-12

-10

 -8

 -6

 -4

 -2

 0

 2

 4

 6

 8

 10

 12

 14

 16

 18

 20

 22

 24

 26

Magnetic FIeld, 

in nanoteslas

t

r

6b

14

15

16

17

18

19

20a

20b

21

22

23

24

26

27

28

29

30

31

32

33a

33b

35

36

37

38a 38b

39

40

41a

41b

42

43

44

45

46

47

48

49

50a

50b

52

53

34

Best----------------least confidence in dip; dip determined from 

asymmetry of reduced-to-pole anomalies (see fig. 5)

Vertical (>85 ̊)

Steep dip (60 ̊ - 85 ̊)

Medium dip (40 ̊- 60 ̊)

Shallow dip (<40 ̊)

Arrow points in dip direction 

of flap

1b

1a

2a 2b

3a

3b

4

5a

5b

5c

5d

6a

7

8

Contact between Yager and Coastal terranes from 

Bachman and others (1984)

Coastal Belt hrust (or contact between Coastal and 

Central Belt terranes) from Bachman and others (1984), 

Wagner and Bortugno (1982), Jayko and others (1989), 

and McLaughlin and others (2000)

36 Magnetic body (see table 2)

Quaternary fault from Jennings and Bryant (2010)

Contact between Yager and Coastal terranes from 

Jayko and others (1989) and McLaughlin and others 

(2000)

Yager terrane conglomerate from McLaughlin and 

others (2000)

Contours of residual, reduced-to-pole magnetic 

field intensity. Contour interval is 2 nanoteslas. 

Hachures indicate closed magnetic lows. Contours 

were computer generated based on a 200-m grid. 

Circles indicate possible locations of boundaries 

between regions of different magnetizations 

calculated automatically from the grid (see 

accompanying text for explanation). Larger circles 

denote gradient amplitudes greater than the mean 

for the study area; smaller circles denote amplitudes less than the mean.

Greenstone or metavolcanic rock from McLaughlin and 

others (2000), Jayko and others (1989), Wagner and 

Bortugno (1982), Kramer (1976), and O’Day (1974).

9

10

11

12

13

25a

25b

51

54

55

56

57

58

Area masked to

emphasize the

Coastal Belt anomalies

Residual, Reduced-to-pole Aeromagnetic Map of the Northern Coast Ranges, California, with Interpreted Dips from Asymmetry of Residual Magnetic Anomalies within the Coastal Belt

King

Range

terrane

124°22'30" 15' 124° 52'30" 45' 37'30" 30' 22'30" 15' 7'30" 123° 122°52'30"

U.S. Department of the Interior

U.S. Geological Survey Scientific Investigations Map 3188

Sheet 3 of 3

Pamphlet accompanies map

1 0 1 2 43 5 6 7 8 9 10 KILOMETERS

SCALE 1:100 000

1 0 1 2 3 4 5 6 7 8 MILES

124°22'30" 15' 7'30" 124° 52'30" 45' 37'30" 30' 22'30" 15' 7'30" 123° 122°52'30"

7'30"

38°22'30"

30'

37'30"

45'

52'30"

39°

7'30"

15'

22'30"

30'

37'30"

45'

52'30"

40°

7'30"

15'

22'30"

40°30'

38°22'30"

30'

37'30"

52'30"

39°

7'30"

22'30"

30'

37'30"

45'

52'30"

40°

7'30"

15'

22'30"

40°30'

45'

15'

Data compiled by Victoria E. Langenheim

GIS database and digital cartography by 

Victoria E. Langenheim

Edited by Theresa Iki; digital cartographic 

production by K. Nimz

Manuscript approved for publication 

October 28, 2011

CALIF.

MAP LOCATION

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

imply endorsement by the U.S. Government

This map was printed on an electronic plotter directly from digital files. Dimensional calibration may vary 

between electronic plotters and between X and Y directions on the same plotter, and paper may change 

size due to atmospheric conditions; therefore, scale and proportions may not be true on plots of this map.

For sale by U.S. Geological Survey, Information Services, Box 25286, Federal Center, Denver, CO 80225, 

1–888–ASK–USGS

Digital files available at http://pubs.usgs.gov/sim/3188/

Suggested Citation: Langenheim, V.E., Jachens, R.C., Wentworth, C.M., and McLaughlin, R.J., 2011, 

Aeromagnetic and aeromagnetic-based geologic maps of the Coastal Belt, Franciscan Complex, 

northern California: U.S. Geological Survey Scientific Investigations Map 3188, pamphlet 20 p., 3 sheets, 

various scales, and database, available at http://pubs.usgs.gov/sim/3188/.

SAN ANDREAS FAULT

MAACAMA FAULT

BARTLETT SPRINGS FAULT

SAN ANDREAS FAULT

Point

Arena

Shelter

Cove

Ukiah

Willits

Lake

Pillsbury

Clear

Lake

Point

Delgada

Cape

Mendocino

Mendocino

Fort

Bragg

Petrolia

Fortuna

Elk

Boonville

Cloverdale

Healdsburg

Bodega Bay

Covelo

Laytonville

Garberville

east-west 

flightline

artifacts?

northeast-southwest

flightline

artifacts?

PACIFIC OCEAN

Fort Ross

Aeromagnetic and Aeromagnetic-based Geologic Maps of the 

Coastal Belt, Franciscan Complex, Northern California

By

V.E. Langenheim, R.C. Jachens, C.M. Wentworth, and R.J. McLaughlin

2011