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 https://doi.org/10.3133/ofr20181024

Suggested Citation: Johnson, S.Y., and Hartwell, S.R., 2018, Seismic-reflection profiles, Offshore of Point Conception map area, 

California, sheet 7 in Johnson, S.Y., Dartnell, P., Cochrane, G.R., Hartwell, S.R., Golden, N.E., Kvitek, R.G., and Davenport, C.W. (S.Y. 

Johnson and S.A. Cochran, eds.), California State Waters Map Series—Offshore of Point Conception, California: U.S. Geological 

Survey Open-File Report 2018–1024, pamphlet 36 p., 9 sheets, scale 1:24,000, https://doi.org/10.3133/ofr20181024.

ISSN 2331-1258 (online)

https://doi.org/10.3133/ofr20181024

DISCUSSION

This map sheet shows seismic-reflection profiles from two different surveys of the Offshore of Point Conception 

map area, providing imagery of the subsurface geology in the westernmost Santa Barbara Channel region. This 

offshore area is characterized by a relatively flat shelf that decreases in slope (from about 1.1° to 0.7°) from southeast 

to northwest as the trend of the coastline changes from westward (east of Point Conception) to northwestward (west 

of Point Conception). 

The high-resolution seismic-reflection profiles displayed on this sheet (figs. 1, 2, 3, 4, 5, 6, 7, 8, 9, 11, 12) were 

collected in 2014 on U.S. Geological Survey (USGS) cruise S–01–13–SC, using the SIG 2Mille minisparker system. 

This system used a 500-J high-voltage electrical discharge fired 1 to 2 times per second, which, at normal survey 

speeds of 4 to 4.5 nautical miles per hour, gives a data trace every 1 to 2 m of lateral distance covered. The data were 

digitally recorded in standard SEG-Y 32-bit floating-point format, using Triton Subbottom Logger (SBL) software 

that merges seismic-reflection data with differential GPS-navigation data. After the survey, a short-window (20 ms) 

automatic gain control algorithm was applied to the data, along with a 160- to 1,200-Hz bandpass filter and a heave 

correction that uses an automatic seafloor-detection window (averaged over 30 m of lateral distance covered). These 

data can resolve geologic features a few meters thick (and, hence, are considered “high-resolution”), down to subbottom depths of as much as 400 m.

Figure 10 shows a migrated, deep-penetration, multichannel seismic-reflection profile collected in 1984 by 

WesternGeco on cruise W–37–84–SC. This profile and other similar data were collected in many areas offshore of 

California in the 1970s and 1980s when these areas were considered a frontier for oil and gas exploration. Much of 

these data have been publicly released and are now archived at the U.S. Geological Survey National Archive of 

Marine Seismic Surveys (Triezenberg and others, 2016). These data were acquired using a large-volume air-gun 

source that has a frequency range of 3 to 40 Hz and recorded with a multichannel hydrophone streamer about 2 km 

long. Shot spacing was about 30 m. These data can resolve geologic features that are 20 to 30 m thick, down to 

subbottom depths of as much as 4 km.

The shelf is underlain by Neogene sedimentary rocks and uppermost Pleistocene to Holocene sediments (see 

sheet 9). Neogene units include the Miocene Monterey Formation and the upper Miocene and lower Pliocene Sisquoc 

Formation. On high-resolution seismic-reflection profiles, these strata commonly yield parallel to subparallel, 

continuous, variable-amplitude, high-frequency reflections (terminology from Mitchum and others, 1977); however, 

these strata are cut by numerous faults and commonly are folded, in many places too steeply folded to be imaged on 

seismic-reflection profiles. Local zones that lack reflections probably also are the result of the presence of interstitial 

gas within the sediments. This effect has been referred to as “gas blanking,” “acoustic turbidity,” or “acoustic 

masking” (Hovland and Judd, 1988; Fader, 1997). The gas scatters or attenuates the acoustic energy, preventing 

penetration. Not surprisingly, this effect is especially prevalent offshore of Point Conception where numerous large 

asphalt mounds (see figs. 5 through 9) and pockmark fields are present on the seafloor (see also, sheet 9).

