WSPC02847

• File Number: 7630.500
• Description: Wild and Scenic - Rio Grande River
• State: CO
• Basin: Statewide
• Date: 9/1/1989
• Author: DOI-BLM
• Title: San Luis Resource Management Plan and Environmental Impact Statement - Draft - Volume I - Introduction-Chapters 1-3
• Water Supply Pro - Doc Type: Report/Study

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AFFECfED ENVIRONMENT

Table 2-5
SELECTED ACID PRECIPITATION DATA ALAMOSA, COLORADO
(pH)

Winter Spring Summer FaD Annual
# lsi # lsi # isi # isi # isi
Year Obs Mean Obs Mean Obs Mean Obs Mean Obs Mean
1987 13 5,80 13 5,86 13 5.16 t3 5,26 52 5,42
1986 13 5,00 13 5,97 13 5,32 13 5.03 52 5,28
1985 13 5,91 13 5,45 13 5.21 13 5.33 52 5,29
1984 13 6,02 13 6,73 t4 5.36 13 5.48 53 5.51
1983 13 5,81 13 5,93 13 5.50 t3 5.51 52 5,58
1982 13 5.31 13 6.13 13 5.68 13 5.47 52 5.59

Source: Natural Resources Ecology Laboratory, n,d.
Note: Precipitation weighted averages. The natural pH of precipitation is approximately 5.6.

SOILS

Soils in the San Luis Resource Area are described in the
following four soil survey reports published by the USDA,
Soil Conservation Service: Alamosa County Area (1973),
Rio Grande County Area (1980), Conejos County Area
(1980), and Saguache County Area (1984). Copies of these
reports are available in the San Luis Resource Area Office.

Over 100 different soil types are present in the planning
area and reflect a variety of parent materials, topographic
positions, and climatic regimes. Most of these soils present
few problems for range, forestry, wildlife, or r=eation
management There are some limitations, however, on most
of these soils for activities such as road building, mineral
development sanitary landfills, reservoir constructions, etc.
Erosion can occur on all of these soils if the vegetative
cover is removed. Seven soil types are especially susceptible
to erosion.

The Commodore and Bushvalley series are rated "severe"
for water erosion susceptibility. These two soil types cover
23,400 acres of the planning area, or about 5 percent of
the total.

The Codette, Costilla, Cotopaxi, Dune Land, and Space
City series are rated "severe" for wind erosion susceptibility.
These soil types cover approximately 17,900 acres of BLM
land, or about 3 percent of the total.

The Commodore soils occur in the steeper foothills of the
Sangre de Cristo Mountains, running in a band from Mount
Blanca to Pancha Pass. The parent materials are metamor-
phic and igneous rocks. Bushvalley soils occur in Saguache
and Conejos Counties. In Saguache County, these soils are

located near Poncha Pass, in upper Kerber Creek, in the
hills north of Saguache Creek, and in the upper reaches
of San Juan, Cottonwood, and Biedel Creeks. In western
Conejos County, Bushvalley soils are in a band running
south from Chicito Peak to Los Mogotes. The parent
mater.als for these soils are volcanic rocks.

The five soil series highly susceptible to wind erosion are
all located along the eastern edge of the San Luis Valley
floor in Saguache and Alamosa Counties. These soils are
formed from eolian sand and sandy alluvium.

Evidence of past accelerated erosion exists in many parts
of the resource area, especially on the western side of the
San Luis Valley. Currently, most of these areas are eroding
very slowly with a gradual trend toward stabilization.

In the southwestern part of the resource area, about 700
acres of the Bighorn Grazing Allotment are still actively
eroding.

Elsewhere, several drainage bottoms supported riparian
vegetation before erosion resulted in channel downcutting
and lowering of the water table. A complete inventory of
such areas has not been made; however, three drainages
(Ford Creek, Poison Gulch, and Sanderson Gulch) appear
to have good potential for restoration of the riparian
vegetation community.

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