San Clemente Island of the Channel Islands in southern California. 

The stair-step-like flat surfaces are marine terraces of different ages. 

Photograph by Dan Muhs, USGS.

Landscapes from the Waves—Marine Terraces of California

Many coastlines 

around the world have stair-step landforms, known 

as marine terraces. Marine terraces make up a 

large part of coastal California’s landscape—from 

San Diego to Crescent City. Find out how these 

landscapes form, why marine terraces are of 

interest to scientists, and where you can explore 

these landscapes.

How Marine Terraces Form

Marine terraces result from the interaction of two geologic 

processes: uplift of the land surface and the natural rise and fall 

of sea level over hundreds of thousands of years. As sea level 

rises, waves move underwater sediment—sand and gravel—back 

and forth against bedrock, acting like sandpaper to hone bedrock 

into flat, broad platforms. 

When sea level falls, wave-cut surfaces are exposed above 

water. Earthquakes on California’s coastal faults, along with 

other processes that deform the Earth’s crust, cause uplift of 

the land surface. When uplift is fast enough, it causes wave-cut 

surfaces to be preserved as marine terraces above the influence 

of the ocean. Where land is not uplifted high enough, wave-cut 

surfaces will be flooded by the rising sea. It is important to note 

that high marine terraces seen along the coast do not represent 

past shorelines at that elevation, rather, they record ongoing 

uplift that occurs simultaneously with fluctuating sea level. The 

crust steadily moves upwards and high sea-level stands erode 

notches into the uplifting terrain.

Marine terrace deposits on Santa Rosa Island, one of the Channel Islands 

in southern California. The geologist pictured here is standing on bedrock 

(the tilted rock layers). Just above the geologist’s head is an old wave-cut 

surface, which is covered by a layer of rounded cobbles that were once 

shoreline sediments. The movement of sediment by wave action acts 

like sandpaper on the bedrock to create the wave-cut surface. Above 

the cobbles are sandy deposits from former beach and river settings that 

covered the wave-cut surface after it formed. 

Photograph by Dan Muhs, USGS.

40

0

−160

−40

−120

−80

100

0

−500

−100

−300

−200

Relative sea level, in meters

Relative sea level, in feet

0 100,000 200,000 300,000 400,000

Years before present

Late Pleistocene and Holocene sea-level curve

Current sea level

Uplift

Sea bed erosion

Wave

energy

dissipation

Terrace

sediment

deposits

−400

Schematic drawing showing the features and formation of a terraced 

coastline. The graph shows how global sea level has changed over the 

past 450,000 years relative to today. Ocean-wave action during high 

sea-level stands in the past eroded wave-cut platforms into bedrock at 

sea level. These platforms were then uplifted by recurring movement 

on nearby faults, thereby preserving the marine terraces from further 

erosive wave action. Older terraces are higher and farther from today’s 

coastline.

U.S. Department of the Interior

U.S. Geological Survey

Fact Sheet 2018–3002

March 2018
Coastal Faults and Uplift

Uplift of the land surface near the California coast is the 

result of movement along nearby faults, accompanied in some 

areas by crustal warping and folding. Scientists estimate uplift 

rates using the elevation of ancient shorelines (distance above 

current sea level), ages of the marine terraces, and estimated 

heights of past sea level. In some locations, such as near Point 

Arena in northern California, marine terraces that formed across 

the San Andreas Fault can provide information concerning slip 

rates on the fault. Continued horizontal movement on the fault 

has offset the uplifted ancient shorelines such that shorelines of 

older terraces are displaced farther than younger ones. Scientists 

use this information to estimate the horizontal slip rate of the 

San Andreas Fault through time, to better understand earthquake 

recurrence intervals.

Marine terraces are some of the most visible landforms in 

Channel Islands National Park in southern California, giving 

all five islands within the park a stair-step-like appearance. The 

lowest—and therefore, youngest—marine terrace along many 

of the islands’ coasts dates to the last major interglacial period, 

which occurred about 120,000 years ago when sea level was 20 

to 26 feet (6 to 8 meters) higher than today. On Anacapa, Santa 

Barbara, and Santa Cruz Islands, this young marine terrace has 

not been uplifted much above the elevation at which it formed. 