Eustasy was an important control on latest Pleistocene to Holocene shelf deposition in the Offshore of Point 

Conception map area. Surficial and shallow sediments were deposited on the shelf in the last about 21,000 years 

during the sea-level rise that followed the last major lowstand and the Last Glacial Maximum (LGM) (Stanford and 

others, 2011). Global sea level was about 120 to 130 m lower during the LGM, at which time the shelf around Point 

Conception was emergent. The post-LGM sea-level rise was rapid (about 9 to 11 m per thousand years) until about 

7,000 years ago, when it slowed considerably to about 1 m per thousand years (Stanford and others, 2011). The 

sediments deposited on the shelf during the post-LGM sea-level rise (above a transgressive surface of erosion) are 

shaded blue in the high-resolution seismic-reflection profiles (figs. 1, 2, 3, 4, 5, 6, 7, 8, 9, 11, 12), and their thicknesses are shown on sheet 8. On most profiles, the base of the post-LGM depositional unit is a flat to concave, 

angular unconformity characterized by an obvious change in reflection properties.

High-resolution seismic-reflection profiles in the Offshore of Point Conception map area primarily show 

Neogene strata that, on a larger scale, are folded within a large, east-west-striking homocline that extends from the 

south flank of the Santa Ynez Mountains (see fig. 1–2 in pamphlet) into the offshore to both the south and west. The 

homocline formed above the blind Pitas Point–North Channel Fault system (fig. 1–3 in pamphlet), as indicated on 

nearby regional cross sections (Redin and others, 2005) and on industry seismic-reflection profiles (see, for example, 

fig. 10; see also, Sorlien and Nicholson, 2015). The tip of the fault system is inferred to be buried to a depth of about 

2 to 3 km below sea level (about 1.5 to 2 sec two-way travel time [TWT]) about 4 to 6 km offshore, beneath the slope 

on the north flank of the Santa Barbara Basin. 

Closely spaced seismic-reflection profiles reveal many shallow, west-northwest-striking folds that have variable 

geometries, lengths, amplitudes, degrees of continuity, and wavelengths. The Government Point Syncline, which is 

the most prominent fold, has been mapped both onshore at Point Conception (Dibblee, 1988a) and offshore to the 

west and east of Point Conception; the syncline has a cumulative length of more than 22 km (see sheet 9). Local 

thickening of post-LGM sediments along the axis of the Government Point Syncline (see figs. 2, 3, 4) could reflect 

syntectonic sedimentation. Onland at Point Conception, Rockwell and others (1992) also documented active folding 

of late Pleistocene marine terraces in the Government Point Syncline. This regionally extensive syncline and many 

shorter, east-west-striking folds and faults probably are rooted in blind thrust faults and back-thrust faults in the 

hanging wall above the Pitas Point–North Channel Fault system (fig. 1–3 in pamphlet).

REFERENCES CITED

Dibblee, T.W., Jr., 1988a, Geologic map of the Lompoc Hills and Point Conception quadrangles, Santa Barbara 

County, California (H.E. Ehrenspeck [1988] and J.A. Minch [2009], eds.): Dibblee Geological Foundation Map 

DF-18, scale 1:24,000.

Fader, G.B.J., 1997, Effects of shallow gas on seismic-reflection profiles, in Davies, T.A., Bell, T., Cooper, A.K., 

Josenhaus, H., Polyak, L., Solheim, A., Stoker, M.S., and Stravers, J.A., eds., Glaciated continental 

margins—An atlas of acoustic images: London, Chapman & Hall, p. 29–30.

Hovland, M., and Judd, A.G., 1988, Seabed pockmark and seepages: London, Graham and Trotman, Inc., 293 p.

Mitchum, R.M., Jr., Vail, P.R., and Sangree, J.B., 1977, Seismic stratigraphy and global changes of sea level, part 

6—Stratigraphic interpretation of seismic reflection patterns in depositional sequences, in Payton, C.E., ed., 

Seismic stratigraphy—Applications to hydrocarbon exploration: Tulsa, Okla., American Association of 

Petroleum Geologists, p. 117–133.

Redin, T., Forman, J., Kamerling, M., and Galloway, J., 2005, Santa Barbara Channel structure and correlation 

sections—CS-32 to CS-42: American Association of Petroleum Geologists, Pacific Section, Publication CS 36, 

12 sheets.

