Loess Sources Changes and Loessial Soil on a Downwind Transect, Boulder-Lafayette Area, Colorado

Abstract

A study of eolian sand and loess of Wisconsin age southeast of Boulder, Colorado, revealed probable sources of the loess and changes in soil development associated with downwind distance from the source. Soil horizon thickness, color, texture, structure, stage of calcium-carbonate development, and depth to calcium carbonate were examined along a downwind transect beginning at Boulder Creek in the northwest, and crossing Coal Creek and Rock Creek to the southeast. The chief source of loess was the Boulder Creek flood plain. The Rock Creek flood plain contributed additional very fine textured loess. Soils developed on the loess show an increase in clay accumulation in the 8-horizon, and decreases in depth to strongest chroma, to the B2t sub-horizon, and to occurrence of calcium carbonate, with distance downwind from the primary source. Soils downwind from Rock Creek reflect the additional loess from that source.