Santa Monica Mountains National Recreation Area

Geologic Resources Inventory Report

Natural Resource Report NPS/NRSS/GRD/NRR—2016/1297

National Park Service

U.S. Department of the Interior

Natural Resource Stewardship and Science
ON THE COVER: Photograph of Boney Mountain (and the Milky Way). The Santa Monica Mountains are part 

of the Transverse Ranges. The backbone of the range skirts the northern edges of the Los Angeles Basin and 

Santa Monica Bay before descending into the Pacific Ocean at Point Mugu. The ridgeline of Boney Mountain is 

composed on Conejo Volcanics, which erupted as part of a shield volcano about 15 million years ago. National 

Park Service photograph available at http://www.nps.gov/samo/learn/photosmultimedia/index.htm.

THIS PAGE: Photograph of Point Dume. Santa Monica Mountains National Recreation Area comprises a vast 

and varied California landscape in and around the greater Los Angeles metropolitan area and includes 64 km 

(40 mi) of ocean shoreline. The mild climate allows visitors to enjoy the park’s scenic, natural, and cultural 

resources year-round. National Park Service photograph available at https://www.flickr.com/photos/

santamonicamtns/albums.
Santa Monica Mountains National Recreation Area

Geologic Resources Inventory Report

Natural Resource Report NPS/NRSS/GRD/NRR—2016/1297

Katie KellerLynn

Colorado State University Research Associate

National Park Service Geologic Resources Division

Geologic Resources Inventory

PO Box 25287

Denver, CO 80225

September 2016

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. 2016. Santa Monica Mountains National Recreation Area: Geologic Resources Inventory report. 

Natural Resource Report NPS/NRSS/GRD/NRR—2016/1297. National Park Service, Fort Collins, Colorado.

NPS 638/134114, September 2016
iii

Contents

Page

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

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

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

Products and Acknowledgments . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xvi

GRI Products . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xvi

Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xvi

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

Geologic Features and Processes . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Plate Boundaries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Faults . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

Folds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

Unconformities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

Rock Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

Formations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

Type Sections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

Paleontological Resources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

Landslides . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

Fluvial Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

Cave and Karst Resources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

Eolian Features and Processes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

Marine and Coastal Resources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

Geologic Resource Management Issues . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35

Landslide Hazards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35

Paleontological Resource Inventory, Monitoring, and Protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

Climate Change Planning and Sea Level Rise . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

Earthquakes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41

Cave and Karst Resource Management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44

Flooding and Dam Failure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45

Abandoned Mineral Lands and Other Disturbed Lands . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45

Geologic History . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47

Subduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47

Transition from Subduction to Transform Plate Motion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49

Transtension . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49

Transpression . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52

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

Geologic Maps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55

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

GRI Poster . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56

Use Constraints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56

Literature Cited . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57

Additional References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63

California Geological Survey Regulatory Maps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63

Earthquake Hazard Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63

ShakeMaps/Earthquake Planning Scenarios . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63

Tsunami Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63

Landslide Resources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63

Climate Change Resources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64
iv

Contents (continued)

Page

Geological Surveys and Societies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64

Geology of National Park Service Areas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64

NPS Resource Management Guidance and Documents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64

US Geological Survey Reference Tools . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64

Appendix A: Scoping Participants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65

2008 Scoping Meeting Participants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65

2015 Conference Call Participants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65

Appendix B: Geologic Resource Laws, Regulations, and Policies . . . . . . . . . . . . . . . . . . . . . . . . . 67

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

Figure 1. Map of Santa Monica Mountains National Recreation Area (in pocket)

Figure 2. Photograph of Los Angeles skyline . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Figure 3. World map of Mediterranean ecosystems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Figure 4. Graphic of subduction zone . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Figure 5. Graphic of a transgression and a regression . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Figure 6. Graphic of the North American plate boundary over time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

Figure 7. Graphic showing rotation of the Western Transverse Ranges block . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

Figure 8. Aerial image of the San Andreas Fault . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

Figure 9. Graphic of fault types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

Figure 10. Screen capture of fault activity map of California . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

Figure 11. Photograph of folds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

Figure 12. Photograph of the Topanga Anticline . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

Figure 13. Geologic time scale . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

Figure 14. Graphic of unconformities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

Figure 15. Photograph of Saddle Peak . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

Figure 16. Photographs of the Topanga Canyon and Sespe Formations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

Figure 17. Photograph of the Sespe Formation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

Figure 18. Photograph Red Rock Canyon Park . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

Figure 19. Photographs of the Vaqueros Formation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

Figure 20. Photographs of granitic rocks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

Figure 21. Photographs of submarine features in the Conejo Volcanics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

Figure 22. Photograph of volcanic bomb in the Conejo Volcanics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

Figure 23. Photograph of oil seeps in the Conejo Volcanics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

Figure 24. Photograph of Sandstone Peak . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

Figure 25. Photographs of the Santa Monica Slate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

Figure 26. Photographs of fossils from the Topanga Canyon Formation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

Figure 27. Photograph of fossil fish in the Modelo Formation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

Figure 28. Photograph of the Vaqueros Formation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

Figure 29. Graphic showing slope movements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

Figure 30. Photograph of the Great Dune . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

Figure 31. Photographs of coastline in Santa Monica Mountains National Recreation Area . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

Figure 32. Portion of GRI GIS data showing landslides . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36

Figure 33. Screen capture of map service showing fire perimeter and landslide susceptibility . . . . . . . . . . . . . . . . . . . . . . . . . . 37

Figure 34. Photograph of the Adamson House . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40

Figure 35. Photograph of the Pacific Palisades . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43

Figure 36. Photograph of the Trabuco Formation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48

Figure 37. Photograph of the Tuna Canyon Formation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48

Figure 38. Photograph of the angular unconformity between the Llajas and Santa Susana formations. . . . . . . . . . . . . . . . . . . . . . 49

Figure 39. Photograph of the Conejo Volcanics on the landscape . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50

Figure 40. Correlation diagram of rocks south of the Malibu Coast Fault . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52

Figure 41. Photographs of San Onofre Breccia . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53

Page
vi

Tables

Page

Table 1. Geologic summary of rock units in Santa Monica Mountains National Recreation Area . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Table 1a. Rock units north of the Malibu Coast Fault. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Table 1a. Rock units north of the Malibu Coast Fault, continued. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Table 1a. Rock units north of the Malibu Coast Fault, continued. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

Table 1b. Rock units south of the Malibu Coast Fault. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Table 2. Clastic sedimentary rock classification and characteristics. . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

Table 3. Volcanic rock classification and characteristics. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

Table 4. Type sections at Santa Monica Mountains National Recreation Area. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

Table 5. GRI GIS data layers for samo_geology.mxd. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56

Table 6. GRI GIS data layers for samo_geohazards.mxd. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56
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 Santa Monica Mountains National Recreation Area (California) in 2008 

and a follow-up conference call in 2015, which were held by the NPS 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 the GRI GIS data.

Literally and figuratively, Santa Monica Mountains 

National Recreation Area (referred to as the “park” 

throughout this report) rises out of the heart of Los 

Angeles. The park is at once an integral part of the city 

and a world apart. More than 18 million people live 

within an hour’s drive of the park, which offers access 

to surprisingly wild places (National Park Service 

2015a).

This GRI report was written for resource managers at 

the park to support science-informed decision making. 

It may also be useful for interpretation. This report 

addresses a fundamental resource and value—scienceinformed stewardship/learning laboratory—in which 

science guides park management, informs policy, and 

lays the groundwork for educating visitors and fostering 

stewardship (National Park Service 2015a). Sections 

of the report discuss distinctive geologic features and 

processes, highlight geologic issues facing resource 

managers, describe the geologic history leading to 

the present-day landscape, and provide information 

about the GRI GIS data that accompany this report. 

This report was prepared using available geologic 

information. No new fieldwork was conducted in 

association with its preparation. 

Mapping by the California Geological Survey (Wills 

et al. 2012; Campbell et al. 2014) served as the sources 

for the GRI GIS data that accompany this report. A 

poster (in pocket) illustrates these data. The GRI GIS 

data cover the area of the park and much of the densely 

populated urban and suburban areas of the southern 

California megalopolis. The GRI GIS data also contain 

mapping from a landslide inventory by Irvine and 

McCrink (2012).

Geologic features and processes that are significant 

for the park include the following. Landscape-scale 

features and processes are discussed before smaller 

scale features and processes.

● Plate Boundaries. The park’s geologic features are 

the result of a complex history of plate-boundary 

evolution. The park is located at a modern 

transform plate boundary where the Pacific plate 

(large, rigid slab of oceanic crust) and North 

American plate (large, rigid slab of continental 

crust) are sliding horizontally past each other. The 

transform plate boundary is associated with the 

San Andreas Fault system. In the past, the margin 

of the continent was associated with a different 

type of plate boundary—a convergent plate 

boundary—where the oceanic Farallon plate was 

subducting beneath (diving under) the continental 

North American plate. During the transition from 

subduction to transform plate motion, a block 

of continental crust, referred to as the Western 

Transverse Ranges block, was caught in a zone of 

deformation at the plate boundary and rotated 

clockwise. In contrast to the generally north–

south orientation of most of the other mountains 

in California, the east–west orientation of the 

Transverse Ranges, of which the Santa Monica 

Mountains are a part, illustrates this incredible 

episode of rotation in the evolution of the plate 

boundary.

● Faults. As recorded in the GRI GIS data, an 

estimated 1,040,089 m (3,412,365 ft or 646 mi) of 

fault segments cut through the park. The primary 

active faults in the Santa Monica Mountains area 

are the Malibu Coast Fault, which run both onshore 

and offshore, and the Anacapa-Dume Fault, which 

is offshore.

● Folds. Folded structures characterize the east–westoriented Santa Monica Mountains. Compression, 

probably related to subduction of the Farallon 

plate below the North American plate, created a 

generally north–south-trending anticline (“A”-

shaped fold) that is revealed in the uplifted Santa 

Monica Slate (the oldest rock in the park). Since 
viii

about 4 million years ago, when the San Andreas 

Fault system made its appearance on the landscape, 

many secondary northwest–southeast-trending 

anticlines and synclines (“U”-shaped folds) have 

been superimposed on the preexisting anticline.

● Unconformities. The rock record at the park 

represents approximately 156 million years of 

geologic time. During this time span, preexisting 

rocks were uplifted and deformed, resulting in 

the interruption of conformable (continuous) 

deposition and the creation of seven notable 

unconformities in the park’s rock record.

● Rock Types. The park has all three major types of 

rocks. Most are sedimentary, though igneous (both 

extrusive and intrusive) and metamorphic rocks 

also occur.

● Formations. A “formation” is a distinctive layer 

or sequence of strata deposited in a comparatively 

short span of geologic time and identified by a 

proper name. Formations are the basic unit used in 

geologic mapping. The park contains 17 formally 

designated formations that were deposited from 

the Late Jurassic Period to the Miocene Epoch. 

Fourteen of these formations are sedimentary, two 

are igneous, and one is metamorphic.

● Type Sections. Type sections (reference localities) 

for eight formations occur within the authorized 

boundary of the park. Containing this many type 

sections is uncommon and notable for any single 

park. The number of type localities within the park 

is probably due to its complex tectonic history 

and position on an active plate boundary, which 

ensured that a wide variety of rock units were 

brought together and exposed. 

● Paleontological Resources. The park contains 

one of the most extensive and diverse fossil 

records in the National Park System, yielding fossil 

vertebrates, invertebrates, plants, microfossils, 

and trace fossils from more than 2,300 known 

fossil localities. The most abundant fossils are 

invertebrates such as bivalves, cephalopods, and 

gastropods; the least abundant are plants. Fossil fish 

make up the majority of vertebrate material.

● Landslides. The park is located near the southern 

boundary of the Transverse Ranges, which 

compose a tectonically active area where uplift 

and extensive folding and faulting have produced 

many steep slopes consisting of deformed and 

weakened rocks. These conditions have resulted 

in the widespread occurrence of landslides; 2,503 

landslides of various types were mapped by Irvine 

and McCrink (2012) within the park. 

● Fluvial Features. Alluvium marks active, 

intermittent, and past streams. Malibu, Solstice, 

and Topanga creeks are perennial streams that flow 

in the park. Other streams have segments that are 

perennial.

● Cave and Karst Resources. Erosion has created 

small sandstone caves in the Chatsworth (Kc), 

Sespe (Ts and Tsp), and Topanga Canyon (“Ttc” 

map units) formations in the park. Continuous 

wave activity has created sea caves in rocky areas 

along the ocean front in the park. The “Bat Cave” 

of Batman and Robin fame, occurs in the park; it 

is not a natural cave but is significant for the park’s 

film-making history. The Grotto, which appears to 

be a talus-style cave in the Conejo Volcanics (“Tco” 

map units), is a popular hiking destination at Circle 

X Ranch. The limestone—Santa Susana Formation 

(Tss and Tssl)—within the park does not exhibit 

characteristic karst features such as sinkholes, but 

karst processes still occur, such as those related to 

groundwater discharge and recharge.

● Eolian Features and Processes. Eolian deposits 

composed of loose, fine- to medium-grained sand, 

silty sand, and silt, form transitory dunes against 

beach-facing cliffs in the park. The “Great Dune,” 

south of Point Mugu on the Pacific Coast Highway, 

is the park’s most noteworthy eolian feature.

● Marine and Coastal Resources. The park’s 

boundary stops at mean high water, so the National 

Park Service does not have any management 

obligations for marine resources. Deep, submarine 

canyons, such as Mugu and Hueneme, off the Santa 

Monica Mountains coastline are of interpretive 

interest, however. In addition, shipwrecks and kelp 

forests are notable submerged resources off the 

coast. The Santa Monica Mountains are known 

for sand and cobble beaches. Beach deposits are 

more-or-less continuous along the 64 km (40 mi) of 

coastline in the park. The authorized boundary also 

contains rocky intertidal areas with tide pools and 

coastal lagoons (e.g., Malibu, Topanga, and Zuma). 

Two prominent marine terraces—Malibu and Point 

Dume—occur in the Santa Monica Mountains area. 

The park contains young marine terrace deposits, 

but their relationship to the area’s prominent 

marine terraces is unknown.
ix

Geologic resource management issues identified during 

the GRI scoping meeting and follow-up conference call 

include the following. They are discussed in order of 

management priority. Park managers are encouraged 

to contact the NPS Geologic Resources Division for 

technical and/or policy assistance with these issues.

● Landslide Hazards. Landslides pose a significant 

threat to park infrastructure and human safety. 

The GRI GIS data show 3,580 landslide deposits 

(“hazard point/area features”) that are part of a 

landslide inventory conducted by the California 

Geological Survey. This inventory, which is 

ongoing, revealed the extent of past movement and 

the probable locus of future activity. Many sources 

of park-specific landslide information are available 

for use by park managers.

● Paleontological Resource Inventory, Monitoring, 

and Protection. At least 2,300 known fossil 

localities occur in the park. A data and/or GIS 

need is to inventory these locations. Development 

of a resource stewardship strategy is also needed. 

As with all National Park Service areas, fossil 

collecting is prohibited in the park. However, this 

regulation may not be common knowledge, and 

with increasing recreational use comes an increased 

potential for illegal fossil collecting within the 

park. Researchers need to acquire permits for 

paleontological investigation and collection within 

the park. Illegal fossil collecting, natural erosion, 

and graffiti threaten the park’s paleontological 

resources. 

● Climate Change Planning and Sea Level 

Rise. Climate change, in conjunction with other 

stressors, will probably affect all aspects of park 

management from natural and cultural resources 

to park operations and visitor experience. Climate 

change will manifest itself not only as shifts in 

mean conditions (e.g., increasing mean annual 

temperature) but also as changes in climate 

variability (e.g., more intense storms and droughts). 

Sea level rise is a primary concern with respect to 

climate change. However, none of the 270 NPS 

“assets” (e.g., buildings, roads, trails, managed 

landscapes, or historic structures) in the park 

are actually situated on the coast, so they all have 

“limited exposure” to 1 meter of sea level rise. 

The National Park Service has developed a variety 

of databases and guidance for managing coastal 

resources and planning for the impacts of climate 

change.

● Earthquakes. Earthquakes can directly damage 

park infrastructure or trigger other hazards such as 

slope movements that may impact park resources, 

infrastructure, or visitor safety. A range of possible 

earthquake magnitudes has been estimated 

for the park. A magnitude 5.3 earthquake has a 

0.8 to 0.9 probability (80%–90% “chance”) of 

occurring within 50 km (30 mi) of the park in the 

next 50 years. A magnitude 6.7 earthquake has 

a 0.40–0.50 probability (40%–50% “chance”) of 

occurring within 50 km (30 mi) of the park in the 

next 50 years. The primary hazard associated with 

earthquakes in the Santa Monica Mountains area 

is shaking produced by the sudden rupture of a 

fault; liquefaction, landslides, tsunami, and seiche 

are secondary hazards. The California Geological 

Survey and other agencies provide information for 

understanding earthquakes and preparing for them.

● Cave and Karst Resource Management. The 

significance of known cave and karst resources 

at the park is low, though the park does contain 

sandstone caves (inland) and sea caves (in rocky 

shoreline areas) that are in need of a comprehensive 

inventory.

● Flooding and Dam Failure. During the winter 

rainy season, streams overflow, flooding park 

infrastructure. During such events, parking lots 

have washed out. Floodwaters also threaten cultural 

resources at Peter Strauss Ranch. Most of the ponds 

in the park are stock ponds used for past ranching. 

Most natural ponds in the park have been dammed 

to increase their areas, resulting in the potential for 

dam failure and damage to downstream cultural 

resources. The estimated 10 largest reservoirs 

within the park do not belong to the National Park 

Service. The primary concern with these reservoirs 

is dam failure and damage to homes, infrastructure, 

and resources below.

● Abandoned Mineral Lands and Other Disturbed 

Lands. Compared to other mountain ranges in 

the area, very little historic prospecting took place 

in the Santa Monica Mountains. Nevertheless, 

mineral exploration resulted in a few World War 

II–vintage quarries in Santa Ynez Canyon (outside 

the park). Also, oil and gas exploration produced 

some dry holes on Point Dume. At present, the 

servicewide abandoned mineral lands (AML) 

database documents no AML sites or features from 

within the park. Future acquisition of lands by the 

National Park Service could result in potential 
x

disturbances on NPS lands; for instance, lands 

in the Santa Susana Mountains, which are under 

consideration for inclusion, have a legacy of oil and 

gas production. Other non–AML disturbed lands 

in the park include Malibu Creek and the stream 

running through Solstice Canyon, which have been 

dammed; excessive sedimentation is an associated 

management issue with these creeks.
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 section 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 the participants of the 2008 

scoping meeting and 2015 conference call (see 

Appendix A) for their assistance in this inventory. 

In particular, thanks very much to Eugene Fritsche

(California State University, Northridge, Department 

of Geological Sciences, professor emeritus) for 

his PowerPoint presentation and the handouts he 

provided at the GRI scoping meeting. This information 

guided writing of the “Geologic History” and other 

sections of this report. Thanks to Stephanie Kyriazis

(Santa Monica Mountains National Recreation Area, 

interpreter) for suggesting many references used in 

writing this report. Thanks to Jim Chappell (Colorado 

State University, geologist/GIS specialist) for his help 

in estimating the lengths of faults and folds in the 

GRI GIS data. Thanks to Trista Thornberry-Ehrlich

(Colorado State University, research associate) for her 

assistance in creating many of the graphics used in this 

report. Thanks to Susan Jordan, Kenneth Adelman, 

and Gabrielle Adelman (California Coastal Records 

Project) for permission to use their photographs. 

Finally, thanks very much to Pam Irvine (California 

Geological Survey, senior engineering geologist) for 

reviewing this report. Her guidance on the park’s 

geologic history was particularly helpful, and her input 

and perseverance are much appreciated.

Review

Pam Irvine (California Geological Survey)

Denise Kamradt (Santa Monica Mountains National 

Recreation Area)

Jason Kenworthy (NPS Geologic Resources Division)

Dale Pate (NPS Geologic Resources Division)

Vincent Santucci (NPS Geologic Resources Division)

Justin Tweet (NPS Geologic Resources Division)

Chris Wills (California Geological Survey)

Editing

Rebecca Port (NPS Geologic Resources Division)

Report Formatting and Distribution

Jason Kenworthy (NPS Geologic Resources Division)

Rebecca Port (NPS Geologic Resources Division)
xii

Source Maps

California Geological Survey

US Geological Survey

GRI Digital Geologic Data Production

James Winter (Colorado State University)

Stephanie O’Meara (Colorado State University)

Andrea Croskrey (NPS Geologic Resources Division)

GRI Poster Design

Chase Winters (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 section describes the regional geologic setting of Santa Monica Mountains National Recreation 

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

Adjacent to Los Angeles—the second largest urban 

area in the United States—Santa Monica Mountains 

National Recreation Area, referred to as the “park” 

throughout this report (fig. 1, in pocket), boasts five 

area codes and 26 zip codes, including the notable 

90210 of Beverly Hills (National Park Service 2015b). 

Extending from Point Mugu to downtown Los Angeles, 

the rugged landscape and geologic features of the Santa 

Monica Mountains serve as an urban refuge and offer 

a variety of exceptional vistas: expansive ocean, rugged 

mountains, urban skyline (fig. 2), rocky outcrops, 

and secluded canyons. Shaped by geologic forces, the 

coastal and mountain scenery provides the setting for 

visitors and residents to enjoy outdoor recreation. This 

setting and the enjoyment it provides is a fundamental 

resource and value of the park (National Park Service 

2015a). 

Born from converging, rotating, and sliding crustal 

plates, the Santa Monica Mountains are home to rare 

and beautiful natural features. These mountains, which 

are approximately 74 km (46 mi) long and 13 km (8 

mi) wide, are part of the Transverse Ranges that stretch 

from the Mojave Desert in southeastern and central 

California and adjoining states into the Pacific Ocean. 

The Channel Islands top the submerged portion of 

the Transverse Ranges. On land, the ranges include 

the Santa Monica, Santa Ynez, San Gabriel, and San 

Bernardino mountains. With respect to the National 

Park System, part of Joshua Tree National Park lies on 

the eastern end of the range, Santa Monica Mountains 

National Recreation Area is part of the range, and 

Channel Islands National Park marks the western extent 

of the range (Lillie 2005). 

Figure 2. Photograph of Los Angeles skyline. The Santa Monica Mountains offer easy access to surprisingly wild places, 

while providing cityscape views from chaparral-covered hills. Photograph from Ray Sauvajot (Santa Monica Mountains 

National Recreation Area, supervisory ecologist, GRI scoping meeting presentation, 7 May 2008).
2

In contrast to most other mountain ranges in California, 

which run roughly north to south, the Transverse 

Ranges are oriented east–west. They were originally 

oriented north–south but rotated approximately 90° 

clockwise as a result of complex interactions at a plate 

boundary. The evolution of this plate boundary includes 

the subduction and breakup of the former Farallon 

plate, fragmentation of the rim of the continent, and the 

development of the San Andreas Fault system, which 

marks the present-day transform plate boundary.

The park protects one of the world’s largest and 

most significant examples of a Mediterranean-type 

ecosystem. Fully functioning native habitats with 

high biodiversity associated with the Mediterranean 

ecosystem is another of the park’s fundamental 

resources and values (National Park Service 2015a). A 

Mediterranean ecosystem is characterized by evergreen 

or drought deciduous shrublands such as “chaparral” 

in California. The old world Mediterranean maquis, 

the Chilean matorral, South African fynbos, and the 

Australian mallee scrub communities characterize 

the Mediterranean ecosystem elsewhere in only five 

relatively small areas around the planet. These areas are 

distributed between roughly 30° and 40° latitude, north 

and south, and are located along the western edges of 

continents (fig. 3). In these locales, the climate—which 

is characterized by mild, rainy winters and warm, 

dry summers—is moderated by cold ocean currents 

(National Park Service 2015c).

The world’s Mediterranean climate has been highly 

favored by humans, and these regions, which cover 

only about 2% of Earth’s total land area, have been 

densely populated and impacted. Urbanization 

along the southern California coastline has resulted 

in the loss of significant natural areas and increasing 

human impacts to natural systems. Nevertheless, the 

Mediterranean-type ecosystem of southern California 

has been identified as one of the world’s “hot spots” for 

biodiversity (National Park Service 2015c). 

Akin to its ecology and geology, the management of the 

park is very complex and fragmented (Ray Sauvajot, 

Santa Monica Mountains National Recreation Area, 

supervisory ecologist, scoping meeting communication, 

7 May 2008). The park consists of a web of protected 

places. Twenty different landowner types, including the 

entire City of Malibu, and more than 70 stakeholder 

groups share responsibilities and jurisdiction within 

the park’s authorized boundary. A total of 62,020 ha 

(153,250 ac) are divided among private landowners, 

local parks, California State Parks, and the National 

Park Service. The National Park Service is steward of 

9,510 noncontiguous hectares (23,500 ac) (National 

Park Service 2015a).

