Observations on and in the moist, cold-climate sand dunes of southwestern Wyoming reveal information that may be useful in interpreting ancient dune structures and paleoclimates. Snow is buried by blowing sand and incorporated into the dunes. Subsequent melting and slumping of some of this snow causes collapse and deformation of the dune stratification. In some cases, the snow is preserved throughout the year. Truncated ripples are formed when the crests of moist ripples are dried and blown away. Recognition of such ripples in the rock record should, therefore, indicate subaerial exposure. Major dune stratification dips downwind at 14° to 18°, much less than the angle-of-repose for dry sand. Apparently, these dips are a function of the high moisture content of the dune, which prevents the formation of avalanche faces. In any case, it should not be expected that all eolian cross-stratification have angle-of-repose dips.