Rockwell, T.K., Nolan, J., Johnson, D.L., and Patterson, R.H., 1992, Ages and deformation of marine terraces 

between Point Conception and Gaviota, Western Transverse Ranges, California, in Wehmiller, J.F., and Fletcher, 

C., eds., Quaternary coasts of the United States—Marine and lacustrine systems: Society of Economic 

Paleontologists and Mineralogists, p. 333–341.

Sorlien, C.C., and Nicholson, C., 2015, Post 1-Ma deformation history of the Pitas Point-North Channel-Red 

Mountain fault system and associated folds in Santa Barbara channel, California: U.S. Geological Survey 

National Earthquake Hazards Reduction Program final report, Award G14AP00012, 24 p., available at 

https://earthquake.usgs.gov/cfusion/external_grants/reports/G14AP00012.pdf.

Stanford, J.D., Hemingway, R., Rohling, E.J., Challenor, P.G., Medina-Elizalde, M., and Lester, A.J., 2011, Sea-level 

probability for the last deglaciation—A statistical analysis of far-field records: Global and Planetary Change, v. 

79, p. 193–203, available at https://doi.org/10.1016/j.gloplacha.2010.11.002.

Triezenberg, P. J., Hart, P. E., and Childs, J. R., 2016, National Archive of Marine Seismic Surveys (NAMSS)—A 

USGS data website of marine seismic reflection data within the U.S. Exclusive Economic Zone (EEZ): U.S. 

Geological Survey data release, accessed May 2016 at https://doi.org/10.5066/F7930R7P [formerly U.S. 

Geological Survey’s National Archive of Marine Seismic Surveys database, available at 

http://walrus.wr.usgs.gov/NAMSS/].

120°30' 120° 119°30'

34°

34°30'

Limit of California’s

State Waters

Kilometers 0 5 10

Santa Barbara Channel

Area of

Map

Santa Barbara CALIF.

MAP LOCATION

Anacapa Is.

Santa Cruz Is.

Santa Rosa Is.

San Miguel Is.

Seismic-Reflection Profiles, Offshore of Point Conception Map Area, California

By

Samuel Y. Johnson and Stephen R. Hartwell

2018 

EAST

160

0 

Approximate depth, in meters

80

240

320

1 km

VERTICAL EXAGGERATION ~ 10

Two-way travel time, in seconds

0

0.1

0.2

WEST

0.3

0.4

Fig. 7

Figure 12. USGS high-resolution minisparker seismic-reflection profile GS–77 (collected in 2014 on cruise S–01–13–CC), which crosses shelf south of Point Conception; see trackline map for location. Profile 

highlights folded and faulted strata beneath continental shelf. Dashed red lines show faults. Magenta symbols show fold axes (diverging arrows, anticlines; converging arrows, synclines). Blue shading 

shows inferred uppermost Pleistocene and Holocene strata, deposited since last sea-level lowstand about 21,000 years ago. Underlying reflectors image deformed Neogene strata. Dashed green lines 

highlight some continuous reflections that reveal structure (not distinctive stratigraphic markers). Dashed yellow lines are seafloor multiples (echoes of seafloor reflector). Fig. 10 Fig. 8 Fig. 9

1 km

VERTICAL EXAGGERATION ~ 10

Two-way travel time, in seconds

0

0.1

0.2

SOUTH

0.3

NORTH

160

0 

Approximate depth, in meters

80

240

Figure 11. USGS high-resolution minisparker seismic-reflection profile GS–60 (collected in 2014 on cruise S–01–13–CC), which crosses shelf east-southeast of Point Conception; see trackline 

map for location. Profile highlights shallow, largely reflection-free bedrock beneath continental shelf. Dashed red lines show faults. Magenta symbol shows anticline axis. Blue shading 

shows inferred uppermost Pleistocene and Holocene strata, deposited since last sea-level lowstand about 21,000 years ago. Dashed green lines highlight some continuous reflections that 

reveal structure (not distinctive stratigraphic markers). Dashed yellow lines are seafloor multiples (echoes of seafloor reflector). Purple triangle shows location of California’s State Waters 

limit (yellow line on trackline map).

