?

?

?

?

? ? ?

?

?

?

?

?

?

? ?

? ?

?

? ? ?

? ? ? ? ? ?

?

? ? ?

COLORADO

MAP LOCATION

TKw

TKw

TKw

TKw

TKw

TKw

TKw

TKu

TKw

TKw

Qac

TKu

Tg

Tg

Trp

Tg

Ygs

Qtp

Qtp

Qtp

Qtp

Qtp

Qtp

Qtp

Qtb

Qls

Qls

Qls

Qls

Qac

Qac

Ygs Yxp Ygs

s

s

s

Om

Om

Dcp d

d

s

Xb

Trp

Qtp

Qac

Qac

Tkw

Tkw

Tkw

Tkw

Om

Om

Om

Dc

Dc

Ml Xb

m

m

m

m

TKw Qac

J8

m

m

m

m

m

m

m

m

m

m

Tl Tl

Tl

Tl

Tl

Tl

Tl

Tl

Tg

Tg

Tg

Tg

Tg

Tg

Tg

Tg

m

m

b

b

m

Tg

b

b

b

b

b

Tkw

Ml

Ml

Ml

Ml

Dc

Dc

d

d

d

d

s

s

s

s

s

Qac

Qac

Qac

Qac

Qac

Qac

Qac

Qtp

Qtp

Qtb

Qtb

Qtb

Qdf

Qac

Qac

Qac

Qac

m

b

b

Qac

Qac

Qdf

Qdf

Qtp

Qtp

Qtp

Qtp

Qtp

Qtp

Tg

Qtp

TKw

Tg

Dc

s

d

Cd

Ml

b

Om

Om

Dc

Qgby

Qtpb

Qtpb

Qtpb Qtb

Qtb

Qtb

Qtb

Qgb

Qgb

Qgb

af

Qtb

Qtb

Qgp

Qa

Qgp

Qgp

Qgp

Qgp

Qgb

Qgpb

Qgpb

Qgpb

Qdf

Qgb

Qgb

Qgp

Qa

Qa

Qa

Qgp

Qdf

Qdf

Qtb

Ygs Tl

Tl

Ygs

Ygs

s

s

s

d

d

d

Om

Om

Om

Dc

Dcp

Dcd Dcp

Ml

Qls Ml

Qls

Qdf

Qa

Tl

Tl

Tl

Tl

Tl

Tl

Tl

Qtp

Tl

Tl

Tl

Qtpb

Qtpb

Qtpb

Qtpb

Qtpb

Qtpb

Qtb

Ygs

Ygs

Ygs

s

s

s

Ygs

Ygs

Qd

Qd

Om

Om

Om

Dc

Dc

Dcd

Dcd

Dcp

Dcp

Qac

Qac

m TKw

Ml

Ml

Ml

b

m Tkw

Tkw

Tkw

Tkw

Tkw

Tkw

Qls

b

d

d

d

s

s

d

Qtpb

Qtpb

Tkw

Qac

Qac

Qgp

Qgp

Qgp

Qgp

Qtb

Qls

Qls

Qls

Qls

Qtb

Qtb

Qtb

Qtb

Xb

Xb

YXmr

YXmr

Xb

YXp

Cs

Ygs

Ygs

Ygs

Ygs

YXp

Qls

Qgp

Qgp

Qgp

Qgp

Qgp

Qac

Qgp

Xb

Xb

Xb

Xb

Xb

Xb

Xb

Xb

Qls

Xb

Ygs

Ygs

Xb

Xb

Qgb

Qtb

Qa

Qa

Qa

Qa

Qa

Qa

Qa

Qa

Qa

Qa

Qa

Qa

Qa

Xb

Xb

Qac

Tr

Tl

J8

J8

Yhd

Tl

YXp

YXp

af

b

Thl

Thl

Thl

Xb

55

54

30

40

45

55 60

70

80

3

7

8

8 45

9 11

11

13

10

10

12

9

9

7

6

7

60

13

17 8

35

35

60

25

8 25

15

17

12

12

27 15 9

20

13 13

14

22

20

19

40

75

55 40

70

55

60

60

12 5 10

10 11

75

57

51 17

35 34

10

27

8

7

75

35

67

26

10

11

6

54

16

32

30

30

50

40

50

15

60

12

9

70

65

45

8

10

25

8

7

7

5

50

75

14

25 25 55

21

18

32

35 28

6

12

5

25

17

14

9

50

20

70

50

80

70

80 80

80

50

50

45 85

40

80

75

50

80 50

50

35

35

11

15 18

13

17 17

8

10 14

17

25

85

27

15

10 20

13

70

11

16

8

60 60

60

50

70

30

55

18

80

70

70

75

70

60

58

70

80

65

14

20

77

60 65

11

55

9

21

11

7

7

40

55

Dcd 50

Pm 85

Ml >200

Qtp/Qtb/Qtpb 120

Ygs 150

TD 210

Ml 5

CR–CO–LN–01–14

20.66±0.48

CR–CO–LN–03–14

 17.81±0.6

CR–CO–LN–02–14

 19.45±0.35

Pb? 50

Pm 35

5

30

22

15

14

40

30

18 18

13 22

45

15

20

20

27

21

14

15

28

16

28 78 70

32

13

37 18

10

8

30

80

80 80

17

18

25

40

25

45

8

14

13

12 16

22

65

75

0

0

35

73 14

15

30

25

8

9

CR–CO–LN

–02–11

22.17

 ±0.39

CR–CO–LN–03–11

 29.55±0.56

CR–CO–LN–04–11

18.52±0.29

CR–CO–LN

–05–11

17.12±0.48

CR–CO–LN–01–11

17.63±0.45

CR–CO–HR–06–11

15.96±0.44

Qtp/Qtb/Qtpb 165

Tdu 383

TD 507

Qtp/Qtb/Qtpb 195 

Tdu 235

TD 500

Qtp/Qtb 68

TD 91

Qtpb 6

Tdu 110

TD 181

Tdu 27

Bedrock 152

TD 152

Qtp/Qtb/Qtpb 215

Tdu 312

TD 500

Tdu 45

TD 50

Qtp/Qtb 45

Tdu 170

TD 500

? ?