When Congress established Santa Monica Mountains 

National Recreation Area on 10 November 1978, it 

became the 295th unit of the National Park System. 

In the National Parks and Recreation Act of 1978, 

which authorized the park, Congress noted “significant 

scenic, recreational, educational, scientific, natural, 

archeological, and public health benefits provide[d] by 

the Santa Monica Mountains and adjacent coastline 

area” (National Park Service 2015d). Completed 

in 2015, the park’s foundation document contains 

significance statements about high biodiversity in a 

Mediterranean ecosystem; recreational opportunities 

in a national park gateway; scientific understanding of 

native vegetation communities, archeological sites, and 

geologic and paleontological features, all in proximity 

to numerous research institutions; scenic resources, 

extending from Point Mugu to downtown Los Angeles, 

including 64 km (40 mi) of coastline (Curdts 2011); 

and film-making history where landscapes continue 

to provide backdrops for film production today (see 

National Park Service 2015a). These statements express 

why the park’s resources and values are important 

enough to merit designation as a unit of the National 

Park System.
3

Figure 3. World map of Mediterranean ecosystems. The Mediterranean ecosystem occurs in five relatively small areas 

around the planet: (1) the area bordering the Mediterranean Sea, (2) southern California and northern Baja California 

(yellow star indicates the location of the park), (3) central Chile, (4) the Cape region of South Africa, and

(5) southwestern and southern Australia. These areas are distributed between roughly 30° and 40° latitude—north and 

south—and are located along the western edges of continents where cold ocean currents moderate the climate.

5

Geologic Features and Processes

This section describes noteworthy geologic features and processes in Santa Monica Mountains 

National Recreation Area.

During the 2008 scoping meeting (see scoping summary 

by KellerLynn 2008) and 2015 conference call, 

participants (see Appendix A) identified the following 

geologic features and processes in the park. Landscapescale features and processes are discussed before 

smaller scale features and processes.

● Plate Boundaries

● Faults

● Folds

● Unconformities

● Rock Types

● Formations

● Type Sections

● Paleontological Resources

● Landslides

● Fluvial Features

● Cave and Karst Resources

● Eolian Features and Processes

● Marine and Coastal Resources

These geologic features and processes contribute to the 

park’s significance of scientific understanding, scenic 

resources, and film-making history (see “Geologic 

Setting and Significance”). Additionally, the park’s 

geologic features and processes are fundamental 

resources and values, specifically as they relate to the 

park’s coastal and mountain landscapes, which are 

shaped by ongoing geologic forces. Also, paleontological 

resources are an “other important resource and value” 

identified in the park’s foundation document (National 

Park Service 2015a).

Plate Boundaries

Profound changes have taken place at the western edge 

of the North American continent, which is the site of 

an evolving plate boundary. The park’s geologic story 

is wrapped up in this complex story of plate-boundary 

evolution (see table 1 and “Geologic History” section). 

The park contains geologic evidence of all three types 

of plate boundaries—convergent, divergent, and 

transform. 

Convergent Boundary

Places where tectonic plates are moving toward 

each other are convergent boundaries. Convergence 

can occur between an oceanic and a continental 

plate, between two oceanic plates, or between two 

continental plates. In the case of southern California, 

convergence was between the oceanic Farallon plate 

and the continental North American plate. The Farallon 

plate subducted beneath the North American plate, 

and Earth’s crust (outermost layer) was recycled into 

Earth’s mantle (zone below the crust and above the 

core). Convergence created a subduction zone from the 

Mesozoic Era through the early to middle Cenozoic Era 

(Oligocene Epoch) (fig. 4). 

The former convergent boundary in southern California 

is characterized by four belts or assemblages of rocks: 

(1) the Sierra Nevada magmatic arc, (2) the Western 

Foothills–Peninsular Ranges accreted arcs, (3) the 

Great Valley forearc basin, and (4) the Coast Ranges–

Franciscan Group accretionary wedge (fig. 4). In 

southern California, elements of these belts can be 

recognized, but the assemblages of rocks have been 

reorganized by more recent (Neogene Period) faulting 

and folding (Atwater 1998). Subduction continues 

today off the coast of northern California, Oregon, 

Washington, and British Columbia as part of the 

Cascadia subduction zone.

Convergent Boundary: Magmatic Arc

The granitic rocks (Kgr) that intruded the oldest 

rocks in the park—the Santa Monica Slate (“Jsm” map 

units)—represent the “magmatic arc” belt, which is 

an arcuate line of plutons, volcanic rocks, or active 

volcanoes formed at a convergent boundary. Most 

of the magma forms by melting in the zone above the 

downgoing plate. The Sierra Nevada and Peninsular 

Ranges, north and south of the park respectively, are 

part of the magmatic arc belt. Yosemite National Park 

(see GRI report by Graham 2012a) offers exceptional 

views of the “roots” of uplifted magma chambers of the 

magmatic arc now exposed as granitic mountains in 

that part of the state. The bedrock at Cabrillo National 

Monument in San Diego contains fragments of the 

rising Peninsular Ranges, which were transported by 
6

Table 1. Geologic summary of rock units in Santa Monica Mountains National Recreation Area

The rock units in the park are separated into table 1a and 1b with respect to the Malibu Coast Fault. The Monterey Shale, Trancas Formation, and 

Zuma Volcanics are only exposed south of the fault, though they are coeval with map units north of the fault. The rocks north of the fault are best 

correlated with the Transverse Ranges whereas the rocks south of the fault are best correlated with the northern Peninsular Ranges. 

Many investigators—for example, Crouch and Suppe (1993), Nicholson et al. (1994), Atwater (1998), and Olson (2006)—have suggested the timing 

of events in the complex tectonic history of the Transverse Ranges. This table uses the approximate dates provided by Fritsche and Weigand (2008), 

which served as a handout during the 2008 GRI scoping meeting. 

Colors in the first column (ages of map units) are standard colors approved by the US Geological Survey to indicate different time periods on geologic 

maps. Shading in the Tectonic and Depositional Setting column highlights the major tectonic regimes: pink = subduction, blue = transition from 

subduction to transtension, tan = transtension, and violet = transpression (see “Geologic History” section). Yellow shading in Map Unit column 

indicates rock units with type sections in the park (see table 4). See tables 2 and 3 for explanations of rock types.

Table 1a. Rock units north of the Malibu Coast Fault.

Age of Map 

Unit from 

GRI GIS 

Data

Date Reported 

by Fritsche and 

Weigand (2008) in 

millions of years ago

Map Unit

(symbol) Rock or Sediment Type Tectonic and Depositional 

Setting

Quaternary 

(late Holocene) Not reported Artificial fill(Qaf)

Compacted, engineered 

or noncompacted, 

nonengineered sand, silt, and 

gravel

Transpression. Developed areas, 

altered or constructed by humans.

Quaternary 

(late Holocene) Not reported Alluvium(Qa)

Unconsolidated gravel, sand, 

and silt

Transpression. Active or recently 

active streambeds.

Quaternary 

(Holocene) Not reported Wash deposits(Qw and Qw1)

Unconsolidated gravel, sand, 

and silt

Transpression. Active or recently 

active streambeds.

Quaternary 

(late Holocene) Not reported Beach deposits(Qb) Loose sand Transpression. Active beaches.

Quaternary 

(late Holocene) Not reported Eolian deposits(Qe) Loose sand, silty sand, and silt Transpression. Mostly transitory dunes against beach-facing cliffs.

Quaternary 

(late Holocene) Not reported Alluvial fan(Qf)

Unconsolidated boulders, 

cobbles, gravel, sand, and silt

Transpression. Active and recently 

active alluvial fans.

Quaternary 

(late Holocene) Not reported

Active coastal estuarine 

deposits

(Qes)

Submerged/saturated silty 

clay Transpression. Estuaries.

Quaternary 

(Holocene and 

Pleistocene?)

Not reported Landslide deposits

(Qls)

Rock detritus from bedrock 

and surficial materials, broken 

in varying degrees

Transpression. Slopes.

Quaternary 

Period 

(Holocene and 

Pleistocene 

epoch)

Not reported Young alluvium

(Qya, Qya2, and Qya1)

Unconsolidated silt, sand, and 

gravel

Transpression. Subaerial canyon 

floors.

Quaternary 

(Holocene and 

late Pleistocene)

Not reported Young alluvial-fan deposits

(Qyf and Qyf2)

Unconsolidated gravel, 

sand, and silt; boulders near 

mountain fronts

Transpression. Flooding streams 

and debris flows.

Quaternary 

(middle to late 

Pleistocene)

Not reported Old alluvium

(Qoa)

Unconsolidated to moderately 

indurated gravel, sand, and 

silt

Transpression. Valley floor, 

floodplain, or alluvial fans.

Quaternary 

(middle 

Pleistocene)

Not reported Old fan deposits

(Qof1, Qof2, and Qof4)

Slightly to moderately 

consolidated silt, sand, and 

gravel 

Transpression. Alluvial fans.

Quaternary

(late 

Pleistocene)

Not reported

Old shallow marine deposits 

on wave-cut surface

(Qom)

Generally unconsolidated 

sand, silty sand, and gravel. 

Some deposits have calcite 

cement.

Transpression. Coastline at former 

sea level.
7

Age of Map 

Unit from 

GRI GIS 

Data

Date Reported 

by Fritsche and 

Weigand (2008) in 

millions of years ago

Map Unit

(symbol) Rock or Sediment Type Tectonic and Depositional 

Setting

Quaternary–

Tertiary

(late Pliocene 

to early 

Pleistocene 

epochs)

Not reported

Sedimentary rocks of the 

Pacific Palisades area

(QTms)

Sedimentary (siltstone and 

sandstone)

Transpression. Marine basin with 

possible slumping along margins.

n/a ~4 Tectonic regime changes from transtension to transpression. Gulf of California opens. Modern San 

Andreas Fault forms. Begin uplift of Santa Monica Mountains.

Tertiary

(late and middle 

Miocene)

~12–4 Modelo Formation

(Tm, Tmd, Tms, Tmb)

Sedimentary (sandstone and 

shale) Transtension. Submarine fan. 

n/a ~13–12 7th unconformity in the park’s rock record—angular unconformity

Tertiary 

(Miocene) ~17–13

Calabasas Formation

(Tcb, Tcbs, Tcbmp, Tcbn, 

Tcbd, Tcbl, and Tcbe)

Type section (see table 4).

Sedimentary (sandstone and 

shale; breccia)

Transtension. Offshore marine, with 

deposition by turbidity currents.

Tertiary

(middle 

Miocene)

~17–15 

Conejo Volcanics

(Tco, Tcod, Tcoaf, Tcoaa, 

Tcoab, Tcob, Tcoadb, Tcobf, 

Tcobb, Tcop, Tcobz, Tcom, 

Tcos, and Tcor)

Type section (see table 4).

Igneous, volcanic (basalt, 

andesitic basalt, basaltic 

andesite, andesite, and 

dacite)

Transtension. Submarine eruptions 

that built into shield volcanoes that 

rose above sea level and produced 

subaerial eruptions.

Tertiary

(middle 

Miocene)

Not reported Intrusive rocks

(Ti, Tid, Tia, and Tib)

Igneous, intrusive (diabase, 

andesite, and basalt) 

Transtension. Marine (intruded 

into Topanga Canyon Formation). 

Exposed in central and western 

Santa Monica Mountains.

Tertiary

(middle 

Miocene)

Not reported Mixed rocks

(Tim)

Igneous, intrusive (basalt), 

intruded into siltstone and 

sandstone

Transtension. Marine (intruded 

into Topanga Canyon Formation). 

Exposed in central and western 

Santa Monica Mountains.

Tertiary

(middle and 

early Miocene)

Not reported

Topanga Group, intrusive and 

extrusive volcanic rocks

(Ttb)

Igneous, basalt flows and 

related hypabyssal (shallow 

intrusive) basaltic rocks

Transtension. Intruded into 

undivided Topanga Group rocks 

(Tt). Have an affinity with Topanga 

Group rocks in the Los Angeles 

Basin. Exposed in eastern Santa 

Monica Mountains.

n/a ~18 Begin rotation of the Western Transverse Ranges block. Extension. Volcanism.

n/a ~18–17 6th unconformity in the park’s rock record—angular unconformity

n/a ~20 Tectonic regime changes from subduction to transtension. Capture of the Monterey microplate by 

the Pacific plate.

Tertiary

(middle and 

early Miocene)

~21–18 

Topanga Canyon Formation

(Ttc, Ttcc, Ttcf, Ttcs, Ttcb, 

Ttcbs, and Ttce)

Type section (see table 4).

Sedimentary (sandstone, 

siltstone, mudstone, and 

conglomerate)

Transition from subduction to 

transtension. Marine, nearshore 

marine, and nonmarine (river).

Tertiary

(early Miocene 

and Oligocene)

~28–21 Vaqueros Formation

(Tv, Tvn, and Tvd)

Sedimentary (sandstone, 

siltstone, and mudstone)

Transition from subduction to 

transtension. Marine and nearshore 

marine.

Tertiary

(early Miocene) ~28–21

Sespe Formation, Piuma 

Member

(Tsp)

Sedimentary (sandstone and 

siltstone)

Transition from subduction to 

transtension. Nonmarine (lake and 

lagoon).

n/a ~28 East Pacific Rise (spreading center) makes contact with western margin of the North American plate.

Table 1a. Rock units north of the Malibu Coast Fault, continued.
8

Age of Map 

Unit from 

GRI GIS 

Data

Date Reported 

by Fritsche and 

Weigand (2008) in 

millions of years ago

Map Unit

(symbol) Rock or Sediment Type Tectonic and Depositional 

Setting

Tertiary

(early Miocene, 

Oligocene, and 

late Eocene)

29–28 Sespe Formation

(Ts)

Sedimentary (“red beds”—

sandstone, mudstone, and 

conglomerate)

Subduction. Deposition of forearc 

sediments. Nonmarine (river 

channel, floodplain, and delta).

n/a ~36–29 5th unconformity in the park’s rock record—disconformity.

Approach of the East Pacific Rise spreading center.

Tertiary

(early Miocene, 

Oligocene, and 

late Eocene)

~41–36 Sespe Formation

(Ts)

Sedimentary (“red beds”—

sandstone, mudstone, and 

conglomerate)

Subduction. Deposition of forearc 

sediments. Nonmarine (river 

channel, floodplain, and delta).

n/a ~48–41 4th unconformity in the park’s rock record—angular unconformity

Tertiary (early to 

middle Eocene) ~50–48 Llajas Formation(Tl)

Sedimentary (sandstone, 

siltstone, and conglomerate)

Subduction. Deposition of forearc 

sediments. Shallow marine and 

coastal alluvial fan.

n/a ~55–50 3rd unconformity in the park’s rock record—angular unconformity

Tertiary (late 

Paleocene to 

early Eocene)

~58–55 Santa Susana Formation

(Tss and Tssl)

Sedimentary (shale [some 

with limestone concretions], 

mudstone, and siltstone 

with interbeds of sandstone 

and lenses of pebble-cobble 

conglomerate; scattered 

lenses and pods of algal 

limestone in siltstone 

sequences)

Subduction. Deposition of forearc 

sediments. Marine and nearshore 

marine.

Tertiary (early? 

Paleocene 

Epoch)

~58–55 Las Virgenes Sandstone

(Tlv)

Sedimentary (sandstone and 

mudstone)

Subduction. Deposition of forearc 

sediments. Nearshore marine and 

nonmarine (coastal river).

Tertiary 

(Paleocene) ~58–55 Simi Conglomerate(Tsi)

Sedimentary (cobble-boulder 

conglomerate)

Subduction. Deposition of forearc 

sediments. Nonmarine (alluvial fans 

and braided rivers).

n/a ~75–58 2nd unconformity in the park’s rock record—angular unconformity.

Runyon Canyon erosion surface (associated with “K-T” boundary).

Late Cretaceous Not reported Chatsworth Formation

(Kc)

Sedimentary (turbidite 

sandstone)

Subduction. Deposition of forearc 

sediments. Marine (mostly 

deposited by turbidity currents).

Late Cretaceous ~90–75 

Tuna Canyon Formation

(Kt, Kte, Ktd, Ktc, and Ktb)

Type section (see table 4).

Sedimentary (sandstone, 

siltstone, and conglomerate)

Subduction. Deposition of forearc 

sediments. Marine.

Late Cretaceous ~91–90 Trabuco Formation

(Ktr) Sedimentary (conglomerate)

Subduction. Deposition of forearc 

sediments. Nonmarine (alluvial fans 

in “Tarzana Canyon”).

n/a ~102–91 1st unconformity in the park’s rock record—nonconformity.

Erosion of subaerial “Tarzana Canyon.”

Late Cretaceous ~102 Granitic rocks

(Kgr) Igneous, intrusive

Subduction. Intrusion associated 

with magmatic arcs. Igneous 

intrusion into the Santa Monica 

Slate.

Late Jurassic ~156–152 

Santa Monica Slate

(Jsm, Jsms, and Jsmp)

Type section (see table 4).

Metamorphic

Subduction. Accretion of island 

arcs. Deposited in a marine setting 

and later metamorphosed.

Table 1a. Rock units north of the Malibu Coast Fault, continued.
9

Table 1b. Rock units south of the Malibu Coast Fault.

Age of Map 

Unit from 

GRI GIS 

Data

Date Reported 

by Fritsche and 

Weigand (2008) in 

millions of years ago

Map Unit

(symbol) Rock or Sediment Type Tectonic and Depositional 

Setting

Tertiary 

(Miocene) Not reported Monterey Shale(Tmt and Tmtd)

Sedimentary (shale, siltstone, 

sandstone)

Transtension. Deep, isolated, distal 

marine basins.

Tertiary (middle 

and early 

Miocene)

Not reported 

Trancas Formation

(Tr and Tra)

Type section (see table 4).

Sedimentary (mudstone, 

shale, claystone, and 

sandstone; also San Onofre 

Breccia)

Transtension. Marine

Tertiary (middle 

and early 

Miocene)

Not reported 

Zuma Volcanics

(Tz)

Type section (see table 4).

Igneous, volcanic (basalt, 

andesite, and dacite)

Transtension. Erupted into 

extensional marine basin. 

n/a ~18 Begin rotation of Western Transverse Ranges block. Extension. Volcanism.

n/a ~20 Tectonic regime changes from subduction to transtension. Microplate capture.

Figure 4. Graphic of subduction zone. The park contains rocks and structures formed during subduction of the Farallon 

plate. The Santa Monica Slate (“Jsm” map units) is part of the “accreted arcs” belt. Granitic rocks (Kgr) are part of 

the “magmatic arc” belt. The sequence of sedimentary rocks consisting of the Trabuco (Ktr) through the Sespe (Ts) 

formations (see table 1) represents deposition in the “forearc basin” belt. Metamorphosed, mid-crustal rocks such as 

the Cretaceous Catalina Schist (not exposed in the park) represent the “accretionary wedge” of material under the 

“forearc basin” sediments. Graphic by Trista Thornberry-Ehrlich (Colorado State University) after Crouch and Suppe 

(1993, figure 2) and Lillie (2005, figure 7.6).
10

streams and deposited in a huge submarine fan (see GRI 

report by KellerLynn in preparation). 

Convergent Boundary: Accreted Arcs

The Santa Monica Slate (“Jsm” map units) represents 

the “accreted arcs” belt. These rocks accumulated 

between 156 million and 152 million years ago in a basin 

within an island arc system (generally curved linear belt 

of volcanoes above a subduction zone), which collided 

with the continental margin and later accreted to the 

edge of the North American continent. 

Convergent Boundary: Forearc Basin

Nine of the park’s sedimentary rock formations—

Trabuco (Ktr) through Sespe (Ts) formations (see table 

1)—represent the “forearc basin” belt. The forearc basin 

is a sedimentary basin that lies between the arc and the 

shelf break at a convergent plate boundary. 

Transgressive–Regressive Cycles

The rocks of the Great Valley forearc basin record 

multiple cycles of marine transgression and regression. 

A transgression occurs when the land surface subsides 

Figure 5. Graphic of a transgression and a regression. (a) During a transgression, the sea advances over the edge of the 

continent, causing the shoreline to retreat. As the water deepens, more landward type sediments are covered by more 

marine type sediments. (b) During a regression, the sea retreats and the shoreline advances. Deep-water sediments are 

covered by more landward type sediments. An example of a marine transgression in the park’s rock record includes 

the Simi Conglomerate (Tsi), Las Virgenes Sandstone (Tlv), and Santa Susana Formation (Tss and Tssl). Graphic by Trista 

Thornberry-Ehrlich (Colorado State University) after Lillie (2005, figure 4.23). 
11

or sea level rises, causing the ocean to advance 

over the continental edge (a landward migration of 

the shoreline). A transgression results in an “onlap 

sequence” where layers of nonmarine sediments are 

covered by shallow-marine sediments, and then by 

deeper marine sediments as the water depth gradually 

increases. Thus, a transgressive sequence will show, for 

example, nonmarine sandstone overlain by shallowmarine shale that is in turn overlain by offshore and 

shelf marine limestone. By contrast, as the land surface 

rises or the sea gradually moves offshore during a 

marine regression (an “offlap sequence”), the rock 

sequence is reversed, with marine sediments gradually 

covered by more terrestrial materials (fig. 5). Multiple 

transgressive-regressive events or cycles result in the 

intertonguing of marine and terrestrial sediments. 

Intertonguing is the intergradation of different rock 

layers commonly shown in a vertical succession of 

wedge-shaped stratum (see fig. 40).

An example of a marine transgression in the park’s 

rock record includes the Simi Conglomerate (Tsi), Las 

Virgenes Sandstone (Tlv), and Santa Susana Formation 

(Tss and Tssl). In the Santa Monica Mountains, the 

Simi Conglomerate consists of conglomerate and 

minor interbedded sandstone representing braided 

river deposits on an alluvial plain. This unit also 

includes iron-stained red beds and concentrations of 

carbonaceous material that serve as a regional marker 

for relative dating in the rock record. The Las Virgenes 

Sandstone consists of a lower unit of sandstone 

deposited by meandering streams on a coastal plain. 

In some locations, this unit also contains red beds and 

a very distinctive bed of iron pisoliths (small, ovoid 

accretionary particles). The upper part of the Las 

Virgenes Sandstone consists of sandstone deposited in a 

nearshore marine environment. Sandstone in the upper 

unit intertongues with the Santa Susana Formation, 

which consists of nearshore to offshore and shelf 

deposits of interbedded mudstone and sandstone with 

lenses of storm-lag deposits (coarse-grained material 

that is left behind following a storm) consisting of 

mollusk shells and, in some places, a calcareous algae 

marker bed. 

Convergent Boundary: Accretionary Wedge

As material is scraped off a subducting plate then 

becomes accreted (attached) to the overriding plate, 

an “accretionary wedge” forms. Portions of the 

accretionary wedge rise above sea level as sediment and 

rock are compressed, folded, and faulted. Elsewhere in 

California, the Coast Ranges represent an accretionary 

wedge of uplifted oceanic rocks. The Coast Ranges–

Franciscan Group accretionary wedge forms the 

landscape of Golden Gate National Recreation Area 

(see GRI report by Port 2016). In the Santa Monica 

Mountains, the Cretaceous Catalina Schist represents 

the accretionary wedge. Catalina Schist is not exposed 

in the park but was encountered at depth in a well 

located south of the Malibu Coast Fault (Yerkes and 

Campbell 1979). Fragments of Catalina Schist comprise 

the San Onofre Breccia (consisting of angular clasts; 

table 2). The breccia is a distinctive part of the Trancas 

Formation (Tr and Tra), which is exposed in the park 

south of the Malibu Coast Fault. 

Divergent Boundary

Divergent boundaries occur along spreading centers 

where plates are moving apart and new crust is 

created by magma pushing up from the mantle. The 

East Pacific Rise is the divergent boundary/spreading 

center associated with the park’s geologic story (fig. 

6). As the East Pacific Rise approached the margin 

of North America (see “Geologic History” section), 

subduction of young, buoyant crust associated with the 

spreading center contributed to the uplifts recorded 

by the terrestrial Sespe Formation (Atwater 1998; see 

“Sedimentary Rocks” section). Also, the unconformity 

in the middle of the lower Sespe Formation (Ts) 

between 36 million and 29 million years ago is evidence 

of the approach of the East Pacific Rise (Fritsche and 

Weigand 2008; see “Unconformities” section). 