On San Miguel and Santa Rosa Islands, however, the youngest 

marine terrace has been uplifted to higher elevation, indicating a greater rate of tectonic uplift on these two islands. Some 

of the highest marine terraces in Channel Islands National 

Park are 1 million years old, such as on San Miguel Island, and 

as much as 2 million years old on Santa Cruz Island. Marine 

terrace deposits on the Channel Islands contain abundant fossil 

marine invertebrates—most of them species that are still living 

today—that provide scientists information about Pacific Ocean 

temperatures off the southern California coast during the recent 

geologic past.

CALIFORNIA

Map location

0 0.5 MILE

0 0.5 1 KILOMETER San Andreas Fault Zone North

Ancient shorelines near Point Arena have been horizontally offset 

across the San Andreas Fault Zone (red line). The green lines on the 

map trace the uplifted shoreline of a 120,000-year-old marine terrace 

and the blue lines trace that of an 80,000-year-old marine terrace. 

Recurring horizontal fault movement has shifted the green shorelines 

about 1.6 miles (2.5 kilometers, km) apart and the blue shorelines 

about 1 mile (1.5 km) apart across the San Andreas Fault.

How Do We Know Bedrock Was Once at Sea Level? Fossils.

The California coast is home to a group 

of clams (from the family Pholadidae) 

that drill into rocks, wood, and sediments in the intertidal zone—the area 

between high and low tide levels. When 

fossils of these clams are found on a 

bedrock surface away from the ocean, 

geologists can be sure that the surface 

was once at sea level. Fossils of other 

clams, corals, and marine snails are also 

sometimes found in sediments deposited 

just above the wave-cut surface, serving 

as additional evidence that they formed 

near sea level. When hiking along cliffs 

and past roadcuts near the coast, you 

may see these fossils. Rocks with holes 

are common on today’s beaches along 

the California coast—in many cases, 

these represent the remnant homes of 

pholad clams.

At Año Nuevo State Park, located along Highway 1 north of Santa Cruz, fossil clams from the 

family Pholadidae are preserved in bedrock (left). Clams are 1 to 2 inches (2.5 to 5 centimeters) 

in size. Right, an uplifted wave-cut platform with holes drilled by pholad clams (foreground). 

Photographs by Dan Muhs, USGS.
Soils

Marine Terrace Soil Chronosequences

As marine terraces are uplifted above the influence of the 

sea, they are colonized by terrestrial plants and animals. Gradually, soils develop on the wave-cut surfaces and the soil profiles 

continue to change with the passage of time. Thus, a stair-step 

progression of marine terraces will show a predictable sequence 

of soils with the oldest, more depleted soils on the highest 

terraces and the youngest, more fertile soils on the lowest 

terraces. This group of soils, progressing from old to young, is 

called a soil chronosequence. 

T1

T2

T3

T4

Ancient sea cliff

Modern sea cliff

Terrace 1 Terrace 2

Horizon A

Horizon C

Horizon A

Horizon AB

Horizon B

Terrace 1 Terrace 2

Horizon A

Horizon C

Horizon A

Horizon AB

Horizon B

T1

T2

T3

T4

Wilder Ranch State Park near Santa Cruz is a good example of the stairstep landscapes and soil chronosequences that are typical of uplifted 

marine terraces (top). Terraces are labeled with a T (numbers increase 

away from the modern shoreline); the base of ancient sea cliffs indicate 

past shorelines. Photograph © 2015 Kenneth and Gabrielle Adelman, 

California Coastal Records Project, californiacoastline.org. Soil pits in 

terrace 1 (left) and terrace 2 (right) are approximately 5 feet (150 centimeters) deep. Both soils started as similar sandy marine sediments. The 

younger soil on terrace 1 has experienced less time for soil development and has just two main soil horizons. Terrace 2 has been exposed 

for longer and has developed four main soil horizons, three of which 

are visible here (soil horizon C is beneath the soil pit). Photographs by 

Marjorie Schulz, USGS. 