2,500

2,600

2,700

2,800

2,900

3,000

3,100

3,200

3,300

3,400

3,500

3,600

3,700

3,800

3,900

MISSOURI HILL

Tennessee Creek

East Tennessee Creek

A

WEST

METERS

A'

EAST

FEET

KILOMETERS

NORTHERN SAWATCH FAULT ZONE MOUNT ZION

Minor extensional faults associated with 

emplacement ofEocene intrusions

BEND IN SECTIONBEND IN SECTION

BEND IN SECTION

BEND IN SECTION

BEND IN SECTION

0 1 2 3 4 5 6 7 8 9 10 11

No vertical exaggeration

10,800

9,800

8,800

11,800

12,800

PERCHED BASEMENT WEDGE

RIO GRANDE RIFT EXTENSIONAL STRUCTURE

s

Qls Qa Qtpb

s

Tl

Tl

Tg

Tl TKw

Tg

Tl

Qtb Qtb Qls Qtp

Qtp

Qtp

Tl

TKw

TKw

TKw

TKw

m

m

OmDcMl b

b

d

Tg

Tl

TKw

TKw

Tl

TKw Trp Trp

Tg

Tg

Tl Tg

Tg

Xb Thl

Xb

Xb

Xb

Xb

Qa TKw

Qa

Qls Qa

s

Qacd

Tl Tg

Qls

[Latitude and longitude in North American Datum 1927 (NAD27); m, meters; cm, centimeters; g/cm3, grams per cubic centimeter; cm/yr, centimeters per year; Be, beryllium; mg, milligrams; qtz, quartz; g, grams; conc., concentration; Al, aluminum; 

ka, thousands of years; %, percent; --, no data] 

Sample identifier Latitude Longitude

Elevation

(m)

Thickness

(cm)

Density

(g/cm3)

Shielding 

correction

Erosion

rate

(cm/yr)

Be

carrier 

(mg)

Mass qtz

(g)

10Be/9

Be 

(×10-15)

10Be conc. 

(×105 atoms/g) (×105 atoms/g)

26Al conc. 26Al/10Be

10Be age

(ka)

26Al age 

(ka)

Uncertainty

(%)

Uncertainty

(%)

26Al age/ 

10Be age

CR–CO–LN–01–14 39.2750272 106.346184 3236 3 2.73 0.9999 0 0.2766 25.271 970±22 7.07±0.16 47.40±1.25 6.70±0.23 20.66±0.48 2.32 21.29±0.57 2.66 1.03

CR–CO–LN–02–14 39.2748902 106.347121 3030 3 2.73 0.9999 0 0.2783 41.551 1,475±26 6.59±0.12 44.20±1.16 6.71±0.21 19.45±0.35 1.78 20.04±0.53 2.65 1.03

CR–CO–LN–03–14 39.2760246 106.348754 3030 3 2.73 0.9999 0 0.2791 30.354 977±33 5.98±0.20 40.80±1.27 6.82±0.31 17.81±0.60 3.36 18.68±0.59 3.14 1.05

Cblk–3509–11 -- -- -- -- -- -- -- 0.2808 -- 4±01 -- -- -- -- -- -- -- --

CR–CO–HR–06–11 39.3550122 106.370884 3248 3 2.73 0.9996 0 0.2697 15.703 539±15 6.14±0.17 44.60±1.93 7.26±0.37 15.96±0.44 2.73 17.85±0.78 4.37 1.12

CR–CO–LN–01–11 39.3415053 106.368624 3236 3 2.73 0.9999 0 0.2875 27.647 978±24 6.76±0.17 46.00±1.65 6.80±0.30 17.63±0.45 2.52 18.50±0.67 3.62 1.05

CR–CO–LN–02–11 39.3209233 106.340185 3036 3 2.73 0.9995 0 0.2801 19.716 815±14 7.69±0.14 51.40±1.41 6.68±0.22 22.17±0.39 1.78 22.83±0.63 2.77 1.03

CR–CO–LN–03–11 39.3231251 106.341468 3036 3 2.73 0.9995 0 0.2825 20.025 1,119±21 10.50±0.20 69.20±2.19 6.59±0.24 29.55±0.56 1.91 30.04±0.97 3.21 1.02

CR–CO–LN–04–11 39.33184 106.354525 3067 3 2.73 0.9998 0 0.2818 39.845 1,358±21 6.40±0.10 43.00±1.18 6.72±0.21 18.52±0.29 1.57 19.14±0.53 2.77 1.03

CR–CO–LN–05–11 39.3305518 106.35682 3064 3 2.73 0.9992 0 0.2842 24.561 763±21 5.87±0.16 39.10±1.30 6.66±0.29 17.12±0.48 2.79 17.58±0.59 3.36 1.03

Cblk–3436–21 -- -- -- -- -- -- -- 0.2876 -- 5±1 -- -- -- -- -- -- -- --

Cblk–3436–11 -- -- -- -- -- -- -- 0.2828 -- 4±1 -- -- -- -- -- -- -- --

1

Blank sample measured for instrument calibration.

Table 1. 10Be and 26Al cosmogenic radionuclide sample data and age analyses. Sampling was carried out following established procedures outlined in Gosse and Phillips (2001). This included recording elevation, latitude, longitude, 

and topographic shielding data for each sample location, which accounts for any hindrance to 10Be and 26Al production from the surrounding skyline. Ages of samples were calculated using the CRONUS-Earth online calculator V.2.2 

following the time-invariant scaling model of Lal (1991) and Stone (2000). Uncertainties are reported at the 1 sigma (σ) (±9 percent external uncertainty; Balco and others, 2008). Consistent with past studies within the region, no 

corrections for erosion or snow cover were applied, which allows for comparison with previous 10Be chronologies reported for the upper Arkansas River valley and central Colorado (Guido and others, 2007; Briner, 2009; Ward and 

others, 2009; Young and others, 2011) when adjustments for production rates are made.

39°

39°30'

107°

40°

107° 106° 105°

40°

105°

39° 106°

Base map from Esri World Terrain Base, 2017

Geographic projection, decimal degrees 

World Geodetic System of 1984 

Figure 1. Geologic setting of the Leadville North, Colo., 7.5' quadrangle. Black box indicates location of mapped quadrangle. Major Laramide 

and older structures shown by heavy black lines. Faults having definitive Pleistocene activity shown by heavy red lines. [UAV, Upper Arkansas 

Valley; AR, Arkansas River] 

Oblique, aerial view to the northeast showing the Leadville North, Colo., 7.5' quadrangle geologic map overlaid on a shaded-relief base map.