Transform Boundary

Transform boundaries form where Earth’s crust is 

neither produced nor destroyed as crustal plates slide 

horizontally past each other. Following subduction, 

the plate boundary in southern California became 

characterized by transform plate motion. Initially, the 

new transform plate boundary (between the Pacific 

plate and North American plate) had significant 

amounts of extension and associated normal faulting 

(see “Faults” section) along which basins dropped 

down, similar to the Basin and Range province 

(Bartolomeo and Longinotti 2010). This stage in the 

development of the plate boundary is referred to as 

“transtension” (transform plate motion and extension). 

Transtension is responsible for the rotation of the 

Western Transverse Ranges block (see “Transverse 

Ranges” section below). “Transpression” (transform 
12

Figure 6. Graphic of the North American plate boundary over time. The four panels illustrate the subduction of the 

Farallon plate, as it was progressively consumed beneath the North American plate, leaving only the Juan de Fuca, 

Rivera, and Cocos plates as remnants today. As the East Pacific Rise made contact with the North American plate, the 

Farallon plate east of the rise began to fracture into microplates. As contact between the Pacific and North American 

plates lengthened, transtension (transform plate motion and extension) replaced subduction about 20 million years 

ago. Rotation of the Western Transverse Ranges block (see fig. 7) began about 18 million years ago; rotation is 

ongoing locally. About 4 million years ago, the tectonic regime changed from transtension to transpression (transform 

plate motion and compression). Large, black arrows show the sense of relative motion between the Pacific and North 

American plates. The red star indicates the location of the park. Note its progression from the North American plate to 

the Pacific plate as the plate boundary evolved. The San Andreas Fault represents the present plate boundary. Graphic 

by Trista Thornberry-Ehrlich (Colorado State University) after Kious and Tilling (1996, p. 7).
13

plate motion and compression) followed transtension 

and characterizes the present-day boundary. 

Transpression is responsible for the development of 

the San Andreas Fault system (see “San Andreas Fault” 

section below).

Transform Boundary: Transverse Ranges 

Rather than being oriented north–south or northwest–

southeast as most of the mountains in California, or 

North America for that matter, the Transverse Ranges 

and their associated folds and faults (see “Faults” and 

“Folds” sections) are oriented east–west. The ranges’ 

orientation illustrates how blocks of Earth’s crust can 

rotate, like ball bearings, when caught in a zone of 

deformation at a plate boundary. 

The Western Transverse Ranges block was originally 

part of a fault-bounded crustal block within the North 

American plate. During the transtensional phase of 

the plate boundary (see “Geologic History” section), 

it was one of three crustal blocks that rifted away 

from the continental margin, became attached to the 

Pacific plate, and began to migrate to the northwest, 

assuming relative Pacific plate motion (Atwater 1998). 

The Western Transverse Ranges block was the most 

inland of these blocks and, therefore, the most deeply 

embedded into the crust. As the Western Transverse 

Ranges block began to move with the Pacific plate, its 

northern end, which was essentially locked into the 

North American crust, did not break away. As a result, 

the central and southern portions of the Western 

Transverse Ranges block began to rotate as a coherent 

structural unit with the locked northern end acting 

as a hinge (Olson 2006). Before rotation, the Western 

Transverse Ranges block was oriented north–south, 

approximately adjacent to the northern Peninsular 

Ranges at present-day San Diego and Anaheim. To 

reach the present configuration of the Transverse 

Ranges, the block rotated clockwise approximately 

90°–110° at an average rate of 5° to 6° per million years 

(fig. 7; Hornafius et al. 1986; Luyendyk 1991). Tanya 

Atwater (University of California, Santa Barbara) 

developed an animation that shows the rotation of the 

Western Transverse Ranges block (see http://emvc.geol.

ucsb.edu/2_infopgs/IP4WNACal/cCalifornia.html). 

This animation may help park staff and visitors alike to 

visualize the complex rotation scenario of the Western 

Transverse Ranges block.

Transform Boundary: San Andreas Fault

The San Andreas Fault extends roughly 1,300 km (810 

mi) through California. The fault segment closest to 

the park is about 80 km (50 mi) to the northeast (fig. 

8). The San Andreas Fault was first identified in 1895 

by Professor Andrew Lawson at the University of 

California, Berkeley, who discovered the northern 

segment. It was named after San Andreas Lake, a 

small body of water that formed in a valley between 

Figure 7. Graphic showing rotation of the Western Transverse Ranges block. As shown on the graphic, the crustal block 

associated with the city of Santa Barbara rolled like a ball bearing trapped within a zone of deformation at the plate 

boundary. Clockwise rotation of the block explains why the Transverse Ranges run east–west, unlike the northwest–

southeast orientation of most mountain ranges in California. The Santa Monica Mountains, including the park (red 

star), lie within the Transverse Ranges. Channel Islands National Park (yellow star) marks the western extension of the 

ranges into the Pacific Ocean. Joshua Tree National Park (purple star) lies at the eastern end of the range. Note in the 

last panel how the San Andreas Fault makes a significant east–west bend at the Transverse Ranges; this is known as 

the “Big Bend.” Graphic by Trista Thornberry-Ehrlich (Colorado State University) after Lillie (2005, figure 7.16).
14

Figure 8. Aerial image of the San Andreas Fault. The San Andreas Fault runs 1,300 km (810 mi) through California. 

It displays right-lateral strike-slip motion (see fig. 9). On the right-hand side of the fault, the North American plate 

is moving southeastward; on the left-hand side, the Pacific plate is moving northwestward. The park lies on the 

Pacific plate. This image is from NASA’s Shuttle Radar Topography Mission (SRTM) with a graphic overlay that shows 

faults (white lines) that have been active in the late Quaternary Period. The fault data are from the US Geological 

Survey. Topographic shading derived from the SRTM elevation model was added to the Landsat image, with a false 

sun illumination from the left (southwest). This synthetic shading enhances the appearance of the topography. The 

Landsat image was acquired on 4 May 2001. The scale varies in this perspective: width of view is 134 km (83 mi); 

height/distance is 150 km (93 mi); vertical exaggeration is 1.8x. NASA Earth Observatory, Image of the Day: Los Angeles 

Faults, 24 December 2002. http://earthobservatory.nasa.gov/IOTD/view.php?id=3067. Annotations by Jason Kenworthy 

(National Park Service).

Figure 9. Graphic of fault types. Movement occurs along a fault plane. Footwalls are below the fault plane, and 

hanging walls are above. In a normal fault, crustal extension (pulling apart) moves the hanging wall down relative 

to the footwall. In a reverse fault, crustal compression moves the hanging wall up relative to the footwall. A thrust 

fault is a type of reverse fault that has a dip angle of less than 45°. In a strike-slip fault, movement is horizontal. 

When movement across a strike-slip fault is to the right, it is a right-lateral strike-slip fault, as illustrated above. When 

movement is to the left, it is a left-lateral strike-slip fault. A strike-slip fault between two tectonic plates is called 

a transform fault. Transtension (transform plate motion and extension) is characterized by strike-slip and normal 

faulting. Transpression (transform plate motion and compression) is characterized by strike-slip faulting and reverse 

and thrust faulting. Graphic by Trista Thornberry-Ehrlich (Colorado State University).
15

the Pacific and North American plates. Following the 

1906 San Francisco earthquake, Lawson concluded 

that the fault extended all the way into southern 

California (Lawson 1908). In 1953, Mason L. Hill and 

Thomas Dibblee astounded the scientific community 

with their conclusion that hundreds of miles of lateral 

movement had occurred along the fault (Hill and 

Dibblee 1953). This idea, which was considered radical 

at the time, has since been substantiated by modern 

studies of plate-tectonic processes. GRI reports about 

Golden Gate National Recreation Area (Port 2016) 

and Pinnacles National Park (Port in preparation) 

provide descriptions of features associated with more 

“pure” transform (horizontal) plate motion in northern 

California, where extension and compression have 

played less of a role along the fault system than in the 

Transverse Ranges. 

In recent times, the San Andreas Fault has taken up the 

bulk of the motion at the plate boundary and thus has 

come to be identified as the transform-plate boundary 

in popular scientific thought. In reality, however, many 

faults (see “Faults” section) make up a broad zone of 

deformation that composes today’s plate boundary.

Faults 

A fault is a fracture in rock along which movement has 

taken place. Movement along faults causes earthquakes 

(see “Earthquakes” section). The three primary types 

of faults are normal, reverse, and strike-slip (fig. 9). 

Faults are classified based on the motion of rocks on 

either side of the fault plane. The faults in the park 

are primarily reverse faults, in which the hanging wall 

(rock immediately above the fault plane) has been 

raised relative to the footwall (rock immediately below 

the fault plane). Reverse faults include thrust and 

Figure 10. Screen capture of fault activity map of California. The Malibu Coast Fault and the Anacapa-Dume Fault are 

the two primary active faults in the park area. Faults are marked by solid and dashed black lines on the graphic. Low 

angle (thrust) faults are marked by lines with triangles that point in the direction of faulting. Bar and ball symbols 

indicate the downthrown side of a fault. Red indicates recent movement. Orange indicates movement during the 

Holocene Epoch (past 11,700 years). Green indicates movement during the late Quaternary Period (past 700,000 years). 

Purple indicates a Quaternary fault (age undifferentiated). Numbers in boxes on the graphic are references to Jennings 

and Bryant (2010). California Geological Survey data at http://maps.conservation.ca.gov/cgs/fam/. 
16

detachment faults. Thrust faults are reverse faults with a 

low angle (<45°) fault plane. Detachment faults are very 

low angle (nearly horizontal) reverse faults with large 

displacement (kilometers to tens of kilometers). 

The Transverse Ranges are known for “blind thrust 

faults,” which are typically low angle structures in 

areas of active folding (Jennings and Bryant 2010; see 

“Folds” section). The upper extent of the fault plane 

may terminate several kilometers below the ground 

surface (hence the term “blind” to describe these 

faults), and the surface expression is often delineated 

by young anticlines. These faults have produced strong 

earthquakes in California, such as the 1994 magnitude 

6.7 Northridge earthquake (see “Earthquakes” section).

As recorded in the GRI GIS data, an estimated 

1,040,089 m (3,412,365 ft or 646 mi) of fault segments 

cut through the park (see poster, in pocket). The 

primary active faults in the Santa Monica Mountains 

area are the Malibu Coast and the Anacapa-Dume faults 

(fig. 10; Pam Irvine, California Geological Survey, senior 

engineering geologist, telephone communication, 9 

June 2016). The Malibu Coast Fault, which was mapped 

in the park and is included in the GRI GIS data, occurs 

both onshore and offshore. The Anacapa-Dume Fault 

occurs offshore and is not included in the GRI GIS data. 

Earthquake potential, hazards, and risk associated with 

the Malibu Coast, Anacapa-Dume, and other faults 

in the Santa Monica Mountains are discussed in the 

“Earthquakes” section.

Folds

Folds are curves or bends in originally flat structures, 

such as rock strata, bedding planes, or foliation. Visually, 

folds are some of the most spectacular structures on 

Earth. They are extraordinary displays of strain and 

conspicuous natural images of how the original shape of 

rock bodies can be changed during deformation (Davis 

1984). Folds exist at multiple scales from a few meters 

at an outcrop (fig. 11) to regional folds that encompass 

many kilometers (see poster, in pocket). 

The two primary types of folds are anticlines, which 

are convex (“A-shaped”), and synclines, which are 

concave (“U-shaped”). As bedrock is compressed by 

tectonic activity, anticlines and synclines form adjacent 

to one another. As mapped on the Los Angeles 30' × 

60' quadrangle (Campbell et al. 2014; scale 1:100,000), 

the GRI GIS data include 164 fold segments—104 

anticlines, one of which was deformed to an extent to 

become overturned, and 60 synclines (see poster, in 

pocket). 

Approximately 102 million–91 million years ago 

(Cretaceous Period; fig. 13), compression, probably 

related to the ongoing subduction of the Farallon 

plate (see “Geologic History” section), produced 

folds in the Santa Monica Slate and created a generally 

north–south-trending anticline, which was later 

rotated (see “Transverse Ranges” section). Three 

angular unconformities in the park’s rock record at 

75 million–58 million, 55 million–50 million, and 48 

million–41 million years ago are evidence of uplift and 

deformation along this anticline (see “Unconformities” 

and “Geologic History” sections).

Since about 4 million years ago, many secondary 

anticlines and synclines formed on the preexisting 

anticline (see poster, in pocket; Eugene Fritsche, 

California State University, Northridge, Department of 

Geological Sciences, professor emeritus, GRI scoping 

presentation, 7 May 2008). Campbell et al. (2014) 

mentioned the “Topanga Anticline” by name in their 

description of the Conejo Volcanics (Tco). Sedimentary 

rocks such as the Topanga Canyon Formation are 

uplifted in the Topanga Anticline in the park. A segment 

of the popular Backbone Trail climbs along the anticline 

(fig. 12). 

Figure 11. Photograph of folds. About 4 million years 

ago, the Santa Monica Mountains formed as a result 

of compression along the plate boundary. Complexly 

deformed shale beds of the Modelo Formation (“Tm” 

map units), shown here along Mulholland Highway about 

2 km (1 mi) west of Las Virgenes Road, are evidence 

of compression. Note person at lower right corner for 

scale. Photograph from Eugene Fritsche (California State 

University, Northridge, Department of Geological Sciences, 

professor emeritus, GRI scoping presentation, 7 May 2008).
17

These relatively young, northwest–southeast-trending 

folds in the park are related to a major change in the 

tectonic regime—from transtension (transform plate 

motion and extension) to transpression (transform 

plate motion and compression) (see “Geologic History” 

section). This change in plate motion caused extensive 

folding and the inversion of normal faults (indicative of 

extension) to reverse faults (indicative of compression). 

The Santa Monica Mountains are an outcome of 

compression and associated folding.

Unconformities

The rock record exposed in the park represents 

approximately 156 million years of geologic time, from 

the Jurassic Period to the present day (fig. 13). Layers 

of rock are referred to as “conformable” where they 

are found to have been deposited essentially without 

interruption. Although particular sites may exhibit 

conformable beds representing significant spans of 

geologic time, no place on Earth contains a full set 

of conformable strata. Breaks in conformable strata 

are called “unconformities.” Each unconformity 

represents a period when deposition ceased or where 

erosion removed previously formed rocks. Because 

unconformities may be widespread across a region, they 

can be useful for correlating rock units and tectonic 

history over long distances.

The rock record in the park records seven 

unconformities (see table 1 and “Geologic History” 

section). In each case, uplift and erosion was followed 

by subsidence and renewed sedimentation. Five of 

the unconformities are angular unconformities, where 

lower rock layers are tilted at a different angle than 

overlying layers. One is a disconformity, which separates 

rock layers that are parallel. One is a nonconformity 

where sedimentary layers were deposited on top of 

igneous or metamorphic rocks (fig. 14).

Figure 12. Photograph of the Topanga Anticline. Rocks formations such as the Topanga Canyon Formation were raised 

up as part of the Topanga Anticline. Note the Backbone Trail traversing the flank of the anticline (arrow). Photograph 

by Alexandra Meyers, available via Wikimedia Commons https://commons.wikimedia.org/wiki/File:Topanga_Canyon.

JPG (Creative Commons Attribution-Share Alike 4.0 International [CC BY-SA 4.0]; https://creativecommons.org/licenses/

by-sa/4.0/deed.en). 
18

Figure 13. 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. Geologic time divisions represented in the GRI GIS data are 

colored orange. GRI map abbreviations for each time division are in parentheses; rocks in the park are J (Jurassic),

K (Cretaceous), T (Tertiary), and Q (Quaternary). Most of the rocks in the park are from the Miocene Epoch (MI). The 

Santa Monica Mountains formed during the Pliocene Epoch (PL); uplift is ongoing (Holocene Epoch [H]). Compass 

directions in parentheses indicate the regional locations of events. Boundary ages are millions of years ago (MYA). 

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

org/index.php/ics-chart-timescale).
19

Runyon Canyon Erosion Surface

The angular unconformity at the base of the Simi 

Conglomerate (Tsi) in the park’s rock record documents 

the time period between 75 million and 58 million 

years ago. Deep, tropical weathering took place on 

this unconformity (Fritsche and Weigand 2008). This 

distinctive erosion/weathering surface, referred to as the 

“Runyon Canyon erosion surface,” and the Paleocene 

and Eocene sedimentary sequence of rocks overlying it 

are important geologic features that have been used to 

establish regional correlations between rock units and 

the tectonic history of the Transverse and the Peninsular 

ranges in southern California (Colburn and Novak 

1989).

Significantly, the Runyon Canyon erosion surface 

coincides with the Cretaceous-Tertiary (“K-T”) 

boundary that marks a massive, worldwide extinction 

event 66.0 million years ago (fig. 13). Now the 

boundary is formally referred to as the CretaceousPaleogene (K-Pg) boundary, though the traditional 

“K-T boundary” terminology is still in common usage. 

This boundary often captures the public’s imagination 

because it resulted in a world without dinosaurs. An 

estimated 50% of all species, including dinosaurs, 

did not survive this extinction event. The accessibility 

of this significant boundary is also of public interest. 

Geologists have identified sites throughout the world, 

some near national parks (see GRI report about Capulin 

Volcano National Monument by KellerLynn 2015), 

where “boundary enthusiasts” can touch the surface. 

The boundary can be seen in several places in the 

Santa Monica Mountains (Colburn and Novak 1989), 

though not all of the sites are located within the park. 

Colburn and Novak (1989) provided sketch maps and 

descriptions of publically accessible sites within the 

Santa Monica Mountains such as Fryman Canyon Park 

in Santa Monica Mountains Conservancy and Runyon 

Canyon Park in the City of Los Angeles.

Rock Types

Geologists classify all rocks into three major types: 

(1) sedimentary, (2) igneous, and (3) metamorphic. 

The park has all three types. Of the 17 named 

formations exposed in the park, 14 are sedimentary, 

two are igneous, and one is metamorphic (see also 

“Formations” section). Table 1 provides a list of 

all the rocks in the park. Tables 2 and 3 summarize 

characteristics of sedimentary and igneous rocks, 

respectively.

Figure 14. Graphic of unconformities. The rock record exposed in the park represents approximately 156 million years 

of geologic time, from the Jurassic Period to the present. This time span includes seven documented unconformities 

including five angular unconformities, one disconformity, and one nonconformity (see table 1). The red “wavy” line 

on the individual graphics indicates the unconformity. Notably, this is not how they look at an outcrop (see fig. 38). 

Graphic by Trista Thornberry-Ehrlich (Colorado State University) after Lillie (2005, figure 2.4).

Table 2. Clastic sedimentary rock classification and characteristics.

Rock Name Clast Size Local Depositional Environment Examples in the Park*

Conglomerate (rounded clasts) 

or Breccia (angular clasts) >2 mm (0.08 in) [larger] Alluvial fan(higher energy) Trabuco Formation

Sandstone 1/16–2 mm (0.0025–0.08 in) Turbidite Chatsworth Formation

Siltstone** 1/256–1/16 mm (0.00015–0.0025 in) Marine or nearshore marine Santa Susana Formation

Claystone** <1/256 mm (0.00015 in) [smaller] Submarine fan

(lower energy) Modelo Formation

*See table 1 for a listing of all sedimentary rock units in the park.

**Claystones and siltstones can also be called “mudstone,” or if they break into thin layers, “shale.”
20

Sedimentary Rocks

Sedimentary rocks are layered strata formed through 

the accumulation and solidification of sediments, which 

may consist of fragments of preexisting rocks, minerals, 

or animal or plant matter. The sediments that make 

up the rocks in the park were deposited in a variety of 

settings, from deep marine to nonmarine/terrestrial 

(table 1), though marine rocks prevail. Sediments that 

were deposited in marine settings millions of year ago 

now sit high in ridges and peaks of the park as a result 

of tectonic forces and the uplift. For example, the 

Topanga Canyon Formation (“Ttc” map units) makes 

up numerous summits and a distinctive anticline in the 

park (see “Folds” section; figs. 13 and 15). The Topanga 

Canyon Formation is highly fossiliferous and contains 

both marine and terrestrial fossils (see “Paleontological 

Resources” section) indicative of nearshore marine 

environments where fluvial activity also played a role. 

The formation consists of sandstone, commonly arkosic 

(feldspar-rich), with interbedded siltstone, pebbly 

sandstone, and pebble-cobble conglomerate (fig. 16). 

The Sespe Formation (Ts and Tsp) is the primary 

terrestrial formation in the park (figs. 16 and 17). It 

consists of a mostly nonmarine sequence of sandstone, 

pebbly sandstone, varicolored mudstone, and pebblecobble conglomerate that was deposited by streams and 

Figure 15. Photograph of Saddle Peak. The Topanga 

Canyon Formation (“Ttc” map units; sandstone, 

siltstone, mudstone, and conglomerate) makes up 

Saddle Peak. During the last 4 million years, these rocks 

were uplifted from a former ocean floor and shoreline 

to 97 m (2,782 ft) above sea level today. Photograph by 

user “MiniHolland” available via Wikimedia Commons 

https://commons.wikimedia.org/wiki/File:Saddle_

Peak,_California.JPG (Creative Commons AttributionShare Alike 3.0 Unported [CC BY-SA 3.0]; https://

creativecommons.org/licenses/by-sa/3.0/deed.en).

Figure 16. Photographs of the Topanga Canyon 

and Sespe Formations. In the upper photograph, 

the Topanga Canyon Formation (gray sandstone) 

was deposited on top of the Sespe Formation (red 

mudstone) in the central Santa Monica Mountains. 

The sequence of marine sandstone (Topanga Canyon 

Formation) over terrestrial sandstone (Sespe Formation) 

indicates a period of subsidence and transgression. 

In the lower photograph, conglomerate beds near 

the base of the Topanga Canyon Formation indicate 

deposition in a cobble beach environment where 

wave action was strong. The exposures in the both 

photographs are along the Calabasas Motorway 

just north of its junction with Red Rock Road. Rock 

hammers (total length approximately 28 cm [11 in]) 

for scale. Photographs from Eugene Fritsche (California 

State University, Northridge, Department of Geological 

Sciences, professor emeritus, GRI scoping presentation, 

7 May 2008).
21

rivers in channels, floodplains, and deltas. The lower 

Sespe Formation (Ts) is characterized by distinctive 

“red beds” in Red Rock Canyon Park (fig. 18). The 

sandstone beds are red chiefly due to the presence 

of ferric oxide (hematite) on the intergranular biotite 

mineral grains; not all beds have the characteristic red 

color. The Piuma Member (Tsp) is distinguished from 

Figure 17. Photograph of the Sespe Formation. As 

shown in an exposure along Rambla Pacifico Road, the 

Sespe Formation commonly consists of river deposits 

such as the conglomerate. Elsewhere, the formation 

also has sandstone and mudstone layers. Rock hammer 

(total length approximately 28 cm [11 in]) for scale. 

Photograph from Eugene Fritsche (California State 

University, Northridge, Department of Geological 

Sciences, professor emeritus, GRI scoping presentation, 

7 May 2008).

Figure 18. Photograph Red Rock Canyon Park. The 

red beds in Red Rock Canyon Park are composed 

of the Sespe Formation (Ts; sandstone, mudstone, 

and conglomerate), which is the primary terrestrial 

formation in the park. Photograph from Eugene 

Fritsche (California State University, Northridge, 

Department of Geological Sciences, professor emeritus, 

GRI scoping presentation, 7 May 2008).

Figure 19. Photographs of the Vaqueros Formation. 

Shown in the upper photograph, the Vaqueros 

Formation crops out at Point Mugu. The thick, crossbedded sandstone was deposited in a shallow marine 

environment. In the lower photograph, rolled over 

layers (dashed red line) in the sandstone formed 

because sand beds deposited on the ocean slope 

or on a submarine fan became unstable soon after 

deposition and slid downhill. The exposure in the 

lower photograph is in a road cut on the north side of 

Pacific Coast Highway about 0.8 km (0.5 mi) west of 

Point Mugu. Upper photograph by Katie KellerLynn 

(Colorado State University). Lower photograph from 

Eugene Fritsche (California State University, Northridge, 

Department of Geological Sciences, professor emeritus, 

GRI scoping presentation, 7 May 2008).
22

the lower Sespe Formation (Ts) by thinner individual 

beds, generally finer grained sandstone, the absence 

of pebble and cobble conglomerate, and greater 

abundance of interbedded lacustrine or lagoonal 

siltstone. Also, the Piuma Member intertongues with 

the Vaqueros Formation (“Tv” map units), a nearshore 

to offshore marine deposit. The Vaqueros Formation 

is a widespread, heterogeneous sequence of thick- and 

medium-bedded sandstone and interbedded siltstone 

and mudstone (fig. 19) that contains a distinctive 

molluscan fauna (see “Paleontological Resources” 

section). A transgressive–regressive cycle of fluvial, 

nonmarine delta, and shelf deposits resulted in 

the intertonguing of the Sespe Formation with the 

fossiliferous sandstone and mudstone of the Vaqueros 

Formation between 28 million and 21 million years ago 

(Fritsche and Weigand 2008).

