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https://nationalmap.gov/3DEP/3dep_prodserv.html.

Walker, J.D., Geissman, J.W., Bowring, S.A., and Babcock, L.E., comps., 2012, Geologic time 

scale v. 4.0: Geological Society of America, https://doi.org/10.1130/2012.CTS004R3C. 

Walker, M.J.C., Berkelhammer, M., Björck, S., Cwynar, L.C., Fisher, D.A., Long, A.J., Lowe, 

J.J., Newnham, R.M., Rasmussen, S.O., and Weiss, H., 2012, Formal subdivision of the 

Holocene Series/Epoch—A discussion paper by a working group of INTIMATE (Integration 

of ice-core, marine and terrestrial records) and the Subcommission on Quaternary 

Stratigraphy (International Commission on Stratigraphy): Journal of Quaternary Science, 

v. 27, no. 7, p. 649–659.

Young, N.E., Briner, J.P., Leonard, E.M., Licciardi, J.M., and Lee, K., 2011, Assessing climatic 

and nonclimatic forcing of Pinedale glaciation and deglaciation in the western United States: 

Geology, v. 39, no. 2, p. 171–174.

U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigations Map 3408

Sheet 2 of 2

A B

Photo 1. Views of Verdos Alluvium (Qv) in gravel-pit exposure in adjacent Brush West 7.5 ́ quadrangle. A,

Section (about 6-meters thick) of cross-bedded sandy gravel interbedded with well-sorted sand. Black 

manganese oxide stains gravel in lower part of photo; reddish yellow iron oxide stains gravel in middle part. 

Soil with well-developed K horizon (white zone) visible at top of section. B, Close up of soil profile. K 

horizon variably cemented with stage III (locally stage IV) carbonate morphology and thick coats (rinds) on 

clasts up to 1-centimeter thick. Shovel is 68-centimeters long. Photographs by M.E. Berry, September 2012 

and June 2016.

A B

C

Photo 2. Views of Nussbaum Alluvium (QNn) in a gravel-pit exposure in northwestern part of Fort Morgan 

7.5 ́ quadrangle. A, Close up of rounded cobbles in indurated conglomerate making up basal section of 

alluvium. Knife is 26 centimeters long. B, Variably cemented cross-bedded sands and pebbly sands. Shovel 

blade is 22 centimeters long. C, Quarried blocks of indurated basal conglomerate. Photographs by 

M.E. Berry, July 2010 and September 2012.

A

B

Qay

Qlg

Photo 3. Views of eolian and alluvial deposits, undivided (Qlg). A, Erosional contact (dashed line) separates Qlg from overlying young sidestream 

alluvium, undivided (Qay), here made up of reworked loess and eolian sand deposited mainly by sheetwash processes. Eroded pedogenic carbonate 

horizon with maximum stage III carbonate morphology marks top of Qlg. B, Close-up view of a gravel bed within Qlg. Knife is 26 centimeters 

long. Photographs by M.E. Berry, June 2013. 

OSL–1–KC UNL–3462 Orchard 577915 4464174 1.7 5.3 20.0 3.8 67.6±3.3 22/30 2.9 5.77±0.32 11.7±1.0 5.0 5.64±0.35 12.0±1.1

OSL–4–KC UNL–3466 Orchard 577915 4464174 2.6 3.3 16.3 4.3 87.8±5.4 24/37 2.1 5.41±0.30 16.2±1.5 5.0 5.23±0.34 16.8±1.7

OSL–5–KC UNL–3463 Orchard 577915 4464174 3.6 3.7 15.8 4.3 80.6±4.8 22/32 2.4 5.45±0.31 14.8±1.4 5.0 5.29±0.35 15.2±1.5

OSL–6–ER UNL–3467 Masters 568185 4455813 0.7 2.9 11.4 3.4 109.7±5.6 20/37 5.0 4.15±0.27 26.4±2.5 5.0 4.15±0.27 26.4±2.5

OSL–7–ER UNL–3468 Masters 568198 4455836 1.0 2.4 8.1 3.7 31.4±2.2 29/37 1.9 4.22±0.25 7.4±0.7 5.0 4.07±0.28 7.7±0.8

