8

7

6

5

4

316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338

HORIZONTAL DISTANCE FROM WEST EDGE OF VALLEY FLOOR, IN METERS

339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361

8

7

6

5

4

ELEVATION, IN METERS

ELEVATION, IN METERS

8

7

6

5

4

254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276

HORIZONTAL DISTANCE FROM WEST EDGE OF VALLEY FLOOR, IN METERS

277 278 279 280 281 282 283 284 285 286 287 307 308 309 310 311 312 313 314 315 316

8

7

6

5

4

ELEVATION, IN METERS

ELEVATION, IN METERS

8

7

6

5

4

209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231

HORIZONTAL DISTANCE FROM WEST EDGE OF VALLEY FLOOR, IN METERS

232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254

8

7

6

5

4

ELEVATION, IN METERS

ELEVATION, IN METERS

8

7

6

5

4

164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186

HORIZONTAL DISTANCE FROM WEST EDGE OF VALLEY FLOOR, IN METERS

187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209

8

7

6

5

4

ELEVATION, IN METERS

ELEVATION, IN METERS

8

7

6

5

4

119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141

HORIZONTAL DISTANCE FROM WEST EDGE OF VALLEY FLOOR, IN METERS

142 143 144 145 146 147 148 149 150 151 152 153 154 155 156

4 m break in section

160 161 162 163 164 165

8

7

6

5

4

ELEVATION, IN METERS

ELEVATION, IN METERS

8

7

6

5

4

74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96

HORIZONTAL DISTANCE FROM WEST EDGE OF VALLEY FLOOR, IN METERS

97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119

8

7

6

5

4

ELEVATION, IN METERS

ELEVATION, IN METERS

6

5

4

29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51

HORIZONTAL DISTANCE FROM WEST EDGE OF VALLEY FLOOR, IN METERS

52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74

6

5

4

ELEVATION, I

ELEVATION, 

20 m break in section

Stream water Sand

Bedding

Surface of ground water and stream water (see note 2)

Sediment sample (see note 3)

EXPLANATION

Coarse-grained early mill tailings Stratigraphic contact-Dashed where uncertain

MnO-stained or cemented gravel and sand (see note 1)

Sandy silt beds

Thin peat beds

Sandy gravel

Fine-grained mill tailings

Sandy granules

Sandy gravel Loose gravel

Brown sandy silt

Brown sandy silt

sand 

silty

sand

Clean gravel

Loose sandy gravel

Loose sandy gravel

no blackening

Bottom of trench

Silty gravelly sand

y g

with silt lenses

Gravel

Blackened

 gravel

Brown

silt

Blackened

sand

Blackened

Blackened sand

gravel

Blackened

sand

Blackened

cemented

sand

Blackened

gravel no

cement

Sand

No black varnish on surface

(extends to 154 m)

Bluish black (SPB 2.5/1) coatings on tops of surficial stones

(extends to 59 m)

Black

gravel

Brown silt Blackened and

locally cemented

sandy gravel

Blackened and

cemented sand and

sandy gravel

Sandy gravel

Inset channel

Very blackened

and cemented

Very blackened

gravel with

some cement

Blackened

gravel

Clean gravel with

minor sand

Blackened

sandy gravel

poorly cemented

Silty

sand

Sandy silt

Orange clay at base

Peat

Peat

X

X

X

X X

X

X

X X

X

X

X

X X

X

X

X X

X X

X

X

X

X X

X

X

X

X

X

X

?

? ?

X

X

Clean pebbles

Coarse tailings

Loose gravel

Loose sandy

gravel

Loose sandy gravel

Brown sandy silt

with clay layers

Blackened

gravel

Enameled iron

cooking pot

Pebbles with buff

and gray coatings

Blackened

sand

Peat

Brick Pebbles

Loose sandy gravel

Loose

gravel

Coarse

blackened

sand

Bottom of trench

Loose gravel

and cobbles

Fe cemented gravel

Brown silty sand

with granules

Cross bedded

coarse tailings

Cloth long

underwear

Sandy gravel

not blackened

Observation

well

Core #280

Iron barrel hoop Coarse tailings

Post-tailings

silty sand bar

Black and cemented

Blackened and cemented inferred

Bottom of trench

9/21/98

9/21/98

Blackened

gravel

Very loose

sandy gravel

Point bar

Site shown in figure 10

Sand

Loose sandy gravel

with talc cement

Sand

Overflow

channel

Sand with tailings

Brown silty sand with

sand, silt and

clay layers

Yellowish-brown (7.5 YR 5/9

to 10 YR 5/8) and olive (5 YR 5/3)

thickly laminated to very thinly

bedded silty clay tailings

White (10YR 8/2) thinly

laminated, crossbedded

(climbing ripples)

very fine sand tailings

10 YR 4/3 (5/3 dry)

dark brown

Loose sandy gravel

Blackened and cemented

sandy gravel

Brown sandy

Granular sand

Loose gravel

Loose gravel

Cemented

Blackened

no cement

Blackened and locally

cemented sandy gravel

Loose sandy pebbles

not blackened;

