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Ferricrete, manganocrete, and bog iron occurrences with selected sedge bogs and active iron bogs and springs in the upper Animas River watershed, San Juan County, Colorado

May 1, 2003

During 1996 to 2000, the Bureau of Land Management, National
Park Service, Environmental Protection Agency, United States
Department of Agriculture (USDA) Forest Service, and the
U.S. Geological Survey (USGS) developed a coordinated
strategy to (1) study the environmental effects of
historical mining on Federal lands, and (2) remediate
contaminated sites that have the greatest impact on water
quality and ecosystem health. This dataset provides
information that contributes to these overall objectives and
is part of the USGS Abandoned Mine Lands Initiative. Data
presented here represent ferricrete occurrences and selected
iron bogs and springs in the upper Animas River watershed in
San Juan County near Silverton, Colorado. Ferricretes
(stratified iron and manganese oxyhydroxide-cemented
sedimentary deposits) are one indicator of the geochemical
baseline conditions as well as the effect that weathering of
mineralized rocks had on water quality in the Animas River
watershed prior to mining. Logs and wood fragments
preserved in several ferricretes in the upper Animas River
watershed, collected primarily along streams, yield
radiocarbon ages of modern to 9,580 years B.P. (P.L.
Verplanck, D.B. Yager, and S.E. Church, work in progress).
The presence of ferricrete deposits along the current stream
courses indicates that climate and physiography of the
Animas River watershed have been relatively constant
throughout the Holocene and that weathering processes have
been ongoing for thousands of years prior to historical
mining activities. Thus, by knowing where ferricrete is
preserved in the watershed today, land-management agencies
have an indication of (1) where metal precipitation from
weathering of altered rocks has occurred in the past, and
(2) where this process is ongoing and may confound
remediation efforts.
These data are included as two coverages-a ferricrete
coverage and a bogs and springs coverage. The coverages are
included in ArcInfo shapefile and ArcInfo interchange file
format.