Igneous Rocks

Igneous rocks formed from magma (molten rock 

material). Where they erupt onto Earth’s surface, 

including the seafloor, they are considered “extrusive” 

(table 3). Where they intrude preexisting rocks in the 

subsurface, they are considered “intrusive.” Although 

the term “volcanic” is sometimes used as a synonym for 

extrusive igneous rocks, “volcanic rocks” can include 

both extrusive rocks and shallow near-surface intrusive 

rocks related to a volcanic system. 

The park has both intrusive and extrusive igneous 

rocks. The oldest igneous rocks in the park are intrusive; 

they consist of granitic rocks (Kgr; fig. 20) that were 

emplaced during the Cretaceous Period (fig. 13). These 

rocks are part of the Sierra Nevada–Peninsular Ranges 

magmatic arc. They intruded the Santa Monica Slate 

(“Jsm” map units; see “Metamorphic Rocks” section). 

Notable extrusive igneous rocks in the park are the 

Conejo Volcanics (“Tco” map units), which cover a large 

Table 3. Volcanic rock classification and characteristics.

Rock Name Silica (SiO2)* Viscosity Explosiveness Rock Formations in the Park

Rhyolite >72%

Viscosity decreases from 

rhyolite (higher viscosity) to 

basalt (lower)

Explosiveness decreases from 

rhyolite (more explosive) to 

basalt (less explosive)

None

Rhyodacite 68%–72% None

Dacite 63%–68% Conejo Volcanics; Zuma Volcanics

Andesite 57%–63% Conejo Volcanics; Zuma Volcanics

Basaltic andesite 53%–57% Conejo Volcanics

Basalt <53% Conejo Volcanics; Zuma Volcanics

*From Clynne and Muffler (2010).

Figure 20. Photographs of granitic rocks. The lightcolored granitic rocks (Kgr) exposed along the trails 

in the Griffith Park area intruded the Santa Monica 

Slate (“Jsm” map units) about 102 million years ago. 

The outcrop in the upper photograph is below Griffith 

Observatory. The close-up view of the rocks in the lower 

photograph is from a trail cut just south of the Griffith 

Park Observatory. Photographs from Eugene Fritsche 

(California State University, Northridge, Department 

of Geological Sciences, professor emeritus, GRI scoping 

presentation, 7 May 2008).
23

area of the western part of the Santa Monica Mountains 

(see “Conejo Volcanics” section). They generally consist 

of flows, breccias (consisting of angular, broken rock 

fragments), and tuffs (consolidated volcanic ash and 

larger particles), as well as related intrusive rocks. 

Separately mapped intrusive rocks (Ti, Tid, Tia, and Tib) 

and mixed rocks (Tim) in the central and western Santa 

Monica Mountains may also be related to the Conejo 

Volcanics and have formed dikes, sills, and plugs in 

the Topanga Canyon Formation. Zuma Volcanics (Tz), 

which are only exposed south of the Malibu Coast 

Fault, mainly consist of extrusive flows, flow breccias, 

and pillow lavas (pillow-shaped masses of lava formed 

in subaqueous environments). 

Conejo Volcanics

The Conejo Volcanics erupted into a marine basin and 

built upwards from the seafloor into shield volcanoes. 

During the GRI scoping field trip, Eugene Fritsche 

(California State University Northridge) pointed out 

a cross section of a 17 million–15-million-year-old 

shield volcano near the intersection of Kanan Road and 

Agoura Road. Fritsche referred to the basal portion of 

this cross section as the “Bowels of Hades” or “Gates 

of Hell.” This portion preserves the conduit through 

which molten rock flowed to the surface.

The Conejo Volcanics in the park contain evidence 

of both submarine and subaerial origins. The rocks 

contain lava flows with “pillows” and oyster beds (fig. 

21; see “Paleontological Resources” section), which are 

indicative of an underwater setting. Lahars (mudflows 

on the flanks of a volcano) near the top of the Conejo 

Volcanics contain petrified logs (see Stadum and 

Weigand 1999) that indicate an elevation of at least 

1,500 m (5,000 ft) above sea level (Eugene Fritsche, 

California State University, Northridge, Department of 

Geological Sciences, professor emeritus, GRI scoping 

presentation, 7 May 2008). The Conejo Volcanics also 

contain volcanic bombs (magma erupted into the air 

and shaped while in flight; “bombs” are more than 

64 mm [2.5 in] across; fig. 22), which are indicative of 

subaerial deposition. 

An unusual phenomenon in the Conejo Volcanics 

is the interbedding of calcareous sandstone and 

volcanic rocks (KellerLynn 2008; see “Paleontological 

Resources” section). Also, the Conejo Volcanics contain 

rare oil seeps (fig. 23). The oil probably migrated from 

older (underlying) marine sedimentary rocks (Pam 

Irvine, California Geological Survey, senior engineering 

geologist, conference call, 17 November 2015).

At 948 m (3,111 ft) above sea level, Sandstone Peak is 

the highest peak in the park (fig. 24). The peak’s name 

is a geologic misnomer because the mountain is made 

up of Conejo Volcanics (igneous rocks) not sandstone 

(a sedimentary rock). The summit consists of the 

Conejo Volcanics, andesitic central zone (Tcoa), which 

is composed of andesitic flows, flow breccias, and 

Figure 21. Photographs of submarine features in the 

Conejo Volcanics. In the upper photograph, pillowshaped masses of basalt are indicators that the lava 

erupted under water. These particular pillow basalts 

are exposed on Yerba Buena Road. In the lower 

photograph, oyster shells in the lava flows are further 

evidence of the submarine origin of the Conejo 

Volcanics. This exposure is in a road cut on Mulholland 

Highway, southeast of Malibu Creek State Park. Rockhammer head (approximately 17 cm [7 in] long) for 

scale. Photographs from Eugene Fritsche (California 

State University, Northridge, Department of Geological 

Sciences, professor emeritus, GRI scoping presentation, 

7 May 2008).
24

agglomerate (volcanic breccia). However, the geologic 

description of the Conejo Volcanics refers to “volcanic 

sandstone” (see samo_geology.pdf in GRI GIS data). 

Furthermore, the breccia and agglomerate at the summit 

resemble sedimentary rocks (Pam Irvine, California 

Geological Survey, senior engineering geologist, written 

communication, 14 June 2016). 

Metamorphic Rocks

Metamorphic rocks are those that have been 

metamorphosed (altered) by high temperature, 

pressure, or fluids. The oldest rocks in the park—Santa 

Monica Slate (“Jsm” map units)—are metamorphic (fig. 

25). The dark gray rocks of the Santa Monica Slate are 

exposed in road cuts in the eastern part of the park. 

They were metamorphosed while being sutured to the 

margin of the North America continent in the Late 

Jurassic–Early Cretaceous periods and then later altered 

by contact metamorphism when they were intruded by 

granitic rocks (Kgr; fig. 20) approximately 102 million 

years ago (see “Geologic History” section).

Figure 22. Photograph of volcanic bomb in the Conejo 

Volcanics. Near the top of the Conejo Volcanics, the 

presence of volcanic bombs—molten rock ejected into 

the air and shaped while in flight; “bombs” are more 

than 64 mm (2.5 in) across—indicates that the volcano 

was subaerial, rising above sea level as a volcanic island. 

This bomb is on Ladyface Mountain west of Kanan 

Road and south of Agoura Road. Lip-balm tube for 

scale. Photograph from Eugene Fritsche (California 

State University, Northridge, Department of Geological 

Sciences, professor emeritus, GRI scoping presentation, 

7 May 2008).

Figure 23. Photograph of oil seeps in the Conejo 

Volcanics. Oil seeps are a rare but distinctive feature 

of the Conejo Volcanics at the park. The oil probably 

migrated from underlying marine sedimentary rocks. 

The estimated area covered by the tar seep in this 

photograph is 18 cm (7 in) wide by 30 cm (12 in) 

high. Photograph by Katie KellerLynn (Colorado State 

University).

Figure 24. Photograph of Sandstone Peak. At

108 m (3,111 ft) above sea level, Sandstone Peak is the 

highest point in the Santa Monica Mountains. Hikers 

can reach the summit via the Backbone Trail, starting 

at Circle X Ranch. The peak is composed of Conejo 

Volcanics, specifically andesitic volcanic rock, although 

its texture and appearance is similar to sandstone. 

Photograph by Flickr user “IvyMIke”, available via 

Wikimedia Commons https://commons.wikimedia.org/

wiki/File:Looking_at_Sandstone_Peak_from_Inspiration_

Point.jpg (Creative Commons Attribution 2.0 Generic 

[CC BY 2.0]; https://creativecommons.org/licenses/by/2.0/

deed.en). 
25

Formations

As shown in the GRI GIS data, the park contains 17 

formally designated formations (table 1). Formations 

are fundamental rock-stratigraphic units and have the 

following attributes: they can be mapped at a regional 

scale; they are distinct from adjoining strata by features 

such as chemical or mineral composition, textures, 

or fossils; and they have definable upper and lower 

contacts.

Some of these formations were originally described and 

named from areas within or near the park (see “Type 

Sections” section). The rock formations north and 

south of the Malibu Coast Fault (see “Faults” section) 

represent distinctly different areas with respect to 

provenance and tectonic history (Yerkes and Campbell 

1979) (see tables 1a and 1b and “Geologic History” 

section).

A formation may be combined with other formations 

to create a group. One formal group—the Topanga 

Group—has exposures in the park. These exposures 

consist of intrusive and extrusive volcanic rocks (Ttb) 

that intruded the undivided Topanga Group (Tt). The 

Calabasas Formation (Tcb), Conejo Volcanics (Tco), 

and Topanga Canyon Formation (Ttc) are the three 

formations formally assigned to the Topanga Group by 

Yerkes and Campbell (1979); they are exposed in the 

central and western Santa Monica Mountains. In the 

eastern Santa Monica Mountains, middle Miocene 

rocks with similar rock types and fossils have been 

informally divided into Topanga Group sandstone, 

siltstone, and conglomerate (Ttss, Ttsl, and Ttcg; see 

GRI GIS data) and the intrusive and extrusive volcanic 

rocks (Ttb).

A formation also may be divided into members. 

Geologists have divided the Calabasas, Topanga 

Canyon, Vaqueros, and Sespe formations into members 

(see samo_geology.pdf in the GRI GIS data). 

Type Sections

The place where a rock formation is best exposed is 

referred to as a “type locality.” More particularly, an 

outcrop may display the formation so well as to become 

a reference location referred to as “type section.” Type 

localities and type sections have both scientific and 

educational significance and are commonly “stops” 

on geological field trips. Because type localities and 

type sections typically occur where a formation was 

originally described and named, they also may have 

historical significance. The names of many well-known 

geologists are linked with type sections and localities. 

Within the park, the names of USGS geologists Robert 

F. Yerkes and Russell H. Campbell are tied to most of 

the type localities (table 4).

Type sections for eight formations occur within the 

authorized boundary of the park (table 4), though the 

Coal Canyon Formation is now considered part of 

Figure 25. Photographs of the Santa Monica Slate. 

The oldest rocks in the park are the metamorphic 

Santa Monica Slate (“Jsm” map units). The road cut 

in the upper photograph exposes the slate along 

the east side of I-405 opposite Mountaingate Drive. 

The dark-gray rocks in the road cut are the slate. The 

close-up view of the slate in the lower photograph is 

from an exposure in a road cut along the east side of 

Skirball Center Drive just south of its intersection with 

Mulholland Drive. Note lens cap in lower photograph 

for scale. Photographs from Eugene Fritsche (California 

State University, Northridge, Department of Geological 

Sciences, professor emeritus, GRI scoping presentation, 

7 May 2008).
26

the Santa Susana Formation (Campbell et al. 2014). 

Having so many type sections in a single NPS area is 

unusual. The high number of type localities within the 

park is probably associated with its complex tectonic 

history and position on an active plate boundary, which 

ensured that a wide variety of rock units were brought 

together and exposed (see “Geologic History” section). 

The NPS Geologic Resources Division is developing a 

database of designated type sections in parks across the 

country. As of August 2016, three national recreation 

areas—Santa Monica Mountains (California), Delaware 

Water Gap (Pennsylvania and New Jersey; see GRI 

report by Thornberry-Ehrlich 2013), and Glen Canyon 

(Utah and Arizona; see GRI report by Graham 2016)—

have the most type sections, each with eight. However, 

as of August 2016, only a fraction of the National Park 

System has been investigated for type sections. The US 

Geological Survey “Geolex” website, http://ngmdb.usgs.

gov/Geolex/search, provides location information and 

nomenclatural summaries for rock formations across 

the country.

Paleontological Resources

Santa Monica Mountains National Recreation Area 

is one of at least 263 parks with paleontological 

resources. The park contains one of the most extensive 

and diverse fossil records in the National Park 

System (Tweet et al. 2014). The park’s foundation 

document (National Park Service 2015a) identified 

paleontological resources as an “other important 

resource or value.” Noteworthy statistics for the park 

include 2,300 known fossil localities, 50 holotype fossils 

(a specimen used in describing a “new” species), and 

type (reference) specimens for at least 50 taxa—16 

snails, 11 foraminifera, 7 seaweeds (4 brown algae 

and 3 red algae), 6 bivalves, 6 fish, 2 ammonites, and 2 

crabs (Tweet et al. 2012; Vince Santucci, National Park 

Service, paleontologist, conference call, 17 November 

2015; Justin Tweet, NPS Geologic Resources Division, 

paleontology technician, email communication, 8 

December 2015). The two most noteworthy fossil 

localities in the Santa Monica Mountains are Old 

Topanga Canyon, where no less than 133 species 

Table 4. Type sections at Santa Monica Mountains National Recreation Area.

Age (millions of 

years ago) Formation Namesake Type locality Reference

Miocene

(23.0–5.3) Calabasas Formation Calabasas Peak

Los Angeles County, exposures 

in Stokes Canyon, in sec. 3, T. 1 

S., R. 17 W., 3 km (2 mi) west of 

Calabasas Peak

Yerkes and Campbell 

(1979)

Miocene

(23.0–5.3) Conejo Volcanics

“Conejo Mountains”—one of 

the most important centers of 

Miocene volcanism in California

Ventura County, exposures at the 

western end of the Santa Monica 

Mountains

Taliaferro (1924)

Miocene

(23.0–5.3)

Topanga Canyon 

Formation Topanga Canyon

Los Angeles County, road cuts on 

Old Topanga Road, in SW/4 sec. 

35, T. 1 N., R. 17 W.

Yerkes and Campbell 

(1979)

Miocene

(23.0–5.3) Trancas Formation Trancas Canyon Los Angeles County, exposures near mouth of Trancas Canyon

Yerkes and Campbell 

(1979)

Miocene

(23.0–5.3) Zuma Volcanics Zuma Canyon

Los Angeles County, exposures on 

west side of canyon about 4 km 

(2.5 mi) north of Point Dume

Yerkes and Campbell 

(1979)

Eocene (?) and 

Paleocene

(66.0–33.9)

Coal Canyon Formation

Note: This formation is 

now considered part 

of the Santa Susana 

Formation.

Carbon (formerly Coal) Canyon

Los Angeles County, exposures 

in S/2 secs. 22 and 27, T. 1 S., R. 

17 W.

Yerkes and Campbell 

(1979)

Upper Cretaceous

(100.5–66.0) Tuna Canyon Formation Tuna Canyon Los Angeles County, exposures in sec. 30, T. 1 S., R. 16 W.

Yerkes and Campbell 

(1979)

Upper Jurassic

(163.5–145.0) Santa Monica Slate Santa Monica Mountains

Extensive exposures east of 

Topanga Canyon, Los Angeles 

County

Hoots (1931)

Note: For more information, see US Geologic Names Lexicon (“Geolex”), a national compilation of names and descriptions of geologic units, at 

http://ngmdb.usgs.gov/Geolex/search.
27

have been identified, and the fossil-fish localities in 

the Modelo Formation (Koch et al. 2004). Resource 

management issues associated with fossils are discussed 

in the “Paleontological Resource Inventory, Monitoring, 

and Protection” section of this report.

Of the 17 formations exposed in the park (table 1), 

16 are known to contain fossils, either in the park or 

elsewhere. Only the Trabuco Formation (Ktr) is not 

known to contain fossils. Fourteen of the formations 

exposed in the park have yielded fossils (see discussion 

below); the other two have the potential to yield fossils, 

though no fossil discoveries have been made to date. 

The ages of known and potential fossils range from 

the Late Jurassic Period to the Quaternary Period 

(fig. 13), representing a span of more than 150 million 

years. The rocks in the park have yielded the remains 

of vertebrates, invertebrates, plants, microfossils, and 

trace fossils. The most abundant fossils are invertebrates 

such as bivalves, cephalopods, and gastropods; the least 

abundant are plants and include leaf and kelp fossils, 

fossil wood, and pollen and spores samples. Fossil fish 

make up the majority of vertebrate material (National 

Park Service 2013). 

The following are particularly noteworthy formations in 

the park with respect to paleontological resources:

● Topanga Canyon Formation (“Ttc” map units). 

This is one of the most fossiliferous formations 

in the park (fig. 26). It is a variable unit, deposited 

during two transgressive–regressive cycles (see 

“Transgressive–Regressive Cycles” section), with 

both marine and nonmarine deposition (Flack 

1993) and both marine and nonmarine fossils. The 

formation has abundant marine fossils, especially 

mollusks (Koch et al. 2004), some of which are 

newly described species (Tweet et al. 2012). It has 

the remains of gastropods, bivalves, barnacles, 

crabs, echinoids, sharks and rays, ray-finned fish, 

sea lions, and whales (Lander 2011). Terrestrial 

fossils in the formation include land plants, small 

reptiles, and mammals (Lander 2011). Investigators 

have found exceptional samples of petrified wood 

from the Fernwood Member of the formation, 

for example, a log that is 15 m (50 ft) long, though 

not intact (John Alderson, Los Angeles County 

Museum, personal communication during scoping, 

7 May 2008). 

● Modelo Formation (“Tm” map units). This is one 

of the most outstanding fossiliferous formations in 

the park. It is best known for its fish fauna (fig. 27). 

The quality of preservation of these specimens is 

remarkable. According to GRI scoping participants, 

these fossil fish are comparable to those of the 

world-famous Green River Formation in Wyoming, 

Utah, and Colorado (KellerLynn 2008). Fossil Butte 

National Monument in Wyoming preserves and 

interprets the exquisite fossils of the Green River 

Formation (see GRI report by Graham 2012b). 

Figure 26. Photographs of fossils from the Topanga Canyon 

Formation. The Topanga Canyon Formation (sandstone, 

siltstone, mudstone, and conglomerate) is the most 

fossiliferous rock unit in the park. It has abundant marine 

fossils, such as gastropods (snail, Cancellaria sp.; upper 

photograph) and bivalves (mussel, Mytilus mathewsonii; 

lower photograph), as well as terrestrial fossils. Scale is in 

centimeters. Photographs from Eugene Fritsche (California 

State University, Northridge, Department of Geological 

Sciences, professor emeritus, GRI scoping presentation, 7 

May 2008).
28

● Sespe Formation (Ts and Tsp). Among a history of 

many marine rocks, the Sespe Formation stands 

out as the primary terrestrial formation in the 

park. Fossil discoveries from this formation in the 

park include both plants and animals: root casts, 

burrows, frogs, tortoises, didelphid marsupials 

(opossums), rodents, pikas, and camels (Whistler 

and Lander 2003; Lander 2011). 

● Conejo Volcanics (“Tco” map units). Fossils in 

volcanic rocks are rare, yet within a small area 

of Malibu Canyon in the park, more than 200 

fossil localities occur in the Conejo Volcanics 

(KellerLynn 2008). The formation is primarily 

composed of volcanic rocks such as basalt but 

is interbedded with sandstone, siltstone, and 

limestone. Fossils in the Conejo Volcanics include 

foraminifera, brachiopods, bivalves, gastropods, 

barnacles, echinoids, worm tubes, fish scales, and 

wood (fig. 21). These fossils are noteworthy because 

of the rarity of carbonate rocks in association 

with submarine volcanism as well as the rarity of 

limestone in the Cenozoic record of the Pacific 

Coast (Tweet et al. 2012).

In addition, the Tuna Canyon Formation (“Kt” map 

units), Chatsworth Formation (Kc), Simi Conglomerate 

(Tsi), Santa Susana Formation (Tss and Tssl), Llajas 

Formation (Tl), Vaqueros Formation (“Tv” map units; 

fig. 28), Zuma Volcanics (Tz), Calabasas Formation 

(“Tcb” map units), Trancas Formation (“Tr” map units), 

and Monterey Shale (“Ttm” map units) have yielded 

fossils in the park (Tweet et al. 2012). Although not a 

designated formation, sedimentary rocks of the Pacific 

Palisades area (QTms) have also yielded fossils (Pam 

Irvine, California Geological Survey, senior engineering 

geologist, written communication, 14 June 2016). The 

Santa Monica Slate (“Jms” map units) and Las Virgenes 

Sandstone (Tlv) have yet to yield fossils in the park but 

have potential based on discoveries outside the park. 

The most likely fossils to be found in the Santa Monica 

Slate are bivalves and ammonites. Logs, brackish 

water mollusks, and invertebrate burrows are the 

most likely fossils for the Las Virgenes Sandstone. The 

Trabuco Formation (Ktr) is not presently known to be 

fossiliferous. No fossils occur in the intrusive igneous 

rocks (Kgr and “Ti” map units) of the park (Tweet et al. 

2012).

Figure 27. Photograph of fossil fish in the Modelo 

Formation. The most notable vertebrate fossils in the 

park are fish, such as Xyne grex (part of a subfamily 

of herring, sardines, and sprats), in the Modelo 

Formation (sandstone and shale). Scale is in centimeters. 

Photograph from Eugene Fritsche (California State 

University, Northridge, Department of Geological 

Sciences, professor emeritus, GRI scoping presentation, 

7 May 2008).

Figure 28. Photograph of the Vaqueros Formation. 

Fossil scallops in the Vaqueros Formation (sandstone, 

siltstone, and mudstone) at Point Mugu indicate 

deposition in a shallow-marine environment, 

approximately 28 million–21 million years ago. Pencil 

for scale. Photograph from Eugene Fritsche (California 

State University, Northridge, Department of Geological 

Sciences, professor emeritus, GRI scoping presentation, 

7 May 2008).
29

Landslides

The park is located near the southern boundary of the 

Transverse Ranges, which compose a tectonically active 

area where uplift and extensive folding and faulting 

have produced many steep slopes of deformed and 

weakened rocks. These conditions have resulted in 

the widespread occurrence of landslides (Irvine and 

McCrink 2012). The hazards associated with landslides 

are discussed in the “Landslide Hazards” section of this 

report.

The term “landslide” refers to a wide variety of 

processes and landforms involving the downslope 

movement, under gravity, of masses of soil and rock 

material. Landslides have a broad range of morphology, 

rates, patterns of movement, and scale (fig. 29). 

With respect to landslides within the park, the GRI GIS 

data (samo_geology.mxd) show only 12 occurrences 

of landslide deposits (Qls). Mapped landslide deposits 

occur mostly in Topanga State Park and north of Sequit 

Point and consist of rock detritus from bedrock and 

surficial materials, broken in varying degrees from 

relatively coherent large blocks to disaggregated small 

fragments. Most of these deposits are Holocene, 

though some dissected landslides may be as old as late 

Pleistocene.

Because only selected landslide deposits are shown 

in these data (samo_geology.mxd), this is only a small 

subset of the actual landslides on the landscape in 

the park. Landslide deposits (Qls) in these data were 

compiled primarily from landslide inventories prepared 

by the California Geological Survey for the Seismic 

Hazard Zonation Program. Only landslides described 

as definite or probable and larger than 50,000 m2

(538,000 ft2 or 12 ac) are shown to preserve the clarity 

of the underlying bedrock geology. Selected historically 

active landslides between 10,000 m2 (108,000 ft2 or 2 

ac) and 50,000 m2 are shown, but no landslides smaller 

than 10,000 m2 are shown on this map. Exceptions to 

these rules include small or questionable landslides 

surrounded by larger probable or definite landslides 

(Campbell et al. 2014).

Significantly, the GRI GIS data set for the park also 

includes a separate ArcMap document file (samo_

geohazards.mxd) and geodatabase (see “Geologic 

Map Data” section) of the locations of 3,580 landslides 

from a landslide inventory prepared by the California 

Geological Survey (Irvine and McCrink 2012). These 

landslide data only include features that were large 

enough to show as polygons at a scale of 1:24,000 

(1 inch = 2,000 feet). Therefore, numerous smaller 

landslides exist but were too small to include in the 

database (Pam Irvine, California Geological Survey, 

senior engineering geologist, written communication, 

11 May 2016). Also, the landslide inventory is ongoing 

(see “Landslide Hazards” section).