Quaternary

Paleocene to Jurasic Sedimentary Rocks

Permian to Cambrian Sedimentary Rocks

Proterozoic Rocks

Fault—Major Laramide and older structures

Neogene Volcanic Rocks, Basalt and lesser rhyolite

Paleocene and Late Cretaceous Intrusive Rocks

Active fault—Definitive Pleistocene activity

EXPLANATION

0 10 20 30 KILOMETERS

0 10 20 30 MILES

Sawatch anticlinorium

70

67

70

Hoosier Pass

Dillon Vail

Aspen

DENVER

BASIN

Red Table Mountain

Fairplay

Bailey

Hartsel

Eagle

Golden

Boulder

SOUTH PARK

FRONT RANGE

GORE RANGE

RAMPART RANGE

SAWATCH RANGE

HOMESTAKE SHEAR ZONE

ELKHORN FAULT

Dillon

Aspen

Fairplay

SOUTH PARK

~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~

~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~

~ ~ ~

Blue

River

Valley

Leadville

MOSQUITO

FAULT

SAWATCH FAULT SYSTEM

UAV/AR

Copyright © 2017 Esri and its licensors. All rights reserved.

106°15

39°22'30"

39°15'

N

39°15'

106°22'30"

106°15

39°22'30"

106°22'30"

Halfmoo n

Creek

East Fork Arkansas Ri ver

Buckeye

Peak

Mount

Zion

Tennessee

Pass Missouri Hill Gore Range

Turquiose Lake

Homestake

Peak

TENNESSEE

PARK

Leadville

Arkansas River

Fremont

Pass

CLIMAX 

MINE Mosquito Range

Sawatch Range

Leadville Fish Hatchery

View to the northeast showing Leadville, Colo., from the flank of Mount Elbert and geographic features relative to the 

Leadville North, Colo., 7.5' quadrangle. Approximate location of the geologic map is shown by the dashed footprint.

COLORADO

Area of figure 1

MAP LOCATION

COLORADO

MAP LOCATION

Inclined bedding—Showing strike and dip

Inclined foliation—Showing bearing and plunge. Inclined lineation arrow 

showing bearing and plunge

Vertical foliation—Showing strike

Inclined porphyry dike attitude—Showing dip. Only appears on unit Tg

Prospect pit or shallow shaft

Shaft—Showing rock unit label and depth to formation observed in shaft in 

feet where available

Tunnel—Long line points in direction of tunnel entrace at surface

Caved tunnel—Long line points in direction of tunnel entrace at surface

Sample location—Showing sample identifier for 10Be age dates in kiloannum. See table 1

Drill hole—Depth to top of Tertiary Dry Union Formation (Tdu) and total 

depth (TD) in feet

Contact—Long dashed where approximately located, short dashed where 

inferred. Short dashed contact lines projected above surface in cross 

section indicate hypothetical orientation

Fault—Long dashed where approximately located, short dashed where 

inferred, dotted where concealed. Question mark where identity or 

existence questionable. Fault attitude tick shows dip. Arrows show 

direction of movement (on cross section only)

Normal fault—Long dashed where approximately located, short dashed 

where inferred, dotted where concealed. Question mark where identity 

or existence questionable

Reverse fault—Long dashed where approximately located, dotted where 

concealed

Horizontal slickenline—Grooves or lineations on fault surface

Horizontal lineation—Showing strike

Fluvial terrace scarp—Hachures point down scarp

Landslide scarp—Hachures point down scarp

Crest line of moraine—Sense of symmetry unspecified

Lineament—Of probable and suspect tectonic origin

Vein—Dashed where approximately located, dotted where concealed. Vein 

attitude tick showing dip. Veins in central and western parts of map 

chiefly pyritic quartz-sulfide in composition and are silver bearing. 

Veins in Buckeye Peak-Mount Zion region are in carbonate rocks and 

are siliceous and gold-bearing

Jack 8 (J8)—Dolomite bed, 1–2 meters thick, within the Minturn Formation 

(m)

Shoreline—Showing open water

10

75

80

55

Ml 5

Tdu 235

TD 500

22

20

CR–CO–LN

–05–11

17.12±0.48

EXPLANATION

Qd

Qtp

Qtb

Qgp

Qgb

Qtpb

? ?

Qgpb

Qgby

?

?

?

?

?

?

?

Qa

Qac Qls

af

Qdf

Ygs YXp

Xb

? ?

?

Yhd

m

J8

b

Ml

Dc

Dcd

Dcp

Om

s

d

TKw

Tl

Tg

TKu

Trp

YXmr

Thl

Tr

late

GLACIAL AND GLACIOFLUVIAL DEPOSITSALLUVIAL AND MASS 

MOVEMENT DEPOSITS

ARTIFICIAL FILL AND

MINE WASTE DEPOSITS

middle

PLIOCENE TO 

LATE CRETACEOUS 

INTRUSIVE ROCKS

PALEOZOIC 

SEDIMENTARY

ROCKS

Pliocene

early

Miocene

Paleocene

Upper

Upper

Lower 

Upper

PENNSYLVANIAN

Lower MISSISSIPPIAN

Middle

Lower

DEVONIAN

CAMBRIAN

MESOPROTEROZOIC

CRETACEOUS

ORDOVICIAN

PALEOPROTEROZOIC

Oligocene

Holocene

Eocene

Pliestocene

Unconformity

late middle

Unconformity

QUATERNARY

TERTIARY

SURFICIAL DEPOSITS

PROTEROZOIC IGNEOUS

AND METAMORPHIC ROCKS

CORRELATION OF MAP UNITS

Tl

GEOLOGIC FRAMEWORK AND HISTORY

The U.S. Geological Survey (USGS) Leadville North quadrangle lies at the northern end of 

the Upper Arkansas Valley (UAV; fig. 1), where the Continental Divide at Tennessee Pass creates a 

low drainage divide between the Colorado and Arkansas River watersheds. The quadrangle 

includes portions of the San Isabel and White River National Forests within Lake County. In the 

eastern half of the quadrangle, the Paleozoic sedimentary section dips generally 10–30° east 

towards the Mosquito fault (McCalpin and others, 2012), a high-angle, west-dipping, Neogene 

normal fault cutting the eastern margin of the Sawatch anticlinorium. This broad, north-south 

trending antiformal uplift, is cut by high-angle, axial reverse faults, and extends northsouth about 120 kilometers (km) from approximately Vail to Salida, Colo., and east-west about 70 

km from approximately Fairplay to Aspen, Colo. (Tweto, 1975). Minor displacements along 

high-angle, east- and west-dipping Laramide-age reverse faults occurred in the core of the northplunging anticlinorium along the western and eastern flanks of Missouri Hill in the north-center of 

the map. Mesoproterozoic and Paleoproterozoic metamorphic and igneous rocks are uplifted along 

the generally east-dipping, high-angle Sawatch fault system and are overlain by at least three 

generations of glacial deposits (units Qtpb, Qtb, and Qtp) in the western part of the quadrangle.

