DECADAL SCALE DYNAMICS OF THE CHRISTMAS VALLEY SAND DUNES, LAKE COUNTY, OREGON

The Christmas Valley sand dunes occupy an area of approximately 6,400 hectares in the eastern part of the Fort Rock Basin of southeastern Oregon. The dune field contains a complex variety of dune types, both active and vegetation-stabilized, and is comprised of three main parts: (1) The Lost Forest lobe, which consists of largely vegetation-stabilized sand sheets, parabolic and linear dunes. There are three smaller areas of active sand sheets and small crescentic dunes within this lobe; (2) The Fossil Lakes lobe, which consists of largely active sand sheets and crescentic and dome dunes; and (3) The South lobe, which consists of vegetation-stabilized parabolic and linear dunes and sand sheets. Geomorphic relations between the three lobes suggest that there have been three main periods of dune construction during the Holocene.

Although the dunes occur in an area of generally low dune mobility, comparison of the position of key elements of the dune field on aerial photographs taken in 1939, 1953, 1974, and 1994 indicates that parts of the dune field are quite active, with eastward extension of parts of the main Fossil lakes lobe occurring at rates of as much as 10.2 m/year. Maximum dune migration rates are associated with period 1953-1974. The most active parts of the dune field lie directly downwind of areas of extensive deflation of late Pleistocene and Holocene lacustrine deposits.

Rates of dune migration are compared with data on climatic parameters and indicate that the main controls of dune activity in this region are vegetation cover and soil moisture, both largely a function of variations in the amount and seasonal distribution of precipitation.