OSL–BC–14 UNL–3498 Weldona 585123 4459026 1.1 4.8 19.5 3.7 67.0±2.8 31/48 7.7 5.23±0.39 12.8±1.2 5.0 5.39±0.34 12.4±1.1

OSL–BC–13 UNL–3499 Weldona 585123 4459026 1.9 4.3 17.6 4.1 79.1±2.9 36/54 6.7 5.33±0.38 14.8±1.3 5.0 5.43±0.35 14.6±1.2

UNL lab9 UNL lab9

OSL–AK–10 UNL–3502 Weldona 592468 4463758 5.1 5.7 23.3 2.7 40.2±1.4 43/54 7.0 4.92±0.35 8.2±0.7 5.0 5.03±0.31 8.0±0.7

OSL–AK–11 UNL–3503 Weldona 592478 4463772 3.5 3.5 9.9 2.6 32.5±1.8 27/35 5.9 3.52±0.24 9.2±0.9 5.0 3.56±0.23 9.1±0.9

OSL–TK–R–12 UNL–3504 Orchard 577216 4463702 8.0 1.5 6.7 3.9 35.8±2.0 48/54 3.3 3.88±0.26 9.2±0.9 5.0 3.81±0.28 9.4±1.0

Field

number

UNL lab

number

UTM

Easting2

UTM

Northing2

Approx.

depth

(m)

U

(ppm)

Th

(ppm)

Dose

rate

(Gy/ka)6

K2O

(wt.%)

CAM De

(Gy)

±1 Std. err.3

Aliquots

(n)4

In situ

H2

O field

(%)5

OSL

age

ka±1σ6

In situ

H2

0 est.

(%)5

Dose

rate

(Gy/ka)7

OSL

age

ka±1σ7

7.5 ́

quad

Table 1. Optically stimulated luminescence (OSL) age estimates with equivalent dose (De) and dose rate data (modified from Berry and others, 2015a).

[UNL Lab, University of Nebraska–Lincoln Luminescence Geochronology Laboratory; quad, quadrangle; UTM, Universal Transverse Mercator; Approx., approximate; m, meter; U, uranium; ppm, parts per 

million; Th, thorium; K2

O, potassium oxide; wt. %, weight percent; %, percent; Gy, gray1; Std. err., standard error; n, number; H2O, water; ka, thousand years; ±1σ, represents estimates of uncertainty given 

at the 67 percent confidence interval]

In situ8 In situ8

1

Gray is an SI unit of absorbed dose of ionizing radiation (Taylor and Thompson, 2008).

2

1927 North American Datum (NAD 27), zone 13.

3

Determined using the Central Age Model (CAM) of Galbraith and others (1999).

4

Accepted disks/all disks.

5

Assumes 100% error in estimated moisture content. Field, moisture content of sample, measured at UNL lab; Est., estimate of moisture content, which may better represent moisture history of sample. 6

Calculated using field moisture content of sample.

7

Calculated using 5% as estimated moisture content.

8

Measured in field with a portable gamma spectrometer.

9

Measured at UNL Lab using high-resolution gamma spectrometry (updated from Berry and others, 2015a, b).

Aeon–1580 Fort 

Morgan 602519 4467910 Humin fraction of 

buried A horizon 0.8 -17.4 0.96

Aeon–1582 602094 4468709 Bison tooth 0.9 -12.7

0.14 

0.59 

0.28

Aeon–2101 602339 4469163 Humin fraction of 

buried A horizon 1.8 -21.4 0.96

Aeon–994 Weldona 592473 4463764 4.7 -6.8 0.98

Aeon–995 Weldona 592473 4463764 Probable Succinea

(single shell) 3.6 -4.6 0.98

Aeon–1064 Orchard 581980 4466741

Probable Succinea

(four shells from 

~15 cm thick bed

3.7 -3.8 1.00

Aeon–950 Orchard 577915 4464174 mostly lignite? 2.5 -23.2 1.00

WC–P–2 2.84±0.03

14.53±0.56

KC–245

0.11±0.02

0.04±0.01 

0.10±0.04 

0.24±0.02

H–R–3,4,5,9

11.95±0.24

43.90±5.69

12.36±0.15

39.80±3.10

4.92±0.07

AK–8

AK–1 11.90±0.28

FMR–3 4.36±0.03

10.22±0.07

10.24±0.06

TIP–Wp115

2.93±0.07

Probable Succinea

(single shell)

Fort 

Morgan

Fort 

Morgan

Laboratory

number

7.5 ́

quad

UTM

Easting2

UTM

Northing2

Material

dated

Approx.

depth

(m) 

δ13C

(‰)3 P6

Field

number

14C age

(

14C ka B.P.)4

Calibrated age

(cal ka B.P.)5

Table 2. Radiocarbon sample information, 14C ages1, and calibrated ages (modified from Berry and others, 2015a). 

