, steep-walled 

valley.

intertonguing. The overlapping of markedly different rocks 

through vertical succession of wedge-shaped layers; 

results in the disappearance of sedimentary bodies in 

laterally adjacent masses. 

joint. A break in rock without relative movement of rocks on 

either side of the fracture surface.

kaolinite. A common white clay mineral composed of mostly 

aluminum oxide.

karren. Channels or furrows caused by solution on massive 

bare limestone surfaces.

lacustrine. Describes a process, feature, or organism 

pertaining to, produced by, or inhabiting a lake.

lagoon. A narrow body of water that is parallel to the 

shore and between the mainland and a barrier island; 

characterized by minimal or no freshwater influx and 

limited tidal flux, which cause elevated salinities. Also, a 

shallow body of water enclosed or nearly enclosed within 

an atoll.

landslide. A collective term covering a wide variety of 

slope-movement landforms and processes that involve the 

downslope transport of soil and rock material en masse 

under the influence of gravity.

lens. A sedimentary deposit that resembles a convex lens 

and is characterized by converging surfaces, thick in the 

middle and thinning out toward the edges.

levee. A long broad low embankment of sand and coarse silt 

built by floodwater overflow along both banks of a stream 

channel.

lignite. An organic sedimentary rock, referred to as “brown 

coal,” with a low fixed carbon content of 25% caused by 

compaction by overlying sediments.

limestone. A carbonate sedimentary rock consisting of more 

than 95% calcite and less than 5% dolomite.

littoral. Pertaining to the benthic ocean environment 

or depth zone between high water and low water; 

also, pertaining to the organisms of that environment. 

Synonymous with “intertidal.” 

loess. Windblown silt-sized sediment.

meander. One of a series of sinuous curves, bends, or turns 

in the course of a stream, produced by a mature stream 

swinging from side to side as it flows across its floodplain 

or shifts its course laterally toward the convex side of an 

original curve.

medium-grained. Describes an igneous rock and texture in 

which the individual crystals have an average diameter 

in the range of 1 to 5 mm (0.04 to 0.2 in.). Also, describes 

sediment or sedimentary rock and texture in which the 

individual particles have an average diameter in the range 

of 1/16 to 2 mm (0.002 to 0.08 in), that is, sand size.

member. A lithostratigraphic unit with definable contacts; a 

subdivision of a formation.

mesa. A broad, flat-topped erosional hill or mountain with 

by steeply sloping sides or cliffs.

mineral. A naturally occurring inorganic crystalline solid 

with a definite chemical composition or compositional 

range.

montmorillonite. A clay mineral of the smectite group, 

which is common in soils, sedimentary rocks, and some 

mineral deposits. They are derived from the alteration of 

volcanic glass and the weathering of primary silicates. 

mudflow. A general term for a landform and process 

characterized by a flowing mass of predominantly finegrained earth material possessing a high degree of fluidity 

during movement.

mollusk. A solitary invertebrate such as gastropods, bivalves, 

and cephalopods belonging to the phylum Mollusca. 

Range: Lower Cambrian to Holocene. 

orogeny. A mountain-building event.

outcrop. Any part of a rock mass or formation that is 

exposed or “crops out” at Earth’s surface. 

oxbow. A closely looping meander in a stream that 

resembles the U-shaped collar of an ox yoke. Synonymous 

with “horseshoe bend.”

paleogeography. The study, description, and reconstruction 

of the physical landscape in past geologic periods.

paleontology. The study of the life and chronology of 

Earth’s geologic past based on the fossil record.

paleosol. An soil layer preserved in the geologic record.

parabolic dune. Crescent-shaped dune with horns or arms 

that point upwind. 

peat. An unconsolidated deposit of semicarbonized plant 

remains in a water-saturated environment, such as a bog 

or fen, and of persistently high moisture content (at least 

75%). It is an early stage or rank in the development of 

coal; carbon content is about 60% and oxygen content is 

about 30% (moisture-free). 

pebble. A small rounded rock, especially a waterworn stone, 

between 4 and 64 mm (0.16 and 2.5 in) across.

pediment. A gently sloping, erosional bedrock surface at the 

foot of a mountain or plateau escarpment.

permeability. A measure of the relative ease with which 

a fluid moves through the pore spaces of a rock or 

unconsolidated deposit.

piping. Erosion or solution by percolating water in a layer 

of subsoil, resulting in the formation of narrow conduits, 

tunnels, or “pipes” through which soluble or granular soil 

material is removed.

plateau. A broad, flat-topped topographic high (terrestrial 

or marine) of great extent and elevation above the 

surrounding plains, canyons, or valleys.

point bar. A low ridge of sand and gravel deposited in a 

stream channel on the inside of a meander, where flow 

velocity slows.

porosity. The percentage of total void space in a volume of 

rock or unconsolidated deposit.
63

progradation. The seaward building of land as a result of 

sedimentary deposition.

quartz. Silicon dioxide, SiO2. The only silicate (silicon + 

oxygen) mineral consisting entirely of silicon and oxygen. 

Synonymous with “crystalline silica.”

radiocarbon age. An isotopic age expressed in years and 

calculated from the quantitative determination of the 

amount of carbon-14 remaining in an organic material. 

Synonymous with “carbon-14 age.”

rincon. Meaning “inside corner or nook” in Spanish and 

used in the southwestern United States for a square-cut 

recess or hollow in a cliff or a reentrant in the borders of a 

mesa or plateau. Also used for a small, secluded valley, and 

for a bend in a stream. 

rock. An aggregate of one or more minerals (e.g., granite), a 

body of undifferentiated mineral matter (e.g., obsidian), 

or a body of solid organic material (e.g., coal).

rockfall. The most rapid type of slope movement in which a 

newly detached fragment of bedrock of any size falls from 

a cliff or other very steep slope, traveling straight down or 

in a series of leaps and bounds down a slope.

sand. A clastic particle smaller than a granule and larger than 

a silt grain, with a diameter ranging from 1/16 to 2 mm 

(0.0025 to 0.08 in).

sand sheet. A sheetlike body of surficial sediment, 

commonly sand, that veneers the underlying stratigraphic 

units (unconsolidated deposits or bedrock) and can range 

in thickness from a few centimeters to tens of meters, with 

a lateral persistence of a few meters to tens of kilometers.

sandstone. Clastic sedimentary rock composed of 

predominantly sand-sized grains.

sediment. An eroded and deposited, unconsolidated 

accumulation of rock and mineral fragments.

sedimentary. Pertaining to or containing sediment. 

sedimentary rock. A rock resulting from the consolidation 

of loose sediment that has accumulated in layers; it may 

be “clastic,” consisting of mechanically formed fragments 

of older rock; “chemical,” formed by precipitation from 

solution; or “organic,” consisting of the remains of plants 

and animals. One of the three main classes of rock—

igneous, metamorphic, and sedimentary. 

sedimentation. The process of forming or accumulating 

sediment into layers, including the separation of rock 

particles from parent rock, the transportation of these 

particles to the site of deposition, the actual deposition or 

settling of the particles, the chemical and other changes 

occurring in the sediment, and the ultimate consolidation 

of the sediment into solid rock. 

seismic. Pertaining to an earthquake or Earth vibration, 

including those that are artificially induced.

seismicity. The phenomenon of movements in the Earth’s 

crust. Synonymous with “seismic activity.”

septaria. A large, 8–90 cm (3–35 in) across, roughly 

spheroidal concretion characterized by a series of 

radiating cracks that are invariably filled or partly filled by 

crystalline minerals, most commonly calcite.

sequence. A succession of geologic events, processes, or 

rocks, arranged in chronologic order to show their relative 

position and age with respect to geologic history as a 

whole. Also, a rock-stratigraphic unit that is traceable 

over large areas and defined by sediment associated with a 

major sea level transgression–regression.

shale. A clastic sedimentary rock made of clay-sized 

particles and characterized by fissility.

sheet erosion. The removal of thin layers of surface material 

more or less evenly from an extensive area of gently 

sloping land by broad continuous sheets of running water, 

rather than by streams flowing in well-defined channels.

sheetflood. A broad expanse of moving, storm-borne water 

that spreads as a thin, continuous, relatively uniform 

film over a large area in an arid region and that is not 

concentrated into well-defined channels; its distance of 

flow is short and its duration is measured in minutes or 

hours, commonly occurring after a period of sudden and 

heavy rainfall.

sheet flow. The downslope movement or overland 

flow of water, in the form of a thin, continuous film, 

over relatively smooth soil or rock surfaces and not 

concentrated into channels larger than rills.

sheetwash. A sheetflood occurring in a humid region. Also, 

the material transported and deposited by the water of a 

sheetwash. Used as a synonym of “sheet flow” and “sheet 

erosion.”

silicate. A mineral group composed of silicon (Si) and 

oxygen (O) plus an element or elements, for example, 

quartz, SiO2

; olivine, (Mg, Fe)2SiO4; and pyroxene, 

(Mg,Fe)SiO3

; as well as the amphiboles, micas, and 

feldspars.

silt. Clastic sedimentary material intermediate in size 

between fine-grained sand and coarse clay, 0.0039 to 

0.063 mm (0.00015 to 0.0025 in) across.

silting. The accumulation of silt suspended throughout a 

body of standing water or in some considerable portion 

of it. In particular, the choking, filling, or covering 

with stream-deposited silt behind a dam or other place 

of retarded flow, or in a reservoir. Synonymous with 

“siltation.”

siltstone. A clastic sedimentary rock composed of silt-sized 

grains.

slope. The inclined surface of any part of Earth’s surface, 

such as a hillslope. Also, a broad part of a continent 

descending into an ocean.

slope movement. The gradual or rapid downslope 

movement of soil or rock under gravitational stress. 

