OREGON GEOLOGY Oregon Department of Geology and Mineral Industries Volume 62, Number 3, July 2000 IN THIS ISSUE: Late Eocene fossil plants of the John Day Formation and Geology and Mineralization of the Blue River mining district DOGAMI PUBLICATIONS Pilot Project: Eugene-Springfield Earthquake Damage and Loss Estimate. Final Report, January 1999, by B. Publications are available from: Nature of the Northwest, 800 Vinson and T.H. Miller. Open-File Report O-00-02, NE Oregon St. #5, Portland, OR 97232, [email protected] 43 p., $10.00. or www.naturenw.org, (503) 872-2750; or from the DOGA- The preliminary damage and loss estimate for 200 se- MI field offices in Baker City, 1831 First Street, (541) 523- lected buildings in the Eugene-Springfield area was pre- 3133, and Grants Pass, 5375 Monument Drive, (541) 476- pared by members of the Department of Civil, Construc- 2496. See also the gray pages at the center of this issue. tion, and Environmental Engineering at Oregon State University. The project scope involves the estimation of Released April 19, 2000: the immediate facility damage and occupant casualties Relative Earthquake Hazard Map of the Eugene- for 100 buildings in Eugene and 100 buildings in Spring- Springfield Metropolitan Area, by G.L. Black, Z. Wang, field for an earthquake producing an effective peak T.J. Wiley, Y. Wang, and D.K. Kiefer. Interpretive Map ground acceleration of 0.3 g, and occurring either at Series IMS–14, 1 map, scale 1:48,000, 16 p. text, $12. 2 a.m. or at 2 p.m. This map incorporates the latest scientific information Released May 18, 2000: showing the risk that residents in the area face from Memorandum: Cape Cove Landslide, Findings from earthquakes. It combines the effects of ground shaking Field Visit, February 10 and March 10, 2000, by G.R. amplification and earthquake-induced landsliding (the Priest. Open-File Report O–00–03, 14 p., $6. third common effect, liquefaction, was found to present no risk) to show the earthquake hazard relative to the The Cape Cove landslide occurred last winter about local geologic conditions. 13 mi south of Yachats. The 14-page report was pro- duced by DOGAMI geologist George R. Priest for the THROUGH THE EYES OF THE Oregon Department of Transportation. The Cape Cove STATE GEOLOGIST landslide affected the coastal Highway 101, when the slope above the highway failed repeatedly from Decem- This column will be continued in our parallel publication, the magazine Cascadia. —ed ber 1999 through February 2000. (Continued on page 83) Mined Land Reclamation Program: 1536 Queen Ave. SE, Albany OREGON GEOLOGY 97321, phone (541) 967-2039, FAX (541) 967-2075. (ISSN 0164-3304) Internet: http://www.proaxis.com/~dogami/mlrweb.shtml Gary W. Lynch, Supervisor. VOLUME 62, NUMBER 3 JULY 2000 The Nature of the Northwest Information Center: Suite 177, 800 Published bimonthly in January, March, May, July, September, November by the Oregon Depart- NE Oregon St. # 5, Portland, OR 97232-2162, phone (503) 872- ment of Geology and Mineral Industries. (Volumes 1 through 40 were entitled The Ore Bin.) 2750, FAX (503) 731-4066 Internet: http://www.naturenw.org Governing Board Donald J. Haines, Manager. Donald W. Christensen, Chair . Depoe Bay Vera E. Simonton. Pendleton Periodicals postage paid at Portland, Oregon. Subscription rates: 1 Barbara Seymour. Salem year, $10; 3 years, $22. Single issues, $3. State Geologist . John D. Beaulieu Address subscription orders, renewals, and changes of address to Ore- Acting Deputy State Geologist . Dennis L. Olmstead gon Geology, Suite 965, 800 NE Oregon Street # 28, Portland 97232. Editor . Klaus K.E. Neuendorf POSTMASTER: Send address changes to Oregon Geology, Suite Production Assistants . Kate Halstead, James Roddey 965, 800 NE Oregon St. # 28, Portland, OR 97232-2162. Main Office: Suite 965, 800 NE Oregon Street # 28, Portland 97232, phone (503) 731-4100, FAX (503) 731-4066. Internet: http://sarvis.dogami.state.or.us Cover photo Baker City Field Office: 1831 First Street, Baker City 97814, phone This splendid view of Broken Top, companion to the Three (541) 523-3133, FAX (541) 523-5992. Sisters in the central Cascade Range, shows the east cirque Mark L. Ferns, Regional Geologist. which contains a small lake impounded by a moraine. Notches in the moraine are reminders of the sometimes overlooked Coastal Field Office: 313 SW Second Street, Suite D, Newport flood hazard such moraine lakes can present. The same year 97365, phone (541) 574-6642, FAX (541) 265-5241. this photo was taken, 1987, saw the publication of a report George R. Priest, Coastal Team Leader. by the U.S. Geologic Survey describing such volcanic hazards Grants Pass Field Office: 5375 Monument Drive, Grants Pass 97526, especially in the Three Sisters region (USGS Open-File Report phone (541) 476-2496, FAX (541) 474-3158. 