[UTM, Universal Transverse Mercator; quad, quadrangle; δ13C, delta carbon-13; ‰, per mil; 14C ka B.P., carbon-14 thousand years before present; 

cal ka B.P., calibrated thousand years before present; P, probability; Approx., approximate; m, meter; cm, centimeter; ±1σ, represents estimates of 

uncertainty given at the 67 percent confidence interval; ±2σ, represents estimates of uncertainty given at the 95 percent confidence interval]

1

Radiocarbon (14C) activity measured by accelerator mass spectrometry (AMS). 2

UTM zone 13, 1927 North American Datum (NAD 27).

3

Relative difference between 13C/12C ratio of carbon extracted from subsample and that of Vienna Pee Dee Belemnite (VPDB) international standard. 4

Conventional radiocarbon age, normalized to -25‰, based on 5,568-year half-life; uncertainty ±1σ.

5

Calibrated age calculated using CALIB 7.0, IntCal13 dataset (Stuiver and Reimer, 1993; Reimer and others, 2013); 0 yr B.P. = 1950 A.D.; uncertainty ±2σ. 

 Calibrated age reported as midpoint of calibrated range. For Aeon–1582, calibration produced more than one age range with a probability of 5 percent or more; therefore, calibrated age 

 used in discussion (0.13 cal ka B.P.) is based on the mean of the ranges weighted by their probabilities and is presented without uncertainties. 6

Probability of calibrated age falling within reported range as calculated by CALIB.

230Th/238U AR±2σ 234U/238U AR±2σ

Carbonate rind (subsample Wp67–1) and layers of bone (subsamples Wp67–2 

through Wp67–11). 

Location of EF–Wp67: UTM 564654E., 4462502N.4

Wp67–1 22.5 1.64 5.7 0.117±0.011 1.221±0.004 11±1.1 1.228±0.004

Wp67–2 83.0 0.325 104 0.1338±0.0012 1.214±0.003 12.70±0.13 1.221±0.003

Wp67–3 107 0.044 1150 0.1520±0.0006 1.210±0.003 14.58±0.07 1.219±0.003

Wp67–5 116 0.025 2300 0.1588±0.0007 1.215±0.003 15.21±0.08 1.224±0.003

Wp67–7 115 0.028 2020 0.1600±0.0007 1.221±0.002 15.26±0.08 1.231±0.003

Wp67–9 116 0.032 1600 0.1458±0.0006 1.217±0.003 13.87±0.07 1.226±0.003

Wp67–11 104 0.124 322 0.1255±0.0006 1.217±0.003 11.82±0.06 1.225±0.003

Innermost carbonate rinds on alluvial clasts. Location of EIC–Wp95: 

UTM 567342E., 4458109N.4

Wp95–A1–1 5.92 0.280 66.9 1.040±0.008 1.125±0.007 248±9 1.252±0.010

Wp95–A1–2 7.36 0.309 76.7 1.061±0.007 1.084±0.003 337±15 1.217±0.009

Wp95–A2–1 10.2 0.274 121 1.065±0.009 1.085±0.003 341±20 1.222±0.012

Wp95–A3–1 7.12 0.549 41.3 1.048±0.009 1.094±0.004 294±13 1.216±0.008

Wp95–B1 7.90 0.901 28.2 1.057±0.01 1.077±0.004 345±24 1.205±0.012

Wp95–B2 7.60 0.509 47.6 1.048±0.007 1.079±0.003 324±15 1.197±0.008

Wp95–B3 9.58 0.672 46.3 1.069±0.007 1.072±0.003 397±27 1.221±0.014

Wp95–E1 9.91 0.461 67.7 1.037±0.006 1.054±0.003 372±21 1.153±0.008

Field

number 

Measured 230Th/232Th AR1

EF–Wp67

EIC–Wp95

Detritus-corrected activity ratios2

Lab sample name U concentration, 

in μg/g

Th concentration,

in μg/g 

230Th/U age

±2σ(ka)3

Initial 234U/238U AR±2σ3

1

Measured activity ratio (AR) corrected for mass fractionation, spike contributions, and procedural blank, and normalized relative to an atomic ratio value for National Institute of Standards 

 and Technology (NIST) Standard Reference Material (SRM) 4321B U-isotope standard of 234U/238U=0.0000529. 2

