Thomas L. Trowbridge ‘Trobe’ Gross

Professor Emeritus, Geology and Geological Engineering

‘Trobe’ Gross was born and raised in Evanston, Illinois.

Work Experience

  • 1953-present Consulting geologist; in recent years emphasis on geothermal energy, phosphate (Peru), and gold exploration and evaluations of ground water, and seismic and volcanic activity (California).
  • 1964-2007 Geology professor, Colorado School of Mines
  • 1955-64 Geology professor, The Colorado College
  • 1949-52 Exploration petroleum geologist, Texaco
  • 1944-46 U.S.Navy, WWII, Pacific Theatre, USS Essex CV9, Aerologist


Fax: 303-273-3859

Professional Organizations

  • Geological Society of America (Senior Fellow)
  • American Association of Petroleum Geologists
  • American Geophysical Union
  • Society Economic Geology
  • Society of Mining Engineering
  • Association of Engineering Geology
  • American Institute of Professional Geologists
  • Rocky Mountain Association of Geologists
  • Colorado Scientific Society
  • Northern California Geological Society
  • American Association of Advanced Science (Fellow)
  • Sigma Xi



  • Ph.D.,1952-55, Geology, Stanford University Dissertation: “Magmatic fluids and long-period seismicity: a geological and fluid dynamical perspective”.
  • BS and MS 1947-49, University of Washington, Seattle
  • 1942-44, 1946-47, University of Arizona, Tucson

Teaching Areas

  • Main effort in undergraduate and graduate courses in structural geology and tectonics. Also courses in History of Geologic Concepts, Regional Geology, Petrology, Volcanology, Field geology, Stratigraphy and sedimentation, Oil and minerals exploration, Seismotectonics, and Geothermal geology and exploration.

Research and Consulting Geologic Activities

  • Diversified and field-based. Currently most devoted to systematic regional geologic mapping in northern California. Other major fields include exploration and mapping for geothermal energy, metalliferous ores, oil and gas, coal, phosphate and metalliferous shales. Also seismotectonic (earthquake risk) and ground water evaluations. Areas of activity have included Western USA, Peru, Australia, Puerto Rico, Hawaii and Samoa. Support has come from large and small industrial companies, and Federal and State agencies. (USGS, NSF, US Forest Service, Department of Energy, Office of Naval Research) (California Geologic Survey, North California counties.)