Synonymous with “mass wasting.”

slope wash. Soil and rock material that is or has been 

transported down a slope under the force of gravity and 

assisted by running water not confined to channels; also, 

the process by which slope-wash material is moved.

soil. The unconsolidated portion of the Earth’s crust 

modified through physical, chemical, and biotic processes 

into a medium capable of supporting plant growth.

spring. A place where groundwater flows naturally from a 

rock or the soil onto the land surface or into a body of 

surface water.
64

stage. A major subdivision of a glacial epoch, particularly 

one of the cycles of growth and disappearance of the 

Pleistocene ice sheets.

strata. Tabular or sheetlike layers of sedimentary rock 

that are visually distinctive from other layers above and 

below. The singular form of the term is stratum, but is less 

commonly used.

stratification. The accumulation or layering of sedimentary 

rocks as strata. Tabular, or planar, stratification refers to 

essentially parallel surfaces. Cross-stratification refers to 

strata inclined at an angle to the main stratification.

stratigraphy. The geologic study of the origin, occurrence, 

distribution, classification, correlation, and age of rock 

layers, especially sedimentary rocks.

stream. Any body of water moving under gravity flow in a 

clearly confined channel.

stream channel. A long, narrow depression shaped by the 

concentrated flow of stream water.

stream terrace. A planar surface alongside a stream valley 

representing the remnants of an abandoned floodplain, 

stream bed, or valley floor produced during a former stage 

of erosion or deposition.

strike. The compass direction of the line of intersection of 

an inclined surface with a horizontal plane.

structural geology. The branch of geology that deals with 

the description, representation, and analysis of structures, 

primarily on a moderate to small scale. The subject is 

similar to tectonics, but the latter term is generally used 

for the analysis of broader regional or historical phases.

structure. The attitudes and relative positions of the rock 

masses of an area resulting from such processes as 

faulting, folding, and igneous intrusion.

subbituminous. Describes black coal, intermediate in rank 

between lignite and bituminous coal; distinguished from 

lignite by higher carbon and lower moisture content. 

subsidence. The sudden sinking or gradual downward 

settling of part of Earth’s surface.

talus. Rock fragments, usually coarse and angular, lying at 

the base of a cliff or steep slope from which they have 

fallen.

tectonic. Describes a feature or process related to large-scale 

movement and deformation of Earth’s crust.

terrace. Any long, narrow, relatively level or gently inclined 

surface (i.e., a bench or steplike ledge) that is bounded 

along one edge by a steeper descending slope and along 

the other edge by a steeper ascending slope, thus breaking 

the continuity of the slope; commonly occurs along the 

margin and above the level of a body of water, marking a 

former water level.

terrestrial. Describes a feature, process, or organism related 

to land, Earth, or its inhabitants.

tidal delta. A delta formed at the mouth of a tidal inlet on 

either the seaward or the lagoon side of a barrier island or 

baymouth bar by changing tidal currents that sweep sand 

in and out of the inlet.

tidal inlet. Any inlet through which water alternately floods 

landward with the rising tide and ebbs seaward with the 

falling tide; specifically a natural inlet maintained by tidal 

currents.

tongue. An extension, projection, or offshoot of a larger 

body of rock, commonly occurring as wedges that 

disappear away from the main body.

topography. The general morphology of Earth’s surface, 

including relief and locations of natural and human-made 

features.

trace fossil. A fossilized feature such as a track, trail, 

burrow, or coprolite (dung), that preserves evidence of an 

organism’s life activities, rather than the organism itself. 

Compare to “body fossil.”

transverse dune. A dune that is elongated perpendicular to 

the prevailing wind direction; the leeward slope stands at 

or near the angle of repose of sand, whereas the windward 

slope is comparatively gentle. 

trend. The direction or bearing of an outcrop of a geologic 

feature such as an ore body, fold, or orogenic belt.

uplift. A structurally high area in Earth’s crust produced by 

movement that raises the rocks.

upwarping. Upward flexing of Earth’s crust on a regional 

scale as a result of the removal of ice, water, sediments, or 

lava flows. 

wash. A broad, gravelly, dry stream bed, generally in the 

bottom of a canyon that is periodically swept by a torrent 

of water. The term is used especially in the southwestern 

United States.

weathering. The physical, chemical, and biological 

processes by which rock is broken down, particularly at 

Earth’s surface.

yazoo. A tributary that is parallel to the main stream channel 

for a considerable distance before joining it, especially 

a stream forced to flow along the outer base of a natural 

levee formed by the main stream. The type example 

is the Yazoo River in western Mississippi, joining the 

Mississippi River at Vicksburg.
65

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Williamson, T. E. 2000. Review of Hadrosauridae (Dinosauria, Ornithischia) from the San Juan Basin, New Mexico. Pages 191–213 

in S. G. Lucas and A. B. Heckert, editors. Dinosaurs of New Mexico. Bulletin 17. New Mexico Museum of Natural History and 

Science, Albuquerque, New Mexico. 

Young, R., and L. Norby, editors. 2009. Geological monitoring. Geological Society of America, Boulder, Colorado. http://nature.nps.

gov/geology/monitoring/index.cfm (accessed 19 May 2014).

Zschetzsche, S., and G. H. Clark. 2004. Soil survey of Chaco Culture National Historical Park, New Mexico. US Department of 

Agriculture, Natural Resources Conservation Service, in cooperation with the US Department of Interior, National Park Service, 

Washington, DC.

75

Additional References

This chapter lists additional references, resources, and websites that may be of use to resource 

managers. Web addresses are valid as of August 2015. Refer to Appendix B for laws, regulations, and 

policies that apply to NPS geologic resources.

Geology of National Park Service Areas

● NPS Geologic Resources Division

Energy and Minerals; Active Processes and Hazards; 

Geologic Heritage:

http://nature.nps.gov/geology/

● NPS Geologic Resources Inventory: http://www.

nature.nps.gov/geology/inventory/index.cfm

● NPS Geoscientist-In-the-Parks (GIP) internship 

and guest scientist program:

http://www.nature.nps.gov/geology/gip/index.cfm

● NPS Views program (geology-themed modules are 

available for Geologic Time, Paleontology, Glaciers, 

Caves and Karst, Coastal Geology, Volcanoes, and a 

variety of geologic parks):

http://www.nature.nps.gov/views/

● USGS Geology of National Parks (including 3D 

imagery): http://3dparks.wr.usgs.gov/

NPS Resource Management Guidance and 

Documents

● Management Policies 2006 (Chapter 4: Natural 

resource management):

http://www.nps.gov/policy/mp/policies.html

● 1998 National parks omnibus management act: 

http://www.gpo.gov/fdsys/pkg/PLAW-105publ391/

pdf/PLAW-105publ391.pdf

● NPS-75: Natural resource inventory and 

monitoring guideline:

http://www.nature.nps.gov/nps75/nps75.pdf

● NPS Natural resource management reference 

manual #77: http://www.nature.nps.gov/Rm77/

● Geologic monitoring manual (Young, R., and 

L. Norby, editors. 2009. Geological monitoring. 

Geological Society of America, Boulder, Colorado): 

http://nature.nps.gov/geology/monitoring/index.

cfm

● NPS Technical Information Center (TIC) (Denver, 

Colorado; repository for technical documents): 

http://www.nps.gov/dsc/technicalinfocenter.htm

Climate Change Resources

● NPS Climate Change Response Program Resources: 

http://www.nps.gov/subjects/climatechange/

resources.htm

● US Global Change Research Program:

http://globalchange.gov/home

● Intergovernmental Panel on Climate Change:

http://www.ipcc.ch/

Geological Surveys and Societies

● New Mexico Bureau of Geology and Mineral 

Resources: http://geoinfo.nmt.edu/

● US Geological Survey: http://www.usgs.gov/

● Geological Society of America:

http://www.geosociety.org/

● American Geophysical Union: http://sites.agu.org/

● American Geosciences Institute:

http://www.americangeosciences.org/

● Association of American State Geologists:

http://www.stategeologists.org/

US Geological Survey Reference Tools

● National geologic map database (NGMDB):

http://ngmdb.usgs.gov/

● Geologic names lexicon (GEOLEX; geologic unit 

nomenclature and summary):

http://ngmdb.usgs.gov/Geolex/geolex_home.html

● Geographic names information system (GNIS; 

official listing of place names and geographic 

features): http://gnis.usgs.gov/

● GeoPDFs (download searchable PDFs of any 

topographic map in the United States):

http://store.usgs.gov (click on “Map Locator”)

● Publications warehouse (many publications 

available online): http://pubs.er.usgs.gov

● Tapestry of time and terrain (descriptions of 

physiographic provinces):

http://tapestry.usgs.gov/Default.html

77

Appendix A: Scoping Participants

The following people attended the GRI scoping meeting for Chaco Culture National Historical Park, 

held on 14 February 2007; a follow-up conference call on 13 February 2014; or a conference call that 

focused on oil and gas issues on 15 April 2014. Discussions during this meeting and calls supplied a 

foundation for this GRI report. The scoping summary document is available on the GRI publications 

website: http://go.nps.gov/gripubs.

