u 0 by Robert J. Carson and Kevin R. Pogue WASHINGTON DIVISION OF GEOLOGY AND EARTH RESOURCES Information Circular 90 January 1996 WASHINGTON STATE DEPARTMENTOF Natural Resources Jennifer M. Belcher - Commissioner of Public Lands Kaleen Cottingham - Supervisor FLOOD BASALTS AND GLACIER FLOODS: Roadside Geology of Parts of Walla Walla, Franklin, and Columbia Counties, Washington by Robert J. Carson and Kevin R. Pogue WASHINGTON DIVISION OF GEOLOGY AND EARTH RESOURCES Information Circular 90 January 1996 Kaleen Cottingham - Supervisor Division of Geology and Earth Resources WASHINGTON DEPARTMENT OF NATURAL RESOURCES Jennifer M. Belcher-Commissio11er of Public Lands Kaleeo Cottingham-Supervisor DMSION OF GEOLOGY AND EARTH RESOURCES Raymond Lasmanis-State Geologist J. Eric Schuster-Assistant State Geologist William S. Lingley, Jr.-Assistant State Geologist This report is available from: Publications Washington Department of Natural Resources Division of Geology and Earth Resources P.O. Box 47007 Olympia, WA 98504-7007 Price $ 3.24 Tax (WA residents only) ~ Total $ 3.50 Mail orders must be prepaid: please add $1.00 to each order for postage and handling. Make checks payable to the Department of Natural Resources. Front Cover: Palouse Falls (56 m high) in the canyon of the Palouse River. Printed oo recycled paper Printed io the United States of America Contents 1 General geology of southeastern Washington 1 Magnetic polarity 2 Geologic time 2 Columbia River Basalt Group 2 Tectonic features 5 Quaternary sedimentation 6 Road log 7 Further reading 7 Acknowledgments 8 Part 1 - Walla Walla to Palouse Falls (69.0 miles) 21 Part 2 - Palouse Falls to Lower Monumental Dam (27.0 miles) 26 Part 3 - Lower Monumental Dam to Ice Harbor Dam (38.7 miles) 33 Part 4 - Ice Harbor Dam to Wallula Gap (26.7 mi les) 38 Part 5 - Wallula Gap to Walla Walla (42.0 miles) 44 References cited ILLUSTRATIONS I Figure 1. Physiographic map of the Columbia Plateau 2 Figure 2. Map showing distribution of the Columbia River Basalt Group 3 Figure 3. Stratigraphic section for the central and southeastern Columbia Plateau 4 Figure 4. General cross section of the field trip area 4 Figure 5. Map showing late Pleistocene glaciers, lakes, and floods in the northwestern United States 5 Figure 6. Map showing the Channeled Scabland of Washington 8 Figure 7. Map showing the route of the field trip 9 Figure 8. Photograph of the Palouse Hills between Walla Walla and Starbuck 9 Figure 9. Photograph of loess north of Dixie IO Figure J 0. Photograph of stripcropping south of Waitsburg 10 Figure 11. Photograph of a quarry east of Waitsburg (Stop 1) 11 Figure l 2. Diagrammatic cross section of Steptoe Butte 11 Figure 13. Photograph of the contact between the Grande Ronde and Wanapum Basalts (Stop 2) 12 Figure 14. Photograph of pillow lava north of Dayton (Stop 2) 12 Figure 15. Diagrammatic cross section of the upper Tucannon River valley 13 Figure 16. Photograph of terracettes on the side of the Tucannon River valley 14 Figure 17. Photograph of Touchet Beds in a roadcut just northwest of Starbuck (Stop 3) 14 Figure 18. Photograph of the contact between two rhythmites in the Touchet Beds 15 Figure 19. Sketch of some characteristics of the Touchet Beds 15 Figure 20. Photograph of the Snake River at the mouth of the Tucannon River 16 Figure 21. Part of the Starbuck 15-minute topographic map showing Missoula floods features 17 Figure 22. Photograph of the Snake River from southeast of Lyons Ferry 17 Figure 23. Photograph of the Snake River between the Tucannon and Palouse Rivers 17 Figure 24. Photograph of the lower Palouse River at the Marmes Rocks helter 18 Figure 25. Photograph of scabland topography along the lower Palouse River iii 19 Figure 26. Photograph of streamlined loess hills southwest of Palouse Falls State Park 19 Figure 27. Photograph of the canyon of the Palouse River 20 Figure 28. Geologic cross section at Palouse Falls 20 Figure 29. Photograph of Palouse Falls (Stop 5) 21 Figure 30. Photograph of the Channeled Scabland at the head of HU or Davin Coulee 22 Figure 31. Photograph of a gravel bar on the floor of Washtucna Coulee 22 Figure 32. Photograph of Was htucna Coulee at an ancestral meander 23 Figure 33. Photograph of Devils Canyon 23 Figure 34. Diagrammatic cross section of intracanyon flows on the east side of Devils Canyon 24 Figure 35. Photograph of three intracanyon flows on the west side of Devils Canyon (Stop 6) 24 Figure 36. Geologic cross section near Lower Monumental Darn 25 Figure 37. Photograph of giant ripple marks at Lower Monumental Dam 25 Figure 38. Photograph of basalt flow overlying gravels south of Lower Monumental Dam (Stop 7) 26 Figure 39. Photograph across the Snake River at Scott gravel bar 27 Figure 