The formation of soil, referred to as pedogenesis, occurs over 

thousands of years and is characterized by a progressive change 

in mineral composition and soil structure. The longer a terrace 

surface is exposed, the older and more nutrient-depleted the soil 

becomes. Young soils are more similar to the starting material, making them nutrient-rich and therefore commonly used 

for agriculture. Older soils are more weathered—the primary 

minerals have dissolved and been replaced by secondary clay 

minerals. Older soils generally have low organic content, are 

nutrient-poor, and are commonly not productive enough for 

row crops. 

Marine terrace soil chronosequences along the California 

coast are of interest to scientists because they allow measurements of many aspects of soil development over time, such as 

changes in nutrients (caused by mineral weathering), soil hydrology (water content), organic matter, and biology. In addition, 

California has a distinct rainfall gradient from north to south—

San Diego is much drier than Eureka—that allows scientists to 

compare soil processes in dry versus wet ecosystems. The study 

of terrace soil chronosequences along this rainfall gradient aids 

our understanding of how soil processes and ecosystems will 

respond to climatic changes.

Soil Nodules

Because iron is an important plant nutrient, scientists seek 

to understand how it migrates and concentrates in soils. Many 

terrace soils along the California coast contain iron nodules, 

which are hard, oval shaped, and usually dark orange or brown 

in color. Their appearance causes nodules to sometimes be 

mistaken for small meteorites; however, the nodules actually 

form within soils. Some soil surfaces in southern California 

and on the Channel Islands are covered by nodules because any 

smaller soil particles have been eroded away, leaving the larger, 

denser nodules behind. Soil nodule abundance decreases northward along the California coast towards wetter climates, indicating that soil nodules either form more easily or are perhaps 

better preserved in the drier soils of central and southern California. If you look closely at soil mounds around gopher holes, 

you may be able to find a soil nodule. How soil nodules form in 

these soils is currently under discussion. Nodules were originally 

thought to form from the effect of wetting and drying cycles on 

iron in the soil, however, more recent study shows microbial 

activity (fungal and 

bacterial) may also be 

important in nodule 

formation.

0 0.5 INCH

0 1 CENTIMETER

Soil nodules revealed on 

the surface of a gopher 

mound after a rainstorm 

(left). Cutting soil nodules in half reveals their complex histories of iron 

cementation (right). USGS photographs by David Stonestrom (left) and 

Marjorie Schulz (right).
Pygmy Forests on the Ecological Staircase

Because old marine terrace soils are nutrient-poor, the lack of 

nutrients can affect vegetation growing on these soils. The difference in nutrient availability causes distinct plant ecosystems 

to grow on terraces of different ages, resulting in an ecological 

staircase superimposed on the sequence of terraces. Extraordinary examples of this can be observed in several northern 

California parks, including Jug Handle State Natural Reserve, 

Russian Gulch State Park, Salt Point State Park, and Van Damme 

State Park. In these places, older marine terraces have a combination of highly weathered soil, low nutrient levels, and poor 

drainage owing to the formation of a dense soil layer, called a 

hardpan. Together, these soil conditions cause stunted growth in 

the local forest—creating a pygmy forest. The pygmy forest is 

home to hardy plants that are of interest to scientists who study 

the characteristics that allow the plants to survive in such an 

unforgiving environment. 