2007 Scoping Meeting Participants

Name Affiliation Position

Tim Connors NPS Geologic Resources Division Geologist

Dabney Ford Chaco Culture National Historical Park Cultural Resource Manager

Katie KellerLynn Colorado State University Geologist/Research Associate

Dave Love New Mexico Bureau of Geology and Mineral Resources Geologist

Lisa Norby NPS Geologic Resources Division Geologist

Brad Shattuck Chaco Culture National Historical Park Natural Resource Manager

Phil Stoffer US Geological Survey Geologist

Heather Stanton Colorado State University Geologist/Research Associate

Barbara West Chaco Culture National Historical Park Superintendent

2014 Conference Call Participants

Name Affiliation Position

Eric Bilderback NPS Geologic Resources Division Geologic Hazards and Disturbed Lands Program 

Lead

Dabney Ford Chaco Culture National Historical Park Cultural Resources Chief

Katie KellerLynn Colorado State University Geologist/Research Associate

Jason Kenworthy NPS Geologic Resources Division Geologist/GRI Reports Coordinator

Dave Love New Mexico Bureau of Geology and Mineral Resources Geologist

Steve Monroe NPS Southern Colorado Plateau Network Hydrologist

Hal Pranger NPS Geologic Resources Division Geologic Features and Systems Branch Chief

Vincent Santucci NPS Geologic Resources Division Senior Geologist/Paleontologist/Washington 

Liaison

Phil Varela Chaco Culture National Historical Park Paleontology Technician

Jim Von Haden Chaco Culture National Historical Park Natural Resources Program Manager

2014 Oil and Gas Issues Conference Call Participants

Name Affiliation Position

Tim Connors NPS Geologic Resources Division Geologist/GRI Maps Coordinator

Katie KellerLynn Colorado State University Geologist/Research Associate

Jason Kenworthy NPS Geologic Resources Division Geologist/GRI Reports Coordinator

Kerry Moss NPS Geologic Resources Division External Energy and Minerals Program 

Coordinator

Lisa Norby NPS Geologic Resources Division Energy and Minerals Branch Chief

Jim Von Haden Chaco Culture National Historical Park Natural Resources Program Manager

Katie Earp Chaco Culture National Historical Park Physical Science Technician

79

Appendix B: Geologic Resource Laws, Regulations, and Policies

The NPS Geologic Resources Division developed this table to summarize laws, regulations, and policies 

that specifically apply to National Park Service minerals and geologic resources. The table does not 

include laws of general application (e.g., Endangered Species Act, Clean Water Act, Wilderness Act, 

National Environmental Policy Act, or National Historic Preservation Act). The table does include the 

NPS Organic Act when it serves as the main authority for protection of a particular resource or when 

other, more specific laws are not available. Information is current as of August 2015. Contact the NPS 

Geologic Resources Division for detailed guidance.

Resource Resource-specific Laws Resource-specific Regulations 2006 Management Policies Paleontology

National Parks Omnibus Management 

Act of 1998, 16 USC § 5937 protects the 

confidentiality of the nature and specific 

location of paleontological resources and 

objects.

Paleontological Resources Preservation 

Act of 2009, 16 USC § 470aaa et 

seq. provides for the management and 

protection of paleontological resources on 

federal lands.

36 CFR § 2.1(a)(1)(iii) prohibits destroying, 

injuring, defacing, removing, digging or 

disturbing paleontological specimens or 

parts thereof.

Prohibition in 36 CFR § 13.35 applies 

even in Alaska parks, where the surface 

collection of other geologic resources is 

permitted.

Regulations in association with 2009 PRPA 

are being finalized (August 2015).

Section 4.8.2 requires NPS to protect 

geologic features from adverse effects of 

human activity.

Section 4.8.2.1 emphasizes Inventory and 

Monitoring, encourages scientific research, 

directs parks to maintain confidentiality of 

paleontological information, and allows 

parks to buy fossils only in accordance with 

certain criteria.

Rocks and Minerals

NPS Organic Act, 16 USC § 1 et seq.

directs the NPS to conserve all resources 

in parks (including rock and mineral 

resources), unless otherwise authorized by 

law.

36 CFR § 2.1 prohibits possessing, 

destroying, disturbing mineral resources...

in park units.

Exception: 36 CFR § 13.35 allows some 

surface collection of rocks and minerals 

in some Alaska parks (not Klondike 

Gold Rush, Sitka, Denali, Glacier Bay, 

or Katmai) by non-disturbing methods 

(e.g., no pickaxes), which can be stopped 

by superintendent if collection causes 

significant adverse effects on park 

resources and visitor enjoyment.

Section 4.8.2 requires NPS to protect 

geologic features from adverse effects of 

human activity.

Park Use of Sand and Gravel

Materials Act of 1947, 30 USC § 601

does not authorize the NPS to dispose of 

mineral materials outside of park units.

None applicable.

Section 9.1.3.3 clarifies that only the 

NPS or its agent can extract park-owned 

common variety minerals (e.g., sand and 

gravel), and:

-only for park administrative uses;

-after compliance with NEPA and other 

federal, state, and local laws, and a 

finding of non-impairment;

-after finding the use is park’s most 

reasonable alternative based on 

environment and economics;

-parks should use existing pits and create 

new pits only in accordance with parkwide borrow management plan;

-spoil areas must comply with Part 6 

standards; and

-NPS must evaluate use of external 

quarries.

Any deviation from this policy requires a 

written waiver from the Secretary, Assistant 

Secretary, or Director.
80

Resource Resource-specific Laws Resource-specific Regulations 2006 Management Policies Upland and Fluvial Processes

Rivers and Harbors Appropriation 

Act of 1899, 33 USC § 403 prohibits the 

construction of any obstruction on the 

waters of the United States not authorized 

by congress or approved by the USACE.

Clean Water Act 33 USC § 1342 requires 

a permit from the USACE prior to any 

discharge of dredged or fill material 

into navigable waters (waters of the US 

[including streams]). 

Executive Order 11988 requires federal 

agencies to avoid adverse impacts to 

floodplains. (see also D.O. 77-2)

Executive Order 11990 requires plans for 

potentially affected wetlands (including 

riparian wetlands). (see also D.O. 77-1)

None applicable.

Section 4.1 requires NPS to manage 

natural resources to preserve fundamental 

physical and biological processes, as well 

as individual species, features, and plant 

and animal communities; maintain all 

components and processes of naturally 

evolving park ecosystems.

Section 4.1.5 directs the NPS to reestablish natural functions and processes 

in human-disturbed components of natural 

systems in parks, unless directed otherwise 

by Congress.

Section 4.4.2.4 directs the NPS to allow 

natural recovery of landscapes disturbed by 

natural phenomena, unless manipulation of 

the landscape is necessary to protect park 

development or human safety. 

Section 4.6.4 directs the NPS to (1) 

manage for the preservation of floodplain 

values; [and] (2) minimize potentially 

hazardous conditions associated with 

flooding.

Section 4.6.6 directs the NPS to manage 

watersheds as complete hydrologic systems 

and minimize human-caused disturbance 

to the natural upland processes that deliver 

water, sediment, and woody debris to 

streams.

Section 4.8.1 directs the NPS to allow 

natural geologic processes to proceed 

unimpeded. Geologic processes...include...

erosion and sedimentation...processes. 

Section 4.8.2 directs the NPS to protect 

geologic features from the unacceptable 

impacts of human activity while allowing 

natural processes to continue.

Caves and Karst Systems

Federal Cave Resources Protection Act 

of 1988, 16 USC §§ 4301 – 4309 requires 

Interior/Agriculture to identify “significant 

caves” on Federal lands, regulate/

restrict use of those caves as appropriate, 

and include significant caves in land 

management planning efforts. Imposes 

civil and criminal penalties for harming 

a cave or cave resources. Authorizes 

Secretaries to withhold information about 

specific location of a significant cave from 

a Freedom of Information Act (FOIA) 

requester. 

National Parks Omnibus Management 

Act of 1998, 16 USC § 5937 protects the 

confidentiality of the nature and specific 

location of cave and karst resources.

36 CFR § 2.1 prohibits possessing/ 

destroying/disturbing...cave resources...in 

park units.

43 CFR Part 37 states that all NPS caves 

are “significant” and sets forth procedures 

for determining/releasing confidential 

information about specific cave locations to 

a FOIA requester.

Section 4.8.1.2 requires NPS to maintain 

karst integrity, minimize impacts.

Section 4.8.2 requires NPS to protect 

geologic features from adverse effects of 

human activity.

Section 4.8.2.2 requires NPS to protect 

caves, allow new development in or on 

caves if it will not impact cave environment, 

and to remove existing developments if 

they impair caves.

Section 6.3.11.2 explains how to manage 

caves in/adjacent to wilderness.
81

Resource Resource-specific Laws Resource-specific Regulations 2006 Management Policies Mining Claims

Mining in the Parks Act of 1976, 16 

USC § 1901 et seq. authorizes NPS 

to regulate all activities resulting from 

exercise of mineral rights, on patented and 

unpatented mining claims in all areas of the 

System, in order to preserve and manage 

those areas.

General Mining Law of 1872, 30 USC 

§ 21 et seq. allows US citizens to locate 

mining claims on Federal lands. Imposes 

administrative and economic validity 

requirements for “unpatented” claims (the 

right to extract Federally-owned locatable 

minerals). Imposes additional requirements 

for the processing of “patenting” claims 

(claimant owns surface and subsurface). 

Use of patented mining claims may be 

limited in Wild and Scenic Rivers and 

OLYM, GLBA, CORO, ORPI, and DEVA. 

Surface Uses Resources Act of 1955, 

30 USC § 612 restricts surface use of 

unpatented mining claims to mineral 

activities.

36 CFR § 5.14 prohibits prospecting, 

mining, and the location of mining claims 

under the general mining laws in park 

areas except as authorized by law.

36 CFR Part 6 regulates solid waste 

disposal sites in park units.

