STATE OF WASHINGTON DEPARTMENT OF NATURAL RESOURCES

Brian Boyle, Commissioner of Public Lands

Art Stearns, Supervisor

DIVISION OF GEOLOGY AND EARTH RESOURCES Raymond Lasmanis, State Geologist

GEOPHYSICAL MAP GM-27

COMPLETE BOUGUER GRAVITY ANOMALY MAP,

CASCADE MOUNTAINS, WASHINGTON

By V

Z.F. DANES AND W.M. PHILLIPS

Prepared In cooperation with U.S. Department of Energy

Contract DE-AC03-79ET27014

1983

For sale by the Departmeni of Natural ResoU?Ces

Price $ 8.25

WASHINGTON STATE DEPARTMENT OF NATURAL RESOURCES BRIAN J. BOYLE, Commissioner of Public Lands ART STEARNS, Supervisor

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Estimated maximum uncertainty of grav­ity measurements 5 mgals

Theoretical gravity IGF (1967)

Bouguer reduction density 2.67 g/cc

Potsdam correction : Gravity base stations adjusted by -13.00 mgals relative to old in­ternational gravity base station at Potsdam .

Terrain corrections : Near terrain correc­tions (Hammer Zone A-D) determined via use of graphs based on geometry of topogra­phy in immediate vicinity of observation points. Distant terrain corrections calcu­lated using the computer program of Plouff (1977)

Principal gravity facts and discussion of terrain corrections available in Dane$ and Phillips (1983)

Note: The companion map to this work, Complete Bouguer Gravity Anomaly Map, Northern Cascade Mountains, Washington (sheet 1), uses a terrain correction method (DaneS, 1982) that differs from the one employed here. Therefore, contour lines on the two maps are not continuous across the 4 7° N. latitude boundary

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SOURCE OF GRAVITY DATA

Goman (1967); KonfCek (1974, 1975); Rowley (1982); Stricklin (1975); Stuart ( 1965); all other data collected by Z. F. DaneS. Gravit y data tied into the Wash­ington gravity base station network (Nilsen, 1976)

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SOUTHERN CASCADES, WASHINGTON DIVISION OF GEOLOGY AND EARTH RESOURCES RAYMOND LASMANIS, State Geologist

Geophysical Map GM-27 Sheet 2 of 2

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COMPLETE BOUGUER GRAVITY ANOMALY MAP, CASCADE MOUNTAINS, WASHINGTON

By • Z.F . DANES

and W.M. PHILLIPS

1983

Scale I :250,000

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Topographic contour interval 200 feet with supplementa,,y contow:s a t 100-foot intervals Transverse Mercato r Projection

Gravity contour interval 5 mgals Gravity contours dashed where uncertain Hachured contour indicates low gravity Location of gravity stations shown by dots

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Topographic base map from portions of the Hoquiam, The

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REFERENCES CITED

DaneS, Z. F.; Phillips, W. M., 1983, Principal facts and a discussion of terrain correc ­tion methods for the complete Bouguer gravity anomaly map of the Cascade Mountains, Washington: Washington Division of Geology and Earth Re­sources Open-File Report 83-1, 15 p., 145 gravity data sheets

Danes, Z. F., 1982, An analytic method for the determination of distant terrain corrections: Geophysics, v. 47, no. 10, p. 1453-1455.

Goman, T., 1967, Gravity survey of Mount St. Helens, Washington: University of Puget Sound Undergraduate Research Project.

.. Konicek, D. L., 1974 , Geophysical survey

in south-central Washington: University of Puget Sound M.S. thesis, 35 p.

KonfCek , D. L., 1975, Geophysical survey in south-central Washington: Northwest Science, v. 49, no . 2, p. 106-117.

Nilsen, Tor, 1976, Washington gravity base station network: Washington Division of Geology and Earth Re­sources Information Circular 59, 83 p.

Plouff, D., 1977, Preliminary documenta­tion for a FORTRAN program to compute gravity terrain corrections based on topography digitized on a geographic grid: U.S. Geological Survey Open-File Report 77-535, 45 p .

Rowley, S. H., 1982, A geophysical investi­gation of Mt. Adams, Washington [abstract): Eos, v. 63, no. 8, p. 174.

Stricklin, C. R., 1975, Geophysical survey of the Lemei Rock-Steamboat Mountain area, Washington : University of Puget Sound M.S. thesis, 23 p.

