Morphology and Genesis of Soils on the Prairie Divide Deposit (Pre-Wisconsin), Front Range, Colorado

Abstract

The Prairie Divide deposit possesses four strengths of pedogenic development. These include intensely and strongly developed soils on the western part of the deposit and moderately and weakly developed types on the mass-wasted eastern portion.

Intensely developed soils in part are typical of Pre-Wisconsin (Pre-Bull Lake) soil genesis and are differentiated from strongly developed soils on basis of abundant clay concentration (50 to 90%) and nearly complete absence of coarse particles (> 2 mm) in truncated, buried B horizons. Strongly developed soils in part represent pedogenesis typical of soils at least as old as early Wisconsin (Bull Lake) and are differentiated from moderately developed profiles by presence of argillic B horizons (35% clay).

Moderately developed soils possess cambic B horizons which commonly have less clay than A horizons. They reflect pedogenesis probably as old as late Wisconsin (Pinedale). Weakly developed soils do not possess B horizons and evidence Holocene soil formation.

In all soils A horizons postdate initial mass-wasting of the deposit and are superposed on strongly and intensely developed soils. Data indicate that these A horizons are divisible pedogenically into at least two parts—an upper, younger horizon developed on a lower older horizon.

It is suggested that intensely developed soils of the Prairie Divide deposit are type examples of long-term or optimum Pre-Wisconsin (possibly in part late Tertiary) weathering and soil formation in the Rocky Mountain region and may be used as an index with which to compare the intensity of development of other supposed Pre-Wisconsin soils.