36 CFR Part 9, Subpart A requires the 

owners/operators of mining claims to 

demonstrate bona fide title to mining 

claim; submit a plan of operations to 

NPS describing where, when, and how; 

prepare/submit a reclamation plan; and 

submit a bond to cover reclamation and 

potential liability.

Section 6.4.9 requires NPS to seek to 

remove or extinguish valid mining claims in 

wilderness through authorized processes, 

including purchasing valid rights. Where 

rights are left outstanding, NPS policy is 

to manage mineral-related activities in 

NPS wilderness in accordance with the 

regulations at 36 CFR Parts 6 and 9A.

Section 8.7.1 prohibits location of new 

mining claims in parks; requires validity 

examination prior to operations on 

unpatented claims; and confines operations 

to claim boundaries.

Nonfederal Oil and Gas

NPS Organic Act, 16 USC § 1 et seq.

authorizes the NPS to promulgate 

regulations to protect park resources and 

values (from, for example, the exercise of 

mining and mineral rights).

36 CFR Part 6 regulates solid waste 

disposal sites in park units.

36 CFR Part 9, Subpart B requires the 

owners/operators of nonfederally owned 

oil and gas rights to

-demonstrate bona fide title to mineral 

rights;

-submit a plan of operations to NPS 

describing where, when, how they intend 

to conduct operations;

-prepare/submit a reclamation plan; and 

-submit a bond to cover reclamation and 

potential liability.

Section 8.7.3 requires operators to comply 

with 9B regulations.

Nonfederal minerals other than oil and gas

NPS Organic Act, 16 USC §§ 1 and 3

Surface Mining Control and 

Reclamation Act of 1977, 30 USC § 

1201 et. seq. prohibits surface coal 

mining operations on any lands within the 

boundaries of a NPS unit, subject to valid 

existing rights.

NPS regulations at 36 CFR Parts 1, 5, 

and 6 require the owners/operators of 

other types of mineral rights to obtain 

a special use permit from the NPS as a 

§ 5.3 business operation, and § 5.7 – 

Construction of buildings or other facilities, 

and to comply with the solid waste 

regulations at Part 6.

SMCRA Regulations at 30 CFR Chapter 

VII govern surface mining operations on 

Federal lands and Indian lands by requiring 

permits, bonding, insurance, reclamation, 

and employee protection. Part 7 of the 

regulations states that National Park System 

lands are unsuitable for surface mining.

Section 8.7.3 states that operators 

exercising rights in a park unit must comply 

with 36 CFR Parts 1 and 5.
82

Resource Resource-specific Laws Resource-specific Regulations 2006 Management Policies Federal Mineral Leasing (Oil and Gas, Salable Minerals, and Non-locatable Minerals)

The Mineral Leasing Act, 30 USC § 181 

et seq., and the Mineral Leasing Act for 

Acquired Lands, 30 USC § 351 et seq. 

do not authorize the BLM to lease federally 

owned minerals in NPS units. 

Exceptions: Native American Lands Within 

NPS Boundaries Under the Indian Allottee 

Leasing Act of 1909, (25 USC § 396), 

and the Indian Leasing Act of 1938 (25 

USC §§ 396a, 398 and 399) and Indian 

Mineral Development Act of 1982 

(25 USC §§ 2101-2108), all minerals 

are subject to lease and apply to Native 

American trust lands within NPS units.

Federal Coal Leasing Amendments Act 

of 1975, 30 USC § 201 does not authorize 

the BLM to issue leases for coal mining on 

any area of the national park system.

36 CFR § 5.14 states prospecting, mining, 

and...leasing under the mineral leasing 

laws [is] prohibited in park areas except as 

authorized by law.

BLM regulations at 43 CFR Parts 3100, 

3400, and 3500 govern Federal mineral 

leasing.

Regulations re: Native American Lands 

within NPS Units:

25 CFR Part 211 governs leasing of tribal 

lands for mineral development. 

25 CFR Part 212 governs leasing of 

allotted lands for mineral development. 

25 CFR Part 216 governs surface 

exploration, mining, and reclamation of 

lands during mineral development. 

25 CFR Part 224 governs tribal energy 

resource agreements.

25 CFR Part 225 governs mineral 

agreements for the development of Indianowned minerals entered into pursuant to 

the Indian Mineral Development Act of 

1982, Pub. L. No. 97-382, 96 Stat. 1938 

(codified at 25 USC §§ 2101-2108).

30 CFR §§ 1202.100-1202.101 governs 

royalties on oil produced from Indian 

leases. 

30 CFR §§ 1202.550-1202.558 governs 

royalties on gas production from Indian 

leases. 

30 CFR §§ 1206.50-1206.62 and §§ 

1206.170-1206.176 governs product 

valuation for mineral resources produced 

from Indian oil and gas leases. 

30 CFR § 1206.450 governs the valuation 

coal from Indian Tribal and Allotted leases.

43 CFR Part 3160 governs onshore oil and 

gas operations, which are overseen by the 

BLM.

Section 8.7.2 states that all NPS units 

are closed to new federal mineral leasing 

except Glen Canyon, Lake Mead and 

Whiskeytown-Shasta-Trinity NRAs.
83

Resource Resource-specific Laws Resource-specific Regulations 2006 Management Policies Soils

Soil and Water Resources Conservation 

Act, 16 USC §§ 2011–2009 provides for 

the collection and analysis of soil and 

related resource data and the appraisal of 

the status, condition, and trends for these 

resources.

Farmland Protection Policy Act, 7 USC 

§ 4201 et. seq. requires NPS to identify 

and take into account the adverse effects 

of Federal programs on the preservation 

of farmland; consider alternative actions, 

and assure that such Federal programs 

are compatible with State, unit of local 

government, and private programs 

and policies to protect farmland. NPS 

actions are subject to the FPPA if they 

may irreversibly convert farmland (directly 

or indirectly) to nonagricultural use and 

are completed by a Federal agency or 

with assistance from a Federal agency. 

Applicable projects require coordination 

with the Department of Agriculture’s 

Natural Resources Conservation Service 

(NRCS).

7 CFR Parts 610 and 611 are the US 

Department of Agriculture regulations 

for the Natural Resources Conservation 

Service. Part 610 governs the NRCS 

technical assistance program, soil erosion 

predictions, and the conservation of private 

grazing land. Part 611 governs soil surveys 

and cartographic operations. The NRCS 

works with the NPS through cooperative 

arrangements.

Section 4.8.2.4 requires NPS to

-prevent unnatural erosion, removal, and 

contamination;

-conduct soil surveys;

-minimize unavoidable excavation; and

-develop/follow written prescriptions 

(instructions).

The Department of the Interior protects and manages the nation’s natural resources and cultural heritage; provides scientific and 

other information about those resources; and honors its special responsibilities to American Indians, Alaska Natives, and affiliated 

Island Communities.

NPS 310/129981, September 2015
National Park Service

U.S. Department of the Interior

Natural Resource Stewardship and Science 

1201 Oak Ridge Drive, Suite 150 

Fort Collins, Colorado 80525

www.nature.nps.gov

EXPERIENCE YOUR AMERICATM
Plate 1. Map of the Chaco Canyon (main) unit of Chaco Culture National Historical Park. The park is in the 

middle of the San Juan Basin in northwestern New Mexico and consists of mesas, canyons, arroyos, and 

buttes, and is famous for spectacular multistoried stone great houses, many of which are marked in green 

as “prehistoric sites” on the map This map shows the main Chaco Canyon unit of the park. The other 

three outlying units are west (Kin Bineola), east (Pueblo Pintado), and south (Kin Ya’a) of the main unit 

(see poster, in pocket). National Park Service graphic. 

Map Unit Properties Table: Chaco Culture National Historical Park, Page 1 of 8

Map Unit Properties Table: Chaco Culture National Historical Park

Investigators mapped the following units in Chaco Culture National Historical Park. A full list and descriptions of all the units are included in the GRI data for the park (chcu_geology.pdf). Bold text refers to sections in the report.

Age Map Unit

(Symbol) Park Unit Geologic Description Geologic Features and Processes Geologic Resource Management Issues Geologic History

QUATERNARY

(Holocene)

Earth dam

(Qaf1)

Kin Ya’a

Kin Bineola

An earth dam (Qaf1) in the Kin Ya’a unit of the 

park surrounds a flowing well. 

Earth dams mapped as part of Qal in the La Vida 

Mission quadrangle were built across washes to 

catch and retain storm water for irrigation and 

livestock. Dams across broader washes may be as 

long as 0.6 km (0.4 mi). Earth (dam fill) material 

was scoured out with scrapers from an extensive, 

nearly flat area in the lower reaches of the dry Kimme-ni-oli channel.

None reported.

Disturbed Lands Restoration—in some places, 

earth dams have totally altered normal drainage 

and sediment deposition along the Kim-me-ni-oli 

Wash.

Human Populations in Chaco Canyon—built in 

the 1930s.

QUATERNARY

(Holocene)

Soil, large area

(Qsl) Kin Bineola

Sedentary soil (not slope-wash deposits) mapped in 

large uninterrupted areas. Derived from bedrock, 

which may be mud, silt, or fine-grained sand. 

Where sand, the surface commonly has hummocks 

around shrubs, but troughs between are shallow 

(not as deep as in stabilized eolian sand). Slight to 

firm crust (caliche) on surface. Obscures bedrock. 

Upper Cretaceous Rocks and Fossils—developed 

principally on mudstone of the Menefee Formation 

(Kmf); derived from weathering of Menefee 

bedrock. Contains small fragments of sandstone 

from bedrock, caliche chips, or ironstone chips 

abundant or sparse in troughs. Ants bring up chips 

of bedrock, especially ironstone chips, around their 

holes. 

