Find North Cascades geologic maps

1982

by R. W. Tabor, R. B. Waitt, Jr., V. A. Frizzell, Jr., D. A. Swanson, G. R. Byerly, and R. D. Bentley

Generalized geologic map of the Wenatchee Quadrangle. Click here for enlarged version with explanation (24K). Availability of Wenatchee quadrangle geologic map Summary of geology (52K) View of map and link to digital data Reference list and sources of data maps (76K) Return to quadrangle location map

The Wenatchee quadrangle embraces a unique and varied geologic terrane of rocks and sediments ranging in age from possibly Precambrian to Holocene. Because the Tertiary and Quaternary stratigraphic record is fairly complete and because the enigmatic Olympic-Wallowa lineament (Raisz, 1945) crosses the area (fig. 1), the stratigraphic and structural relations displayed are important to an understanding of the Tertiary and Quaternary geologic history of the Pacific Northwest.

Early reconnaissance by I. C. Russell (1893, 1900) and mapping by G. 0. Smith and F. C. Calkins (1903, 1904, 1906) established a bedrock stratigraphy that has withstood later scrutiny remarkably well. Their work has been built upon, rather than replaced, by more recent geologic studies (see sources of data maps). The most influential early work on Quaternary deposits was by Bretz (1925, 1930) in the Columbia River valley and by Page (1939b) in the Wenatchee River valley. The Wenatchee quadrangle is the southeastern of four 1:100,000 maps composing the 1:250,000 Wenatchee 1 x 2 degree sheet. (see Figure 1, Snoqualmie Pass geologic map sheet) We are mapping and compiling the geology of the four 1:100,000 quadrangles with the purpose of refining Tertiary and Quaternary stratigraphy and structure.

We mapped the Wenatchee quadrangle during the years 1975 through 1978. While there is overlapping responsibility for the map data for some units, the primary mapping responsibilities are: Tabor and Frizzell for the pre-Miocene rocks; Swanson, Byerly, and Benfley for the Miocene Yakima Basalt Subgroup and Ellensburg Formation; and Waitt for the Pliocene and Quaternary deposits.

Acknowledgments

Sharon Allshouse and Eduardo Rodriquez aided in the field in 1975, Jay Coburn, Van Johnson, and Ron Tal in 1976, and Kim Marcus, Margaret Goddard, Bill Gaum, and Jorge Rodreguez in 1977. Bill Gaum was particularly helpful with potassium- argon dating done for this project. J. C. Yount helped differentiate the two Holocene drifts in the Enchantment Lakes area. We thank Charles W. Naeser for fission-track data on specific samples. Naeser and Charles Meyers helped considerably with the fission-track dating achieved by Virgil Frizzell for this study. We have especially profited from discussion with R. D. Brown, R. L. Gresens, R. B. Miller, S. C. Porter, J. A. Vance, C. M. Wentworth, and J. T. Whetten.