~ 3.5 miles (6 kilometers)

~650 feet (200 meters)

Future

terrace

Terrace 5 ~500,000 years old

7

5

5

6

5

3

4

3

2

1

Pygmy forestPygmy forest

Pygmy

forest

Terrace 4 ~400,000 years old

Terrace 3

~300,000 years old

Terrace 2

~200,000 years old

 Terrace 1

~100,000 years old

3

4

5

1

2

6

7

Sand dunes

Beach deposits

Sandstone terraces cut by waves

Nutrient-poor soil

Hardpan

Coastal scrub

Beach pine, Bishop pine, and 

 Sitka spruce

Redwood, grand fir, Bishop pine, 

 and Douglas fir

Bishop pine forest

Mendocino cypress, Bolander, 

 and Bishop pine

Bishop pine, Douglas fir, and 

 manzanita

Douglas fir forest

EXPLANATION

Cross sectional view of marine terraces illustrating the ecological 

staircase in Mendocino County. Modified from a figure by Michael 

Kauffmann, available at http://blog.conifercountry.com/2014/07/

the-ecological-staircases-of-mendocino-county/.

Dynamic Landscapes

Born of the erosive action of ocean waves, uplifted above the 

influence of the sea, and then subjected to varying climatic and 

environmental conditions, marine terraces represent a dynamic 

landscape—one at the intersection of tectonics, sea level fluctuation, and the effect of climate. As a result, marine terraces 

provide ample opportunity to study these processes through 

time, leading to a better understanding of seismic hazards, past 

climates, and soil development. By conducting this research, 

the U.S. Geological Survey is leading the way to make better 

informed decisions about our dynamic planet.

Acknowledgements

The authors would like to thank Channel Islands National 

Park, Mills Laguna Ranch, Wilder Ranch State Park, Dale 

Maharidge, and Tim Hyland of California State Parks for the 

many years of access for research.

Where to Find Marine Terraces

Publicly accessible lands 

in California that have good 

views of marine terraces.

0 50 100 MILES

0 50 100 KILOMETERS

1

2

3

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20 22

21 23

24 25

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34 35

41

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N

5

395

101

80

5

101

10

15

40

395

Pacific

Ocean

Crescent City

Map image is the intellectual property 

of Esri and is used herein under license. 

© 2014 Esri and its licensors. 

All rights reserved.

CALIFORNIA

San Diego

1. Prairie Creek Redwoods 

State Park

2. Patrick’s Point State Park

3. Trinidad State Beach

4. King Range National 

Conservation Area

5. MacKerricher State Park

6. Jug Handle State Natural 

Reserve

7. Point Cabrillo Light Station 

State Historical Park

8. Russian Gulch State Park

9. Mendocino Headlands 

State Park

10. Van Damme State Park

11. Manchester State Park

12. Point Arena-Stornetta, Calif. 

Coastal National Monument

13. Gualala Point Regional Park

14. Salt Point State Park

15. Fort Ross State Historic 

Park

16. Sonoma Coast State Park

17. Point Reyes National 

Seashore

18. Golden Gate National 

Recreation Area

19. McNee Ranch State Park

20. San Gregorio State Beach

21. Pomponio State Beach

22. Pescadero Marsh 

Natural Preserve

23. Año Nuevo State Park

24. Cotoni-Coast Dairies, Calif. 

Coastal National Monument

25. Wilder Ranch State Park

26. Natural Bridges State 

Beach

27. Seacliff State Beach

28. Manresa State Beach

29. Sunset State Beach

30. Garrapata State Park

31. Andrew Molera State Park

32. Hearst San Simeon State 

Park

33. Fiscalini Ranch Preserve

34. Harmony Headlands State 

Park

35. Montaña de Oro State Park

36. Jalama Beach County Park

37. Gaviota State Park

38. El Capitán State Beach

39. Point Mugu State Park

40. Point Dume State Beach

41. Channel Islands National 

Park

42. Torrey Pines State Natural 

Reserve

43. Cabrillo National Monument

By Marjorie Schulz,1

Corey Lawrence,1 Dan Muhs,1

Carol Prentice,1 and Sam Flanagan2

1

U.S. Geological Survey.

2

Bureau of Land Management.

Edited by Monica Erdman 

Layout by Suzanne C. Roberts

ISSN 2327-6916 (print)

ISSN 2327-6932 (online)

https://doi.org/10.3133/fs20183002