Alluvial Fill—possibly equivalent to the Naha 

alluvium of Hack (1941) (Qn).

Eolian Processes—sandy soil areas and stabilized 

eolian sand areas may grade from one to the other. 

No issues of dust storms or eolian transport 

reported.

Human Populations in Chaco Canyon—may be 

equivalent to Naha alluvium (Qn), and thus of 

interest for Geoarcheology.

QUATERNARY

(Holocene)

Soil, small area

(Qss) Kin Bineola

Sedentary soil (not slope-wash deposits) mapped in 

small areas or within a larger area broken up by 

other map units. Derived from bedrock, which may 

be mud, silt, or fine-grained sand. Where sand, the 

surface commonly has hummocks around shrubs, 

but troughs between are shallow (not as deep as in 

stabilized eolian sand). Slight to firm crust (caliche) 

on surface. Obscures bedrock. 

Upper Cretaceous Rocks and Fossils—developed 

principally on mudstone of the Menefee Formation 

(Kmf); derived from weathering of Menefee 

bedrock. Contains small fragments of sandstone 

from bedrock, caliche chips, or ironstone chips 

abundant or sparse in troughs. Ants bring up chips 

of bedrock, especially ironstone chips, around their 

holes.

Alluvial Fill—possibly equivalent to the Naha

Alluvium of Hack (1941) (Qn).

Eolian Processes—sandy soil areas and stabilized 

eolian sand areas may grade from one to the other. 

No issues of dust storms or eolian transport 

reported.

Human Populations in Chaco Canyon—may be 

equivalent to Naha alluvium (Qn), and thus of 

interest for Geoarcheology. 

QUATERNARY

(Holocene and Pleistocene?)

Alluvium and eolian 

deposits

(Qae)

Kin Bineola Windblown silt and sand reworked by running 

water.

Eolian Features—occurs on mesas, benches, and 

in broad valleys.

Eolian Processes—provides material for dust 

storms and sand transport.

Dynamic Sedimentation—after incision of Chaco 

Canyon, sediments began to fill it, including 

windblown silt and sand and material transported 

by running water.

QUATERNARY

(Holocene)

Slope-wash deposit

(Qswd) Kin Bineola Most deposits developed on mudstone of the 

Menefee Formation (Kmf).

Upper Cretaceous Rocks and Fossils—may be 

partly mantled by chips and cobbles of Cretaceous 

sandstone from nearby outcrops or partly to fully 

mantled by chips of ironstone from broken

concretions.

Sheetwash Alluvium and Slope-Wash Deposits 

and—deposited by overland flow. Occurs on gently 

sloping smooth surfaces swept bare of vegetation. 

Eolian Processes—margins of slope-wash areas 

commonly irregular; slope-wash material 

interfingers with stabilized eolian sand or soil. No 

issues with dust storms or eolian transport 

reported.

Dynamic Sedimentation—after incision of Chaco 

Canyon, sediments began to fill it, including 

material deposited by overland flow.
Investigators mapped the following units in Chaco Culture National Historical Park. A full list and descriptions of all the units are included in the GRI data for the park (chcu_geology.pdf). Bold text refers to sections in the report. 

Map Unit Properties Table: Chaco Culture National Historical Park, Page 2 of 8 

Age Map Unit

(Symbol) Park Unit Geologic Description Geologic Features and Processes Geologic Resource Management Issues Geologic History

Upper Cretaceous Rocks and Fossils—derived 

from shale or sandstone bedrock, or reworked from 

deposits of older alluvium. Contains clasts of 

sandstone and sideritic ironstone from local 

QUATERNARY 

(Holocene)

Alluvium

(Qal)

Chaco Canyon

Kin Bineola

Sand, silt, and clay deposited along major 

drainages. Generally about 1.5 m (5 ft) thick, but 

ranges from less than 3 m (10 ft) to more than 15 

m (15 m) in Escavada Wash channel. 

bedrock. Contains fragments of Cretaceous 

petrified wood.

Chaco Canyon—occurs in the lowest channels cut 

into floodplains of larger ephemeral streams. Makes 

up bed of Chaco Wash.

Dynamic Sedimentation and Arroyo 

Development—stream-deposited clay, silt, sand, 

and gravel along major drainages.

Disturbed Lands Restoration—earth dams are 

part of unit Qal in the Kin Bineola unit of the park 

(see description for Qaf1).

Piping—not an issue for piping, which occurs in 

older alluvial fill on the floor of Chaco Canyon.

Dynamic Sedimentation—modern alluvium 

stream channels.

in 

Alluvial Fill—“modern alluvium” mapped in 

Chaco Canyon and Kin Bineola units. 

Chaco Canyon—deposited in arroyos and on valley 

floors since the development of Chaco Arroyo. 

Locally incised by very recent arroyos,

QUATERNARY 

(upper Holocene)

Alluvial deposits,

unit 1

(Qa1)

Kin Ya’a

Mostly light-yellowish-gray sand and gravel. 

Generally thin, probably does not exceed 3 m (10 

ft) thick. 

Dynamic Sedimentation and Arroyo 

Development—generally mantles the broad valley 

floodplains downstream from the arroyos. 

Underlain by alluvium of unit 2 (Qa2).

Alluvial Fill—mapped in Kin Ya’a unit; Robertson 

(1992) did not use terms of Hack (1941) such as 

“Naha” or “Tsegi” to differentiate alluvial deposits.

Piping—potential for piping in tributary 

and the walls of Chaco Arroyo.

canyons Human Populations in Chaco Canyon—

deposited since the beginning of the latest cy

arroyo cutting.

cle of 

Eolian Features—includes some eolian sand 

reworked by flood waters.

Tinajas and Charcos—Qa1 includes minor clay 

and silt deposited in ephemeral ponds and 

reservoirs.

QUATERNARY 

(Holocene)

Naha Alluvium

(1941)

(Qn)

of Hack Pueblo Pintado

Chaco Canyon

Grayish brown, poorly consolidated, laminated and 

cross-stratified sand and silt that fill ephemeral 

washes. Qn overlies Tsegi Alluvium along deep 

arroyos. Ranges from 3 to 6 m (10 to 20 ft) thick.

Chaco Canyon—as shown on source maps and in 

the GRI GIS data, the floor of Chaco Canyon is 

covered by Qn and Qnt. 

Alluvial Fill—use of “Naha Alluvium” in Chaco 

Canyon may not be appropriate because the timing 

of deposition of this alluvium is unclear and a 

correlation between the type locality in Arizona and 

Chaco Canyon has not been established.

Sheetwash Alluvium and Slope-Wash 

Deposits—Qn contains some rounded chert and 

quartzite pebbles, and some sheetwash with blocks 

of sandstone along valley walls.

Piping—Qn has potential for piping in tributary 

canyons and the walls of Chaco Arroyo.

Human Populations in Chaco Canyon—Qn

relates to the most intense occupation of Chaco 

Canyon. Contains abundant archeological remains, 

especially pottery, along Chaco Wash. Contains 

abundant ceramic artifacts near Pueblo Pintado. 

Geoarcheology—Qn is significant for studying the 

relationships between prehistoric humans and the 

environment at Chaco Canyon. 
Investigators mapped the following units in Chaco Culture National Historical Park. A full list and descriptions of all the units are included in the GRI data for the park (chcu_geology.pdf). Bold text refers to sections in the report. 

Map Unit Properties Table: Chaco Culture National Historical Park, Page 3 of 8

Age Map Unit

(Symbol) Park Unit Geologic Description Geologic Features and Processes Geologic Resource Management Issues Geologic History

QUATERNARY

(Holocene)

Naha and Tsegi 

Alluviums of Hack 

(1941)

(Qnt)

Chaco Canyon

These alluviums were mapped as a single undivided 

unit in parts of Chaco Canyon.

Naha Alluvium: grayish brown, friable to slightly 

hard, thinly laminated and cross-stratified sand and 

silt in discontinuous layers. Thickness ranges from 

10 ft (3 m) to more than 6 m (20 ft). 

Tsegi Alluvium: yellowish-gray or grayish-brown, 

firmly consolidated, fine to coarse sand, silt, and 

clay containing several clay and humus-rich layers. 

About 3 m (10 ft) thick.

Chaco Canyon—as shown on source maps and in 

the GRI GIS data, the floor of Chaco Canyon is 

covered by Qn and Qnt.

Alluvial Fill—use of “Naha Alluvium” in Chaco 

Canyon may not be appropriate because the timing 

of deposition of this alluvium is unclear and a 

correlation between the type locality in Arizona and 

Chaco Canyon has not been established.

Sheetwash Alluvium and Slope-Wash 

Deposits—Qnt contains some sheetwash alluvium 

and alluvial fans along valley walls.

Piping—Qnt has potential for piping in tributary 

canyons and the walls of Chaco Arroyo.

Human Populations in Chaco Canyon—Tsegi 

alluvium was deposited before pottery was in use 

but does contain a few stone tools from archaic 

cultures.

Geoarcheology—Qnt is significant for studying 

the relationships between prehistoric humans and 

the environment at Chaco Canyon.

QUATERNARY

(Holocene)

Alluvial deposits, unit 2

(Qa2) Kin Ya’a

Yellowish-gray, unconsolidated silt, sand, and 

gravel. Grades upslope into colluvium (Qc). 

Observed thickness 0–4 m (0–13 ft), but probably 

more than 8 m (26 ft) thick in some alluviated 

valleys.

Chaco Canyon—deposited in aggraded valley 

bottoms and on floodplains. 