  • Over 100 peer-reviewed. Numerous geologic maps and attending reports on California areas especially, i.e., Sierra Nevada, Basin and Range, and Cascades. Other subjects: geothermal energy in W. USA and Hawaii, geology of marine phosphates, tectonics in Rocky Mountains, regional hydrogeologic framework in Basin and Range, etc. Some selected publications are as follows:
  • 2001-2009, Geologic map and report of the Alturas 100K (1/2×1 degree) quadrangle, Modoc County, California. Includes four 15′ quads and sixteen 7.5′ quads. California Geologic Survey, in preparation. Geologic map and report of the west half of the Cedarville 100K quadrangle, Modoc County, California. Includes four 15′ quads. California Geologic Survey in preparation.
  • 2000, Geologic maps and reports on the following five 15′ quadrangles in northern California: Portola, Blairsden, Chilcoot, Loyalton, and Sierraville: Calif. Div. Mines and Geology, in press; four others in preparation
  • 1992, Geologic map of the Eagle Lake 1/2 x 1 degree quadrangle, Lassen County, California: Calif. Div. Mines and Geology OFR 92-14 (authored with Saucedo and Wagner), scale 1:100,000
  • 1991, Geologic map of the Susanville 1/2 x 1 degree quadrangle, Lassen and Plumas Counties, California: Calif. Div. Mines and Geology OFR 91-1 (authored with Saucedo and Wagner), scale 1:100,000
  • 1990, Eagle Lake volcanic field, California, p.222-24 in Volcanoes of North America, eds. Wood and Kienle, Cambridge Univ. Press
  • 1989, Phosphorites in the Mantaro Phosphate Field, central Andes, Peru, p.131-36 in Phosphate Deposits of the World, v.2 Phosphate Rock Resources, eds. Notholt, Sheldon, and Davidson, Internat’l. Geol. Correlation Programme Project 156: Phosphorites, Cambridge Univ. Press
  • 1989, Geology of the Death Valley region, Nevada and California: Studies of Geology and Hydrology in the Basin and Range Province, southwestern United States for isolation of high-level radioactive waste – characterization of the Death Valley region, Nevada and California: U.S.Geol.Surv. Prof. Paper 1370-F, p.F5-F19 (authored with Smith)
  • 1989, Quaternary tectonism on the Death Valley region, Nevada and California:ibid. p.F24-F27 (authored with Sargent)
  • 1987, Subsurface geology and drilling geothermal systems: a summary: Subsurface Geology, Petroleum, Mining, Construction, 5th ed.. eds. LeRoy, LeRoy, Schwochow, and Raese: Colo. Sch. Mines Press, Golden, 1002 p. (authored with Campbell)
  • 1986, Potassium-argon ages of Late Miocene to Late Quaternary volcanic rocks in the Susanville – Eagle Lake area, Lassen County, California: Isochron/West, n.45,p.5-11 (authored with McKee)
  • 1986, Geologic map of the Marlette Lake 7 1/2′ quadrangle, Nevada: Nev.Bur. Mines and Geology, (Lake Tahoe area), Map 2Cg, scale 1:24,000
  • 1985, Geologic map of the Glenbrook 7 1/2′ quadrangle, Nevada: ibid. (Lake Tahoe area), Map 2Bg, scale 1:24,000
  • 1984, Geologic map and report of the State Line Peak 7 1/2′ quadrangle, Nevada and California: ibid., Map 82, scale 1:24,000
  • 1979, Geothermal energy in the Basin and Range Province, p.361-70 in Basin and Range Symposium, eds. Newman and Goode, Rocky Mt. Assoc. Geol. and Utah Geol. Soc. Guidebook (authored with Keller)
  • 1979, Results of an experimental drill hole at the summit of Kilauea volcano, Hawaii: Jour. Volcanology amd Geothermal Research, v.5, p.345-85 (authored with Keller, Murray, and Skokan)
  • 1978, Late Quaternary tectonic controls of occurrence of geothermal systems in the Gerlach-Hualapai Flat area, northwestern Nevada: Colo. Sch. Mines Quart., v.73,n.3, p.11-14
  • 1975, Geothermal energy in the Pacific Ocean region: Final Rept. to the Office of Naval Research, Arlington, VA, 110 p. with maps and appendix reports (authored with Keller)
  • 1974, Geology of Colorado in relation to geothermal energy potential: Colo. Geol. Surv. Bull.35, p.11-39
  • 1972, Stratigraphy of the carbonate, black shale, and phosphate of the Pucara Group (Upper Triassic-Lower Jurassic), Central Andes, Peru: Geol. Soc. Amer. Bull., v.83, p.407-28 (authored with Szekely)
  • 1972, Tectonics of the Rocky Mountain Province: Geologic Atlas of the Rocky Mountains: Rocky Mt. Assoc. Geol., Denver, p.35-44
  • 1971, Geothermal energy: geology, exploration, and developments, Pts. I and II: Colo. Sch. Mines Research Inst. Mineral Industries Bull. v.14, n.6, 14 p. and v.15, n.1, 16 p.
  • 1967, Coal resources of southwestern Utah – potential for utilization in steam-electric power generation plants: U.S. Bur. Mines IC 8326, 78 p. (authored with Hileman and Ward)
  • 1965, Kolob, Kanab, and Kaiparowits coal fields in southwestern Utah: Guidebook to Geology of Utah No.19, p.121-33, Geology of southcentral Utah, Utah Geol. Soc. and Intermtn. Assoc. Petrol. Geol., Salt Lake City
  • 1960, Geologic formations and structure of the Colorado Springs area, Colorado: Guide to the Geology of Colorado, eds. Weimer and Haun, Geol. Soc. Amer., Rocky Mt. Assoc. Geol., and Colo. Sci. Soc, p.188-95
  • 1959, Structure and petrology of the northeast part of the Soda Mountains, San Bernardino County, California: Geol. Soc. Amer. Bull., v.70, n.12, pt.1, p.1509-48

Awards and Recognitions

  • Winner of the Thomas Dibblee Medal for Excellence in Field Geology and Mapping, 2003, Santa Barbara, California