40. Topographic map showing surficial geology at the leading edge of the Juniper Dunes 28 Figure 41. Photograph of the northern part of the Juniper Dunes 28 Figure 42. Photograph of transverse dunes, Juniper Dunes Wilderness 29 Figure 43. Photograph of parabolic dunes, Juniper Dunes Wilderness 29 Figure 44. Photograph of Ice Harbor Dam 29 Figure 45. Photograph of a view down the Snake River from Ice Harbor Dam 30 Figure 46. Diagrammatic cross sections of the basalts near Ice Harbor Darn 30 Figure 47. Photograph of Saddle Mountains Basalt east of Ice Harbor Dam (Stop 8A) 31 Figure 48. Photograph of an invasive flow east of Ice Harbor Dam (Stop 8B) 31 Figure 49. Photograph of a tuff cone west of Ice Harbor Dam (Stop 9A) 32 Figure 50. Photograph of tuff breccia west of Ice Harbor Dam (Stop 9A) 32 Figure 51. Photograph of flows and dike west of Ice Harbor Darn (Stop 9B) 33 Figure 52. Photograph of WaJlula Gap and the delta of the Walla Walla River 34 Figure 53. Photograph of WaJJula fault zone east of Wallula Gap 34 Figure 54. Photograph of fault at Wallula (Stop 10) 35 Figure 55. Close-up photograph of the fault at Wallula (Stop 10) 35 Figure 56. Photograph of Wallula Gap on the Columbia River 36 Figure 57. Photograph across the Columbia River at Two Sisters 36 Figure 58. Photograph of Two Sisters, Wallula Gap 38 Figure 59. Photograph of alluvial fan and talus at the Washington- Oregon state line (Stop 12) 39 Figure 60. Photograph of the west side of Wallula Gap near the Washington-Oregon border 39 Figure 61. Photograph of the Olympic-Wallowa lineament east of Wallula Gap 40 Figure 62. Cross section of the lower Walla Walla River valley 40 Figure 63. Diagram of north roadcut at Divide 40 Figure 64. Photograph of unconformities at Divide (Stop 13) 41 Figure 65. Photograph of Mount St. Helens set S tephra in Touchet Beds north of Touchet 42 Figure 66. Photograph of elastic dikes in Touchet Beds north of Touchet (Stop 14) 43 Figure 67. Photograph of Touchet Beds in the Little Grand Canyon south of Lowden 44 Figure 68. Photograph of a view northwest of Little Grand Canyon south of Lowden iv Flood Basalts and Glacier Floods: Field Trip Guide to the Geology of Parts of Walla Walla, Franklin, and Columbia Counties, Washington Robert J. Carson and Kevin R. Pogue Department of Geology Whitman College Walla Walla, WA 99352 GENERAL GEOLOGY OF age from about 350 million to about 200 million years and SOUTHEASTERN WASHINGTON were accreted to western North America about l 00 million This field trip guide covers the geology of some of the areas years ago. These terranes were later intruded by Late Meso­ affected by two of the best documented catastrophic events in zoic granitic rocks and covered by Tertiary volcanic rocks. Earth's history: enormous basaltic lava flows that began to Most of the Miocene basalt flows (Fig. 2), which total as much cover the land about 17 million years ago (Baksi, 1989) and as 3 km thick in the Walla Walla Plateau section, originated in giant glacier outburst floods (termed jokulhlaups) that started the Blue Mountains section, where there were long fissures about 15,300 years ago (Waitt, 1985). These events are in through which the lava poured. Magma in the fissures solidi­ large part responsible for the shape of the landscape of eastern fied to form dikes. Washington, where the Earth's youngest basalt plateau was swept by the largest documented floods in geologic history. Magnetic Polarity The Columbia Plateau is a physiographic province, an area From time to time, at apparently random intervals, the Earth's that has somewhat similar rocks, landforms, soils, climate, and magnetic field reverses. Currently, it is ' normal' or N, but vegetation. Most of the rocks at the surface are basalt. Erosion about 800,000 years ago it was 'reversed' or R. There have and deposition by jokulhlaups shaped much of the surface, but been numerous polarity reversals over geologic time, and streams have cut the land and left de­ posits as well, and wind has piled up Approximate sand dunes. The soils are thick on WASHINGTON Scale windblown silt (referred to as loess) •N 0 50 100 mi and immature to nonexistent on sand, gravel, and basalt. The area receives 0 50 100 km as little as 20 cm annual precipitation and is considered arid. The natural vegetation is sagebrush shrubland MONTANA and short-grass prairie (Hunt, 1974). - ' The Columbia Plateau is bordered on the north and east by the Rocky Mountains, on the south by the Basin and Range Province, and on the west by the Cascades (Fig. 1). The plateau province is divided into several phys­ iographic sections. This field trip takes us through the central part of the Walla Walla Plateau section, ad­ jacent to the northwest flank of the Blue Mountains section.