Alluvial Fill—Qa2 mapped by Robertson (1992) in 

Kin Ya’a unit; did not use terms of Hack (1941) 

such as “Naha” or “Tsegi.”

Eolian Features—Qa2 contains thin clay lenses 

and eolian deposits.

Piping—Qa2 has potential for piping in tributary 

canyons and the walls of Chaco Arroyo.

Eolian Processes—locally, contains thin clay lenses 

and eolian deposits. Generally stabilized by 

vegetation and incipient soil formation. Dust storms 

and sand transport not known to be an issue. 

Dynamic Sedimentation—deposited before the 

beginning of the latest cycle of arroyo cutting.

QUATERNARY

(upper Pleistocene to Holocene)

Sheetwash alluvium

(Qsw) Chaco Canyon

Poorly consolidated clay, silt, and coarse to medium 

sand containing rock fragments ranging from 

pebbles to large sandstone slabs. Most clasts are 

from underlying Menefee Formation. Chiefly 

sheetwash material derived from shale and 

sandstone bedrock on gently sloping tops of mesas 

and gently to steeply sloping valley walls. In part 

derived from older surficial deposits. Locally wellcemented on southern side of Chaco Canyon 

between Wijiji and Pueblo del Arroyo sites. Up to 6 

m (20 ft) thick.

Alluvial Fill—small areas of gravelly sheetwash 

alluvium (Qsw) along Fajada Wash may be 

equivalent to gravelly Jeddito alluvium (Qj) in the 

gravel pit 0.8 km (0.5 mi) southwest of the park 

headquarters. May also be equivalent to “Fajada 

gravel” of Hall (1977, 2010).

Sheetwash Alluvium and Slope-Wash 

Deposits—Qsw was deposited by overland flow.

Eolian Features—Qsw locally covered by 

unmapped eolian sand.

Rockfall—Qsw includes small unmapped rockfalls 

and talus cones derived from bedrock on steep 

valley walls, and colluvium subjected to creep on 

steep slopes.

Paleontological Resource Inventory and 

Monitoring—Qsw contains petrified wood.

Dynamic Sedimentation—after incision of Chaco 

Canyon, sediments began to fill it, including 

material deposited by sheetfloods.

QUATERNARY

(upper Pleistocene to upper Holocene)

Eolian sand

(Qes) Chaco Canyon

Fine-grained, windblown sand. Includes both 

younger and older deposits. 

Younger eolian sand: White, well-sorted, crossstratified loose quartz sand in active barchan and 

climbing dunes. More than 12 m (40 ft) thick in 

active dune fields along the Chaco River and Chaco 

Wash.

Older eolian deposits: Light-brown, slightly 

consolidated, fine to medium sand containing 

subrounded to rounded, frosted quartz grains in 

stabilized linear dunes and sand sheets on the 

uplands. More than 2 m (7 ft) thick in older sand

deposits.

Eolian Features—Qes composes dunes and sand 

sheets.

Eolian Processes—Qes generally stabilized by 

vegetation. Younger eolian sand may be prone to 

transport.

Dynamic Sedimentation—after incision of Chaco 

Canyon, sediments began to fill it, including 

windblown sand.
Investigators mapped the following units in Chaco Culture National Historical Park. A full list and descriptions of all the units are included in the GRI data for the park (chcu_geology.pdf). Bold text refers to sections in the report. 

Map Unit Properties Table: Chaco Culture National Historical Park, Page 4 of 8 

Age Map Unit

(Symbol) Park Unit Geologic Description Geologic Features and Processes Geologic Resource Management Issues Geologic History

QUATERNARY

(Pleistocene to Holocene) 

Older eolian deposits

(Qoe) Kin Ya’a

Moderate-yellowish-brown, pale-reddish-brown, 

and dusky-yellow, fine- to very fine grained silt; 

somewhat clayey and oxidized; caliche moderately 

to well developed. Some older eolian deposits 

(Qoe) are mixed with and mapped as colluvium 

(Qc), older alluvium (Qoa), and pediment gravel 

(Qp). Up to 6 m (20 ft) thick.

Eolian Features—Qoe covers large areas as 

blanket-like deposits on flanks and tops of ridges 

and low mesas; lightly masks many areas mapped 

as bedrock. Large-scale seif dunes, some combined 

with barchan dunes, rise 1–6 m (3–20 ft) above the 

blanket-like deposits in places.

Eolian Processes—semi-consolidated sand and silt, 

commonly stabilized by vegetation and soil 

formation, thus dust storms and sand transport are 

not known to be an issue.

Dynamic Sedimentation—after incision of Chaco 

Canyon, sediments began to fill it, including 

windblown sand and silt.

QUATERNARY

(Pleistocene? to Holocene) 

Alluvial fan deposits

(Qf) Kin Ya’a Poorly sorted, unconsolidated sand, silt, 

Grades laterally into colluvium (Qc).

and gravel. 

Chaco Canyon—Qf consists of fan-shaped 

deposits on side canyons and in the upper parts of 

some main stream valleys.

Eolian Features—parabolic dunes are associated 

with large alluvial fans (Qf) at the mouths of 

tributary canyons. 

Badlands—small alluvial fans (Qf) form in badlands 

topography as water and sediment pass through 

soil pipes and discharge at the base of slopes. 

Piping—small alluvial fans (Qf) form as a result of 

piping in badlands topography.

Cut-and-Fill Cycles—Qf formed by aggradation 

where the detrital bed load exceeded the capacity 

of the streams to transport it out of the canyon.

QUATERNARY

(Pleistocene to Holocene) 

Colluvium

(Qc) Kin Ya’a

Unsorted to poorly sorted silt, sand, and gravel 

deposited on valley walls between talus slopes and 

alluvium (Qa1, Qa2) in stream valleys; includes 

some valley alluvium (Qa1, Qa2). Grades laterally 

into fan (Qf) deposits.

Sheetwash Alluvium and Slope-Wash 

Deposits—sheetwash has moved some Qc. 

Eolian Features—deposits of Qc include some 

eolian sand (Qe).

Rockfall—Qc

processes and

material has moved by mudflow 

includes some talus debris (Qt).

Dynamic Sedimentation—Qc

formation of Chaco Canyon. 

deposited since the 

QUATERNARY 

(upper Pleistocene to lower Holocene)

Jeddito Alluvium

Hack (1941)

(Qj)

of 

Chaco Canyon

Dark-yellowish-brown sand containing moderate 

yellowish-brown, angular, pebble- to cobble-sized 

clasts of sandstone and very dark brown to black, 

pebble-sized clasts of ironstone. Along Kin Klizhin 

and Fajada washes, most clasts are from the 

underlying Menefee Formation (Kmf). Forms a 

terrace about 7 m (23 ft) above the Chaco River, 

Fajada Wash, and Kin Klizhin Wash. Maximum 

thickness along Fajada Wash about 10 m (30 ft).

Quaternary Fossils—Qj may contain proboscidian 

remains.

Alluvial Fill—use of “Jeddito Alluvium” in Chaco 

Canyon may not be appropriate because the timing 

of deposition of this alluvium is unclear and a 

correlation between the type locality in Arizona and 

Chaco Canyon has not been established. Along 

Fajada Wash, a reddish-brown, well-developed 

Altithermal (dry postglacial interval) soil formed in 

the upper part of the alluvium. Altithermal soil is 

exposed locally in the lower parts of arroyo walls 

along Chaco Wash, which indicates that near the 

center of the wash, Qj forms a deep and rarely 

exposed fill.

Sheetwash Alluvium and Slope-Wash 

Deposits—some Qj along Fajada Wash was 

deposited by overland flow.

Abandoned Mineral Lands—Pleistocene gravel 

deposit (exact unit unknown) was mined for sand 

and gravel for administrative uses until the late

1980s.

Paleontological Resource Inventory and 

Monitoring—the ongoing inventory has thus far 

focused on Upper Cretaceous rocks in Chaco 

Culture National Historical Park. No proboscidian 

remains found, to date.

Piping—Qj has potential for piping in tributary 

canyons and the walls of Chaco Arroyo.

Human Populations in Chaco Canyon and

Geoarcheology—deposition of Qj predates 

human occupation of Chaco Canyon, though some 

clasts in Qj were a source of flaking material for the 

manufacture of prehistoric stone tools.
Investigators mapped the following units in Chaco Culture National Historical Park. A full list and descriptions of all the units are included in the GRI data for the park (chcu_geology.pdf). Bold text refers to sections in the report. 

Map Unit Properties Table: Chaco Culture National Historical Park, Page 5 of 8

Age Map Unit

(Symbol) Park Unit Geologic Description Geologic Features and Processes Geologic Resource Management Issues Geologic History

QUATERNARY

(upper Pleistocene)

Gravelly sand

(Qgs7) Chaco Canyon

Very pale brown, dark-yellowish-brown, or grayish

orange, gravelly, medium to coarse sand containing 

pebbles averaging about 2 cm (1 in) across. Pebbles 

decrease in abundance upward through a deposit. 

Size and composition of clasts varies with location 

and proximity of source. 

Deposits occur as sheets overlying pediment-like 

surfaces that cut across nonresistant bedrock and 

slope toward the Chaco River or other local major 

valleys.

The three youngest geomorphic levels of gravelly 

sand are present in the park area, and range from 

18–60 m (60–200 ft) above the local drainage.

Qgs7 covers the youngest and lowest of three 

erosion surfaces in the park.

Chaco Canyon—at least seven erosion surfaces 

and their associated gravelly sand deposits are in 

the drainage basin of the Chaco River. Each reflects 

an erosional episode related to changes in the 

grade of the Chaco River or the San Juan River.