The Paleoproterozoic rocks within the quadrangle are chiefly composed of biotite gneiss and 

schist (unit Xb) and are part of the Paleoproterozoic Colorado province (Bickford and others, 

1986). These metamorphic rocks were originally deposited and (or) intruded as marine sediments 

interlayered with mafic and felsic rocks along the southern margin of the Archean North American 

craton between 1,780 and 1,730 Ma (Bickford and others, 1986; Boardman and Condie, 1986; 

Aleinikoff and others, 1993; Reed and others, 1993; Chamberlain, 1998; Mueller and Frost, 2006; 

Premo and others, 2007). These rocks were accreted to the present southern border of Wyoming as 

a series of island arcs and back-arc basin deposits during the Medicine Bow orogeny of 

Chamberlain (1998) between 1,780 and 1,740 Ma.

Following this continental suturing event, Mesoproterozoic rocks of the Berthoud Plutonic 

Suite (Tweto, 1987) intruded the region as large batholiths. The St. Kevin Granite (U-Pb age 

1,444±15 Ma; Moscati and others, 2012) is one in this quadrangle. All of the Mesoproterozoic 

granitic rocks in the region are very similar in mineralogy and texture, indicating a period in which 

large, regional batholiths were emplaced. Areas mapped as mixed rock (unit YXmr) surrounding 

the igneous bodies of the St. Kevin Granite were originally called migmatite by Tweto (1974). 

However, upon closer examination, they show more intrusive relationships than depth burial metamorphism. We interpret these areas to be country rock of chiefly unit Xb that has been extensively 

intruded and partially assimilated into stocks and plutons of the St. Kevin Granite. Pegmatites in 

the quadrangle are within and crosscut all Paleoproterozoic and Mesoproterozoic rocks, demonstrating complex relationships between multiple Proterozoic, and possibly younger, geologic events.

With the onset of the Paleozoic era, shallow seas extended across this region and most of 

North America. Sedimentary rocks within the quadrangle associated with this period begin with the 

transgressive Upper Cambrian Sawatch Quartzite (Cs), lying unconformably on a relatively flat 

Neoproterozoic or Early Cambrian erosional surface, and end with the Middle Pennsylvanian 

Belden Formation (b). Interim Paleozoic transgressive-regressive marine sequences are preserved 

within the Dotsero Formation (Cd) through the Leadville Limestone (Ml). During the Middle 

Pennsylvanian, the orogeny that formed the Ancestral Rockies began (De Voto, 1980), uplifting 

Proterozoic basement rock and eroding the overlying Paleozoic sedimentary section. Uplift 

associated with this orogenic event is generally marked by Middle Pennsylvanian Minturn (m) 

and Permian Maroon Formations unconformably overlying Proterozoic rocks. Within the quadrangle, the only evidence for the Ancestral Rockies orogenic episode is the regressive, coarser 

clastic Minturn Formation overlying the Belden Formation.

Following the event that formed the Ancestral Rockies, the region underwent a long interval 

of erosion that lowered the topography. By Late Jurassic, the region was relatively flat, allowing 

encroachment of the Western Interior Seaway and deposition of thick, Cretaceous marine 

sediments. During the Late Cretaceous to Paleocene Laramide orogeny, contractional deformation 

formed the broad Sawatch anticlinorium, and the White porphyry group (TKw) (71.8–64.1 Ma; 

Tweto, 1974), which includes the Pando Porphyry, was emplaced. Based on the amount of displacement within the Laramide-age (Paleocene–Cretaceous), basement-cored structure (as observed 

at Missouri Hill and Tennessee Pass), relatively little reverse offset (about 400 m; Behre, 1953) 

occurred on faults in this uplift, and structural change was mainly regional upwelling on a broad arch.

Igneous activity continued from the Paleocene into the Eocene, lasting from 62 to 40 Ma 

(Pearson and others, 1962; Kellogg and others, 2017). Within the quadrangle, these 62–40 Ma 

intrusive units include the Lincoln Porphyry (Tl) and Gray porphyry group (Tg), which have been 

subdivided during previous mapping into various geographic location names (Behr, 1953; Tweto, 

1974), but have no substantial compositional distinction from one another. As the Laramide 

orogeny and associated igneous activity waned in the Eocene (Tweto, 1975), broad erosional 

surfaces began to form across central Colorado and the southern Rocky Mountains (Epis and 

Chapin, 1975). Remnants of these broad erosional surfaces are not found within the quadrangle, but 

these relict surfaces are preserved farther south along the southern end of the Mosquito Range and 

to the east in South Park and in the Front Range (Epis and Chapin, 1975; Chapin and Cather, 1983; 

Chapin and Kelley, 1997; Kirkham and others, 2006; Ruleman and others, 2011; Houck and 

others, 2012; Kirkham and others, 2012).

Following the late Eocene erosional interval, regionally extensive Oligocene volcanism began, 

and is generally associated with inception of the Rio Grande rift and extensional deformation in the 

region (Tweto, 1979; Kirkham and Rogers, 1981; McCalpin and others, 2012). This is represented 

in the quadrangle by normal faulting, uplift, and exhumation of the Sawatch anticlinorium. 

Oligocene volcanic rocks (Trp) have very limited exposure within the quadrangle. Based on the 

regional spatial distribution of Oligocene volcanic centers in adjacent and more northerly locations 

(for example, hypabyssal rocks of unit Trp about 29 Ma at Camp Hale and down the Eagle River 

Valley; McCalpin and others, 2012), it is possible that a larger, buried Oligocenesourced pluton and (or) stock exists in the subsurface of the quadrangle. Tweto and Case (1972) 

attempted to differentiate the pluton sequence in the subsurface using geophysical data to 

differentiate Cretaceous–Eocene intrusives from the country rock and the extensive St. Kevin 

batholith. Higher resolution gravity and aeromagnetic data, coupled with the extensive drill-hole 

data in the region, would be needed to better constrain these interpretations of significant 

rift-related, Oligocene intrusive activity in the subsurface.

The western margin of the upper Arkansas Valley graben is bound by the east-dipping northern 

Sawatch fault zone (NSFZ). Discontinuous lineaments and linear bedrock escarpments occur along 

the trace of the NSFZ west of Tennessee Pass. No displacement of late Pleistocene, or Last Glacial 

Maximum (LGM) (about 22 ka), deposits and landforms was identified on the NSFZ south of the 

quadrangle by Widmann and others (1998) and Ostenaa and Nelson (2002), nor was any identified 

during this mapping effort. However, relict bedrock escarpments, lineaments, and depressions 

suggestive of prior Quaternary displacement are present to the west of Tennessee Pass and 

generally trend north-northwest.