Of the 3,580 landslides in the GRI GIS data, 2,503 were 

mapped within the park. Based on the type of material 

and movement exhibited, landslide deposits may be 

categorized into types (fig. 29). The types of landslides 

in the park are, in order of prevalence, rockslide 

(2,039), debris slide (400), debris flow (31), rockfall 

(22), earthflow (8), debris spread (2), and rock flow 

(1). Notably, the California Geological Survey uses a 

modified version of the classification shown in figure 29.

Rockslides, the most prevalent type in the park, involve 

sliding bedrock that moved but remained largely 

intact. Debris slides, the second most prevalent type 

in the park, initially move as a shallow intact slab of 

material but break up after short distances into “falls” 

and “flows” (discussed below). Debris slides consist of 

coarse-grained soil, mostly in unconsolidated sandy or 

gravelly units but also in residual soils that form inplace from the weathering of bedrock. Falls are masses 

of soil or rock that dislodge from steep slopes and free 

fall, bounce, or roll downslope. Flows mobilize as a 

deforming, viscous mass without a discrete failure plane 

(a zone of weakness at the base of a rock mass where 

movement typically takes place). 

In the park, rockslides and debris slides are most 

abundant in Tertiary-age sedimentary rocks that have 

been deformed by folding and faulting or contain weak 

clay layers (Irvine and McCrink 2012). Irvine and 

McCrink (2012) provided further information about 

these two types of landslides, as well as descriptions 

of the other types of landslides in the park. These 

descriptions are included in the ancillary map 

information document (samo_geology.pdf) for the GRI 

GIS data.

Fluvial Features

Malibu, Solstice, and Topanga creeks are perennial 

streams that flow in the park. Other streams have 

segments that are perennial. Runoff from developed 

areas creates unnatural streams and a perennial source 

of surface water (KellerLynn 2008).
30

Figure 29. Graphic showing slope movements. Different types of slope movement are defined by material, nature 

of the movement, rate of the movement, and moisture content. Rockslides followed by debris slides (red boxes on 

graphic) are the most prevalent types of landslide in the park. The California Geological Survey uses a modified version 

of this classification, as do the GRI GIS data. Graphic by Trista Thornberry-Ehrlich (Colorado State University) redrafted 

using a graphic and information in Varnes (1978). Rates of movement are from Cruden and Varnes (1996).
31

Alluvium marks active, intermittent, and past streams, 

ranging in age from Pleistocene to Holocene (table 1 

and fig. 13). Map units associated with fluvial activity 

include alluvium (Qa), young alluvium (“Qya” map 

units), and old alluvium (Qoa). Mappers divided the 

alluvial deposits in the park based on age. Alluvium 

(Qa; late Holocene Epoch) is the youngest and locally 

encompasses areas of historic flooding, including 

deposits behind flood-control structures. Young 

alluvium (Qya, Qya2, and Qya1; Holocene and late 

Pleistocene epochs) consists of unconsolidated, 

generally friable, stream-deposited silt, sand, and gravel 

on floodplains, locally including related alluvial fans and 

streambeds where those were not mapped separately. 

Deposits of young alluvium are clearly related to 

depositional processes that are still ongoing. Deposits 

of old alluvium (Qoa; late to middle Pleistocene 

Epoch) may be dissected to varying degrees or have 

soil development; these deposits have been uplifted or 

otherwise removed from active sedimentation in stream 

channels.

Cave and Karst Resources

Santa Monica Mountains National Recreation Area 

is one of at least 160 parks with caves and/or karst 

resources in the National Park System. Caves are 

naturally occurring underground voids such as 

solutional caves (commonly associated with karst), 

lava tubes (tunnel-like caves in a lava flow after lava has 

stopped flowing), sea caves (clefts or cavities in a sea 

cliff), talus caves (a void among collapsed boulders), 

regolith caves (formed by soil piping), and glacier 

caves (ice-walled caves) (Toomey 2009). Known caves 

in the park include sandstone caves in the Topanga 

Canyon (“Ttc” map units), Sespe (Ts and Tsp), and 

Chatsworth (Kc) formations. These caves are erosional 

features scattered throughout the park. Eagle Rock, 

Eagle Springs, and Garapito Canyon are notable areas 

with sandstone caves (KellerLynn 2008). In addition, 

where subjected to continuous wave action, sea caves 

have formed in several locations of rocky points along 

the ocean front in the park (Dale Pate, NPS Geologic 

Resources Division, National Cave and Karst Program 

Manager, written communication, 10 December 2015). 

A popular hiking destination in the park is the Grotto 

at Circle X Ranch. Scoping participants noted that a 

stream runs through and around the Grotto, and online 

photographs commonly show a waterfall cascading over 

the entrance area. Scoping participants did not identify 

the Grotto as a significant cave feature (KellerLynn 

2008), and not much is known about its geology. Based 

on online photographs, however, it appears to be a 

talus-type cave; it probably occurs in Conejo Volcanics 

(see GRI GIS data).

North of the park, the Simi Hills contain many small 

caves and rock shelters (KellerLynn 2008). Although 

these caves are outside the park, they are of interest to 

park managers as significant cultural sites, which have 

been highlighted in archeological studies and reports. 

The Simi Hills’ caves and rock shelters are within the 

extent of the GRI GIS data. 

The “Bat Cave” of Batman and Robin fame is in the 

park. It consists of a tunnel in an old quarry near 

Hollywood; it is not a natural cave and would, therefore, 

not be included in a cave resource inventory (see “Cave 

and Karst Resource Management” section). However, 

this feature is of interest for the park’s film-making 

history, which merited a significance statement in the 

park’s foundation document (National Park Service 

2015a).

Karst is a landscape that forms through the dissolution 

of soluble rocks, commonly carbonate rocks such as 

limestone or dolomite (Toomey 2009). In the park, 

the Santa Susana Formation (Tss and Tssl), which is 

primarily shale, contains scattered pods and lenses 

of algal limestone and gray limestone concretions 

(hard, compact nodules). Also, the Fernwood Member 

of the Topanga Canyon Formation (Ttcf), which is 

predominantly sandstone, contains minor amounts of 

limestone. Neither formation has sink holes, caves, or 

other characteristic features of karst landscapes (Pam 

Irvine, California Geological Survey, senior engineering 

geologist, email communication, 17 November 2015). 

Nevertheless, smaller amounts of limestone [e.g., in 

pods and lenses] can still have active karst processes 

[e.g., groundwater discharge, recharge, and flow] (Dale 

Pate, NPS Geologic Resources Division, National Cave 

and Karst Program Manager, written communication, 

10 December 2015). 

Eolian Features and Processes

Eolian (also spelled “aeolian”) refers to windblown 

erosion, transportation, and deposition of sediments 

(Lancaster 2009). Features created by eolian processes 

include depositional landforms and deposits such as 

dunes, loess, and sand sheets, as well as erosional forms 

such as desert pavement, yardangs, and ventifacts. 
32

The GRI GIS data include eolian deposits (Qe). These 

consist of loose, fine- to medium-grained sand, silty 

sand, and silt along the coastline of the park. This 

material forms transitory dunes against beach-facing 

cliffs.

The “Great Dune” is the only “charismatic” eolian 

feature in the area. The dune, which is about 120 m 

(400 ft) tall, is a popular recreation destination (Barlow 

2011). It is about 3.5 km (2.2 mi) south of Point Mugu 

along the Pacific Coast Highway and covers an area 

of roughly 50,639 m2

 (545,074 ft2 or 13 ac) (fig. 30). 

Compared to sand dunes in other NPS areas (e.g., see 

GRI reports about Great Sand Dunes National Park 

and White Sands National Monument by Graham 2006 

and KellerLynn 2012, respectively), this dune is not of 

huge dimensions, but it is the only one of any size in the 

park and is a good example of ongoing eolian processes 

(KellerLynn 2008).

Marine and Coastal Resources

The park’s boundary stops at mean high water, so 

marine resources are minimal compared to other NPS 

areas such as Virgin Islands National Park (see GRI 

report by Hall and KellerLynn 2010), Buck Island Reef 

National Monument (see GRI report by KellerLynn 

2011), and Dry Tortugas National Park (see GRI report 

by Port 2014), which are known for their reefs. Golden 

Gate National Recreation Area near San Francisco (see 

GRI report by Port 2016) contains marine areas. 

Shipwrecks and kelp forests are notable submerged 

resources off the coast in the Santa Monica Mountains 

area, but the National Park Service has no management 

obligations at these locations. According to scoping 

participants, submarine canyons are of interpretive 

interest (KellerLynn 2008); for instance, the west end 

of Mugu Canyon is one of deepest submarine canyons 

off the coast of North America. Also, the only natural 

deep-water port between San Diego and San Francisco 

is located at Port Hueneme, approximately 11 km (7 mi) 

northwest of Point Mugu. 

Coastal resources are located in a transition zone 

between marine and terrestrial environments and 

include characteristics of both. Coastal environments—

shaped by wind, waves, tides, and weathering—may 

include tidal flats, estuaries, river deltas, wetlands, 

dunes, beaches, barrier islands, bluffs, headlands, and 

rocky tide pools. Coastal processes include both erosion 

as evidenced by wave-cut cliffs, sea caves (see “Cave and 

Karst Resources”), and other features (e.g., an arch in 

the park), and accretion, as evidenced by beaches. 

The Santa Monica Mountains are known for sand and 

cobble beaches. Beach deposits (Qb) are more-or-less 

continuous along the 64-km (40-mi) coastline in the 

park, from Point Mugu to Santa Monica Pier (figs. 1 

and 31). The GRI GIS data also include active coastal 

estuarine deposits (Qes), primarily landward of Laguna 

Point and surrounding Mugu Lagoon. These deposits 

occur where a coastal body of water meets the current 

Figure 30. Photograph of the Great Dune. The “Great Dune” is the most notable eolian feature in the park. It is 

located along the Pacific Coast Highway south of Point Mugu. Note cars for scale. California Coastal Records Project, 

Image 200405486, taken 23 October 2004; http://www.californiacoastline.org/cgi-bin/image.cgi?image=200405486&m

ode=sequential&flags=0&year=2004. Copyright © 2002-2016 Kenneth & Gabrielle Adelman, California Coastal Records 

Project, www.Californiacoastline.org. 
33

of a stream. The authorized boundary of the park also 

contains rocky intertidal areas with tide pools and 

coastal lagoons (e.g., Malibu, Topanga, and Zuma).

The GRI GIS data include old shallow marine deposits 

on wave-cut surface (Qom). As an indication of age, 

some wave-cut surfaces show slight to moderate soil 

development. Moreover, overlying deposits locally 

contain molluscan fauna of the late Pleistocene Epoch 

(Addicott 1964).

Erosion of the shoreline produced these wave-cut 

platforms in bedrock, which were later covered by 

sedimentary deposits such as sand, silty sand, and 

gravel of nearshore marine, beach, estuarine, lagoonal, 

or continental dune origins. These features are the 

equivalent of marine terraces, representing abandoned 

strips of coastline at two or more altitudes above 

present sea level. The old shallow marine deposits on 

wave-cut surface (Qom) in the park have not been 

correlated to the prominent marine terraces in the area, 

of which there are two: (1) the higher, older Malibu 

Terrace (Davis 1933; Birkeland 1972); and

(2) the lower, younger Point Dume (or Pacific Palisades) 

Terrace (McGill 1989). The Malibu Terrace formed 

about 320,000 years ago when sea level was 4 m (13 ft) 

higher than at present. The Point Dume Terrace formed 

about 125,000 years ago when sea level was about 6 m 

(20 ft) higher than at present (Shaller and Heron 2004). 

An intermediate terrace, the Corral Terrace, formed 

about 200,000 years ago when sea level was nearly the 

same as present (Shaller and Heron 2004). Although the 

Point Dume Terrace formed under conditions of higher 

sea level, referred to as a “highstand,” than the Malibu 

Terrace, the Malibu Terrace is higher today because of 

uplift that occurred between the two highstands (Tweet 

et al. 2012). Because of tilting and uplift over the past 

320,000 years, the terraces are not found at consistent 

elevations. For example, the Point Dume Terrace is at 

sea level west of Point Dume but about 90 m (300 ft) 

above sea level to the east (Soper 1938).

As climate continues to change, sea level rise is a major 

concern for coastal resources within the park. See 

“Climate Change Planning and Sea Level Rise” section.

Figure 31 (right). Photographs of coastline in Santa 

Monica Mountains National Recreation Area. The park 

stretches from roughly Point Mugu (upper photograph) 

past Point Dume (middle photograph) to Santa Monica 

Pier (lower photograph), spanning 64 km (40 mi) along 

the Pacific Ocean and Santa Monica Bay. The park’s 

coastline has very different morphology and geology, 

depending on a specific location. Upper: The Vaqueros 

Formation (Tvd; siltstone or mudstone) is exposed at 

Point Mugu. Middle: The Monterey Shale (Tmt) crops 

out at Point Dume. Lower: Beach deposits (Qb; sand) 

were mapped at Santa Monica Pier. California Coastal 

Records Project, Image 8705162, taken June 1987, http://

www.large.images.californiacoastline.org/images/1987/

large/2/8705162.JPG; Image 8129, taken 30 October 

2002, http://www.large.images.californiacoastline.

org/images/2002/large/9/8129.JPG; and Image 

200802289, taken 18 September 2008, http://www.

californiacoastline.org/cgi-bin/image.cgi?image=20080

2289&mode=sequential&flags=0&year=2008. Copyright 

© 2002-2016 Kenneth & Gabrielle Adelman, California 

Coastal Records Project, www.Californiacoastline.org.

35

Geologic Resource Management Issues

This section 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 

Santa Monica Mountains National Recreation Area. The NPS Geologic Resources Division provides 

technical and policy assistance for these issues.

During the 2008 scoping meeting (see scoping summary 

by KellerLynn 2008) and 2015 conference call, 

participants (see Appendix A) identified the following 

geologic resource management issues. They are ordered 

with respect to management priority.

● Landslide Hazards

● Paleontological Resource Inventory, Monitoring, 

and Protection

● Climate Change Planning 

● Earthquakes

● Cave and Karst Resource Management

● Flooding and Dam Failure

● Abandoned Mineral Lands and Other Disturbed 

Lands

Resource managers may find Geological Monitoring

(Young and Norby 2009) useful for addressing some 

of these geologic resource management issues. An 

online version of Geological Monitoring is available at 

http://go.nps.gov/geomonitoring. 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, suggested methods of monitoring, and case 

studies.

Landslide Hazards

The GRI GIS data provide evidence of the Santa 

Monica Mountains’ susceptibility to landslides. The 

data show the ubiquitous nature of landslides (fig. 32) 

with 3,580 geohazard features marked as both point 

features (symbols) and area features (colored polygons). 

Scoping participants noted that landslides pose a 

significant threat to park infrastructure and human 

safety. Big, deep landslides destroy roads; small quick 

landslides kill people (KellerLynn 2008). 

In actuality, even more landslides than those included 

in the GRI GIS data occur on the landscape: smaller 

features were not mapped by Irvine and McCrink 

2012; scale 1:24,000), and the landslide inventory 

by the California Geological Survey is ongoing (see 

“Landslides” section). Since the 2012 inventory, 

more landslides, especially along highways, have 

been added to the California Geological Survey’s 

landslide database (GRI conference call participants, 

17 November 2015). The database is now available 

at http://maps.conservation.ca.gov/cgs/lsi/. Updates 

include additional existing maps and new landslides. 

Sources of new landslides are aerial photos (e.g., from 

post-fire overflights), notable events covered by the 

media, locally reported failures (e.g., from the Ventura 

County geologist), and updates from geoengineering 

consultants tasked with mitigating hazards (GRI 

conference call participants, 17 November 2015). 

Generally speaking, weak rocks such as shale and 

claystone; unconsolidated deposits, including artificial 

fill; and past landslide deposits are susceptible to 

landslides. Steep slopes add to the susceptibility of 

an area. Additionally, anthropogenic alteration of the 

landscape such as roads (e.g., undercutting a landslide 

deposit), other infrastructure (adding weight to a 

deposit), or irrigation (adding moisture) can affect 

slope, increasing its susceptibility to landslides. Also, 

earthquakes and storms can trigger landslides, and 

fire can denude vegetation, increasing susceptibility 

to landslides (see “Earthquakes” and “Climate 

Change Planning” sections). The State of California, 

Department of Conservation, provides an online 

map service at http://maps.conservation.ca.gov/cgs/

firelandslide/ that shows fire perimeter and deep 

landslide susceptibility (fig. 33). This map service was 

based on work by Wills et al. (2011).

In addition to the GRI GIS data, sources of 

landslide information specific to the park include 

Steensen (2005), which is a trip report summarizing 

reconnaissance of unstable slopes and erosional 

features following winter 2004–2005 when recordsetting precipitation in southern California initiated 

numerous landslides and erosional events; the GRI 

scoping summary (KellerLynn 2008); and a geologic 
36

resources foundation summary (National Park Service 

2013). Helpful online resources are listed in the 

“Additional References” section of this report. Scoping 

participants suggested the following resources:

● Campbell (1975) is USGS Professional Paper 851. 

Scoping participants identified this publication 

as a significant source of information about slope 

movements at the park.

● Highland and Bobrowsky (2008) is a “landslide 

handbook” published by the US Geological Survey.

● Wieczorek and Snyder (2009)—the Geological 

Monitoring chapter about slope movements—

described five vital signs for understanding and 

monitoring slope movements: (1) types of landslide, 

(2) landslide causes and triggers,

(3) geologic materials in landslides,

(4) measurement of landslide movement, and

(5) assessment of landslide hazards and risks. 

● Work by Susan H. Cannon at the US Geological 

Survey is applicable to the park. Reports can be 

found by searching “Susan Cannon” on the USGS 

Publications Warehouse at https://pubs.er.usgs.

gov/. Although Cannon has recently retired, the 

US Geological Survey continues work on the cycle 

of landsliding and fires in California; for example, 

Dennis Staley is conducting research in the park 

(Conference call, 17 November 2015).

Figure 32. Portion of GRI GIS data showing landslides. The GRI GIS data (see samo_geohazards.mxd) contain 3,580 

hazard area features that delineate past landslides throughout the park and vicinity. The brown and red forms on 

the graphic represent rockslides and soil slides in the Zuma Canyon area. The arrows point in the direction of flow. 

The hottest color (red) indicates the most recent activity. The labels are map symbols of various rock formations and 

unconsolidated deposits (see table 1 and GRI GIS data). The pink lines are anticlines and synclines. The red line is the 

park boundary. Data are plotted over ESRI National Geographic basemap layer. Sources: National Geographic, Esri, 

DeLorme, HERE, UNEP-WCMC, USGS, NASA, ESA, METI, NRCAN, GEBCO, NOAA, increment P Corp.
37

Paleontological Resource Inventory, 

Monitoring, and Protection

All paleontological resources are nonrenewable and 

subject to science-informed inventory, monitoring, 

protection, and interpretation as outlined by the 

2009 Paleontological Resources Preservation Act (see 

Appendix B). As of August 2016, National Park Service 

regulations associated with this act had been signed. 

Regulations for other agencies in the Department of 

Interior were awaiting signatures.

The variety of landowners and management strategies 

within the park highlight the need for the development 

of a resource stewardship strategy for paleontological 

resources that would contain specific management 

guidance, as well as a visitor use management plan. 

These needs were identified in the park’s foundation 

document (National Park Service 2015a). In addition, 

the foundation document identified the need for 

an inventory of fossil locations in the park’s GIS. 

Documentation of fossil localities is necessary for 

evaluating their accessibility as it relates to protection 

from potential theft as well as a site’s worthiness for 

interpretation and visitors’ ability to access it. Such 

an inventory is the first step in assessing a locality’s 

condition and determining an appropriate monitoring 

plan.

Inventory

With respect to inventorying the park’s paleontological 

resources, Tweet et al. (2012) provided a list of 

relevant publications for the Santa Monica Mountains. 

Investigators have been collecting, studying, and 

describing these paleontological resources since 

1906, and opportunities abound for continued 

paleontological research and collaboration with nearby 

universities as well as partnerships and public outreach 

with the Natural History Museum of Los Angeles 

County and the La Brea Tar Pits (National Park Service 

2015a).

Figure 33. Screen capture of map service showing fire perimeter and landslide susceptibility. Two factors are important 

for reading this map: (1) weak rocks and steep slopes are more susceptible to landslides, and (2) recent wildfires 

increase the likelihood of landslides. The white to dark-red areas indicate susceptibility to deep landslides. Darker 

reds have a higher susceptibility. Many areas in the park are highly susceptible. Recent fires are outlined in blue (see 

the legend at http://maps.conservation.ca.gov/cgs/firelandslide/); for example, the area of the 2013 Spring Fire at the 

western edge of the park. That fire covered 9,740 ha (24,060 ac).
38

Three NPS publications provide park-specific 

information: Koch and Santucci (2003), Koch et 

al. (2004), and Tweet et al. (2012) (see “Literature 

Cited” section). Also, a paper by Tweet et al. (2014) 

summarized these NPS publications and provided 

more recent findings. Of significance for resource 

management and inclusion in the park’s GIS, Hoots 

(1931) documented many of the known fossil localities 

(KellerLynn 2008). 

Monitoring

In the Geological Monitoring chapter about 

paleontological resources, 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. These vital signs may be useful for 

addressing identified threats (discussed below). Park 

managers are encouraged to contact the NPS Geologic 

Resources Division for assistance.

Protection

Varying access and land management regulations 

throughout the park likely contribute to confusion 

over fossil collecting prohibitions and research 

permit requirements. Furthermore, with increasing 

recreational use comes an increased potential for illegal 

fossil collecting within the park.

The park’s foundation document (National Park 

Service 2015a) listed the following three threats to the 

park’s paleontological resources:

● Illegal amateur fossil collecting is a major threat to 

the preservation of the paleontological history. The 

removal of fossils happens on a recurring basis in 

all areas of the mountains, even those not governed 

by the National Park Service. More fossiliferous 

locations in the surrounding area should be 

protected by the National Park Service, state parks, 

or the Mountains Recreation and Conservation 

Authority in order to prevent any further removal.

● Natural erosion of the landscape can impact the 

preservation of the fossils in several sites.

● Graffiti is becoming a major threat to the 

paleontological resources.

Similarly, Tweet et al. (2014) noted coastal and 

mountain erosion, landslides, theft, and vandalism as 

threats. Koch et al. (2004) reported that many of the 

fossil fish localities in the Modelo Formation have been 

destroyed or made inaccessible as a result of private 

construction.

Visitor use and access is a “key issue” identified in the 

park’s foundation document (National Park Service 

2015a). The variety of land owners, and associated 

management priorities, within the park’s authorized 

boundary highlights the interrelationship between a key 

issue (visitor use and access) and an important resource 

and value (paleontological resources). These issues 

are also related to stressors—housing development, 

road distance and accessibility, and human footprint—

identified in the park’s natural resource condition 

assessment (Stoms et al. 2013). 

Interpretation

The local community has roots in fossil collecting 

since the 1930s, with many adults maintaining their 

enthusiasm for fossils from childhood visits to the 

Old Topanga Canyon fossil locality (Koch et al. 

2004). Opportunities for interpretation abound in a 

park with a wealth of paleontological resources (see 

“Paleontological Resources” section) to a public with 

a long-term interest. Significantly, however, the Old 

Topanga Canyon fossil locality is privately owned, 

and visitors are not presently allowed on the property 

(National Park Service 2015a). Similarly, access and 

the lack of visitor infrastructure are issues for Fossil 

Ridge Park, another important fossil locality in the 

Santa Monica Mountains. Thus past practices and the 

patchwork of land ownership in the Santa Monica 

Mountains are likely to cause confusion about which 

fossil localities can be accessed and/or where fossil 

collecting is allowed.