Signifies greater stream power than today.

Abandoned Mineral Lands—Pleistocene gravel

deposit (exact unit unknown) was mined for sand 

and gravel for administrative uses until the late 

1980s.

Human Populations in Chaco Canyon—

represents an ancient stream network, which 

predates habitation of Chaco Canyon.

Chaco Canyon—marks one of seven erosion 

surfaces that represent the downcutting of the 

Chaco River (and the development of Chaco 

Canyon). 

San Juan Basin—quartzitic sandstone, quartz, and 

chert clasts are mostly from the Paleocene Ojo 

Alamo Sandstone, which crops out 12 km (7 mi) 

north of the park; ironstone and clinker (baked 

coal) are mostly from the Fruitland Formation (Kf); 

sandstone and ironstone clasts along the Chaco 

River are mostly from the Cliff House Sandstone 

(Kch) and Menefee Formation (Kmf). 

QUATERNARY

(upper Pleistocene)

Gravelly sand

(Qgs6) Chaco Canyon

See description for Qgs7. 

Qgs6 is about 24 m (80 ft) above present drainage 

level. As much as 6 m (20 ft) thick.

Chaco Canyon—at least seven erosion surfaces 

and their associated gravelly sand deposits are in 

the drainage basin of the Chaco River. Each reflects 

an erosional episode related to changes in the 

grade of the Chaco River or the San Juan River.

Signifies greater stream power than today

Abandoned Mineral Lands—Pleistocene gravel

deposit (exact unit unknown) was mined for sand 

and gravel for administrative uses until the late 

1980s.

Human Populations in Chaco Canyon—

represents an ancient stream network, which 

predates habitation of Chaco Canyon.

Chaco Canyon—marks one of seven erosion 

surfaces that represent the downcutting of the 

Chaco River (and the development of Chaco 

Canyon). 

QUATERNARY

(upper Pleistocene)

Gravelly sand

(Qgs5) Chaco Canyon

See description for Qgs7.

Qgs5 covers the oldest and highest of three erosion 

surfaces in the park.

Chaco Canyon—at least seven erosion surfaces 

and their associated gravelly sand deposits are in 

the drainage basin of the Chaco River. Each reflects 

an erosional episode related to changes in the 

grade of the Chaco River or the San Juan River.

Signifies greater stream power than today

Abandoned Mineral Lands—Pleistocene gravel

deposit (exact unit unknown) was mined for sand 

and gravel for administrative uses until the late 

1980s.

Human Populations in Chaco Canyon—

represents an ancient stream network, which 

predates habitation of Chaco Canyon.

Chaco Canyon—marks one of seven erosion 

surfaces that represent the downcutting of the 

Chaco River (and the development of Chaco 

Canyon). 

QUATERNARY

(Pleistocene)

Gravel

(Qg) Chaco Canyon

Quartzitic and lithic pebbles and cobbles. Overlies 

Cliff House Sandstone, at northern end of West 

Mesa. Thickness about 1.5 m (5 ft).

Upper Cretaceous Rocks and Fossils—composed 

largely of chunks of sandstone and fragmented 

ironstone concretions of the Menefee Formation.

Chaco Canyon—Pleistocene gravel deposited on 

uplands. Differs markedly from terrace gravels of 

the Chaco River. 

Abandoned Mineral Lands—Pleistocene gravel 

deposit (exact unit unknown) was mined for sand 

and gravel for administrative uses until the late 

1980s.

Human Populations in Chaco Canyon—

represents an ancient stream network, which 

predates habitation of Chaco Canyon.

Development of Chaco Canyon—signifies 

greater stream power than today.
Investigators mapped the following units in Chaco Culture National Historical Park. A full list and descriptions of all the units are included in the GRI data for the park (chcu_geology.pdf). Bold text refers to sections in the report. 

Map Unit Properties Table: Chaco Culture National Historical Park, Page 6 of 8 

Age Map Unit

(Symbol) Park Unit Geologic Description Geologic Features and Processes Geologic Resource Management Issues Geologic History

UPPER CRETACEOUS

Pictured Cliffs 

Sandstone

(Kpc)

Chaco Canyon

Upper part: yellowish-gray to grayish-orange, 

thick-bedded and cross-bedded, well-sorted, 

friable, fine-grained sandstone comprises the upper 

part of the formation. 

Lower part: consists of alternating thin beds of 

yellowish-gray to moderate-brown, fine-grained to 

very fine grained sandstone and light-gray to darkgray, silty shale. 

Total thickness about 18 m (60 ft).

Upper Cretaceous Rocks and Fossils—Kpc

contains fossil marine invertebrates and casts and 

impressions of burrows (the trace fossil 

Ophiomorpha major) whose outer walls have a 

knobby appearance that resembles a corn cob; 

indicative of nearshore marine environment. Upper 

part forms cliffs, and contains brown, hard, round, 

slabby, calcareous sandstone concretions that are 

parallel to bedding and as large as 1.2 m (4 ft) 

across. Lower part forms low bluffs, and contains 

thin discontinuous layer of hard fine-grained 

ironstone.

Paleontological Resource Inventory and 

Monitoring—ongoing inventory since 2005 of 

Upper Cretaceous rocks in Chaco Culture National 

Historical Park indicates very high potential for new 

and scientifically significant material in Kpc. 

Western Interior Seaway—Kpc represents final 

retreat of the seaway from the San Juan Basin. 

Coastal delta front, beach, and stream channel 

settings.

UPPER CRETACEOUS

Lewis Shale

(Kl)

Chaco Canyon

Pueblo Pintado

Upper part: calcareous sandy shale that contains 

decreasing abundance downward of light-brown 

sandstone beds 0.3-1.5 m (1-5 ft) thick, and is 

transitional upward with the Pictured Cliffs 

Sandstone (Kpc).

Middle part: light-gray to dark-olive or olive-gray 

claystone and siltstone that contains a few thin 

sandstone zones and scattered beds of sandy 

concretionary limestone. 

Upper Cretaceous Rocks and Fossils—calcareous 

concretions in the formation contain marine 

invertebrate fossils equivalent in age to middle 

Pierre Shale (Upper Cretaceous, Campanian) of 

eastern Colorado. Bentonite beds in Lewis Shale 

originated as volcanic ash.

Paleontological Resource Inventory and 

Monitoring—ongoing inventory of Upper 

Cretaceous rocks in Chaco Culture National 

Historical Park indicates very high potential for new 

and scientifically significant material in Kl. 

Western Interior Seaway—represents marine 

deposition between a major transgressive–

regressive cycle. Offshore marine setting.

Lower part: sandy and transitional into underlying 

Cliff House Sandstone (Kch). 

Total thickness about 30 m (100 ft).

Cliff House Sandstone

UPPER CRETACEOUS

(Kch) 

Upper sandstone/bed

(Kchu) 

White to light-gray 

sandstone, upper unit

(Kchwu) 

White to light-gray 

sandstone, lower unit

(Kchwl) 

Middle sandstone

(Kchm) 

Chaco Canyon

Pueblo Pintado

White to dark -yellowish-orange, thin- to thickbedded, fine- to coarse-grained, lenticular and 

cross-bedded or massive sandstone. Contains gray 

or brown carbonaceous shale lenses. Intertongues 

with both Lewis Shale and Menefee Formation. 

Some tongues of Menefee Formation are mapped 

with the Cliff House; other tongues are mapped 

separately. Cliff House Sandstone is as much as 430 

ft (131 m) thick.

Upper Cretaceous Rocks and Fossils—forms 

high bold cliffs and ridges. Kchl dominates the view 

in the Chaco Canyon. Contains Ophiomorpha 

major, which is a trace fossil (burrows) indicative of 

a nearshore marine environment and activity of 

marine fossil invertebrates, and highly fossiliferous 

beds containing clams. 

Quaternary Fossils—may contain pack rat 

(Neotoma spp.) middens in cave shelters.

Cave Shelters—cave shelters form along the shalesandstone contact between the Cliff House 

Coal Resources and Mining—contains coal beds, 

particularly in Kchl. 

Rockfall—stratigraphic arrangement of overlying 

Cliff House Sandstone and underlying Menefee 

Formation creates rockfall hazards.

Paleontological Resources Inventory and 

Monitoring—one of the two most fossiliferous 

units in Chaco Culture National Historical Park; the 

other is Kmf. Preliminary results of an ongoing 

inventory indicate that the potential for new and 

scientifically significant material is very high.

Planning and research strategy in progress.

Western Interior Seaway—represents a marine 

transgression. Nearshore marine environment such 

as barrier islands.

Intermediate unit

(Kchi) 

Sandstone and Menefee Formation. Efflorescence—building stone in Chacoan 

structures prone to salt weathering, which may 

accelerate deterioration of stone and mortar.

Lower sandstone

(Kchl)
Investigators mapped the following units in Chaco Culture National Historical Park. A full list and descriptions of all the units are included in the GRI data for the park (chcu_geology.pdf). Bold text refers to sections in the report. 

Map Unit Properties Table: Chaco Culture National Historical Park, Page 7 of 8

Age Map Unit

(Symbol) Park Unit Geologic Description Geologic Features and Processes Geologic Resource Management Issues Geologic History

UPPER CRETACEOUS

Menefee Formation

(Kmf) Chaco Canyon

Heterogeneous sequence of thick, lenticular beds of 

grayish-yellow to brown, fine- to medium-grained, 

cross-bedded sandstone and interbeds of duskyyellow to olive-gray, sandy shale and mudstone, 

moderate-brown, sandy limestone; and lenticular 

beds of carbonaceous shale and shaly coal; also, 

claystone, siltstone, and black carbonaceous shale. 