Ratios corrected for an assumed Th-bearing detrital component having an atomic Th/U of 4 with the following activity ratios and 2σ errors: 232Th/238U=1.276±0.64; 234U/238U=1.0±0.1; and 230Th/238U=1.0±0.25. 3 230Th/U ages, initial 234U/238U activity ratios (ARs), and associated errors are calculated using detritus-corrected activity ratio values. 4

UTM zone 13, 1927 North American Datum (NAD 27).

Table 3. U-Th concentrations, U-series isotope compositions, and calculated 230Th/U ages and initial 234U/238U activity ratios for subsamples of 

EF–Wp67 and EIC–Wp95 (from Berry and others, 2015b). 

[Abbreviated version of table 1-1 in Paces (2015). Note that ±2σ represents estimates of uncertainty given at the 95 percent confidence level; μg/g, 

micrograms per gram; σ, sigma; ka, thousand years]

Geologic map of the Fort Morgan 7.5’ quadrangle, Morgan County, Colorado

By

Margaret E. Berry,1

 Emily M. Taylor,1 Janet L. Slate,1 James B. Paces,1 Paul R. Hanson,2 and Theodore R. Brandt1

2018

To learn about the USGS and its information products visit

https://www.usgs.gov/

1-888-ASK-USGS

This report is available at

https://doi.org/10.3133/sim3408

1

U.S. Geological Survey

2

University of Nebraska–Lincoln, School of Natural Resources

Publishing support provided by 

Denver Publishing Service Center

Edit and digital layout by J.A. Herrick

Manuscript approved for publication May 24, 2018

Any use of trade, firm, or product names is for descriptive purposes only and does not imply 

endorsement by the U.S. Government.

Although this information product, for the most part, is in the public domain, it also contains 

copyrighted materials as noted in the text. Permission to reproduce copyrighted items must 

be secured from the copyright owner.

Although these data have been processed successfully on a computer system at the USGS, 

no warranty expressed or implied is made regarding the display or utility of the data on any 

other system or for general or scientific purposes, nor shall the act of distribution constitute 

any such warranty. The USGS or the U.S. Government shall not be held liable for improper or 

incorrect use of the data described and/or contained herein.

ISSN 2329-132X (online)

https://doi.org/10.3133/sim3408

For more information concerning this publication, contact

Center Director, USGS Geosciences and Environmental Change Science Center

Box 25046, Mail Stop 980

Denver, CO 80225

(303) 236-5344

Or visit the Geosciences and Environmental Change Science Center Web site at

https://gec.cr.usgs.gov/

ScienceBase citation: Berry, M.E., Taylor, E.M., Slate, J.L., Paces, J.B., Hanson, P.R., and Brandt, T.R., 

2018, Data release for the geologic map of the Fort Morgan 7.5’ quadrangle, Morgan County, Colorado: 

U.S. Geological Survey data release, https://doi.org/10.5066/F7QC02PQ.

ScienceBase citation for geochronology of the river corridor: Berry, M.E., Hanson, P.R., Paces, J.B., 

Taylor, E.M., and Slate, J.L., 2018, Data release of OSL, 14C, and U-series age data supporting geologic 

mapping along the South Platte River corridor in northeastern Colorado: U.S. Geological Survey data 

release, https://doi.org/10.5066/F7QN65M3.

Suggested citation: Berry, M.E., Taylor, E.M., Slate, J.L., Paces, J.B., Hanson, P.R., and Brandt, T.R., 

2018, Geologic map of the Fort Morgan 7.5’ quadrangle, Morgan County, Colorado: U.S. Geological 

Survey Scientific Investigations Map 3408, 2 sheets, scale 1:24,000, https://doi.org/10.3133/sim3408.