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Show The Dunes: The Shifting Sand Dunes are located at the eastern ( downwind) end of Christmas Lake Valley. This major dune field has received almost no attention in the literature, only a few of the other dunes ( located elsewhere in Fort Rock Lake basin) have been previously studied [ 9, 11]. The dune area is about 30 km long and 10 km wide and consists of two northeast- trending, megaparabolic dunes, one of which is very active today, the other is largely covered by trees and sagebrush comprising the Lost Forest Research Natural Area [ 1, 16]. Active dunes superposed on the megaparabolic structure include barchan and transverse forms that have linear ridges on them, indicating a weak bimodal wind regime. Linear dunes, dome dunes, and parabolic dunes are also present. The main deflation areas occur at the western end of the dune field, and include Fossil Lake. Based on stratigraphic interpretation of superposition relationships in aerial photographs, the dune field preserves a minimum of three major Holocene dune- building events [ 1]. The main constituents of the Shifting Sand Dunes are volcanic glass and devitrified glass fragments, plagioclase crystals, basalt lithic fragments, aggregates of silt and clay- sized volcanic ash, pyroxenes, opaque minerals ( mostly magnetite), and trace occurrences of fossil fragments and other minerals [ 1]. The dune sands are a mixture of sand deflated from the ancient lake bed and sand- sized tephra deposited by the terminal eruptions of Mt. Mazama. Some Outstanding Issues: Work by Edgett [ 1] found that thermal infrared images can be useful in interpreting the recent inputs of sand from local sources into the dune field. However, the timing of events which have shaped the Shifting Sand Dunes field is unknown. There appears to have been at least three dune- building events. How do these tie into the Holocene history of the basin? Were any dunes present before the Mt. Mazama eruption? Is the Lost Forest a remnant of Pleistocene forests, as proposed by Berry [ 16], or was the forest initiated after the Mt. Mazama eruptions provided the pumice- rich, sandy soil needed for the forest's survival in the desert environment? Studies in other dune fields, such as Kelso Dunes, California, suggest that dune fields provide useful climate records [ 17]. Can the Shifting Sand Dunes field be used as a tool to further our understanding of the Holocene history of the northwestern Great Basin? Future work in the area must focus on obtaining dates for events which shaped this dune field. References: [ 1] Edgett, K. S. ( 1994) pp. 145- 201 in Ph. D. Diss., Arizona State Univ., Tempe. [ 2] Forbes, C. F. ( 1973) Ph. D. Diss., Univ. Oregon, Eugene. [ 3] Freidel, D. E. ( 1994) pp. 21- 40 in Univ. Oregon Anthropol Papers 50. [ 4] Dole, H. M. ( 1942) M. S. Thesis, Oregon State, Corvallis. [ 5] Allison, IS. ( 1966) Oregon State Univ. Stud. Geol, 9. [ 6] Allison, IS. ( 1979) Oregon State Dept. Geol. Min. Res., Spec. Pap. 7. [ 7] Kittleman, L. R. ( 1973) GSA Bull, 84,2957- 2980. [ 8] Greenspan, R. L. ( 1985) Ph. D. Diss., Univ. Oregon, Eugene. [ 9] Benjamin, J. E. ( 1989) M. S. Thesis, Univ. Oregon, Eugene. [ 10] Hatton, R. R. ( 1989) Ph. D. Diss., Univ. Oregon, Eugene. [ 11] Mehringer, P. J., and W. J. Cannon ( 1994) pp. 283- 327 in Univ. Oregon Anthropol Papers 50. [ 12] Bedwell, S. F. ( 1970) Ph. D. Diss., Univ. Oregon, Eugene. [ 13] Willig, J. A. ( 1988) pp. 417- 482 in Nevada State Museum Anthropol. Papers 21. [ 14] Grayson, D. K. ( 1993) The Desert's Past: A Natural Prehistory of the Great Basin, Smithsonian Institution Press. [ 15] Grayson, D. K. ( 1979) pp. 427- 457, in Volcanic Activity and Human Ecology, Academic Press. [ 16] Berry, D. W. ( 1963) Ph. D. Diss., Oregon State Univ., Corvallis. [ 17] Lancaster, N. ( 1993) Natl. Geogr. Res. Explor., 9, 444- 459. |