1.0

0

Two-way travel time, in seconds

2.0

3.0

1 km

VERTICAL EXAGGERATION ~ 1.5

Figure 10. Industry, 2-D, migrated, multichannel air-gun seismic-reflection profile WC–84–288 (collected in 1984 on WesternGeco survey W–37–84–SC; from USGS National 

Archive of Marine Seismic Surveys [Triezenberg and others, 2016]), which extends south from Point Conception; see trackline map for location. Note that profile has similar 

horizontal scale to USGS high-resolution seismic-reflection profiles shown in figures 1, 2, 3, 4, 5, 6, 7, 8, 9, 11, and 12, but it has much less vertical exaggeration (1.5:1); note also 

that profile has not been depth converted and so no depth scale is shown, but it probably extends to depths of about 4 km. Profile highlights blind, north-dipping faults of 

westernmost part of Pitas Point–North Channel Fault system (dashed red lines). Magenta symbols show fold axes (diverging arrows, anticline; converging arrows, syncline). 

Dashed green lines highlight some continuous reflections that reveal depositional patterns and structure (not distinctive stratigraphic markers). Dashed yellow lines are 

seafloor multiples (echoes of seafloor reflector). Purple triangle shows location of California’s State Waters limit (yellow line on trackline map).

SOUTH

Fig. 8

Fig. 12

NORTH

Fig. 7

NORTH

160

0 

Approximate depth, in meters

80

240

1 km

VERTICAL EXAGGERATION ~ 10

Two-way travel time, in seconds

0

0.1

0.2

SOUTH

0.3

Figure 9. USGS high-resolution minisparker seismic-reflection profile GS–03 (collected in 2014 on cruise S–01–13–CC), which crosses shelf southeast of Point Conception; see 

trackline map for location. Profile highlights asphalt mound and structure in shallow bedrock beneath continental shelf. Dashed and queried red line shows possible fault. Magenta 

symbols show fold axes (diverging arrows, anticline; converging arrows, possible syncline). Blue shading shows inferred uppermost Pleistocene and Holocene strata, deposited 

since last sea-level lowstand about 21,000 years ago. Dashed green lines highlight some continuous reflections that reveal structure (not distinctive stratigraphic markers). Dashed 

yellow lines are seafloor multiples (echoes of seafloor reflector). Purple triangle shows location of California’s State Waters limit (yellow line on trackline map). Fig. 12

asphalt 

mound

fault

Point Conception 

 Anticline

?

NORTH

160

0 

Approximate depth, in meters

80

240

1 km

VERTICAL EXAGGERATION ~ 10

Two-way travel time, in seconds

0

0.1

0.2

SOUTH

0.3

Figure 8. USGS high-resolution minisparker seismic-reflection profile GS–07 (collected in 2014 on cruise S–01–13–CC), which crosses shelf south of Point 

Conception; see trackline map for location. Profile highlights asphalt mound and structure in shallow bedrock beneath continental shelf and upper slope. 

Magenta symbols show fold axes (diverging arrows, anticline; converging arrows, syncline). Blue shading shows inferred uppermost Pleistocene and Holocene 

strata, deposited since last sea-level lowstand about 21,000 years ago. Dashed green lines highlight some continuous reflections that reveal structure (not 

distinctive stratigraphic markers). Dashed purple line is prominent angular unconformity. Dashed yellow lines are seafloor multiples (echoes of seafloor 

reflector). Purple triangle shows location of California’s State Waters limit (yellow line on trackline map). Fig. 10 Fig. 12

asphalt 

mound

1 km

VERTICAL EXAGGERATION ~ 10

Two-way travel time, in seconds

0

0.1

0.2

SOUTH

0.3

NORTH

160

0 

Approximate depth, in meters

80

240

Fig. 12

Fig. 10

asphalt 

mound

Figure 7. USGS high-resolution minisparker seismic-reflection profile GS–11 (collected in 2014 on cruise S–01–13–CC), which crosses shelf southwest of 

Point Conception; see trackline map for location. Profile highlights asphalt mound and structure in shallow bedrock beneath continental shelf and upper 

slope. Dashed red lines show faults. Magenta symbol shows syncline axis. Blue shading shows inferred uppermost Pleistocene and Holocene strata, 

deposited since last sea-level lowstand about 21,000 years ago. Dashed green lines highlight some continuous reflections that reveal structure (not 

distinctive stratigraphic markers). Dashed yellow lines are seafloor multiples (echoes of seafloor reflector).