As with all National Park Service areas, fossil collecting 

is prohibited in the park. Also, researchers need to 

acquire permits for paleontological investigation and 

collection within the park. These regulations, however, 

may not be common knowledge. Consequently, fossilfocused public outreach and education by the National 

Park Service and its management partners in Santa 

Monica Mountains Recreation Area should include 

a clear discussion about fossil resource management 

regulations for the different areas and landowners. Park 

managers are encouraged to contact the NPS Geologic 

Resources Division about developing an interpretive 

message.
39

Recommendations

Koch et al. (2004) made the following 

recommendations: (1) conduct active resource 

management at Old Topanga Canyon fossil site;

(2) promote research, particularly at the Old Topanga 

Canyon site, the Modelo fossil fish beds, and fossil 

wood deposits; (3) patrol known sites; (4) continue 

cooperation with state parks, conservancies, museums, 

and universities; (5) develop a Project Management 

Information System (PMIS) statement for fossil 

resource protection; (6) assess the commercial value 

of fossils preserved within the park; (7) provide 

training for park staff in fossil resource protection; 

and (8) increase public awareness of NPS fossil 

regulations. Tweet et al. (2012) recommended that 

these recommendations in Koch et al. (2004) be 

reviewed in order to check progress and determine if 

any should be modified or dropped. In addition, Tweet 

et al. (2012) made the following recommendations: 

(1) monitor significant sites at least once per year; (2) 

compile a list and contact local researchers, perhaps 

annually, for assistance in evaluating new discoveries 

and keeping park staff up-to-date on recent discoveries; 

(3) encourage park staff members to observe exposed 

sedimentary rocks and associated eroded deposits for 

fossil material while conducting their usual duties, and 

photodocumenting and monitoring any occurrences 

of in situ paleontological resources; (4) encourage 

park staff to take part in paleontological field trips with 

trained paleontologists; (5) schedule site monitoring 

by a trained paleontologist during future construction 

projects or archeological excavations in order to 

document and protect fossil resources; and (6) contact 

the NPS Geologic Resources Division for technical 

assistance with paleontological resource management 

issues. The NPS Fossils and Paleontology website 

(http://go.nps.gov/fossils_and_paleo) provides more 

information

Climate Change Planning and Sea Level Rise

Climate change, in conjunction with other stressors, 

will probably affect all aspects of park management 

from natural and cultural resources to park operations 

and visitor experience (National Park Service 2015a). 

The park’s foundation document noted climate change 

scenario planning as a data need (National Park Service 

2015a). Appendix B of this report lists various laws and 

policies that provide guidance pertaining to climate 

change, and the “Additional References” section 

provides links to websites containing information about 

climate change, sea level rise, and storm surge. 

Increased frequency and severity of wildfires and 

area burned is a primary threat in the park from 

climate change (National Park Service 2015a). The 

park’s natural resource condition assessment (Stoms 

et al. 2013) found that fire frequency could increase 

dramatically (62%–88%) by the end of the century as a 

result of climate change. An increase in fire frequency 

could in turn induce more landslides (see “Landslides” 

and “Landslide Hazards” sections). Another threat is 

extreme weather conditions (e.g., drought) resulting 

from climate change. The outcome of the current 

drought and widespread dieback of chaparral shrubs 

in the park is unknown, but loss of vegetation is likely 

to be a factor for landslides (GRI conference call 

participants, 17 November 2015). 

Climate change will manifest itself as shifts in mean 

conditions (e.g., increasing mean annual temperature). 

Stoms et al. (2013) found that climate models 

consistently projected a 25%–34% increase in “growing 

degree days” by 2100 at the park scale, resulting in 

future conditions that are currently found in the 

western Mojave Desert. Minimum winter temperatures 

are projected to increase by 2.1°C–2.8oC (3.4oF–4.6oF) 

while maximum summer temperatures are projected 

to increase by 4.0°C–5.3oC (6.8oF–9.1°F). Seasonality, 

measured as the standard deviation of monthly mean 

temperatures, is projected to increase by 16%–60%. 

Precipitation projections are variable, either increasing 

or decreasing, depending on the outcome of a particular 

global climate model. 

Climate change will also manifest itself as changes 

in climate variability (e.g., more intense storms and 

droughts). This is a factor for landslides because high 

levels of precipitation can lead to slope instability 

and erosional hazards (National Park Service 2015a). 

Additionally, storm surge height is estimated to increase 

0.94 m (3.08 ft) over the next 50 years and 0.96 m (3.14 

ft) over the next 100 years (Caffrey 2015), which will 

impact coastal areas in the park. 

Sea level rise is a primary concern with respect to 

climate change. The park is one of 111 parks that the 

National Park Service has identified as being vulnerable 

to sea level rise. Historical sea level trends calculated 

from the Santa Monica tide gauge (9410840) show that 

each year between 1933 and 2014, sea level rose 1.5 mm 
40

(0.06 in) (Caffrey 2015). Depending on the emissions 

scenario, sea level is projected to increase between 14 

cm (0.48 ft) and 15 cm (0.49 ft) by 2050, and between 

35 cm (1.16 ft) and 49 cm (1.57 ft) by 2100 (Caffrey 

2015). In response to sea level rise, property owners are 

armoring shorelines. This practice is affecting currents 

and sediment transport and deposition (National Park 

Service 2015a), which could impact park resources such 

as beaches.

Peek et al. (2015) determined that no NPS “assets” 

(e.g., buildings, roads, trails, managed landscapes, or 

historic structures) in the park are situated on the coast. 

Thus, all 270 assets have “limited exposure” to 1 meter 

of sea level rise. During GRI scoping, participants 

mentioned that private houses along the coast are at risk 

from sea level rise, in particular the historic Adamson 

House, which is part of Malibu Lagoon State Beach 

(a state park) within the national recreation area (fig. 

34). With respect to coastal resources, climate change 

could alter recreational opportunities such as surfing, 

and ecosystems such as beaches and kelp forests 

(KellerLynn 2008).

The National Park Service has developed a variety of 

databases and guidance for managing coastal resources 

and planning for the impacts of climate change: 

● A handbook (Beavers et al. in review) will provide 

climate change adaptation guidance to park 

managers in NPS areas vulnerable to sea level 

change. The handbook will also provide guidance 

on developing communication and education 

materials about climate change impacts.

● A report (Schupp et al. 2015) presented case 

studies of the many ways that park managers are 

implementing adaptation strategies for threatened 

resources across the country. This publication 

does not include any examples from Santa Monica 

Mountains National Recreation Area, but some 

of the topics (e.g., cultural resource inventory 

and vulnerability assessments, and developing 

multiagency vision for an urban coastline) are 

applicable to resource management at the park.

● Reference manuals that guide coastal resource 

management include NPS Reference Manual #39-

1: ocean and coastal park jurisdiction, which can 

provide insight for park managers in parks with 

boundaries that may shift with changing shorelines 

(http://www.nps.gov/applications/npspolicy/

DOrders.cfm); and NPS Reference Manual #39-

2: beach nourishment guidance for planning and 

managing nourishment projects (https://irma.nps.

gov/App/Reference/Profile/2185115).

● A cultural resources climate change response 

strategy, which is under development, will connect 

climate science with historic preservation planning. 

The summary report from the 2014 “Preserving 

Coastal Heritage” workshop identified and 

described six climate change adaptation options for 

cultural resources and cultural landscapes: (1) no 

active intervention, (2) offset stressors, (3) improve 

resilience, (4) manage change, (5) relocate or 

facilitate movement, and (6) document and release. 

Additional information about the workshop, and 

associated presentations and reports, are available 

at https://sites.google.com/site/democlimcult/.

● The NPS Geologic Resources Division and NPS 

Climate Change Response Program are developing 

sea level rise and storm surge data that park 

managers can use for planning purposes over 

Figure 34. Photograph of the Adamson House. No 

NPS “assets” (infrastructure or historical/cultural 

resources) are situated on the coast, so none are directly 

susceptible to 1 meter of sea level rise. However, GRI 

scoping participants mentioned that private houses 

along the coast are at risk, in particular the historic 

Adamson House, which is part of Malibu Lagoon State 

Beach and within the park’s authorized boundary. 

California Coastal Records Project, Image 200405831, 

taken 23 October 2004, (http://www.californiacoastline.

org/cgi-bin/image.cgi?image=200405831&mode=seq

uential&flags=0&year=2004). Copyright © 2002-2016 

Kenneth & Gabrielle Adelman, California Coastal 

Records Project, www.Californiacoastline.org.
41

multiple time horizons. The project is scheduled 

for completion in 2016 and will analyze rates of 

sea level rise coupled with potential storm surge in 

105 of the vulnerable parks in order to project, for 

each park, the combined elevations of storms surge 

and sea level by 2030, 2050, and 2100. Numbers 

from this project (Caffrey 2015) were used in the 

preceding discussion.

● The NPS Water Resources Division, Ocean 

and Coastal Resources Branch, website (http://

www.nature.nps.gov/water/oceancoastal/) has 

information about servicewide programs, as well 

as resources and resource management programs 

at ocean, coastal, and Great Lakes parks. Shoreline 

maps of each park, along with shoreline and water 

acreage statistics from Curdts (2011), are available 

at http://nature.nps.gov/water/oceancoastal/

shorelinemaps.cfm.

● The NPS Geologic Resources Division Coastal 

Geology website (http://go.nps.gov/grd_coastal) 

provides information about coastal hazards, climate 

change, human impacts, and research.

In addition, the California Coastal Sediment 

Management Workgroup has a website

(http://www.dbw.ca.gov/csmw/) that provides links 

to spatial data, including beach profiles and coastal 

armoring, which could be incorporated into the 

park’s GIS. Also, historical storm data are stored and 

maintained as a GIS database by the NPS Geologic 

Resources Division; original data available at

http://www.ncdc.noaa.gov/oa/ibtracs/. 

Park managers developing monitoring protocols can 

contact their NPS Inventory & Monitoring Network 

coordinator and/or consult suggested protocols such as 

those in the Geological Monitoring chapter by Bush and 

Young (2009), which described methods for monitoring 

the following vital signs: (1) shoreline change, (2) coastal 

dune geomorphology, (3) coastal vegetation cover, 

(4) topography/elevation, (5) composition of beach 

material, (6) wetland position/acreage, and (7) coastal 

wetland accretion. 

Earthquakes

Earthquakes are ground vibrations that occur 

when rocks suddenly move along a fault, releasing 

accumulated energy (Braile 2009; see “Faults” and 

“Transform Boundary” sections). The magnitude 

of an earthquake represents the amount of energy 

released. The scale measuring the magnitude of an 

earthquake (i.e., Richter scale) is logarithmic. Thus the 

magnitude-6.7 Northridge earthquake released 126 

times more energy than the magnitude-5.3 Mugu Point 

earthquake; these earthquakes are discussed below. 

The US Geological Survey provides a calculator for 

earthquake magnitude at http://earthquake.usgs.gov/

learn/topics/calculator.php. 

According to USGS earthquake probability mapping 

(http://geohazards.usgs.gov/eqprob/2009/index.php), 

a magnitude 5.3 earthquake has a 0.8 to 0.9 probability 

(80%–90% “chance”) of occurring within 50 km (30 

mi) of the Thousand Oaks’ zip code (91360) in the next 

50 years. A magnitude 6.7 earthquake has a 0.40–0.50 

probability (40%–50% “chance”) of occurring. This 

range of earthquake magnitudes (i.e., 5.3–6.7) falls 

within the range suggested by scoping participants to 

affect the park (KellerLynn 2008).

Hazards associated with earthquakes at the park include 

shaking, liquefaction and landslides, tsunami, and 

seiche. Each of these is described in sections below.

The Malibu Coast and Anacapa-Dume faults are the 

primary active faults in the Santa Monica Mountains 

(fig. 10; Pam Irvine, California Geological Survey, 

senior engineering geologist, email communication, 

15 June 2016). The Malibu Coast Fault was the source 

of the magnitude-5.3 Point Mugu earthquake in 1973, 

discussed below (California Division of Mines and 

Geology 1973). The Anacapa-Dume Fault is assumed 

responsible for generating the historic 1930 Santa 

Monica earthquake (magnitude 5.2) and the 1979 

and 1989 Malibu earthquakes, each of which were 

magnitude 5.0 (Ziony and Yerkes 1985; Hauksson 1990).

The east-trending Malibu Coast Fault bounds the 

Santa Monica Mountains on the south. It is a reverse 

fault with left-lateral movement. The fault is 34 km 

(21 mi) long and has several parallel strands that run 

near the communities of Malibu and Pacific Palisades 

(Southern California Earthquake Data Center 2016). 

The length of a fault is significant because the longer the 

fault, the larger the potential earthquake can be (Wells 

and Coppersmith 1994). The Malibu Coast Fault has 

a known slip rate of approximately 0.3 mm (0.01 in) 

per year. The slip rate may be higher at its eastern end, 

where it meets the Santa Monica Fault (east of the park) 

(Southern California Earthquake Data Center 2016).
42

Originally recognized on the basis of bathymetric 

contours in Santa Monica Bay, the Anacapa-Dume Fault 

is a near-vertical offshore escarpment exceeding 600 m 

(2,000 ft) locally, with a total length of 105 km (62 mi) 

(Yerkes and Wentworth 1965; Junger and Wagner 1977). 

The fault occurs as close as 5.8 km (3.6 mi) offshore 

south of Malibu at its western end, but trends northeast 

where it apparently merges with the offshore segment(s) 

of the Santa Monica Fault, thus lying as close as 3 km 

(2 mi) south of the Malibu Beach/Carbon Beach area. 

Because the Anacapa-Dume Fault appears to truncate 

the northwest-striking, strike-slip Palos Verdes fault 

zone of Peninsular Ranges affinity, the Anacapa-Dume 

Fault is considered the present-day southern margin of 

the zone of thrust faults that punctuate the Transverse 

Ranges province (General Plan Task Force 2016). 

The Anacapa-Dume Fault has a known slip rate of 

approximately 0.3 mm (0.01 in) per year (Jennings and 

Bryant 2010).

The Hollywood Fault and the Santa Monica Fault, 

which are at or close to the base of the Santa Monica 

Mountains, also are potential sources of earthquakes 

that would affect the eastern Santa Monica Mountains 

(Pam Irvine, California Geological Survey, senior 

engineering geologist, email communication, 15 

June 2016). Both of these faults are reverse faults 

with left-lateral movement. The Hollywood Fault 

has the potential to produce an earthquake between 

magnitude 5.8 and 6.5; liquefaction and earthquakeinduced landslides are hazards (California Geological 

Survey 2014). The Santa Monica Fault has a probable 

magnitude of 6.0–7.0 (Southern California Earthquake 

Data Center 2016). The California Geological Survey 

produced an earthquake planning scenario/shakemap 

for the Santa Monica Fault and other faults in the 

Santa Monica Mountains (see “Additional References” 

section). 

Point Mugu and Northridge Earthquakes

The effects of past earthquakes can provide an 

understanding of what to expect from a future 

earthquake. The Point Mugu earthquake, which shook 

the Santa Monica Mountains on 21 February 1973, was 

the third-strongest US earthquake and the strongest in 

the contiguous 48 states that year. It was responsible for 

at least five injuries and more than $1 million damage 

in the Point Mugu–Oxnard area, though damage was 

mainly confined to the epicentral area. Large boulders 

fell onto Highway 1 at Point Mugu, partially blocking 

the road. More than 7,000 customers were without 

electricity for hours. Most damage reported was to 

windows, ceilings, plaster, chimneys, and shelved goods, 

though structural damage and broken pipes were also 

reported (Southern California Earthquake Data Center 

2016).

Another earthquake of interest for the Santa Monica 

Mountains is the 1994 Northridge earthquake, which 

occurred on 17 January 1994 on the Northridge Thrust 

(a thrust fault also known as the Pico Thrust). The 

fault is north of the park about 30 km (20 mi) west–

northwest of Los Angeles and/or 2 km (1 mi) south–

southwest of Northridge. The earthquake produced 

the strongest ground motions ever instrumentally 

recorded in an urban setting in North America. Damage 

was widespread; sections of major freeways collapsed, 

parking structures and office buildings collapsed, and 

numerous apartment buildings suffered irreparable 

damage. Damage to wood-frame buildings, especially 

apartments, was very widespread in the San Fernando 

Valley and Santa Monica areas. The high accelerations, 

both vertical and horizontal, lifted structures off of 

their foundations and/or shifted walls laterally. The 

earthquake revealed that the systems of concealed faults 

under the Los Angeles area are more complex than 

previously thought (Southern California Earthquake 

Data Center 2016).

Shaking

The primary hazard associated with earthquakes in 

the Santa Monica Mountains area is shaking produced 

by the sudden rupture of a fault. It is these ground 

motions that are felt and that cause most of the damage. 

Although an earthquake has only one magnitude and 

epicenter, different locations will experience different 

shaking levels. The strongest shaking occurs very near 

the fault and dies off as seismic waves travel away. Away 

from the fault, natural basins filled with sediments trap 

some waves and create pockets of stronger shaking 

with longer durations. Not every basin traps waves in 

every earthquake (Jones et al. 2008). The US Geological 

Survey provides “shakemaps” that show the area 

affected and intensities of shaking of the Northridge 

and other earthquakes (see “Additional References” 

section).

Liquefaction and Landslides

Large earthquakes in southern California can trigger 

liquefaction (a phenomenon in which the strength 
43

and stiffness of sediment or soil is reduced by 

earthquake shaking) and landslides (see “Landslides” 

and “Landslide Hazards” sections). Conditions for 

liquefaction, that is loosely packed, water-logged 

sediments at or near the ground surface, commonly 

occur in coastal areas, at the mouths of rivers, and in 

artificial fill (Qaf). With respect to the park, the Santa 

Clara River/Oxnard Plain areas of Ventura County and 

portions of the coastal basin or flatland areas of Los 

Angeles County are susceptible to liquefaction. 

Shaking in the Santa Monica Mountains area has the 

potential to generate thousands of individual landslides 

(Jones et al. 2008). The most common manifestation 

of the Northridge earthquake in the Santa Monica 

Mountains was the rockfalls and rockslides that fell 

onto roads from the platy shale layers of the Modelo 

Formation (“Tm” map units) exposed in deep cuts 

(Barrows et al. 1995). Also, bluff failure is likely in the 

Pacific Palisades area and Santa Monica Canyon (Pam 

Irvine, California Geological Survey, senior engineering 

geologist, telephone communication, 9 June 2016). 

During the Northridge earthquake, the Pacific Palisades 

experienced locally spectacular bluff failures along the 

Pacific Coast Highway (fig. 35). The collapse of bluffs 

damaged or destroyed several homes and caused the 

closure of the highway between Chautauqua Boulevard 

and Temescal Canyon Road for several days. Ongoing 

failures are likely following a large earthquake, perhaps 

during the next rainy season, where brittle bluff-top 

terrace deposits, which are very susceptible to slumping, 

developed cracks from the strong shaking (Barrows et 

al. 1995).

The California Geological Survey provides liquefaction 

and landslide hazard zone maps for all of the 

quadrangles (scale 1:24,000) covering the park and 

surrounding areas (see “Additional References” 

section). 

Figure 35. Photograph of the Pacific Palisades. The sedimentary rocks of the Pacific Palisades area (Qtms) are 

susceptible to slumping, which may be triggered by earthquake shaking. The bluffs occur along the Pacific Coast 

Highway. Photograph by Katie KellerLynn (Colorado State University).
44

Tsunami

Scoping participants concluded that tsunamis 

(earthquake-generated waves) are not a significant 

hazard in the park because much of the park’s coastline 

is protected by the Channel Islands and the offshore 

shelf and slope. Nevertheless, scoping participants 

thought large, submarine landslides had the potential to 

cause local-scale tsunami. For example, large submarine 

slides have occurred in the Santa Barbara Basin and off 

the northwestern edge of the San Pedro shelf (into the 

Santa Monica Basin) (Chris Wills, California Geological 

Survey, geologist, email communication, 16 September 

2008). Flooding and wave activity would be expected. 

The most vulnerable objects would be people on the 

beaches, houses or other buildings constructed on 

or near the beach, and bridges over the streams near 

the beach, such as along the Pacific Coast Highway at 

Malibu Creek and Corral Creek. People could be swept 

away by the waves and drowned; buildings and bridges 

could be undermined and collapse or carried away by 

the currents; buildings and other structures could be 

battered by debris carried by the currents (General Plan 

Task Force 2016).

The California Geological Survey has completed 

tsunami inundation maps for the entire coastline in 

the park (see “Additional References” section). NOAA 

provides tsunami information and warnings for the 

entire Pacific Rim area, including the west coast of 

the continental United States, Alaska, and Hawaii (see 

“Additional References” section).

Seiche

Seiche (standing waves in an enclosed or partially 

enclosed body of water such as Santa Monica Bay) 

may be triggered by local submarine earthquakes, and 

sometimes by large, more distant, regional earthquakes. 

This phenomenon was recorded at Santa Monica 

following moderate (magnitude 5.0–5.2) earthquakes 

under Santa Monica Bay in 1930, 1979, and 1989. 

The maximum height of these long period waves was 

about 0.6 m (2 ft). If such oscillations occurred during 

storm conditions or unusually high tides, damaging 

coastal inundation could result. The duration of these 

oscillations may be several hours (General Plan Task 

Force 2016).

Earthquake Risk

Risk is the likelihood of a hazard causing losses and is 

a combination of the probability of a hazard occurring 

and the value of assets in harm’s way (Holmes et al. 

2013). A risk analysis specific to the park has not been 

conducted, but park managers are encouraged to 

contact the NPS Geologic Resources Division with 

questions about earthquake risk. GRD staff can conduct 

risk assessment of unstable slopes that could be 

triggered to fail during an earthquake. 

Detailed information about earthquake risk is provided 

by scenarios, such as the HAZUS scenario and 

annualized earthquake loss estimation for California 

(Chen et al. 2011) and the ShakeOut Scenario (Jones 

et al. 2008). Scenarios estimate the scale and extent of 

damage, social disruption, and economic losses due to 

potential earthquakes. In addition, many organizations 

provide information about risk and preparedness that 

would be useful for park planning (see “Additional 

References” section).

Cave and Karst Resource Management

The Federal Cave Resources Protection Act of 1988 

requires the following: (1) identification of “significant 

caves” in NPS areas, (2) the regulation or restriction of 

use as needed to protect cave resources, and

(3) the inclusion of significant caves in land 

management planning. The act also imposes penalties 

for harming a cave or cave resources and exempts park 

managers from releasing specific location information 

for significant caves in response to a FOIA request (see 

Appendix B).

The “Cave and Karst Resources” section of this report 

describes the known cave and karst resources in the 

park, and Soto (2013) completed a cave and karst 

resource summary. However, the park is in need of 

a comprehensive cave inventory (KellerLynn 2008; 

National Park Service 2013; Soto 2013). The NPS 

Geologic Resources Division could assist park managers 

in initiating an inventory, which should include physical 

maps and an inventory of features and animal use (Dale 

Pate, NPS Geologic Resources Division, National Cave 

and Karst Program Manager, written communication, 

10 December 2015). Following an inventory, the NPS 

Geologic Resources Division could assist park managers 

in developing a cave management plan, as needed. Such 

plans include a comprehensive evaluation of current 

and potential visitor use and activities, as well as a plan 

to study known and discover new caves. The NPS 

Cave and Karst Resources website (http://go.nps.gov/

cavesandkarst) provides more information.
45

Some of the following vital signs, described by Toomey 

(2009) in Geological Monitoring, may be of interest and 

use to park managers in developing a monitoring plan: 

(1) cave meteorology, such as microclimate and air 

composition; (2) airborne sedimentation, including dust 

and lint; (3) direct visitor impacts, such as breakage of 

cave formations, trail use in caves, graffiti, and artificial 

cave lighting; (4) permanent or seasonal ice; (5) cave 

drip and pool water, including drip locations, rate, 

volume, and water chemistry, pool microbiology, and 

temperature; (6) cave microbiology; (7) stability issues 

associated with breakdown, rockfall, and partings;

(8) mineral growth of speleothems, such as stalagmites 

and stalactites; (9) surface expressions and processes 

that link the surface and the cave environment, 

including springs, sinkholes, and cracks; (10) regional 

groundwater levels and quantity; and (11) fluvial 

processes, including underground streams and rivers.

The following connections exist between cave/karst 

resources and other resources in the park:

● Paleontological. The park contains fossiliferous 

limestone, which is both a cave/karst resource and 

a paleontological resource. Limestone occurs as 

part of the Fernwood Member (Ttcf) of the highly 

fossiliferous Topanga Canyon Formation and in 

the Santa Susana Formation (Tss and Tssl) (see 

“Paleontological Resources” section).

● Biological. A study by Brown and Berry (2005) 

identified the presence of 11 bat species in the 

park. Whether bats are using the caves as habitat 

is unclear, however (National Park Service 2013). 

The caves at the park might host endemic and 

endangered species that need to be documented or 

protected. Park managers are encouraged to contact 

the NPS Biological Resources Division

(http://nature.nps.gov/biology) for more 

information. White-nose syndrome (WNS) is a 

fungus that is killing bats in the eastern and central 

United States, and was recently detected in the West 

Coast (Cornwall 2016). 

● Hydrological. Human consumption and disposal of 

water affects local and regional hydrologic systems, 

including groundwater discharge and underground 

streams, which can impact cave and karst systems. 

Monitoring water resources at the park is a need 

because urban development threatens hydrological 

resources and potentially cave and karst resources. 

Park managers are encouraged to contact the NPS 

Water Resources Division (http://nature.nps.gov/

water) for more information about water quality 

and quantity.