During the Pleistocene, multiple glacial cycles eroded and exhumed older rock units. Within 

the quadrangle, glacial deposits associated with three Marine Oxygen Isotope Record stages (MIS; 

2, 6, and possibly one definitive glacial episode during MIS10–8 [about 374–243 ka]; Lisiecki and 

Raymo, 2005) have been identified. Immediately west-northwest of the town of Leadville, glacial 

deposits of the oldest stage (pre-Bull Lake) extend much farther west than subsequent glaciations 

and most likely converged with the pre-Bull Lake Turquoise Lake terminal complex. Later Bull 

Lake and Pinedale glaciations (MIS 6 and MIS 2, respectively) were less extensive and glacial 

complexes from the Mosquito and Sawatch Ranges did not converge west of Leadville at the 

Turquoise Lake terminal moraine complex. New cosmogenic ages presented herein are generally 

consistent with ages of other LGM (about 22–21 ka) and deglaciation (about 14–13 ka) deposits in 

the region (Young and others, 2011). Madole (1986) defines the LGM to have occurred between 

30–12 ka. Two outlying ages of 29.55±0.6 and 30.04±0.97 ka for 10Be and 26Al, respectively 

(table 1, sample CR–CO–LN–03–11), were determined from boulders on the LGM terminal 

moraine approximately 8 km below its source-region cirque, yielding a glacial growth-and-advance 

rate from cirque headwall to terminal moraine from about 30 to 22 ka of 1 meter per year (m/yr). 

This rate is strikingly similar to the LGM deglaciation rate from recessional moraines on the 

eastern flank of Mount Massive proposed by Mason and others (2011) and Ruleman and others 

(2013) of 1 m/yr from 22 to 14 ka.

FAULT MAPPING 

AND SUBSURFACE DATA

Surficial faults have been mapped based on displaced surficial deposits and disrupted 

geomorphic landforms, drainages, and fluvial trends along discontinuous lineaments of suspect 

tectonic origin. Original bedrock faults of Tweto (1974) were field checked and remapped for 

lateral continuity, displacement of consecutive units, and structural significance. Based on this 

work, bedrock faults have been simplified and organized into a structural framework, in an attempt 

to eliminate the confusing myriad of minor faults and fractures produced from tectono-magmatic 

emplacement processes clearly having occurred in the region. Stratigraphic relationships and subdivision of units and contacts within the Paleozoic section were originally mapped by Tweto (1974) 

as part of an extensive subsurface survey during 1948–1959. Underneath the town of Leadville, the 

complex fault and fracture pattern of Tweto (1974) was retained on this map to demonstrate the 

complexity involved in any future structural or hydrologic modeling of the area. Elsewhere, concealed and inferred fault projections from Tweto (1974) across newly mapped areas of surficial 

deposits have been simplified to eliminate over interpretation of fault linkage and improve geologic 

map clarity. Subsurface depth measurements and locations are shown on the map and the unit 

nomenclature, labeling, and interpretation of Tweto (1974) has been updated to include new 

tectonic interpretations of aggradation of sequential glacial deposits (for example, Tweto’s 

unit Qd, “Diamicton,” to a depth of 200 feet in the subsurface is changed to Qtp, Qtb, and Qtpb)

ACKNOWLEDGMENTS

We would like to thank Robert Kirkham of GeoLogical Solutions and Jeremy Workman 

(USGS) for their in-depth reviews of both the geology and geodatabase. We would also like to give 

our gratitude to the U.S. Forest Service Leadville Ranger District for providing housing and logistical 

support when needed. We thank Anya Hess from the Denver Publishing Service Center (USGS) for 

her geologic insight and editorial efforts in presentation of the geologic map and accessory files. 

This project has been funded under the National Cooperative Geologic Mapping Program.

REFERENCES

Aleinikoff, J.N., Reed, J.C., Jr., and Wooden, J.L., 1993, Lead isotopic evidence for the origin of Paleo- and 

Mesoproterozoic rocks of the Colorado Province, U.S.A.: Precambrian Research, v. 63, p. 97–122.

Balco, Greg, Stone, J.O., Lifton, N.A., and Dunai, T.I., 2008, A complete and easily accessible means of calculating surface 

exposure ages or erosion rates from 10Be and 26Al measurements: Quaternary Geochronology, v. 3, p. 174–195.

Beaty, D.W., Cunningham, C.G., Harrison, W.J., Landis, G.P., Merchant, J.S., Naeser, C.W., and Wendlandt, R.F., 1990, 

Origin of the ore deposits at Gillman, Colorado, in Beaty, D.W., Landis, G.P., and Thompson, T.B., eds., Carbonatehosted sulfide deposits of the central Colorado mineral belt: Economic Geology Monograph no. 7, p. 255–265.

Behre, C.H., Jr., 1953, Geology and ore deposits of the west slope of the Mosquito Range: U.S. Geological Survey 

Professional Paper 235, 176 p., 20 pl., scale variable. [Also available at https://pubs.er.usgs.gov/publication/pp235.]

Benson, Larry; Madole, R.F.; Phillips, William; Landis, Gary; Thomas, Terry; and Kubic, Peter, 2004, The probable 

importance of snow and sediment shielding on cosmogenic ages of north-central Colorado Pinedale and prePinedale moraines: Quaternary Science Reviews, v. 23, p. 193–206. [Also available at 

https://doi.org/10.1016/j.quascirev.2003.07.002.] 

Benson, Larry; Madole, R.F.; Landis, Gary; and Gosse, John, 2005, New data for late Pleistocene Pinedale alpine 

glaciation from southwestern Colorado: Quaternary Science Reviews, v. 24, p. 49–65. [Also available at 

https://doi.org/10.1016/j.quascirev.2004.07.018.] 

Bickford, M.E., Van Schmus, W.R., and Zietz, Isidore, 1986, Proterozoic history of the mid-continent region of North 

America: Geology, v. 14, p. 492–496.

Birkeland, P.W., 1999, Soils and geomorphology (3rd ed.): New York, Oxford University Press, 430 p.

Bohannon, R.G., and Ruleman, C.A., 2013, Geologic map of the Mount Sherman 7.5' quadrangle, Lake and Park 

Counties, Colorado: U.S. Geological Survey Scientific Investigations Map 3271, scale 1:24,000, accessed 

October 24, 2017, at https://doi.org/10.3133/sim3271.