1 km

VERTICAL EXAGGERATION ~ 10

Two-way travel time, in seconds

0

0.1

0.2

SOUTHWEST

0.3

NORTHEAST

160

0 

Approximate depth, in meters

80

240

asphalt mounds

Figure 6. USGS high-resolution minisparker seismic-reflection profile GS–12 (collected in 2014 on cruise S–01–13–CC), which crosses shelf west-southwest of 

Point Conception; see trackline map for location. Profile highlights large asphalt mound complex and structure in shallow bedrock beneath continental shelf and 

upper slope. Dashed red lines show faults. Magenta symbol shows syncline axis. Blue shading shows inferred uppermost Pleistocene and Holocene strata, 

deposited since last sea-level lowstand about 21,000 years ago. Dashed green lines highlight some continuous reflections that reveal structure (not distinctive 

stratigraphic markers). Dashed yellow lines are seafloor multiples (echoes of seafloor reflector). Purple triangle shows location of California’s State Waters limit 

(yellow line on trackline map).

1 km

VERTICAL EXAGGERATION ~ 10

Two-way travel time, in seconds

0

0.1

0.2

SOUTH

0.3

NORTH

160

0 

Approximate depth, in meters

80

240

Government Point Syncline

Figure 5 (left). USGS high-resolution minisparker seismic-reflection profile GS–16 (collected in 2014 on cruise S–01–13–CC), which 

crosses shelf west of Point Conception; see trackline map for location. Profile highlights large asphalt mound and structure in 

shallow bedrock beneath continental shelf. Dashed red line shows fault. Magenta symbol shows syncline axis. Blue shading shows 

inferred uppermost Pleistocene and Holocene strata, deposited since last sea-level lowstand about 21,000 years ago. Dashed green 

lines highlight some continuous reflections that reveal structure (not distinctive stratigraphic markers). Dashed yellow lines are 

seafloor multiples (echoes of seafloor reflector). Purple triangle shows location of California’s State Waters limit (yellow line on 

trackline map).

asphalt 

mound

1 km

VERTICAL EXAGGERATION ~ 10

Two-way travel time, in seconds

0

0.1

0.2

NORTHWEST

0.3

SOUTHEAST

160

0 

Approximate depth, in meters

80

240

Figure 4. USGS high-resolution minisparker seismic-reflection profiles GS–79 and northwestern part of GS–78 (both collected in 2014 on cruise S–01–13–CC), which cross midshelf area between Point 

Conception and Point Arguello; see trackline map for location. Profiles highlight folds in shallow bedrock beneath continental shelf. Magenta symbols show fold axes (diverging arrows, anticlines; converging 

arrows, synclines). Blue shading shows inferred uppermost Pleistocene and Holocene strata, deposited since last sea-level lowstand about 21,000 years ago. Dashed green lines highlight some continuous 

reflections that reveal structure (not distinctive stratigraphic markers). Dashed yellow lines are seafloor multiples (echoes of seafloor reflector).

Government Point

 Syncline

GS–79 GS–78

Fig. 1

Fig. 2Fig. 3

20° bend

in profile

1 km

VERTICAL EXAGGERATION ~ 10

Two-way travel time, in seconds

0

0.1

0.2

SOUTHWEST

0.3

NORTHEAST

160

0 

Approximate depth, in meters

80

240

Figure 3. USGS high-resolution minisparker seismic-reflection profile GS–19 (collected in 2014 on cruise S–01–13–CC), which crosses shelf between Point Conception and Point Arguello; see 

trackline map for location. Profile highlights faults and folds in shallow bedrock beneath continental shelf. Dashed red lines show faults. Magenta symbols show fold axes (diverging arrows, 

anticline; converging arrows, syncline). Blue shading shows inferred uppermost Pleistocene and Holocene strata, deposited since last sea-level lowstand about 21,000 years ago. Dashed 

green lines highlight some continuous reflections that reveal structure (not distinctive stratigraphic markers). Dashed purple line shows unconformity. Dashed yellow lines are seafloor 

multiples (echoes of seafloor reflector). Purple triangle shows location of California’s State Waters limit (yellow line on trackline map).