Flooding and Dam Failure

During the winter rainy season, streams may overtop 

their channels and overflow their banks, flooding 

park infrastructure. During such events, parking lots 

have washed out. Also, floodwaters threaten cultural 

resources at Peter Strauss Ranch (KellerLynn 2008). 

Twenty eight “water” polygons, including lakes and 

reservoirs, are part of the GRI GIS data. Most of 

the small water bodies in the park are stock ponds 

that were used for past ranching (GRI conference 

call participants, 17 November 2015). As part of a 

national wetlands inventory, park staff documented 

all known vernal ponds in the park (KellerLynn 2008). 

Most natural ponds in the park have been dammed to 

increase their areas, and an outcome is the potential 

for dam failure and damage to downstream cultural 

resources. Park managers are considering whether to 

maintain these small reservoirs or restore the ponds to 

natural conditions (KellerLynn 2008). The estimated 10 

largest water bodies within the park are reservoirs and 

do not belong to the National Park Service. The primary 

concern with these reservoirs is dam failure and damage 

to homes below (KellerLynn 2008). 

Malibu Creek and the stream running through Solstice 

Canyon have been dammed. Excessive sedimentation is 

a management issue in these areas.

A variety of publications and resources provide parkspecific or servicewide information and management 

guidance about upland and fluvial processes (see 

“Additional References” section and Appendix B of 

this report). Park managers are encouraged to contact 

the NPS Geologic Resources Division for technical 

assistance.

Abandoned Mineral Lands and Other 

Disturbed 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, for which the National Park Service takes 

action under various authorities to mitigate, reclaim, 

or restore in order to reduce hazards and impacts to 

resources.
46

The NPS AML database and Burghardt et al. (2014) list 

no AML features or sites within the park. Park managers 

are encouraged to contact the NPS Geologic Resources 

Division with information about (see discussion 

below) or assistance with any AML features or sites. 

All AML features and sites should be inventoried and 

documented in the servicewide database. 

Compared to other mountain ranges in the Transverse 

Ranges, very little historic prospecting occurred in 

the Santa Monica Mountains. Nevertheless, mineral 

exploration resulted in a few limestone quarries in the 

Santa Ynez Canyon area (KellerLynn 2008). Notably, 

an adjoining canyon to Santa Ynez Canyon is named 

“Quarry Canyon,” which is within the park’s authorized 

boundary in Topanga State Park. Quarry Canyon 

incised into the Santa Susana Formation (Tss), which 

contains lenses and pods of algal limestone (see “Cave 

and Karst Resource Management” section), and Sespe 

Formation (Ts). Scarred limestone, as well as sandstone, 

cliffs along Quarry Canyon give testament to onceextensive, and controversial, early to mid-20th century 

extractive industries associated with noted real estate 

developer Alphonzo Bell (California Department of 

Parks and Recreation 2009). The topographic map 

of the area shows one quarry in the Santa Susana 

Formation (Tssl) in the vicinity of Santa Ynez Canyon 

but outside the park.

Oil and gas exploration and development produced 

some dry holes on Point Dume. Point Dume is within 

the authorized boundary of the park but not currently 

administered by the National Park Service. 

Oil and gas production took place on lands within 

the Santa Susana Mountains north of the park. The 

National Park Service is currently conducting a 

resource study of lands that have the potential to be 

acquired. Some of these properties in the Santa Susana 

Mountains may include disturbed lands (Denise 

Kamradt, Santa Monica Mountains National Recreation 

Area, GIS specialist, conference call, 17 November 

2015). Park managers are encouraged to contact the 

NPS Geologic Resources Division for assistance with 

disturbed lands restoration (see http://go.nps.gov/grd_

dlr). 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.
47

Geologic History

This section describes the chronology of geologic events that formed the present landscape of Santa 

Monica Mountains National Recreation Area.

This summary of the park’s geologic history follows 

Fritsche and Weigand (2008), which served as a handout 

during the 2008 GRI scoping meeting. Table 1 presents 

a tabular version of the geologic history described 

in this section, including a chronology and brief 

descriptions of map units, depositional settings, colors 

representing major tectonic regimes, and locations of 

unconformities. 

Notably, the nature and timing of some of these 

geologic events remains controversial and different 

models proposed over the years continue to evolve 

as new information becomes available. Sources of 

information that helped to inform this section include 

Crouch and Suppe (1993), Nicholson et al. (1994), 

Atwater (1998), Ingersoll and Rumelhart (1999), and 

Olson (2006). The timing of events in those sources may 

vary from Fritsche and Weigand (2008).

Southern California was once the site of a convergent 

boundary, where the Farallon plate subducted beneath 

the North American plate. As Farallon plate subduction 

progressed, the northern end of a divergent boundary—

the East Pacific Rise—made contact with the subduction 

zone. Through a process of microplate capture and 

stalling of plate subduction, the convergent boundary 

evolved into a transform boundary, where the Pacific 

and North American plates slide horizontally past each 

other. However, the new plate boundary in southern 

California was never a pure transform boundary but 

included an extensional component (“transtension”) 

then a compressional component (“transpression”). 

Transtension was responsible for reconfiguration of 

the continental rim, including rotation of the Western 

Transverse Ranges block, eruption of the Conejo 

Volcanics, and deposition of sediments in extensional 

marine basins. After Baja California was captured by 

the Pacific plate, transtension changed to transpression, 

which continues to cause folding, uplift, tilting, and 

faulting in the Santa Monica Mountains.

Subduction

As dinosaurs walked the Earth in the Jurassic and 

Cretaceous periods (fig. 13), two tectonic plates—one 

oceanic, the Farallon, and one continental, the North 

American—converged off the western edge of the 

continent. A subduction zone was created where the 

thinner, denser Farallon plate descended beneath the 

thicker, more buoyant North American plate (fig. 4). 

In California, the convergent margin, which existed 

from the Mesozoic Era through the early Cenozoic 

Era (Paleogene Period), is characterized by four belts 

or assemblages of rocks aligned subparallel to the 

generally northwest–trending continental margin 

(see “Convergent Boundary” section). Figure 4 

shows a cross section of this continental-margin 

subduction system, as well as four the lithotectonic 

belts, their inferred tectonic settings, and the associated 

correlations with rocks in the Santa Monica Mountains 

and surrounding area.

Three of these belts are recognized in the rocks of the 

park. First, the “accreted arcs” belt is represented by 

the Santa Monica Slate (“Jsm” units; table 1). Sediments 

that were later metamorphosed to become slate were 

deposited between 156 million and 152 million years 

ago in an ocean basin that may have been associated 

with an island arc system adjacent to the continentalmargin subduction zone. The island arc terrane was 

later accreted to the continent during the Late Jurassic–

Early Cretaceous (?) periods (Crouch and Suppe 1993; 

Schweickert 2015). Second, about 102 million years ago 

(Cretaceous Period), melting of the subducting Farallon 

plate produced plutons (bodies of rock formed by an 

igneous intrusion) that intruded the Santa Monica 

Slate; granitic rocks (Kgr) in the park represent these 

plutons. These rocks are part of the “magmatic arc” 

belt (fig. 4) and are associated with the granitic rocks in 

the Peninsular Ranges south of the park and the Sierra 

Nevada north of the park. Third, the “forearc basin” 

belt is represented by a sequence of Upper Cretaceous–

Oligocene sedimentary rocks in the park (discussed 

below). 

Folding of the Santa Monica Slate, perhaps as a result of 

compression related to the subduction of the Farallon 

plate, produced a generally north–south-trending 

anticline. As the slate and granitic plutons were uplifted 

as part of the anticline, all overlying rocks were eroded 

away, creating an unconformity (a nonconformity) 
48

and leaving the Santa Monica Slate and granitic rocks 

exposed at the surface. The nonconformity separates 

the metamorphic Santa Monica Slate (“Jsm” map 

units) and intruded igneous granitic rocks (Kgr) 

from overlying sedimentary rocks. It is the oldest 

unconformity recorded in the park’s rock record and 

formed 102 million–91 million years ago (Cretaceous 

Period).

While the nonconformity developed, deep erosion also 

produced a west-trending, subaerial canyon. Evidence 

of this canyon occurs near Tarzana, California, so it 

is referred to as “Tarzana Canyon” (Eugene Fritsche, 

California State University, Northridge, Department of 

Geological Sciences, professor emeritus, GRI scoping 

presentation, 7 May 2008). The canyon had a minimum 

depth of 400 m (1,300 ft) as indicated by the thickness 

of alluvial-fan and river deposits of the Trabuco 

Formation (Ktr), which filled it. Trabuco Formation 

sediments were deposited about 91 million–90 million 

years ago (Late Cretaceous Period) (fig. 36). 

Atop the Trabuco Formation, the sedimentary 

succession of forearc-basin rocks related to the Great 

Valley belt is recorded by the Tuna Canyon Formation 

(Kt) and its informal members (Ktb, Kte, Ktd, Ktc, and 

Ktb) as well as the Chatsworth Formation (Kc). These 

sediments were deposited between 90 million and 

75 million years ago in fan-delta and submarine-fan 

environments (fig. 37). 

As subduction continued between 75 million and 

58 million years ago (Late Cretaceous Period–late 

Paleocene Epoch), existing rocks were uplifted and 

deformed. Erosion accompanied uplift and produced 

a second unconformity (an angular unconformity) 

upon which a subdued, subaerial Tarzana Canyon was 

reestablished. This unconformity is called the Runyon 

Canyon erosion surface, which is a regionally significant 

feature that also marks the K-T boundary, more 

formally known as the Cretaceous-Paleogene (K-Pg) 

boundary (see “Unconformities” section).

The distinctive Paleocene to Eocene sedimentary 

sequence that was deposited on the Runyon Canyon 

erosion surface includes the Simi Conglomerate (Tsi), 

the Las Virgenes Sandstone (Tlv), and Santa Susana 

Formation (Tss and Tssl) (Colburn and Novak 1989). 

These rocks represent a marine transgression (see 

“Transgressive–Regressive Cycles” section) that took 

place about 58 million–55 million years ago. 

Figure 36. Photograph of the Trabuco Formation. Between 

91 million and 90 million years ago, alluvial fans and 

streams deposited sand, gravel, cobbles, and boulders 

that now compose the Trabuco Formation, which filled 

“Tarzana Canyon.” The exposure shown here is in a 

canyon just north of Mulholland Drive. The large size of 

the boulders suggests a powerful mountain stream. Rock 

hammer (total length approximately 28 cm [11 in]) for 

scale. Photograph from Eugene Fritsche (California State 

University, Northridge, Department of Geological Sciences, 

professor emeritus, GRI scoping presentation, 7 May 2008).

Figure 37. Photograph of the Tuna Canyon Formation. 

This photograph taken at an exposure along Mullholland 

Drive shows a close-up view of the sandstone portion of 

the Tuna Canyon Formation. The Tuna Canyon Formation 

was deposited in fan-delta and shallow- to deep-marine 

submarine-fan environments. Rock hammer (total length 

approximately 28 cm [11 in]) for scale. Photograph from 

Eugene Fritsche (California State University, Northridge, 

Department of Geological Sciences, professor emeritus, GRI 

scoping presentation, 7 May 2008).
49

Uplift, erosion, and renewed mild deformation along 

the previous anticlinal trace produced a third and fourth 

unconformities (angular unconformities) at about 55 

million–50 million years ago and 48 million–41 million 

years ago (Eocene Epoch). These unconformities 

bracket the Llajas Formation (Tl) in the rock record 

at the park (fig. 38). The Llajas Formation, which 

consists of a nonmarine alluvial to shallow-marine basal 

conglomerate and overlying shallow-marine to offshore 

shelf deposits of sandstone and siltstone, was deposited 

during a marine transgression about 50 million–48 

million years ago (Eocene Epoch). 

The fifth unconformity (a disconformity) in the park’s 

rock record occurs in the middle of the lower Sespe 

Formation (Ts). It developed about 36 million–29 

million years ago as the approach of the East Pacific 

Rise caused regional uplift of the North American 

continental margin (see “Divergent Boundary” section). 

Deposition of the Sespe (Ts) nonmarine fluvial and 

deltaic sediments resumed between 29 million and 

28 million years ago. These sediments record the final 

stages of subduction-related deposition. 

Transition from Subduction to Transform 

Plate Motion

The uppermost part of the Sespe Formation—the 

Piuma Member (Tsp)—and the overlying Vaqueros 

Formation (“Tv” map units) were probably deposited 

in an extensional basin that formed at the site of 

the former forearc basin between 28 million and 21 

million years ago (Fritsche 1998; Fritsche and Weigand 

2008). Between 21 million and 18 million years ago, 

the Topanga Canyon Formation (“Ttc” map units) was 

deposited atop the Vaqueros Formation during two 

transgressive–regressive cycles. The Topanga Canyon 

Formation consists of both nonmarine and marine 

sediments that originated in fluvial, marine delta, and 

continental-shelf settings. 

The Piuma Member of the Sespe Formation, the 

Vaqueros Formation, and the early Miocene part of 

the Topanga Canyon Formation were deposited during 

the transition from subduction to transform plate 

motion. At 28 million years ago, the East Pacific Rise 

encountered the western margin of North America. 

As the spreading center approached the subduction 

zone, the Farallon plate east of the rise began to fracture 

into microplates. The fragment of the Farallon plate in 

the vicinity of the future Transverse Ranges is referred 

to as the “Monterey microplate” (Atwater 1970). 

This fragment of the Farallon plate continued to be 

subducted, but at a much slower rate than adjacent 

microplates. This was due to a dramatic decrease 

in spreading at the then Pacific plate–Monterey 

microplate boundary; divergent motion ceased about 

20 million years ago, prior to complete subduction 

of the Monterey microplate (Nicholson et al. 1994). 

When spreading ceased between the Pacific plate and 

Monterey microplate, the microplate was in a sense 

“captured” by, or locked onto, the Pacific plate. This 

event is important because the Monterey microplate, 

which was previously being subducted obliquely to the 

northeast, began to assume Pacific–plate relative motion 

that was more northwesterly (Nicholson et al. 1994; 

Atwater and Stock 1998). This change signified the 

beginning of transform plate motion in proto–southern 

California (Olson 2006).

Transtension

The transform boundary in southern California was 

initially characterized by transtension (transform 

plate motion and extension). At least three significant, 

interrelated events accompanied transtension between 

Figure 38. Photograph of the angular unconformity 

between the Llajas and Santa Susana formations. When 

southern California was mildly uplifted between 55 million 

and 50 million years ago, the area was eroded, and a 

third unconformity surface formed. The exposure shown 

in the figure is on Rambla Pacifico Road just north of its 

intersection with Las Flores Canyon Road. The orange line 

on the photograph marks the unconformity. Photograph 

by Pam Irvine (California Geological Survey).
50

20 million and 4 million years ago: (1) rifting and 

rotation of the Western Transverse Ranges block,

(2) volcanism, and (3) sediment deposition in 

extensional basins.

Rotation

Transtension coupled with irregularities in the 

geometry of the plate boundary led to deformation 

of the continental crust and formation of three large, 

fault-bounded blocks (Atwater 1998). As plate motion 

changed from convergent to transform, the basal shear 

generated by the underlying Monterey microplate 

separated these north–south-oriented blocks from 

North America (fig. 7). The outer two blocks became 

attached to the Pacific plate and have been transported 

up the coast and slightly seaward ever since (Atwater 

1998). The third block, the Western Transverse Ranges 

block, which was farther inland than the other two, 

was trapped at its northern end against the North 

America plate by a bend in the plate boundary and, as 

a consequence, began to rotate clockwise, inserting its 

southern end between the other two blocks. Rotation 

of the Western Transverse Ranges block explains why 

today’s Transverse Ranges run east–west in contrast 

to the northwest–southeast orientation of most 

other mountain ranges in California (see “Transform 

Boundary” section). 

Rotation continues to the present day, though 

interpretations vary. For example, Luyendyk (1991) 

preferred to interpret the available paleomagnetic data 

as indicating a constant rotation rate from 18 million 

years ago to the present. Ingersoll and Rumelhart 

(1999), by contrast, interpreted these data as indicating 

rapid rotation of the entire block from 18 million to 

12 million years ago, with complex local rotations 

thereafter.

Between 18 million and 17 million years ago, crustal 

extension, deformation, and erosion resulting from 

rifting and rotation of the Western Transverse Ranges 

block created an angular unconformity that was covered 

by volcanic rocks (see “Volcanism” section below). This 

is the sixth unconformity in the park’s rock record and 

is evidence that significant tectonic deformation was 

occurring prior to the onset of volcanism in the Santa 

Monica Mountains.

Volcanism

As rifting, rotation, and crustal extension continued, 

Earth’s stretching and thinning crust allowed magma 

to intrude the overlying crustal rocks and erupt at the 

surface, producing a period of volcanism in the Santa 

Monica Mountains area. Most of the volcanism took 

place near the site of rifting between the Western 

Transverse Ranges block and Peninsular Ranges at 

what is now the southern edge of the rotated Western 

Transverse Ranges. Intrusive and extrusive volcanic 

rocks (Ttb), which are exposed in the eastern Santa 

Monica Mountains, represent the onset of volcanism. 

Mixed rocks (Tim) and intrusive rocks (Ti, Tid, Tia, and 

Tib), which intruded the preexisting Topanga Canyon 

Formation, also represent this period of volcanism. 

The mixed and intrusive rocks in the central and 

western Santa Monica Mountains are associated with 

the Conejo Volcanics (“Tco” map units; fig. 39), which 

erupted and accumulated at the bottom of the ocean. 

Conejo Volcanics formed a volcanic complex that 

included shield volcanoes that rose above sea level. 

The Conejo volcanic complex represents one of the 

largest middle Miocene accumulations of intrusive and 

extrusive rocks in southern California (see “Igneous 

Rocks” section). 

Figure 39. Photograph of the Conejo Volcanics on the 

landscape. Boney Mountain and other peaks along the 

Backbone Trail are composed of Conejo Volcanics (“Tco” 

map units). National Park Service photograph.
51

Extensional Basins

As a result of ongoing crustal extension in proto–

southern California during the Miocene Epoch, older 

basins were significantly modified and several separate 

sub-basins or depositional centers were formed. Basin 

development is related to microplate-capture events 

along the continental margin (Ingersoll and Rumelhart 

1999). These incipient basins, which heralded the 

beginnings of the Los Angeles Basin, accommodated 

sediment influx during two different phases of 

basin development in the middle Miocene Period 

and middle-to-late Miocene Period (Ingersoll and 

Rumelhart 1999). 

In the Santa Monica Mountains, middle Miocene 

sedimentary and volcanic (see “Volcanism”) rocks 

of the Topanga Group were deposited in extensional 

basins during a period of rapid subsidence from 

about 18 million to 12 million years ago resulting from 

Monterey microplate capture and onset of rifting, 

extension, and rotation (Ingersoll and Rumelhart 

1999). The Calabasas Formation (“Tcb” map units), the 

youngest formation of the Topanga Group, consists of 

deep-water sandstone and shale beds that intertongue 

with and overlie the Conejo Volcanics. They were 

deposited by offshore marine turbidity (sediment-laden 

density) currents while the Conejo Volcanics were 

erupting from nearby volcanoes.

Continued rotation, deformation, uplift, and erosion 

created an angular unconformity about 13 million–12 

million years ago (Miocene Epoch). This is the 

seventh unconformity preserved in the Santa Monica 

Mountains area; it occurs at the base of the Modelo 

Formation in the park’s rock record. This unconformity 

may be related to the Pacific plate capture of the 

remaining pieces of the Farallon plate, which were being 

subducted beneath Baja California between 14 million 

and 12 million years ago. 

That plate-capture event and the subsequent change in 

plate boundary configuration may have also initiated 

the formation of the basins into which sediments of the 

Modelo Formation (“Tm” map units) were deposited 

(Ingersoll and Rumelhart 1999) between 12 million 

and 4 million years ago (Fritsche and Weigand 2008). 

The Modelo Formation was deposited as deep-water 

submarine fans (sandstone) interbedded with finer 

grained sediments. It represents submergence and a 

transgression in rapidly subsiding transtensional basins.

Rock Sequence South of the Malibu Coast Fault

The rocks exposed south of the Malibu Coast Fault 

(table 1b) in the central and western Santa Monica 

Mountains consist of the Zuma Volcanics (Tz; basaltic 

submarine volcanic rocks), Trancas Formation (Tr and 

Tra; marine mudstone, sandstone, and conglomerate), 

and Monterey Shale (Tmt and Tmtd; calcareous and 

dolomitic shale). These overlapping units split into 

many thin tongues and pinch out and disappear laterally 

east and west (fig. 40). These strata are generally coeval 

with the Topanga Group and Modelo Formation north 

of the fault (see “Formations” section and table 1a). 

The Trancas Formation contains lenses of a locally 

prominent sedimentary breccia—the San Onofre 

Breccia (fig. 41)—which is composed almost entirely 

of angular clasts of Early Cretaceous Catalina Schist 

(part of the Franciscan Subduction Complex or 

“accretionary wedge” belt; fig. 4). In the park area, the 

San Onofre Breccia in the Trancas Formation crops out 

along the beach at Lechuza Point and at Point Dume. 

The occurrence and distribution of this distinctive 

breccia provides important clues to understanding the 

early to middle Miocene tectonic evolution of the plate 

boundary in southern California, in particular rotation 

of the Western Transverse Ranges block and the 

opening of the proto–Los Angeles Basin to the east. 

In the central Santa Monica Mountains, the sequence of 

rocks south of the Malibu Coast Fault differs from the 

rocks north of the fault because it (1) is missing the Late 

Cretaceous to Paleogene forearc basin strata,

(2) commonly contains lenses of San Onofre Breccia, 

and (3) is inferred to have been deposited on Catalina 

Schist basement rocks. The rock sequence south of 

the Malibu Coast Fault is more similar to the section 

of rocks on the Palos Verdes Peninsula (south of the 

park) and strata in the inner-continental borderland 

(offshore southern California). The rocks south of 

the Malibu Coast Fault were deposited in extensional 

basins in an area in the inner-continental borderland 

where the gap that formed in the wake of the rotating 

Western Transverse Ranges block had widened enough 

to expose the underlying metamorphosed mid-crustal 

basement rock (i.e., Catalina Schist), which was uplifted, 

eroded, and incorporated as clasts into the San Onofre 

Breccia. Extension and crustal thinning at that time also 

allowed for the upwelling of mantle material and the 

formation of magma that intruded the overlying rocks 

and erupted into marine basins as sediments were being 

deposited on an irregular surface of Catalina Schist.
52

Transpression

Approximately 4 million years ago (Pliocene Epoch), 

the tectonic regime of southern California completely 

changed when the Pacific plate captured Baja California 

and began transporting it northwestward, ramming its 

northern end into southern California. Another way to 

describe this event is that the southern section of the 

Pacific–North America plate boundary shifted from the 

Pacific coast into the Gulf of California and the plate 

boundary had to break a new path across southern 

California, reconfiguring itself to connect to this new 

inland plate boundary. The transtensional system 

was largely deactivated at this time, and the southern 

California segments of the San Andreas Fault system 

were formed (Atwater 1998). 

The pressure of Baja California pushing northwest 

against southern California bolstered transpression. 

In this new configuration, the Western Transverse 

Ranges block is snagged at its (now) eastern end, against 

the “Big Bend” in the San Andreas Fault (fig. 7). As a 

result, the block is moving westward around the bend 

and shortening north–south. Compression associated 

with the bend is forcing up the land along preexisting 

structures (faults and folds), raising the Santa Monica 

Mountains. Initiation of mountain building, cessation 

of deposition of the Modelo Formation (“Tm” map 

units), left-shearing of the entire mountain range, and 

left-slip faulting on the Benedict Canyon and Malibu 

Coast faults are geologic evidence of transpression 

(Fritsche and Weigand 2008). 

To accommodate the western motion of the Western 

Transverse Ranges block around the Big Bend, major 

left-lateral faults (fig. 9) have formed along the southern 

edge of the block, and many preexisting Miocene 

normal faults (associated with extension) have been 

inverted into reverse faults (associated with transform 

plate motion) (Atwater 1998). At the southern edge of 

the Transverse Ranges, faulting is causing the uplift of 

the Santa Monica Mountains and the Channel Islands. 

Numerous young folds and uplifted, tilted marine 

terraces on the Channel Islands are evidence of ongoing 

shortening and uplift (Sorlien and Pinter 1997; Sorlien 

et al. 1998). In addition, crustal shortening—related to 

movement along blind thrust faults, in the subsurface

Figure 40. Correlation diagram of rocks south of the Malibu Coast Fault. The Zuma Volcanics (Tz), Trancas Formation 

(Tr and Tra), and Monterey Shale (Tmt and Tmtd) intertongue and pinch out laterally east and west in the central and 

western Santa Monica Mountains. Deposition took place in an extensional basin during much of the Miocene Epoch. 

