PRELIMINARY GEOLOGIC MAP OF THE BOZEMAN 30’ x 60’ QUADRANGLE SOUTHWESTERN MONTANA Compiled and mapped by Susan M. Vuke1, Jeffrey D. Lonn1, Richard B. Berg1, and Karl S. Kellogg2 Montana Bureau of Mines and Geology Open File Report MBMG 469 2002 Minor revisions: 1/03 Text revised and plate removed: 6/03 References added, Plate 2 removed: superseded by Geologic Map of Western and Northern Gallatin Valley (Vuke, 2003). Page 2 text changed to reflect this. 1Montana Bureau of Mines and Geology 2U.S. Geological Survey This report has been reviewed for conformity with Montana Bureau of Mines and Geology’s technical and editorial standards. Partial support has been provided by the STATEMAP component of the National Cooperative Geologic Mapping Program of the U.S. Geological Survey under contract number 02HQAG0038, and Montana Department of Transportation under contract CFDA number 20.205. PRELIMINARY GEOLOGIC MAP OF THE BOZEMAN 30’ x 60’ QUADRANGLE This geologic map of the Bozeman 30’x 60’ quadrangle is released with the intention that it will be followed by a revised version that incorporates new mapping of the Cenozoic deposits, including Geologic Map of Northern and Western Gallatin Valley, Southwestern Montana (Vuke, 2003). Ash samples have been collected for 40Ar/39Ar dates from Tertiary beds in the Madison bluffs and Storey Hills areas, and the results will also be included in a future version of the enclosed map. The senior author has made tentative structural interpretations on the enclosed map that are based on map patterns but with only minimal subsurface data. These interpretations were not shown on the earlier blueline version of Plate 1 (MBMG Open file report 334). Faults shown as concealed or inferred are speculative. It is clear from surface mapping, however, that many faults, especially those that strike northwest- southeast, have had multiple episodes of reactivation that may include reversal of vertical movement and strike-slip movement. Only the last episode of movement or the net movement is indicated on the map. Cross sections and discussion are not provided with this map, but they will be included with the future revised version. The map user is referred to the extensive bibliography provided with the map for more information at this time. Susan Vuke Montana Bureau of Mines and Geology 1300 W. Park St. Butte, Montana 59701 [email protected] 2. CORRELATION DIAGRAM BOZEMAN 30 x 60 QUADRANGLE Cenozoic and Mesozoic Quaternary Qaf Qal Qc Qls Holocene Qgr Cenozoic Qg Pleistocene QTaf QTgr ? ? Pliocene unconformity ? ? ? Ts Tsuf Tsuc Miocene ? ? ? unconformity ? ? ? Tdc ? Oligocene Tdcl Tertiary Trb Tre Tca Ts ? unconformity ? ? ? Tca Tba Trs Tre Trvi Tmc ? Tav Eocene ? ? Trr ? unconformity ? ? ? ? ? ? TKjb TKl TKqm TKa TKda KAg? ? ? ? ? ? Kit unconformity Kem Kse Mesozoic unconformity Upper Cretaceous Cretaceou Ket Kcof s unconformity Kmt Kt Lower Kk Cretaceous unconformity Jurassic Triassic Jm Jme Je unconformity @d 3. CORRELATION DIAGRAM (continued) BOZEMAN 30’ x 60’ QUADRANGLE Paleozoic and Precambrian Pp Permian PIPpq IPq Pennsylvanian I P M a IPMabs unconformity Mmc Mississippian Mm Ml MDt Dj Devonian Paleozoic Djm D mr unconformity Єgs Єsr DЄmr Єpi Єp Єpm Єm Cambrian Єw Єf unconformity Ydb Yla Proterozoic unconformity Precambrian KAg? Aum Aamh Archean Aif Aqa Aq Aqfg 4. GEOLOGIC MAP SOURCES AND INDEX OF 7.5’ QUADRANGLES BOZEMAN 30’ x 60’ QUADRANGLE 112o 111o 46o Doherty Negro Milligan Three Logan Nixon Horse- Flathead Moun- Hollow Canyon Forks Gulch shoe Pass tain 1, Creek 12, 18, 9, 18, 20, 24, 20, 26, 27, 43 23, 27 28, 31, 8, 11, 8, 14, 8, 14, 26, 39, 30, 40, 32, 35 28, 32, 35, 43 21, 38 41, 43 43 35 Jefferson Sapping- Willow Three Manhat- Manhat- Belgrade Miser Island ton Creek Forks SE tan SW tan Creek 8, 11, 29 29, 36 29, 36, 4, 27, 43 11, 31, 8, 11, 8, 11, 14, 19, 38, 43 43 14, 31 14, 19, 21, 3, 42 42 Pony Harrison Willow Norris Madison Anceney Boze- Boze- Creek NE Plateau man man Reser- Hot 25, 29, 5, 13, voir Springs 36 29, 36 7, 17, 7, 17, 43 11, 19, 2, 8, 11, 8, 11, 19 8, 10, 38, 43 31, 38, 19, 22 22 11, 19, 42, 43 Potosi Maltbys Norris Bear Cherry Ruby Gallatin Wheeler Peak Mound Trap Creek Moun- Gateway Moun- Creek Canyon tain tain 3, 8, 10, 36, 43 6, 36, 43 7, 15, 36 2, 7, 16 2, 22, 8, 2, 8, 19, 2, 8, 19, 19, 34, 33 22, 33 34, 38, 37, 38, 42 42 45o30’ Numbers above correspond with reference list on next page. 5. GEOLOGIC MAP SOURCES AND INDEX OF 7.5’ QUADRANGLES BOZEMAN 30’ x 60’ QUADRANGLE Numbers below correspond with index of map sources on next page. Published, thesis, and dissertation maps 1. Alexander, R.G., Jr., 1951, pl. 1, scale 1:25,344. 