Abstract This geological field site, notorious for strong, persistent, unidirectional winds that have created classic eolian landforms, is located in the SW¼ Sec.30, T.25N., R.84W., Carbon County, Wyoming (Figs.1), 1,). The area is readily accessible via paved road by traveling north from the town of Sinclair, Wyoming, a distanceof 30 mi (48 km) on the Seminoe Road. This highway is the main access route to Seminoe State Park. The locale is on public land, administered by the Bureau of Land Management, but it borders on private ranch land to the north and state-owned land to the west. The area is within the broad, windswept zone of central Wyoming (Fig. 1) known as the Wyoming Wind Corridor(Marrs and Kolm, Kolm 1982). The large active dunes at this site and older stabilized dunes in the area are part of the Seminoe Dune Field (Fig. 1) 2). Most dunes in the area are marginally stabilized parabolic dunes. The few active dunes are relatively large and slow moving with active fronts and partially stabilized tails.

Sand dunes, dune fields, playa lakes, playa sediment plumes, blowouts, and scour streaks can be recognized from LANDSAT imagery (resolution ∼80 m) and high-altitude aerial photography (resolution ∼5 m). The abundance of such features in the southern Wyoming test area confirms a major wind corridor with local areas of extremely strong winds indicated by concentrations of eolian features. The abundance of sand and semiarid climate of the area are also important factors in the development of eolian features. Elongate eolian features indicate the direction of flow of strong winds through the area. Streamlines interpreted from these directional indicators parallel streamlines derived from wind measurements obtained by over-flights at low altitudes with specially instrumented aircraft. The streamlines interpreted from imagery yield only a two-dimensional representation of the flow pattern. But, in areas of stably stratified flow, this plan view provides a first approximation of the flow pattern useful for identifying high wind-energy areas. Smaller wind channels within the Wyoming wind corridor display energies at least two to three times greater than adjacent areas. The dimensions and types of eolian features that develop in a high-wind area are greatly influenced by moisture, vegetation, sand supply, cementation, and other factors such that wind strength and/or persistence does not correlate strongly with either the type or dimensions of eolian features. Dune spacings and other harmonic distribution patterns observed in the eolian features, however, correlate with certain windflow patterns. Spaced dune groups and playa clusters are found in areas where gravity waves develop in the near-surface air-flow. Diagonal alignments of eolian features are interpreted to be the result of helical circulation cells aligned parallel to the main flow direction. Strong turbulence is characteristic of scoured areas on the lee side of topographic highs. These local characteristics of windflow can have important effects on average wind energy and on the performance of wind-driven energy systems; thus, they are critical in siting of wind generators and other structures. Relative estimates of average wind velocities can be made by correlating the streamline data and eolian activity in a region of unknown wind energy to a similar area where wind measurements are available. Direct estimates of average wind velocity may also be possible by computations relating average wind velocity to the average migration rates of dunes. Field observations suggest that the dunes are most active during summer and autumn months. Wind velocity estimates derived from the Wyoming dunes should represent the strong summer winds rather than the extremely strong winter winds that sweep the area while the dunes are frozen. Conversely, blowouts with playa lakes are most active in the autumn and winter months (after spring runoff has evaporated). Thus, the playa lake blowouts should develop in response to the stronger autumn and winter winds. Length-to-width ratios of playas and playa plumes were tested as possible indicators of average wind velocities. The shape ratios of playas in the Northern Laramie Basin test area indicate a mature (very active) playa field (indicative of extremely strong winds), but correlations of shape ratios with other data have, so far, failed to yield quantitative estimates of mean wind velocities. The wind/landform relationships observed in each of the three test areas were employed in compiling a wind-energy prediction map for the southern Wyoming test region. This map shows the dominant patterns of windflow in the southern Wyoming wind corridor and the location of areas of extreme winds within the corridor. The map indicates areas of particularly high wind-energy potential and regions where special flow conditions persist. Mean wind velocity values obtained from permanent meteorological stations are plotted on the map for reference.

The Ferris Dune Field of south-central Wyoming lies in a topographically-regulated “corridor” of high wind that extends over much of southern Wyoming. Examination of geomorphology, sedimentology, and stratigraphy reveals that winds did not vary significantly in either average direction or speed during the Holocene period, but variations in precipitation, and hence plant growth, produced varying degrees of eolian activity. Deposition of dune sand resulted mainly from a decrease in the carrying capacity of the wind as it encountered the Ferris-Seminoe Mountain barrier. The Ferris dunes geomorphically resemble other dune fields in the western United States. Phytogenic dunes, varying in size and shape from small blowout dunes to large, well-developed parabolic dunes, dominate the landscape. A few actively migrating dunes occur both where the stabilized ground surface has been disturbed and where the highest wind speeds occur. Mineral analyses indicate that the Ferris dune sands were derived primarily from the Tertiary Battle Spring Formation. The Killpecker Dune Field “tail” sands and certain Cretaceous through Paleocene sandstones exposed along the Lost Soldier Divide were lesser contributors. The valley of Clear Creek reveals a relatively continuous Holocene section of interbedded dune and interdunal pond deposits. Bioturbated, low-angle (less than 15°) bedding, which characterized large portions of the eolian sands exposed there, attests to the long-term influence of vegetation and moisture on dune activity. Artifacts recovered in the vicinity of Clear Creek demonstrate Late Plains Archaic to Late Prehistoric occupations in this area. Radiocarbon dates from Clear Creek, comparison of Clear Creek chronology to other radiometrically-dated geologic-climatic events from the western United States, and theoretical dune migration rates reveal a general sequence of geologic-climatic events for the Ferris Dune Field: Eolian activity had begun in the Ferris-Lost Soldier area by at least ca. 9,950 to 10,330 years b.p. Major depositional intervals (indicating widespread Ferris dune activity) correlate with two radiocarbon-dated periods of drought. The first occurred between ca. 7,660 and 6,460 years b.p.; the second occurred following ca. 6,460 years b.p. (and lasted until ca. 5,500 years b.p.). Since the last major depositional (drought) interval, the climate in the Ferris-Lost Soldier area has moderated. Drought intervals have been short and vegetation has largely stabilized the dunes.

Data from airborne air-sensing probes reveal wave structures in the planetary boundary layer of the atmosphere in the wind corridor of south-central Wyoming. The airflow, which is nearly laminar throughout much of the region, responds in a series of resonant lee waves when it encounters topographic obstacles. Gravity waves and turbulent mixing are associated with a downward transport of vertical momentum and occur in the region of accelerated windflow in the central Wyoming wind corridor. Kelvin-Helmholtz waves are prevalent in the area of hydraulic jump at Windy Gap. Understanding of such waves and their controls is essential to siting of wind-energy systems in high-wind regions like the Wyoming wind corridor and in interpreting the mechanisms for development and migration of eolian landforms.