The Zuma Volcanics erupted during the early and middle Miocene Epoch in an expanding submarine basin. The Trancas 

Formation was deposited during the early and middle Miocene Epoch as mud, sand, and gravel entered the basin. 

The Monterey Shale formed during the early, middle, and late Miocene Epoch as silt settled into a deep marine basin. 

Graphic by Trista Thornberry-Ehrlich (Colorado State University) after Yerkes and Campbell (1979, figure 5). 
53

of the northern Los Angeles Basin and valleys and 

hills north of the park—is causing earthquakes, such 

as the Northridge earthquake (see “Earthquakes” 

section).

Sedimentary rocks in the park that have been 

deposited since transpression began are limited to 

a few exposures of sedimentary rocks of the Pacific 

Palisades area (QTms). This unit consists of locally 

fossiliferous marine siltstone and sandstone. It also 

includes a basal sedimentary breccia (landslide?) 

unit, which probably resulted from submarine 

slumping on the margin of the basin (McGill 1989). 

As shown in the GRI GIS data, Quaternary (“Q”) 

units record deposition in primarily terrestrial 

settings during the last 2.6 million years. Changing 

sea levels—influenced by tectonic uplift locally and 

the growth and melting of ice sheets globally—have 

affected landscape development. Marine terraces 

document past sea-level highstands. These features 

were mapped as old shallow marine deposits on 

wave-cut surface (Qom). Quaternary features in 

the park also include old fan deposits (Qof1, Qof2, 

and Qof4; late Pleistocene Epoch, 126,000–11,700 

years ago) and old alluvium (Qoa; middle to late 

Pleistocene Epoch, 781,000–11,700 years ago). “Old” 

deposits have been uplifted and are no longer active 

sites of sedimentation. 

Young alluvial-fan deposits (Qyf and Qyf2) of late 

Pleistocene and Holocene age (126,000–0 years 

ago) were deposited chiefly by flooding streams 

and debris flows and are associated with modern 

alluvial fans. In addition, streams deposited young 

alluvium (Qya, Qya1, and Qya2) on canyon floors. 

Like young alluvial-fan deposits, young alluvium is 

related to ongoing processes. The most recent (in the 

last 11,700 years; Holocene Epoch) fluvial activity 

is recorded by alluvial fans (Qf) and alluvium (Qa). 

Also, Holocene wash deposits (Qw and Qw1) are 

chiefly stream deposited but include some debrisflow deposits. 

Landslides—represented by landslide deposits (Qls) 

as well as hazard point/area features in the GRI GIS 

data—are a primary feature of the park’s landscape 

(see “Landslides” section). The exact timing of the 

onset of landsliding is unclear but may have started 

as much as 126,000 years ago (late Pleistocene 

Figure 41. Photographs of San Onofre Breccia. The Trancas 

Formation contains distinctive beds of San Onofre Breccia, 

which is composed almost entirely of angular clasts of Early 

Cretaceous Catalina Schist. The schist is part of the Franciscan 

Subduction Complex or “accretionary wedge” belt (fig. 4). 

The breccia represents regional extension where the Catalina 

Schist basement rocks became exhumed. Photographs by Pam 

Irvine (California Geological Survey).
54

Epoch). Landsliding is ongoing (see “Landslide 

Hazards” section).

The park also contains modern estuaries, dunes, and 

beaches. Active coastal estuarine processes transport 

and deposit submerged/saturated silty clay (Qes). The 

wind creates eolian deposits (Qe), primarily transitory 

dunes against beach-facing cliffs, such as the “Great 

Dune” (see “Eolian Features and Processes” section). 

Beach deposits (Qb) consist of loose sand from 

reworked fluvial-deltaic and nearshore deposits.

Archeological evidence indicates that humans arrived 

in the northern Channel Islands at least 13,000 years 

ago (Erlandson et al. 2007). Humans have remained on 

the landscape of southern California since that time. 

Modern anthropogenic activities include construction, 

mining, and quarrying as represented by artificial fill 

(Qaf). Artificial fill is composed of sand, silt, and gravel 

that is commonly compacted and engineered. Only 

large deposits of artificial fill are shown in the GRI 

GIS data, but such deposits (mapped at scale 1:24,000) 

illustrate the ongoing influence of humans on the 

landscape.
55

Geologic Map Data

This section summarizes the geologic map data available for Santa Monica Mountains National 

Recreation Area. A poster (in pocket) displays the geologic map data draped over imagery of the park 

and surrounding area. Complete GIS data are available at the GRI publications website:

http://go.nps.gov/gripubs.

Geologic Maps

Geologic maps facilitate an understanding of an area’s 

geologic framework and the evolution of its present 

landscape. Using designated colors and symbols, these 

maps portray the spatial distribution and temporal 

relationships of rocks and unconsolidated deposits. The 

American Geosciences Institute website, http://www.

americangeosciences.org/environment/publications/

mapping, provides more information about geologic 

maps and their uses.

Source Maps

The GRI GIS data include essential elements of 

the source maps such as map unit descriptions, a 

correlation chart of units, a map legend, map notes, 

cross sections, figures, and references.

The GRI team used the following source maps to 

produce the Digital Geologic Map of Santa Monica 

Mountains National Recreation Area, California

(samo_geology.mxd).

Campbell, R. H., C. J. Wills, P. J. Irvine, and B. J. Swanson. 

Digital preparation by C. I. Gutierrez and M. D. O’Neal. 

2014. Preliminary geologic map of the Los Angeles 30' × 

60' quadrangle, California (scale 1:100,000; version 2.0). 

California Geological Survey and the US Geological Survey, 

Sacramento, California, and Washington, DC.

Tan, S. S., K. B. Clahan, C. S. Hitchcock, C. I. Gutierrez, and 

M. T. Mascorro. 2004. Geologic map of the Camarillo 

7.5-minute quadrangle, Ventura County, California 

(scale 1:24,000; version 1.0). Preliminary Geologic Maps. 

California Geological Survey, Sacramento, California.

Wills, C. J., R. H. Campbell, and P. J. Irvine. 2012. Geologic 

map database of the Santa Monica Mountains region, 

Los Angeles and Ventura counties, California (scale 

1:24,000). Unpublished data. California Geological Survey, 

Sacramento, California.

The data from Campbell et al. (2014) was used to cover 

the following (14) 7.5' quadrangles: Beverly Hills, 

Burbank, Calabasas, Canoga Park, Hollywood, Malibu 

Beach, Moon Park, Newbury Park, Point Dume, Simi 

Valley West, Thousand Oaks, Topanga, Triunfo Pass, and 

Van Nuys. The data from Wills et al. (2012) was used to 

cover the Camarillo and Point Mugu 7.5' quadrangles. 

All geologic features within these quadrangles were 

captured and included in the GRI GIS data (samo_

geology.mxd). Folds and related fold map symbology 

were captured from Tan et al. (2004; scale 1:24,000).

In addition, the GRI team used the following source 

map to produce the Digital Geohazards Map of Santa 

Monica Mountains National Recreation Area, California

(samo_geohazards.mxd).

Irvine, P. J., and T. P. McCrink. 2012. Landslide inventory 

of the Santa Monica Mountains region, Los Angeles and 

Ventura counties, California (scale 1:24,000). Unpublished 

data. California Geological Survey, Sacramento, California.

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 the park using data model version 2.3. 

The GRI Geologic Maps website, http://go.nps.gov/

geomaps, provides more information about GRI map 

products. 

GRI GIS data are publically 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 from the unit 

list.

The following components are part of the GRI GIS 

data:

● A GIS readme file (samo_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 (tables 5 and 6);
56

● Federal Geographic Data Committee (FGDC)–

compliant metadata;

● An ancillary map information document (samo_

geology.pdf) that contains information captured 

from source maps;

● ESRI map documents (samo_geology.mxd; samo_

geohazards.mxd) that display the GRI GIS data; and

● A KML/KMZ version of the map data viewable in 

Google Earth.

GRI Poster

A poster of the GRI GIS data (samo_geology.mxd) 

draped over shaded relief of the park and surrounding 

area is included with this report. Not all GIS feature 

classes are included on the poster (table 5). Geographic 

information and selected park features have been 

added to the poster. Digital elevation data and added 

geographic information are not included in the GRI 

GIS data set, but are available online from a variety of 

sources. Contact GRI for assistance locating these data. 

No poster was prepared for the geohazards data (samo_

geohazards.mxd).

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 upon the information 

provided here. Please contact GRI 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 

expected to be horizontally within 12 m (40 ft) of their 

true locations for scale 1:24,000 and 51 m (167 ft) of 

their true locations for scale 1:100,000.

Data Layer On Poster? Google Earth 

Layer?

Geologic Attitude and 

Observation Localities No No

Volcanic Line Features Yes Yes

Map Symbology No No

Folds Yes Yes

Faults Yes Yes

Linear Dikes Yes Yes

Geologic Contacts Yes Yes

Geologic Unit Labels Yes Yes

Geologic Units Yes Yes

Table 5. GRI GIS data layers for samo_geology.mxd.

Data Layer On Poster? Google Earth 

Layer?

Hazard Point Features No, see fig. 32 for 

partial view of data No

Hazard Area Feature 

Boundaries

No, see fig. 32 for 

partial view of data Yes

Hazard Area Features No, see fig. 32 for 

partial view of data Yes

Table 6. GRI GIS data layers for samo_geohazards.mxd.
57

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Stadum, C. J., and P. W. Weigand. 1999. Fossil wood from the middle Miocene Conejo Volcanics, Santa Monica Mountains, 

California. Southern California Academy of Sciences Bulletin 98(1):15–25. http://scholar.oxy.edu/scas/vol98/iss1/3/. 

Steensen, D. L. 2005. April 2005 reconnaissance of unstable slopes and erosional features, Santa Monica Mountains National 

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Stoms, D. M., P. A. Jantz, and F. W. Davis. 2013. Natural resource condition assessment: Santa Monica Mountains National 

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Sespe and Vaqueros formations, Orange County, and from the Sespe and equivalent marine formations in Los Angeles, Santa 

Barbara, and Ventura counties. Bulletin of the American Museum of Natural History 279:231–268.

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monitoring. Geological Society of America, Boulder, Colorado. http://go.nps.gov/geomonitoring.

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Yerkes, R. F., and R. H. Campbell. 1979. Contributions to stratigraphy: stratigraphic nomenclature of the central Santa Monica 

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Angeles County, California. Open-File Report 65-179. US Geological Survey, Reston, Virginia.

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Ziony, J. I., and R. F. Yerkes. 1985. Evaluating earthquake hazards in the Los Angeles region: an earth-science perspective. Pages 

43–91 in J. I. Ziony, editor. Professional Paper 1360. US Geological Survey, Reston, Virginia.

https://pubs.er.usgs.gov/publication/pp1360.
63

Additional References

This section lists additional references, resources, and websites that may be of use to resource managers. 

Web addresses are valid as of August 2016. Refer to Appendix B for laws, regulations, and policies that 

apply to NPS geologic resources.

California Geological Survey Regulatory Maps 

● http://maps.conservation.ca.gov/cgs/

informationwarehouse/index.html (includes 

seismic hazards, landslides, liquefaction, and fault 

evaluations)

Earthquake Hazard Information

● California Geological Survey earthquake 

information: http://www.conservation.ca.gov/cgs/

geologic_hazards/earthquakes/Pages/index.aspx

● California Geological Survey fault activity maps: 

http://www.conservation.ca.gov/cgs/cgs_history/

Pages/2010_faultmap.aspx (zoom in for the park 

area or other areas within the state).

Also, an interactive map viewer:

http://maps.conservation.ca.gov/cgs/fam/

● California Geological Survey HAZUS scenario and 

annualized earthquake loss estimation (Special 

Report 222; Chen et al. 2011): ftp://ftp.consrv.

ca.gov/pub/dmg/rgmp/2011%20Annualized%20

Losses/CGS_SR222_%20Losses_Final.pdf

● California Geological Survey map showing 

earthquake shaking potential for California: 

http://www.conservation.ca.gov/cgs/information/

publications/ms/Documents/MS48_revised.pdf

● California Geological Survey seismic hazards 

maps: http://maps.conservation.ca.gov/cgs/

informationwarehouse/index.html

● California Office of Emergency Services:

http://myhazards.caloes.ca.gov/ (for discovering 

the hazards that exist in an area and how to reduce 

risk)

● Earthquake Country Alliance:

http://www.earthquakecountry.org/ (earthquake 

hazards and preparedness in California)

● NPS Geologic Resources Division seismic 

monitoring information: http://go.nps.gov/

geomonitoring

● Southern California Earthquake Center:

http://www.scec.org/ucerf (forecast of earthquakes)

● Southern California Earthquake Data Center 

significant earthquakes and faults:

http://scedc.caltech.edu/significant/fault-index.

html (primary archive of seismological data for 

southern California)

● US Geological Survey: http://earthquake.usgs.

gov/earthquakes/states/index.php?regionID=5

(California earthquake information)

ShakeMaps/Earthquake Planning Scenarios

● 1971 San Fernando earthquake:

http://earthquake.usgs.gov/earthquakes/shakemap/

sc/shake/San_Fernando/

● 1994 Northridge earthquake:

http://earthquake.usgs.gov/earthquakes/shakemap/

sc/shake/Northridge/

● 2008 ShakeOut Scenario:

http://earthquake.usgs.gov/earthquakes/shakemap/

sc/shake/shakeout2_full_se/

● 2014 Encino earthquake:

http://earthquake.usgs.gov/earthquakes/shakemap/

sc/shake/15476961/

● Santa Monica Mountains, magnitude 6.6 

earthquake: ftp://ftp.consrv.ca.gov/pub/dmg/rgmp/

CalEMA2009/Appendix%20A/S19%20Santa%20

Monica%20Fault%20Scenario.pdf

Tsunami Information

● California Emergency Management Agency 

earthquake and tsunami hazards and mitigation 

information: http://hazardmitigation.calema.ca.gov/

hazards/natural/seismic/hazards

● California Geological Survey tsunami inundation 

maps and information: http://maps.conservation.

ca.gov/cgs/informationwarehouse/index.html

http://www.conservation.ca.gov/cgs/geologic_

hazards/Tsunami/Inundation_Maps/Pages/index.

aspx

● NOAA’s National Weather Service, Pacific Tsunami 

Warning Center: http://ptwc.weather.gov/

Landslide Resources

● California Geological Survey:

http://www.conservation.ca.gov/cgs/geologic_

hazards/landslides/Pages/LandslideTypes.aspx
64

● NPS Geologic Resources Division:

http://go.nps.gov/geohazards

http://go.nps.gov/monitor_slopes

● US Geological Survey: http://landslides.usgs.gov/

Climate Change Resources

● Intergovernmental Panel on Climate Change 

(IPCC): http://www.ipcc.ch/

http://www.climatechange2013.org/report

● NOAA historical storm data:

http://www.ncdc.noaa.gov/ibtracs/

● NOAA tides and currents:

http://www.tidesandcurrents.noaa.gov/sltrends/

● NPS Climate Change Response Program Resources: 

http://www.nps.gov/subjects/climatechange/

resources.htm

● NPS storm surge mapping:

http://mariacaffrey.com/storms

● US Army Corps of Engineers (USACE) sea level 

calculator:

http://www.corpsclimate.us/ccaceslcurves.cfm 

● US Global Change Research Program:

http://globalchange.gov/home

Geological Surveys and Societies

● California Geological Survey:

http://www.conservation.ca.gov/cgs

● US Geological Survey: http://www.usgs.gov/

● American Geophysical Union: http://sites.agu.org/

● American Geosciences Institute:

http://www.americangeosciences.org/

● Association of American State Geologists:

http://www.stategeologists.org/

● Geological Society of America:

http://www.geosociety.org/

Geology of National Park Service Areas

● NPS Geologic Resources Division—Energy 

and Minerals, Active Processes and Hazards, and 

Geologic Heritage: http://go.nps.gov/geology/

● NPS Geologic Resources Inventory:

http://go.nps.gov/gri

● NPS Geoscientist-In-the-Parks (GIP) internship 

and guest scientist program: http://go.nps.gov/gip

● 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://go.nps.gov/views

NPS Resource Management Guidance and 

Documents

● 1998 National Parks Omnibus Management Act: 

http://www.gpo.gov/fdsys/pkg/PLAW-105publ391/

pdf/PLAW-105publ391.pdf

● Geologic monitoring manual:

http://go.nps.gov/geomonitoring

● Management Policies 2006 (Chapter 4: Natural 

resource management):

http://www.nps.gov/policy/mp/policies.html

● 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/

● NPS Technical Information Center (TIC) (Denver, 

Colorado; repository for technical documents): 

http://www.nps.gov/dsc/technicalinfocenter.htm

http://etic.nps.gov/

US Geological Survey Reference Tools

● California Seafloor Mapping Program:

http://walrus.wr.usgs.gov/mapping/csmp/

http://www.opc.ca.gov/2010/03/

mapping-californias-seafloor-2/

● Geologic glossary (simplified definitions):

http://geomaps.wr.usgs.gov/parks/misc/glossarya.

html

● 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”)

● National geologic map database (NGMDB):

http://ngmdb.usgs.gov/

● 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
65

Appendix A: Scoping Participants

The following people attended the GRI scoping meeting for Santa Monica Mountains National 

Recreation Area, held on 7 May 2008, or the follow-up report writing conference call, held on 17 

November 2015. Discussions during these meetings supplied a foundation for this GRI report. The 

scoping summary document is available on the GRI publications website: http://go.nps.gov/gripubs.

2008 Scoping Meeting Participants

Name Affiliation Position

John Alderson Los Angeles County Museum Research Associate/Invertebrate 

Paleontology

Lane Cameron NPS Mediterranean Coast Network Network Coordinator

Brendan Clarke Santa Monica Mountains National Recreation Area GIS Technician

Guy Cochrane US Geological Survey Geophysicist/Coastal Marine Geologist

Gary Davis National Park Service (retired) Science Advisor

Eugene Fritsche California State University Northridge Professor Emeritus

Bruce Heise NPS Geologic Resources Division Geologist/GRI Program Coordinator

Pam Irvine California Geological Survey Senior Engineering Geologist

Denise Kamradt Santa Monica Mountains National Recreation Area GIS Specialist

Katie KellerLynn Colorado State University Geologist/Research Associate

Stephanie Kyriazis Santa Monica Mountains National Recreation Area Interpreter

Greg Mack NPS Pacific West Region Geologist

John Minch Santa Barbara Museum of Natural History Dibblee Map Editor

Tarja Sagar Santa Monica Mountains National Recreation Area Biological Science Technician

Ray Sauvajot Santa Monica Mountains National Recreation Area Supervisory Ecologist

Tony Valois Santa Monica Mountains National Recreation Area Biological Science Technician

Chris Wills California Geological Survey Senior Engineering Geologist

2015 Conference Call Participants

Name Affiliation Position

Pam Irvine California Geological Survey Senior Engineering Geologist

Denise Kamradt Santa Monica Mountains National Recreation Area GIS Specialist

Katie KellerLynn Colorado State University Geologist/Research Associate

Jason Kenworthy NPS Geologic Resources Division Geologist/GRI Reports Coordinator

Vincent Santucci NPS Geologic Resources Division Geologist/Washington Liaison

Chris Wills California Geological Survey Supervising Engineering Geologist

67

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 2016. 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 2016).

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.
68

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.
69

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).

Coastal Features and Processes

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).

Coastal Zone Management Act, 16 USC 

§ 1451 et. seq. requires Federal agencies 

to prepare a consistency determination for 

every Federal agency activity in or outside 

of the coastal zone that affects land or 

water use of the coastal zone.

Clean Water Act, 33 USC § 1342/Rivers 

and Harbors Act, 33 USC 403 require that 

dredge and fill actions comply with a Corps 

of Engineers Section 404 permit.

Executive Order 13089 (coral reefs) 

(1998) calls for reduction of impacts to 

coral reefs.

Executive Order 13158 (marine 

protected areas) (2000) requires every 

federal agency, to the extent permitted by 

law and the maximum extent practicable, 

to avoid harming marine protected areas.

36 CFR § 1.2(a)(3) applies NPS regulations 

to activities occurring within waters subject 

to the jurisdiction of the US located 

within the boundaries of a unit, including 

navigable water and areas within their 

ordinary reach, below the mean high water 

mark (or OHW line) without regard to 

ownership of submerged lands, tidelands, 

or lowlands.

36 CFR § 5.7 requires NPS authorization 

prior to constructing a building or other 

structure (including boat docks) upon, 

across, over, through, or under any park 

area.

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 4.8.1 requires NPS to allow natural 

geologic processes to proceed unimpeded. 

NPS can intervene in these processes 

only when required by Congress, when 

necessary for saving human lives, or when 

there is no other feasible way to protect 

other natural resources/ park facilities/

historic properties.

Section 4.8.1.1 requires NPS to:

-Allow natural processes to continue 

without interference,

-Investigate alternatives for mitigating the 

effects of human alterations of natural 

processes and restoring natural conditions, 

-Study impacts of cultural resource 

protection proposals on natural resources, 

-Use the most effective and natural-looking 

erosion control methods available, and 

-Avoid putting new developments in areas 

subject to natural shoreline processes 

unless certain factors are present.
70

Resource Resource-specific Laws Resource-specific Regulations 2006 Management Policies Climate Change

Secretarial Order 3289 (Addressing 

the Impacts of Climate Change on 

America’s Water, Land, and Other Natural 

and Cultural Resources) (2009) requires 

DOI bureaus and offices to incorporate 

climate change impacts into long-range 

planning; and establishes DOI regional 

climate change response centers and 

Landscape Conservation Cooperatives to 

better integrate science and management 

to address climate change and other 

landscape scale issues.

Executive Order 13653 (Preparing the 

United States for the Impacts of Climate 

Change) (2013) outlines Federal agency 

responsibilities in the areas of supporting 

climate resilient investment; managing 

lands and waters for climate preparedness 

and resilience; providing information, data 

and tools for climate change preparedness 

and resilience; and planning.

Executive Order 13693 (Planning for 

Federal Sustainability in the Next Decade) 

(2015) established to maintain Federal 

leadership in sustainability and greenhouse 

gas emission reductions.

President’s Climate Action Plan (2013), 

http://www.whitehouse.gov/sites/default/

files/image/president27sclimateactionplan.

pdf 

None applicable.

Section 4.1 requires NPS to investigate 

the possibility to restore natural ecosystem 

functioning that has been disrupted by past 

or ongoing human activities. This would 

include climate change, as put forth by 

Beavers et al. (in review).

NPS Climate Change Response Strategy

(2010) describes goals and objectives to 

guide NPS actions under four integrated 

components: science, adaptation, 

mitigation, and communication.

Policy Memo 12-02 (Applying National 

Park Service Management Policies in the 

Context of Climate Change) (2012) applies 

considerations of climate change to the 

impairment prohibition and to maintaining 

“natural conditions”.

Policy Memo 14-02 (Climate Change and 

Stewardship of Cultural Resources) (2014) 

provides guidance and direction regarding 

the stewardship of cultural resources in 

relation to climate change.

Policy Memo 15-01 (Climate Change 

and Natural Hazards for Facilities) (2015) 

provides guidance on the design of facilities 

to incorporate impacts of climate change 

adaptation and natural hazards when 

making decisions in national parks.

DOI Manual Part 523,

Chapter 1 establishes policy and provides 

guidance for addressing climate change 

impacts upon the Department’s mission, 

programs, operations, and personnel.

Revisiting Leopold: Resource 

Stewardship in the National Parks

(2012) will guide US National Park natural 

and cultural resource management into 

a second century of continuous change, 

including climate change.

Climate Change Action Plan (2012) 

articulates a set of high-priority no-regrets 

actions the NPS will undertake over the 

next few years

Green Parks Plan (2013) is a long-term 

strategic plan for sustainable management 

of NPS operations.
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 638/134114, September 2016
Natural Resource Stewardship and Science 

1201 Oak Ridge Drive, Suite 150 

Fort Collins, Colorado 80525

www.nature.nps.gov

National Park Service

U.S. Department of the Interior

EXPERIENCE YOUR AMERICATM
Figure 1. Map of Santa Monica Mountains National Recreation Area. The park consists of a web of protected places. Twenty different landowner types, including the entire City of Malibu, and more than 70 stakeholder groups share 

responsibilities and jurisdiction within the park’s authorized boundary. A total of 62,020 ha (153,250 ac) are divided among private landowners, local parks, California State Parks, and the National Park Service. The National Park Service is 

steward of 9,510 noncontiguous hectares (23,500 ac) (National Park Service 2015a). National Park Service map available at https://www.nps.gov/hfc/cfm/carto.cfm.