Government Point

 Syncline

1 km

VERTICAL EXAGGERATION ~ 10

Two-way travel time, in seconds

0

0.1

0.2

SOUTHWEST

0.3

0.4

NORTHEAST

160

0 

Approximate depth, in meters

80

240

320

Figure 2. USGS high-resolution minisparker seismic-reflection profile GS–22 (collected in 2014 on cruise S–01–13–CC), which crosses shelf between Point Conception and Point Arguello; see trackline map for 

location. Profile highlights faults and folds in shallow bedrock beneath continental shelf. Dashed red lines show faults. Magenta symbols show fold axes (diverging arrows, anticlines; converging arrows, synclines). 

Blue shading shows inferred uppermost Pleistocene and Holocene strata, deposited since last sea-level lowstand about 21,000 years ago. Dashed green lines highlight some continuous reflections that reveal 

structure (not distinctive stratigraphic markers). Dashed yellow lines are seafloor multiples (echoes of seafloor reflector). Purple triangle shows location of California’s State Waters limit (yellow line on trackline 

map).

Fig. 4

Fig. 4

Government Point

 Syncline

1 km

VERTICAL EXAGGERATION ~ 10

Two-way travel time, in seconds

0

0.1

0.2

SOUTHWEST

0.3

NORTHEAST

160

0 

Approximate depth, in meters

80

240

Figure 1. USGS high-resolution minisparker seismic-reflection profile GS–24 (collected in 2014 on cruise S–01–13–CC), which crosses shelf between Point Conception and Point 

Arguello; see trackline map for location. Profile highlights faults and folds in shallow bedrock beneath continental shelf. Dashed red lines show faults. Magenta symbols show 

fold axes (diverging arrows, anticline; converging arrows, synclines). Blue shading shows inferred uppermost Pleistocene and Holocene strata, deposited since last sea-level 

lowstand about 21,000 years ago. Dashed green lines highlight some continuous reflections that reveal structure (not distinctive stratigraphic markers). Dashed yellow lines are 

seafloor multiples (echoes of seafloor reflector). Purple triangle shows location of California’s State Waters limit (yellow line on trackline map). Fig. 4

ONE MILE = 0.869 NAUTICAL MILES

1 0.5 0 1 KILOMETER

7000 3500 0 7000 FEET

2 1 0 2 MILES

SCALE 1:50 000

APPROXIMATE MEAN

DECLINATION, 2018

MAGNETIC NORTH

12 / ° 1 2

TRUE NORTH

GIS database and digital cartography by Peter Dartnell 

and Stephen R. Hartwell

Manuscript approved for publication February 13, 2018

Onshore elevation data from National Oceanic and 

Atmospheric Administration (NOAA) Office for Coastal 

Management's Digital Coast (available at 

http://www.csc.noaa.gov/digitalcoast/data/coastallidar/) 

and from U.S. Geological Survey’s National Elevation 

Dataset (available at http://ned.usgs.gov/). Offshore 

shaded-relief bathymetry from map on sheet 2, this 

report. California’s State Waters limit from NOAA Office of 

Coast Survey 

Universal Transverse Mercator projection, Zone 10N

NOT INTENDED FOR NAVIGATIONAL USE

120°25'

120°25'

120°30'

120°30'

34°30

34°30'

34°25'

34°25'

Fig. 1

Fig. 2

Fig. 3

Fig. 4

Fig. 5

Fig. 6

Fig. 7

Fig. 8

Fig. 9

Fig. 10

Fig. 11

Fig. 12

Figure 1

Figure 10

Trackline Map

EXPLANATION

Tracklines of select seismic-reflection 

surveys—Thick lines show locations 

of profile lines depicted in figures; 

thin lines show full extent of surveys

Survey S–01–13–CC (USGS)

Survey W–37–84–SC (WesternGeco)

Survey W–40–85–SC (WesternGeco)

 3-nautical-mile limit of California’s 

State Waters

Area of “no data”—Areas near shoreline 

not mapped owing to insufficient 

high-resolution seafloor mapping data

Point Conception

Open-File Report 2018–1024

Sheet 7 of 9

Pamphlet accompanies map

U.S. Department of the Interior

U.S. Geological Survey