APPROXIMATE MEAN

DECLINATION, 1998

MAG

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ETIC 

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RTH

TRUE NORTH

14

FERRICRETE, MANGANOCRETE, AND BOG IRON OCCURRENCES WITH SELECTED SEDGE BOGS AND ACTIVE IRON BOGS AND SPRINGS 

IN PART OF THE ANIMAS RIVER WATERSHED, SAN JUAN COUNTY, COLORADO

By

Douglas B. Yager, Stanley E. Church, Philip L. Verplanck, and Laurie Wirt 

2007

Base from U.S. Geological Survey 1997, 3.3 ft (1 m) resolution digital orthoquadrangles. Quadrangles used include Ironton, Handies Peak, Ophir, Silverton, and Howardsville.

U.S. DEPARTMENT OF THE INTERIORU.S. GEOLOGICAL SURVEY

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Figure 2. Alluvial ferricrete along Mineral Creek between Middle and South Forks of Mineral Creek (view to west). Outcrop is about 30 m thick and rests on granitoid porphyry bedrock. Ferricretes form in paleo-alluvial terrace deposits where terrace sands and gravels are cemented by iron oxyhydroxide minerals. 

Figure 3. Alluvial ferricrete above mouth of Cement Creek (view to south). Kendall Mountain in distance.

Figure 4. Log in alluvial ferricrete along Middle Fork Mineral Creek is below and about 400 m downstream from Bonner mine. Note log cemented in place by iron oxyhydroxide cement. The radiocarbon age of this log is 790 yr B.P. Logs encased in ferricrete throughout the upper Animas River watershed range in age from modern to 9,150 yr B.P.

Figure 5. Alluvial ferricrete at mouth of Middle Fork Mineral Creek. 

Figure 6. An active iron spring located about 240 m above the confluence of Mineral Creek and Middle Fork Mineral Creek forms where organics and iron precipitates accumulate. Note acidophyllic, dark-green sphagnum moss at base of spring.

Figure 7. Iron spring in lower Prospect Gulch near head of Cement Creek (view to south). Bog iron and colluvial ferricrete deposits are preserved adjacent to spring.

Figure 8. Alluvial ferricrete at base of excavated foundation (town of Silverton). Builders commonly encounter ferricrete "hardpan" when excavating foundations throughout the town. 

Figure 15. Sedge bog in South Fork Mineral Creek subbasin. Sedges, grwillows are prevalent along bog margins. Dark area of photograph is wasaturated, about 15 cm deep, and consists of both living and decaying segrasses, mosses, and shrubs (photograph by M.R. Stanton, U.S. GeologiSurvey).

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38°00' 

107°45' 

107°52'30" 

37°52'30" 

37°45' 

107°37'30"

37°22'30

37°15' 

IRONTON

SILVERTON

OPHIR

10 0 10 20 30 40 

10 0 10 20 30 

Animas

River

Durango

COLORADO

Animas River 

watershed boundary

in Colorado

Figure 1. Index map of Animas River watershed.

Ferricrete mapping accomplished along Mineral Creek and tributary subbasins by P.L. VerplFerricrete mapping along Cement Creek basin and tributary subbasins accomplished by S.E. Yager (1996 - 2001). Other areas were mapped in reconnaissance by S.E. Church and D.B. Ycompiled by D.B. Yager and Tracy Sole.

Snowslide

1 .5 0 1 KILOMETER

SCALE 1:24 000

1 1/ 2 0 1 MILE