Boardman, S.J., and Condie, K.C., 1986, Early Proterozoic bimodal volcanic rocks in central Colorado, U.S.A., 

Part II—Geochemistry, petrogenesis and tectonic settings: Precambrian Research, v. 34, p. 37–68.

Briner, J.P., 2009, Moraine pebbles and boulders yield indistinguishable 10Be ages—A case study from Colorado, USA: 

Quaternary Geochronology, v. 4, p. 299–305.

Brugger, K.A., 2007, Cosmogenic 10Be and 36Cl ages from late Pleistocene terminal moraine complexes in the Taylor 

River drainage basin, central Colorado, USA: Quaternary Science Reviews, v. 26, p. 494–499.

Bryant, Bruce, and Naeser, C.W., 1980, Significance of fission-track ages of apatite in relation to the tectonic history of 

the Front and Sawatch Ranges, Colorado: Geological Society of America Bulletin, Part 1, v. 91, p. 156–164. [Also 

available at https://doi.org/10.1130/0016-7606(1980)91<156:TSOFAO>2.0.CO;2.]

Bryant, Bruce, Marvin, R.F., Naeser, C.W., and Mehnert, H.H., 1981, Ages of igneous rocks in the South 

Park-Breckenridge region, Colorado, and their relation to the tectonic history of the Front Range uplift, in Shorter 

contributions to isotope research in the western United States: U.S. Geological Survey Professional Paper 1199 A–E, 

p. 13–35. [Also available at https://pubs.usgs.gov/pp/1199a-e/report.pdf.]

Cappa, J.A., and Bartos, P.J., 2007, Geology and mineral resources of Lake County, Colorado: Colorado Geological 

Survey Resource Series 42, 59 p. [Available on CD-ROM.]

Chamberlain, K.R., 1998, Medicine Bow orogeny—Timing of deformation and model of crustal structure produced during 

continent-arc collision, ca. 1.78 Ga, southeastern Wyoming: Rocky Mountain Geology, v. 33, no. 2, p. 259–277.

Chapin, C.E., and Cather, S.M., 1983, Eocene tectonics and sedimentation in the Colorado Plateau-Rocky Mountain 

area, in Lowell, J.D., ed., Rocky Mountain foreland basins and uplifts: Denver, Colo., Rocky Mountain Association 

of Geologists, p. 33–56.

Chapin, C.E., and Kelley, S.A., 1997, The Rocky Mountain erosion surface in the Front Range of Colorado, in Boyland, 

D.W., and Sonnenberg, S.A., eds., Geologic history of the Colorado Front Range, Colorado Front Range

Guidebook: Denver, Colo., Rocky Mountain Association of Geologists, p. 101–114.

Chronic, John, 1964, Geology of the southern Mosquito Range, Colorado: The Mountain Geologist, v. 1, p. 103–113.

Coe, J.A., Ruleman, C.A., Godt, J.W., Matthews, Vincent, Goehring, B.M., Lucha, Pedro, Deuell, A.E., and Reeves, 

R.R., 2013, Long-term measurement of ridge-spreading movements (sakungen) at Bald Eagle Mountain, central

Colorado [abs.]: Geological Society of America, Abstracts with Programs, v. 45, no. 7, p. 643.

Cunningham, C.G., Naeser, C.W., Marvin, R.F., Luedke, R.G., and Wallace, A.R., 1994, Ages of selected intrusive rocks 

and associated ore deposits in the Colorado mineral belt: U.S. Geological Survey Bulletin 2109, 31 p. [Also 

available at https://pubs.usgs.gov/bul/2109/report.pdf.] 

De Voto, R.H., 1980, Pennsylvanian stratigraphy and history of Colorado, in Kent, H.C., and Porter, K.W., eds., 

Colorado geology: Denver, Colo., Rocky Mountain Association of Geologists, p. 71–101.

Emmons, S.F., 1886, Geology and mining industry of Leadville, Colorado: U.S. Geological Survey Monograph 12, 

parts I and II, 770 p. [Also available at https://pubs.er.usgs.gov/publication/m12.] 

Emmons, S.F., Irving, J.D., and Loughlin, G.F., 1927, Geology and ore deposits of the Leadville mining district, 

Colorado: U.S. Geological Survey Professional Paper 148, 368 p. [Also available at 

https://pubs.er.usgs.gov/publication/pp148.] 

Epis, R.C., and Chapin, C.E., 1975, Geomorphic and tectonic implications of the post-Laramide, late Eocene erosion 

surface in the Southern Rocky Mountains: Geological Society of America Memoir 144, p. 45–74.

Gosse, J.C., and Phillips, F.M., 2001, Terrestrial in situ cosmogenic nuclides—Theory and application: Quaternary 

Science Reviews, v. 20, no. 14, p. 1475–1560.

Guido, Z.S., Ward, D.J., and Anderson, R.A., 2007, Pacing the post-last glacial maximum demise of the Animas Valley 

and the San Juan Mountain ice cap: Geology, v. 35, p. 739–742.

Houck, K.J., Funk, J.A., Kirkham, R.M., Carroll, C.J., and Heberton-Morimoto, A.D., 2012, Marmot Peak quadrangle 

geologic map, Chaffee and Park Counties, Colorado: Colorado Geological Survey Open-File Report 12–07, 

scale 1:24,000. 

Kellogg, K.S., Shroba, R.R., Bryant, Bruce, and Premo, W.R., 2008, Geologic map of the Denver West 30' × 60' 

quadrangle, north-central Colorado: U.S. Geological Survey Scientific Investigations Map 3000, pamphlet 48 p., 

scale 1:100,000, accessed October 24, 2017, at https://pubs.usgs.gov/sim/3000/.

Kellogg, K.S., Shroba, R.R., Premo, W.R., and Bryant, Bruce, 2011, Geologic map of the eastern half of the Vail 30' × 60' 

quadrangle, Eagle, Summit, and Grand Counties, Colorado: U.S. Geological Survey Scientific Investigations 

Map 3170, pamphlet 49 p., 1 sheet, scale 1:100,000, accessed October 24, 2017, at https://pubs.usgs.gov/sim/3170/.

Kellogg, K.S., Shroba, R.R., Ruleman, C.A., Bohannon, R.G., McIntosh, W.C., Premo, W.R., Cosca, M.A., Moscati, 

R.J., and Brandt, T.R., 2017, Geologic map of the upper Arkansas River valley region, north-central Colorado: U.S.