local sandy lenses

Loose sandy gravel

not blackened

Coarse tailings

Young sand bar

Post-tailings

silty sand bar

Loose sandy gravel

Blackened sandy gravel

Blackened and cemented gravel

Fine-grained tailings

Blackened sand Loose gravel

Tailings

Blackened

and cemented

locally loose

Blackened

and cemented

gravel

Loose sandy gravel

Observation well

Blackened and

cemented gravel

Loose gravel

Inset bar

Inset bar

Silty sand

with tailings

Blackened and cemented

sandy gravel

Loose sandy gravel

Channel

Loose gravel Loose gravel

Iron stained

slightly cemented

(not black)

sandy gravel

Sandy gravel

with iron stain

Sand Peat

Silty sand and

sandy silt with

clay layers

Loose pebble gravel

9/20/98 Clean pebbly sand

Blackened and cemented

sandy gravel

Blackened Silty sand

Sandy silt

7/23/98

Bottom of trench

Clean gravel

Silt

Sand

Clean

gravel

Pebble sand

Clean sandy

gravel

Sandy pebble

gravel

Peat

Peat

Peat

Peat

Sand

Brown sandy silt

Core #4

Clean sandy

pebble

gravel

Clean loose

sandy gravel

Brown sandy silt with

clay and sand lenses

Channel

Pebbly sand

Silt with orange tailings

Channel

Sand

Sand

Peat

Brown sandy silt

Blackened

gravel

Blackened

gravel

Cast iron 

stove leg

Bottom of trench

Sand

Silt

Silt

Slightly

blackened

gravel

Observation well

Rubber

machine

belt

Sandy gravel

Loose sandy pebble gravel

Silt

Silty sand

Very sandy

gravel

Silty sand

Road

bed

fill

Silt

Sandy gravel

Colorado State Road 110

Blackened sandy gravel

Loose sandy pebble gravel

Loose pebble gravel

Bottom of trench 9/24/98

9/24/98

9/24/98

Stream

Loose pebble gravel

Silt

Silt Silt Silt

Clean loose sandy

pebble gravel

Slightly blackened

sandy gravel

Loose sandy gravel

Observation well Blackened pebble gravel

Loose

gravel

Sandy gravel

Pebbly sand

Locally blackened

pebble gravel

Brown sandy silt

Loose

pebble

gravel Very sandy gravel

Pebble gravel

Sandy gravel

Bottom of trench

Loose

sandy

gravel

Sandy lenses

Peat

Peat

Peat

Fine-grained tailings Coarse tailings

Cemented gravel

Brown sandy silt

Brown sandy silt

Brown sandy silt

Silty sand

Pebbly sand

Pebbly silty sand

Loose sandy gravel

Cemented gravel

Orange 

and gray

tailings

Pebble

road bed

Sandy gravel spoil

with coal and

tailings

Loose sandy

pebble gravel Brown silt Olive

tails?

Silt and gravel road bed

Silverton Northern

Railroad bed

constructed ca 1896

Riprap

Railroad tie

Silty sand turf

Cemented gravel

Loose gravel

Light olive gray

(5Y 6/2) at surface

Elevation datum approximately 2,980 meters above mean sea level

View looking upstream (north)

Vertical exaggeration x2

No black varnish at surface

Black varnish on top surface of stones (extends to 277 m)

No black varnish at surface (extends to 191 m) Black varnish at surface

STRATIGRAPHY OF LATE HOLOCENE CHANNEL AND FLOOD-PLAIN DEPOSITS EXPOSED IN A TRENCH EXCAVATED ACROSS THE ANIMAS RIVER VALLEY FLOOR

1.4 KILOMETERS DOWNSTREAM OF THE EUREKA TOWNSITE, SAN JUAN COUNTY, COLORADO

By

Kirk R. Vincent and John G. Elliott

2007

NOTES

[The location of the trench is shown in figs. 1, 2, and 4B (see text of Chapter E22). The sediments are shown in the photographs of figs. 10, 11, and 12]

1. The compounds staining or cementing the clastic sediment are rich in manganese and iron (see fig. 10). The boundaries of polygons of stained or cemented gravel were not given a special line style, so as not to obscure contacts between 

sedimentary beds or stratification within beds. At many locations the boundary of staining or cementation coincided with a stratigraphic contact or internal bedding. At other locations, however, the margin of staining or cementation did 

not coincide with a contact or bedding, and this is illustrated by the absence of a black boundary line.

2. The levels of the ground-water table, and water surface of streams, were all measured between August 11 and 26, 1998, with one exception. The ground-water table was measured in a test excavation at 187 m on July 23, 1998, and during the 

following 2 months the water table declined about 1 meter (see water level at 193 m). During that season an algal mat sealed the streambeds, and evidently the ground water drained because it was not being recharged by infiltrating 

stream water (see fig. 10).

3. Organic material was sampled for radiocarbon dating, and the results are shown in table 7 and figure 13. The fine-fraction of clastic sediment was sampled for geochemical analysis. The geochemical results are shown in table 8 and figure 14, 

and the data are included in the database of Sole and others (this volume, Chapter G).

Mapping by K.R. Vincent