Stuart, D.J., 1965, Gravity data and Bouguer gravity map for western Washington: U.S . Geological Survey Open-File Re­port, 7 p., 46 gravity sheets, 1 map.

ACKNOWLEDGMENTS

Prepared under U.S. Department of Energy contract number DE-AC03 ·7 9ET27014

M. E. Comfort, D. B. Palmiter, and B. H. Vaughn assisted with collection of gravity data and preparation of the map. Special thanks to the University of Puget Sound students, colleagues, and friends who as­sisted with field and office work

WASHINGTON STATE DEPARTMENT OF NATURAL RESOURCES BRIAN J_ BOYLE, Commissioner of Public Lands ART STEARNS, Supervisor

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MAP LOCATION

Theoretical gravity IGF (1967)

Bouguer reduction density 2.67 glee

Potsdam correction: Gravity base stations adjusted by -13.00 mgals relative to old in­Lernational gravity base station at Potsdam.

Terrain corredions : Near terrain correc­tions (Hammer Zone A·D) determined via use of graphs based on geometry of topogra­phy in immediate vicinity of observation points. Distant terrain corrections calcu­lated using the analytical method of DaneS (1982)

Principal gravity facts and discussion of terrain corrections available in DaneS and Phillips (1983)

Nole : The companion map to this work, Complete Bouguer Gravity Anomaly Map, Southern Cascade Mountains, Washington (sheet 2), uses a terrain correction meohod (Plo uff, 1977 ) that differs from the o ne employed he1·e. Therefore, contour lines on the two maps are not conlinuous ac,·oss the 41° N. latitude boundary

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SOURCE OF GRAVITY DATA

Aiken (1970); Campbell and Johnson (1982}; Lepp ( 1978); Stuart (1965); all olher data collected by Z. F. DaneS. Gravity data t ied inlo the w~shington gynvit.y b,ise station network (Nilsen, 1976)

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COMPLETE BOUGUER GRAVITY ANOMALY MAP,

CASCADE MOUNTAINS, WASHINGTON

By •

Z.F. DANES and

W.M. PHILLIPS

1983

Scale I :250,000

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Topogrnphic contour interval 200 feet with supplementa>:y contours at 100-fooe in1ervals

Transvtrse Mercator Projection

Gravity contour interval 5 mg-als Gravity contours dashed where uncertain HC1chured contour indicates low (:Tavity Location of gravity stations shown by dots

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DIVISION OF GEOLOGY AND EARTH RESOURCES RAYMOND LASMANTS, State Geologist

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REFERENCES CITED

Aiken, C. L., 1970. Gravimetric profiles across norChern Cascades employing minimum assumptions as to snbsurface density distribution: University of Washington M.S. thesis, 134 p.

Campbell, D. S.; Johnson , D. J., 1982, Bouguer gravity study of Enumclaw/ Pinnacle Peak, Washington : North­west Science, v. 56, no. 2, p. 90-lQO.

DaneS, Z. f., 1982, An analytic method for the determination of distant terrain corrections: Geophysics,\'. 47, no. 10, p. 1453-1455.

DaneS, Z. F.; Phillips, W. M., 1983, Principal facts and a discussion of terrain correc· tion methods [or the complete Bouguer gravity anomaly map of the Cascade Mountains, Washington: Washington Division of Gcolog:,' and Em·th Re­sources Open-Fi !e Report 83-1, 15 p., 145 gravity data sheets.

L<.!pp, L. R., 1978, Geophysical investi­gation of southeastern Puget Sound lowland, Washington, USA , Univer­sity o f Puget Sound B.S. thesis, 11 p.

Nilsen, Tor, 1976, Washington gravity base station network : Washington Division of Geology and Earth Re­sources Information Circular 59, 83 p.

Plouff, D., 1977, Preliminary documenta­tion for a FORTRAN program to compute gravity terrain corrections based on topography digitized on a geograph ic grid: U.O. Geological Survey Open-F ile Report 77-535, 45 p.

Stuart, D.J., 1965, Gravity data and Bouguer gravity map for western Washington: U.S. Geological Survey Open-File Re· purt, 7 p., 46 ~T«viLy ,;heeL~, 1 map.

ACKNOWLEDGMENTS

Prepared under U.S. Department of Energy contract number DE-AC03-79ET27014

M. E. Comfort, J. Dibb, D. B . Palmiter, and B. H. Vaughn assisted with collection of gravity dat:1 and preparation of thQ map. Special thanks to the University of Puget Sound students, colleagues, and friends who assisted with field and office work