Large areas of the Upper Colorado River Basin are underlain by saline geologic formations which contribute to the dissolved load or salinity of the Colorado River. The marine Mancos Shale is the most extensive saline formation outcropping in the Upper Basin and it is a major diffuse source of salinity. The soluble mineral content (SMC) of Mancos Shale can be as high as 20% but averages about 6% for areas of shale without interbedded sandstones. The major soluble mineral is gypsum.
The Mancos Shale is composed of three landform types: badlands, pediments, and alluvial valley floors. Pediments and pediment remnants are relatively stable landforms. Channel incision of alluvial valley floors can produce large quantities of sediment, however, salt contribution will be lower because alluvium has been leached and it has a lower SMC than in-situ Mancos Shale. Sediment and salt yield from badlands can be highly variable due to sediment storage and flushing effects, but overall erosion is rapid and runoff salinity is high. Experimental erosion studies on Mancos hillslopes reveal a positive relationship between salt production and sediment yield.