Exposed thickness is about 165 m (540 ft).

Upper Cretaceous Rocks and Fossils—forms 

slopes that underlie the steep canyon walls in 

Chaco Culture National Historical Park. Widely 

exposed in southern San Juan Basin. Base of the 

formation crops out 30 km (19 mi) south of the 

park. Very fossiliferous, including petrified wood, 

casts of palm leaves and bark impressions, termite 

burrows, fragmentary dinosaur bones, turtle 

specimens, and crocodilian remains.

Badlands—badlands topography common on 

exposures of Menefee Formation, especially Kmfaj

(see below).

Cave Shelters—cave shelters form along the shalesandstone contact between the Cliff House 

Sandstone and Menefee Formation.

Coal Resources and Mining—coal beds occur 

sporadically in the upper 75 m (250 ft). The coal 

beds are commonly burned at the outcrop; red 

outcrops across from Casa Chiquita are result of 

burned coal.

Rockfall—stratigraphic arrangement of overlying 

Cliff House Sandstone and underlying Menefee 

Formation creates rockfall hazards.

Paleontological Resources Inventory and 

Monitoring—one of the two most fossiliferous 

units in Chaco Culture National Historical Park; the 

other is Cliff House Sandstone. Preliminary results 

of an ongoing inventory indicate a very high

potential for new and scientifically significant 

material, especially in Kmf. Planning and research 

strategy in progress.

Western Interior Seaway—deposited between a 

major marine regression (retreat) and transgression

(advance). Lowland swamp, estuary, and beach 

settings.

UPPER CRETACEOUS

Tongues of Menefee 

Formation

(Kmft)

Chaco Canyon

Gray and brown, lenticular sandstone interbedded 

with black, carbonaceous shale, gray claystone and 

siltstone. As much as 24 m (80 ft) thick.

Scott et al. (1984) showed Kmft as underlying 

Kchu and intertonguing with Kch. Mytton and 

Schneider (1987) showed Kmf as underlying Kchu

and intertonguing with Kchl, Kchi, Kchwl, Kchm, 

and Kchwu.

Upper Cretaceous Rocks and Fossils—Kmft

represents two or more separate tongues extending 

and thinning into the Cliff House Sandstone 

northward from main body of Menefee Formation 

(Kmf). Stratigraphic connection, however, has since 

been removed by erosion in the area. No mention 

of fossils in source map data.

Coal Resources and Mining—contains some thin 

beds of highly weathered coal.

Western Interior Seaway—represents shoreward 

lagoons southwest of Cliff House Sandstone barrier 

islands.

UPPER CRETACEOUS

Menefee Formation

Allison Member

(Kmfa)

Kin Bineola

Interbedded sequence of yellowish gray and dusky

yellow to grayish olive shale and minor siltstone; 

very pale orange to pale yellowish brown, very finegrained to medium-grained, well to poorly sorted, 

lenticular, cross-bedded, calcareous sandstone; and 

minor carbonaceous shale. As much as 609 m 

(1,998 ft) thick.

Upper Cretaceous Rocks and Fossils—forms 

slopes that underlie the steep canyon walls in 

Chaco Culture National Historical Park. Menefee 

Formation is very fossiliferous, including petrified 

wood, casts of palm leaves and bark impressions, 

termite burrows, fragmentary dinosaur bones, 

turtle specimens, and crocodilian remains.

Coal Resources and Mining—contains a few 

lenticular subbituminous coal beds less than 35 cm

(14 in) thick. 

Paleontological Resources Inventory and 

Monitoring—one of the two most fossiliferous 

units in Chaco Culture National Historical Park; the 

other is Cliff House Sandstone. Preliminary results 

of an ongoing inventory indicate a very high

potential for new and scientifically significant 

material, especially in the Menefee Formation.

Planning and research strategy in progress.

Western Interior Seaway—deposited between a 

major marine regression (retreat) and transgression 

(advance). Continental setting.

UPPER CRETACEOUS

Menefee Formation

Allison Member, Juans 

Lake Beds of Miller 

(1984)

(Kmfaj)

Kin Bineola

Fine-grained, light-gray to white, thin- to thickbedded sandstone and dark-gray mudstone that 

weathers light gray. Bands of dusky-brown organicrich mudstone (humate) several feet thick are in 

upper part of beds. Carbonaceous shale units are 

common. Base of Kmfaj is defined as the lowest 

occurrence of calcareous concretions. About 750 ft 

(230 m) thick.

Upper Cretaceous Rocks and Fossils—

characterized by numerous large calcareous 

concretions that are present at base or top of some 

sandstone units, but are less common downward. 

The presence of calcareous concretions 

distinguishes this unit from lower part of Allison 

Member (Kmfal). Kmfaj also contain small 

ironstone (siderite) concretions scattered along 

individual horizons or coalescing into thin beds.

Fossiliferous, especially in badlands terrain.

Badlands—primary unit that forms badlands 

topography in Chaco Culture National Historical 

Park.

Coal Resources and Mining—very local thin coal 

lenses occur in uppermost part of beds.

Paleontological Resources Inventory and 

Monitoring—one of the two most fossiliferous 

units in Chaco Culture National Historical Park; the 

other is Cliff House Sandstone. Preliminary results 

of an ongoing inventory indicate a very high 

potential for new and scientifically significant 

material, especially in the Menefee Formation.

Planning and research strategy in progress.

Western Interior Seaway—deposited between a

major marine regression (retreat) and transgression 

(advance).Continental setting.

Later, concretions developed underground as 

groundwater flowed through sedimentary strata.
Investigators mapped the following units in Chaco Culture National Historical Park. A full list and descriptions of all the units are included in the GRI data for the park (chcu_geology.pdf). Bold text refers to sections in the report. 

Map Unit Properties Table: Chaco Culture National Historical Park, Page 8 of 8 

Age Map Unit

(Symbol) Park Unit Geologic Description Geologic Features and Processes Geologic Resource Management Issues Geologic History

UPPER 

CRETACEOUS

Menefee Formation

Lower part of Allison 

Member

(Kmfal)

Kin Bineola

Fine-grained sandstone, gray mudstone, and minor 

amounts of siltstone; no calcareous concretions and 

few ironstone (siderite) concretions. About 735 ft 

(225 m) thick, of which only the uppermost 35 ft 

(11 m) is exposed in the La Vida Mission 

quadrangle.

Upper Cretaceous Rocks and Fossils—no 

calcareous concretions and few siderite concretions. 

Menefee Formation is very fossiliferous, including 

petrified wood, casts of palm leaves and bark 

impressions, termite burrows, fragmentary dinosaur 

bones, turtle specimens, and crocodilian remains.

Paleontological Resources Inventory and 

Monitoring—one of the two most fossiliferous 

units in Chaco Culture National Historical Park; the 

other is Cliff House Sandstone. Preliminary results 

of an ongoing inventory indicate a very high

potential for new and scientifically significant 

material, especially in the Menefee Formation. 

Planning and research strategy in progress.

Western Interior Seaway—deposited between a 

major marine regression (retreat) and transgression 

(advance). Continental setting. 

UPPER CRETACEOUS

Crevasse Canyon 

Formation 

Gibson Coal Member

(Kcg)

Kin Ya’a

Lithology highly variable and laterally discontinuous. 

Includes very light to dark-gray carbonaceous shale, 

siltstone, and claystone; and yellowish-gray and 

grayish-yellow to white, poorly to well-sorted 

sandstone. Thickness ranges from 104 m (341 ft) to 

37 m (121 ft).

Upper Cretaceous Rocks and Fossils—most of 

the sandstone beds appear to represent estuarine, 

fluvial-channel, distributary-channel, or splay 

deposits. Contacts generally sharp, but locally 

intertongue with, or grade laterally into, tidalchannel and marine-beach and bar deposits of the 

overlying Hosta Tongue (Kplh; see GRI GIS data) 

and underlying Dalton Sandstone Member of the 

Crevasse Canyon Formation (Kcda). Contain 

carbonaceous plant debris, petrified logs; some 

beds are bioturbated.

Coal Resources and Mining—contains 12 or 

more lenticular and discontinuous, subbituminous 

coal beds, 15–36 cm (6–14 in) thick.

Paleontological Resource Inventory and 

Monitoring—ongoing inventory of Upper 

Cretaceous rocks in Chaco Culture National 

Historical Park indicate a very high potential for 

new and scientifically significant material.

Western Interior Seaway—represents marine 

regression/retreat. Lagoon, estuary, and beach 

settings.

UPPER CRETACEOUS

Crevasse Canyon 

Formation 

Dalton Sandstone 

Member 

(Kcda)

Kin Ya’a Generally very light gray to yellowish gray and very 

pale orange sandstone. 25–55 m (82–180 ft) thick.

Upper Cretaceous Rocks and Fossils—forms 

prominent cliffs consisting of 1–3 massive units, 

each 2–22 m (7–72 ft) or more thick. Contains 

abundant carbonized plant debris and detritus, fish 

teeth, and broken shell fragments; some beds are 

bioturbated or burrowed, and contain the trace 

fossils Ophiomorpha, Thalassinoides, and Skolithos. 

Paleontological Resource Inventory and 

Monitoring—ongoing inventory of Upper 

Cretaceous rocks in Chaco Culture National 

Historical Park indicates a very high potential for 

new and scientifically significant material.

Western Interior Seaway—represents marine 

regression/retreat. Lagoon, tidal, estuarine, 

foreshore, upper shoreface, and lower shoreface 

settings.