Rates of Soil Development
We dug 11 backhoe pits on 3 fan surfaces (west, north fan A, and south fan) to assess soil development.
Map showing location of soil pit sites
Field descriptions and laboratory analysis of the soil pits suggest that the fan ages can be distinguished on the basis of relative weathering.
We used the Profile Development Index (PDI) of Harden (1982) to quantify soil development in each pit. PDI's and maximum clay percent in the B horizons were compared with cosmogenic data from the nearest sampled boulders.
Table of PDI values and ages of nearest sampled boulders
PDI values and maximum clay% rise with increasing age
PDI an clay% versus cosmogenic age
When compared with PDI's determined by Harden and Taylor (1983) for chronosequences in 4 different climatic settings, PDI's for Fish Springs fans are much lower with respect to age. The significantly lower PDI values at Fish Springs suggest that the rate of soil development on the fans has been slow compared to the other sites studied by Harden and Taylor.
Comparison of PDI's versus age