87–41. See also Ore Bin, v.29 [1966], no. 10, p. 182–188). Thomas J. Wiley, Regional Geologist. Photo by contributor John H. Whitmer of Issaquah, Wash. 50 OREGON GEOLOGY, VOLUME 62, NUMBER 3, JULY 2000 Late Eocene fossil plants of the John Day Formation, Wheeler County, Oregon by Steven R. Manchester, Florida Museum of Natural History, PO 117800, University of Florida, Gainesville, FL 32611-7800 ABSTRACT Fossil leaves, fruits, and seeds are described from a late Eocene lacus- trine deposit in the lower part of the John Day Formation on the southern slope of Iron Mountain east of Clarno, Wheeler County, Oregon. The Whitecap Knoll locality is closely bracketed with radiometric dates and hence provides a new datum for the evaluation of floristic and climat- ic change in the late Eocene. The fossil-bearing shale is above the member A ignimbrite, dated 39.17 ± 0.15 Ma, and below a tuff dated 38.4 ± 0.7 Ma and is considered to be about 38.8 Ma. The plant assem- blage includes an aquatic compo- nent (Nelumbo, Ceratophyllum), and Figure 1. Oblique northwesterly aerial view of the south slope of Iron Moun- a woodland component with broad- tain, showing (1) position of the lacustrine shale from which the Whitecap Knoll leaved deciduous plants (Pla- flora has been obtained, (2) the Whitecap Knoll locality from which the Ar/Ar tanaceae, Fagaceae, Juglandaceae, date was obtained, and (3) the lacustrine shales of the Slanting Leaf Beds (Iron Ulmaceae, Aceraceae), a few broad- Mountain assemblage) of the Bridge Creek flora of the John Day Formation. leaved evergreen plants (Mahonia, Cinnamomophyllum), and a few unidentified ferns but apparently no conifers. The flora lacks the diversity of broad-leaved evergreen taxa present in the middle Eocene floras of the underlying Clarno Formation, but retains a few “Clarno taxa” not known in the overlying Bridge Creek flora (Ailanthus and Eucommia). The intermediate character of this flora in comparison with middle Eocene la- custrine floras of the Clarno Forma- tion and lower Oligocene floras of the Bridge Creek flora provides some evidence for a gradational transition from the Eocene subtropical vegeta- tion to the Oligocene temperate forests in this region. Figure 2. Students working at the Whitecap Knoll shale locality, with White- cap Knoll in central part of the image and Slanting Leaf Beds to the far left. INTRODUCTION Paleontologically, the John Day 1925; Merriam, 1930; Rensberger, However, fossils from the lowermost Formation of Oregon is probably 1973) and the still older plant fossil part of the formation, which in- best known for its spectacular mam- assemblages of the lower Oligocene cludes late Eocene strata, have re- malian fossils of early Miocene age Bridge Creek flora (Chaney, 1927; ceived relatively little attention. Flo- (e.g., Cope, 1880, 1886; Thorpe Meyer and Manchester, 1997). ras of late Eocene age are known OREGON GEOLOGY, VOLUME 62, NUMBER 3, JULY 2000 51 from the John Day Formation in the land and Retallack, 1994, p. 137) has Wolfe (1992, p. 428) called atten- Gray Butte area of Jefferson County, mostly temperate deciduous species tion to physiognomic differences be- but the precise ages are difficult to (Meyer and Manchester, 1997). The tween vegetation of the John Day determine because the associated Eocene-Oligocene boundary is current- Gulch flora of the Clarno Formation volcanic rocks there are highly al- ly placed at about 34 m.y. (Prothero, (assumed to be about 40 m.y. old tered (Smith and others, 1998). 1995); thus the Slanting Leaf Beds but not radiometrically dated) and The Whitecap Knoll flora (Figures assemblage provides a glimpse of the the Bridge Creek flora of the John 1, 2; Bestland and Retallack, 1994) vegetation that became established Day Formation (radiometrically dated near the northern boundary of the within about half a million years after at 33.6–32.6 Ma; McIntosh and oth- Clarno Unit of John Day Fossil Beds the boundary. Was the climatic and ers, 1997). Whereas the former fossil National Monument in Wheeler floristic change abrupt, occurring over assemblage is interpreted as Micro- County, Oregon, provides a rare op- a brief interval of less than one mil- phyllous Broad-Leaved Evergreen for- portunity to examine a late Eocene lion years, or was it rather gradual? est and contains thermophilic plants plant community that is well brack- Detailed investigations of paleosol such as cycads and bananas (genus eted with radiometric dates. These and alluvial sequences of the Clarno Ensete), the latter represents broad- dates indicate that the deposit and and John Day Formations in Wheeler leaved deciduous forest. The diverse the species contained within it are and Grant Counties, Oregon, with leaf and fruit flora of John Day Gulch approximately 38.8 million years old. ages approximated on the basis of has not yet been described, and its This flora thus provides an important inferred rates of sedimentation and age remains speculative.