Geological Survey Scientific Investigations Map 3382, pamphlet 70 p., 2 sheets, scale 1:50,000. [Also available at

https://doi.org/10.3133/sim3382.]

Kirkham, R.M., Keller, J.W., Houck, K.J., and Lindsay, N.R., 2006, Geologic map of the Fairplay East quadrangle, Park 

County, Colorado: Colorado Geological Survey Open-File Report 06–09, scale 1:24,000. 

Kirkham, R.M., Houck, K.J., Carroll, C.J., and Heberton Morimoto, A.D., 2012, Geologic map of the Antero Reservoir 

quadrangle, Park and Chaffee Counties, Colorado: Colorado Geological Survey Open-File Report 12–01, 

scale 1:24,000. 

Kirkham, R.M., Houck, K.J., Funk, Jonathan, Mendel, David, and Sicard, K.R., 2012, Geologic map of the Minturn 

 quadrangle, Eagle County, Colorado: Colorado Geological Survey Open-File Report 12–08, scale 1:24,000.

Kirkham, R.M., and Rogers, W.P., 1981, Earthquake potential in Colorado, a preliminary evaluation: Colorado 

 Geological Survey Bulletin 43, 175 p., 19 figs., 3 pls., scales 1:62,500, 1:500,000, and 1:1,000,000. 

Lal, Devendra, 1991, Cosmic ray labeling of erosion surfaces—In-situ nuclide production rates and erosion models: 

Earth and Planetary Science Letters, v. 104, p. 424–439.

Lanphere, M.A., Champion, D.E., Christiansen, R.L., Izett, G.A., and Obradovich, J.D., 2002, Revised ages for tuffs of 

the Yellowstone Plateau volcanic field—Assignment of the Huckleberry Ridge Tuff to a new geomagnetic polarity 

event: Geological Society of America Bulletin, v. 114, p. 559–568.

Lisiecki, L.E., and Raymo, M.E., 2005, A Pliocene-Pleistocene stack of 57 globally distributed benthic records: 

Paleoceanography, v. 20, PA1003. [Also available at https://doi.org/10.1029/2004PA001071.]

Mach, C.J., 1992, Geology and mineral deposits of the Kokomo district: Fort Collins, Colo., Colorado State University, 

M.S. thesis, 154 p.

Madole, R.F., 1986, Lake Devlin and Pinedale glacial history, Front Range, Colorado: Quaternary Research, v. 25, p. 43–54.

Marvin, R.F., Mehnert, H.H., Naeser, C.W., and Zartman, R.E., 1989, U.S. Geological Survey radiometric ages 

compilation C—Part five—Colorado, Montana, Utah, and Wyoming: Isochron/West, no. 53, p. 14–19.

Maslyn, R.M., 1977, Late-Mississippian paleokarst in the Aspen region, Colorado area: Golden, Colo., Colorado School 

of Mines, M.S. thesis, 123 p.

Mason, Cody, Ruleman, C.A., and Kenny, Ray, 2011, Rate and timing of deglaciation using 10Be cosmogenic nuclide 

surface exposure dating, Mt. Massive Wilderness, Colorado, USA: Geological Society of America Abstracts with 

Programs v. 43, no. 5, p. 65.

McCalpin, J.P.; Temple, Jay; Sicard, Karri; Mendel, David; and Ahmad, Bashir, 2012, Geologic map of the Climax quadrangle, Lake and Park Counties, Colorado: Colorado Geological Survey Open-File Report 12–09, scale 1:24,000.

Moscati, R.J., Premo, W.R., and DeWitt, E.H., 2012, SHRIMP-RG U-Pb geochronology and trace element geochemistry 

of zircons from Proterozoic granitic plutons in the Sawatch Range, Colorado, USA: Geological Society of America 

Abstracts with Programs, v. 44, no. 7, p. 234.

Mueller, P.A., and Frost, C.D., 2006, The Wyoming Province—A distinctive Archean craton in Laurentian North 

America: Canadian Journal of Earth Sciences, v. 43, no. 10, p. 1391–1397.

Myrow, P.M., Taylor, J.F., Miller, J.F., Ethington, R.L., Ripperton, R.L., and Allen, Joseph, 2003, Fallen 

arches—Dispelling myths concerning Cambrian and Ordovician paleogeography of the Rocky Mountain region: 

Geological Society of America, v. 115, no. 6, p. 695–713.

Nelson, A.R., and Shroba, R.R., 1998, Soil relative dating of moraine and outwash-terrace sequences in the northern part 

of the upper Arkansas valley, central Colorado, U.S.A.: Arctic and Alpine Research, v. 30, no. 4, p. 349–361.

Ostenaa, D.A., and Nelson, A.R., 2002, Stop 1–2, Quaternary faulting at the Eddy Creek site, Sawatch fault, in McCalpin, 

J.P., Nelson, A.R., Ostenaa, D.A., and Valdez, A., eds., Neotectonics of the Rio Grande rift in Colorado, 2002 Denver 

annual meeting, Oct. 27–30, 2002: Geological Society of America Guidebook to Field trip, Guidebook 8, 115 p.

Pearson, R.C., Tweto, Ogden, Stern, T.W., and Thomas, H.H., 1962, Age of Laramide porphyries near Leadville, 

Colorado, in Short papers in geology and hydrology, articles 60–119: U.S. Geological Survey Professional 

Paper 450–C, p. C78–C80. [Also available at https://pubs.er.usgs.gov/publication/pp450C.] 

Premo, W.R., Kellogg, K.S., and Bryant, Bruce, 2007, SHRIMP U-Pb zircon ages for Paleoproterozoic basement rocks 

from the northern and central Colorado Front Range—A refinement of the timing of crustal growth in the Colorado 

Province: Geological Society of America Abstracts with Programs, v. 39, no. 6, p. 221.

Reed, J.C., Jr., Bickford, M.E., and Tweto, Ogden, 1993, Proterozoic accretionary terranes of Colorado and southern 

Wyoming, in Van Schmus, W.R., and Bickford, M.E., eds., Transcontinental Proterozoic provinces, in Reed, J.C., 

Jr., Bickford, M.E., Houston, R.S., Link, P.K., Rankin, D.W., Sims, P.K., and Van Schmus, W.R., eds., Precambrian— 

Conterminous U.S., The geology of North America: Geological Society of America, v. C–2, p. 211–228.

Richmond, G.M., 1983, Stratigraphy and correlation of glacial deposits of the Rocky Mountains, the Colorado Plateau, 

and the ranges of the Great Basin, in Sibrava, Vladimir, Bowen, D.Q., and Richmond, G.M., eds., Quaternary 

glaciations of the Northern Hemisphere, Report of the International Geological Correlation Programme (IGCP) 

Project No. 24: Quaternary Science Reviews, v. 5, p. 99–127.