2. Clabaugh, S.E., and Armstrong, F.C., 1950, pl. 11, scale 1:125,000. 3. Custer, S.G., 1995a, Figs. 7-9. 4. Davis, W.E., Kinoshita, W.T., and Robinson, G.D., 1965. 5. Elliott, W.S., 1998a, scale 1:24,000. 6. Elliott, W.S., 1998b, scale 1:24,000. 7. Feichtinger, S.H., 1970, pl. 1, scale 1:24,000. 8. Fix, P.F., 1940, pl. 21, scale 1:126,720. 9. Glaman, L.R.B., 1991, pl. 1, scale 1:12,000. 10. Glancy, P.A., 1964, pl. 1, scale 1:24,000. 11. Hackett, O.M., Visher, F.N., McMurtrey, R.G., and Steinhilber, W.L., 1960, pl. 2, scale 1:63,360. 12. Hendrix, T.E., and Stellavato, N., 1976, Fig. 10–1, scale 1:62,500. 13. Hoh, A.M., 1997. 14. Hughes, G.C., 1981, pl. 1, scale 1:63,000. 15. Kellogg, K.S., 1994, scale 1:24,000. 16. Kellogg, K.S., 1995, scale 1:24,000. 17. Kellogg, K.S., and Vuke, S.M., 1996, scale 1:24,000. 18. Lofgren, D.L., 1985, pl. 1, scale 1:24,000. 19. Lonn, J.D., and English, A.R., 2002, scale 1:48,000 20. Ludman, A., 1965, pl. 1, scale 1:6,000. 21. McMannis, 1955, pls. 1 and 2, scale 1:48,000. 22. Mifflin, M.D., 1963, scale 1:31,680. 23. Mitchell, M.M., 1987, pl. 1, scale 1:24,000. 24. Moore, G.T., 1954, pl. 1, scale 1:6,000. 25. O’Neill, J.M., 1983, pl. 1, scale 1:50,000. 26. Richard, B.H., 1966, pls. 1-4, scale 1:24,000; pl. 5 scale 1:60,000; Fig. 10 scale 31,680. 27. Robinson, G.D., 1963, pl. 1, scale 1:48,000. 28. Sayers, F.E., 1962, pl. 8, scale 1:33,000. 29. Schmidt, C.J., 1975, pl. 1, scale 1:24,000. 30. Schmidt, C.J., and O’Neill, J.M., 1982, Fig. 17, scale 1:168,960. 31. Schneider, G.B., 1970, pl. 1, scale 1:24,000. 32. Spahn, R.A., Jr., 1967, pl. 1, scale 1:24,000. 33. Tilley, C.W., 1976, pl. 1, scale 1:24,000. 34. Tysdal, R.G., 1966, pl. 1, scale 1:31,680. 35. Verrall, P., 1955, pl. 1, scale 1:24,000. 36. Vitaliano, C.J., and Cordua, W.S., 1979, scale 1:62,500. 37. Weber, W.J., 1965, pl. 1, scale 1:28,800. Unpublished maps, excluding thesis and dissertation maps 38. Berg, R.B., Montana Bureau of Mines and Geology 39. Cox, B., Earthworks, Inc., for Golden Sunlight Mines, Inc. 40. Dresser, H., Montana Tech of the University of Montana, A stereo picture guide to some of Montana’s thrust faults (1996) 41. Hanneman, D., Whitehall Geogroup, Inc., for Golden Sunlight Mines, Inc. 42. Lonn, J.D., Montana Bureau of Mines and Geology 43. Vuke, S.M., Montana Bureau of Mines and Geology Entire quadrangle Vuke, S.M., Berg, R.B., Lonn, J. D., and Kellogg, K.S., 1995, scale 1:100,000. 6. DESCRIPTION OF MAP UNITS BOZEMAN 30’ x 60’ QUADRANGLE Note: Thicknesses are given in feet because original field maps were on 7.5’ quadrangles with contour intervals in feet. To convert feet to meters (the contour interval unit on this map), multiply feet x 0.3048. Qal Alluvium (Holocene)—Light gray to light brown gravel, sand, silt, and clay deposited in stream and river channels, on floodplains, and on low terraces as much as about 20 ft above modern streams and rivers. Moderately sorted to well sorted. Larger clasts subangular to well rounded. Composition varies, but includes clasts of Archean metamorphic rocks, Precambrian orthoquartzite, Paleozoic limestone and quartzite, vein quartz, and volcanic rocks. Clasts of some smaller streams originating in Tertiary uplands are dominantly granule size and smaller and may include rip-up clasts. Thickness variable, but may be as much as 50 ft in channels of Jefferson, Madison, and Gallatin Rivers. Loess (Holocene and Pleistocene) (Not mapped)—Tan, calcareous silt, clay, and sand that mantles many areas. Thickness as much as 4 ft on hilltops, thinner on slopes. Qc Colluvium (Holocene and Pleistocene)—Light grayish-brown deposits on gentle slopes in the Tobacco Root Mountains. Mostly sand, silt, and clay with many fewer cobbles and pebbles. Thickness unknown, but maximum thickness is probably less than 30 ft. Qat Alluvial terrace deposit (Holocene and Pleistocene) Qaf Alluvial fan deposit (Holocene and Pleistocene)—Light gray to light brown gravel, sand, silt, and clay deposited where Hyalite Creek crosses an abrupt change in slope gradient (where the fault- bounded northern Gallatin Range meets the Bozeman valley) extending for about 7 miles into the valley, and similarly from 1 to 5 miles into the Gallatin Valley from the front of the Bridger Range.