Richmond, G.M., and Fullerton, D.S., 1986, Introduction to Quaternary glaciations in the United States of America, in

Richmond, G.M., and Fullerton, D.S., eds., Quaternary glaciations in the United States of America: Quaternary 

Science Reviews, v. 5, p. 3–10.

Ruleman, C.A., Bohannon, R.G., Bryant, Bruce, Shroba, R.R., and Premo, W.R., 2011, Geologic map of the Bailey 30' x 

60' quadrangle, north-central Colorado: U.S. Geological Survey Scientific Investigations Map 3156, pamphlet 38 p., 

scale 1:100,000.

Ruleman, C.A., Goehring, B.M., Mason, Cody, and Lundstrom, S.C., 2013, Late Pleistocene glacial maximum and 

deglaciation of the northern Sawatch Range, Mount Massive, Colorado: Geological Society of America Abstracts 

with Programs, v. 45, no. 7, p. 551.

Schildgen, Taylor; Dethier, D.P.; Bierman, Paul; and Caffee, Marc, 2002, 26Al and 10Be dating of late Pleistocene and 

Holocene fill terraces—A record of fluvial deposition and incision, Colorado Front Range: Earth Surface Process 

and Landforms, v. 27, p. 773–787.

Stark, J.T., and Barnes, F.F., 1935, Geology of the Sawatch Range, Colorado: Colorado Scientific Society Proceedings, 

v. 13, no. 8, p. 467–479.

Stone, J.O., 2000, Air pressure and cosmogenic isotope production: Journal of Geophysical Research, v. 105, p. 753–759.

Thompson, T.B., and Arehart, G.B., 1990, Geology and origin of the ore deposits in the Leadville district, Colorado— 

Part 1—Geologic studies of orebodies and wall rocks, in Beaty, D.W., Landis, G.P., and Thompson, T.B., eds., 

Carbonate-hosted sulfide deposits of the central Colorado mineral belt: Economic Geology Monograph 7, p. 130–156.

Tweto, Ogden, 1951, Form and structure of sills near Pando, Colorado: Geological Society of America Bulletin, v. 62, 

p. 507–532.

Tweto, Ogden, 1961, Late Cenozoic events of the Leadville district and upper Arkansas Valley, Colorado, in Short 

papers in the geologic and hydrologic sciences: U.S. Geological Survey Professional Paper 424–B, p. B133–B135.

Tweto, Ogden, 1974, Geologic map of the Holy Cross quadrangle, Eagle, Lake, Pitkin, and Summit Counties, Colorado: 

U.S. Geological Survey Miscellaneous Geological Investigations Map I–830, scale, 1:62,500. [Also available at 

https://pubs.er.usgs.gov/publication/i830.] 

Tweto, Ogden, 1975, Laramide (Late Cretaceous–early Tertiary) orogeny in the southern Rocky Mountains: Geological 

Society of America Memoir 144, p. 1–44.

Tweto, Ogden, 1979, The Rio Grande rift system in Colorado, in Riecker, R.E., ed., Rio Grande rift—Tectonics and 

Magmatism: Washington, D.C., American Geophysical Union, p. 33–56.

Tweto, Ogden, 1987, Rock units of the Precambrian basement in Colorado, in Geology of the Precambrian basement in 

Colorado: U.S. Geological Survey Professional Paper 1321–A, p. A1–A54, 1 pl., scale 1:1,000,000.

Tweto, Ogden, and Case, J.E., 1972, Gravity and magnetic features as related to geology in the Leadville 30-minute 

quadrangle, Colorado: U.S. Geological Survey Professional Paper 726–C, 31 p.

Tweto, Ogden, and Lovering, T.S., 1977, Geology of the Minturn 15-minute quadrangle, Eagle and Summit Counties, 

Colorado: U.S. Geological Survey Professional Paper 956, 96 p.

Tweto, Ogden, and Pearson, R.C., 1964, St. Kevin Granite, Sawatch Range, Colorado, in Short papers in geology and 

hydrology, articles 122–172, Geological Survey research 1963: U.S. Geological Survey Professional Paper 475–D, 

p. D28–D32. [Also available at https://pubs.er.usgs.gov/publication/pp475D.]

U.S. Geological Survey, 2010, Divisions of geological time—Major chronostratigraphic and geochronological units: U.S. 

Geological Survey Fact Sheet 2010–3059, 2 p. [Also available at https://pubs.er.usgs.gov/publication/fs20103059.]

Wallace, A.R., 1993, Geologic setting of the Leadville mining district, Lake County, Colorado: U.S. Geological Survey 

Open-File Report 93–343, 20 p. [Also available at https://pubs.er.usgs.gov/publication/ofr93343.] 

Ward, D.J., Anderson, R.S., Guido, Z.S., and Briner, J.P., 2009, Numerical modeling of cosmogenic deglaciation records, 

Front Range and San Juan Mountains, Colorado: Journal of Geophysical Research, v. 114, F01026 [Also available 

at https://doi.org/10.1029/2008JF001057.]

Widmann, B.L., Kirkham, R.M., Houck, K.J., and Lindsay, N.R., 2006, Geologic map of the Fairplay West quadrangle, 

Park County, Colorado: Colorado Geological Survey Open-File Report 06–07, scale 1:24,000. 

Widmann, B.L., Bartos, P.J., Madole, R.F., Barba, K.E., and Moll, M.E., 2004, Geologic map of the Alma quadrangle, Park 

and Summit Counties, Colorado: Colorado Geological Survey Open-File Report 04–03, scale 1:24,000. 

Widmann, B.L., Kirkham, R.M., Houck, K.J., and Lindsay, N.R., 2011, Geologic map of the Jones Hill quadrangle, Park 

County, Colorado: Colorado Geological Survey Open-File Report 11–04, scale 1:24,000.

Widmann, B.L., Kirkham, R.M., Keller, J.W., Poppert, J.T., and Price, J.B., 2005, Geologic map of the Como quadrangle, Park County, Colorado: Colorado Geological Survey Open-File Report 05–04, scale 1:24,000. 

Widmann, B.L., Kirkham, R.M., and Rogers, W.P., 1998, Preliminary Quaternary fault and fold map and database of 

Colorado: Colorado Geological Survey Open-File Report 98–8, 331 p., 1 pl., scale 1:500,000.

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

forcing of Pinedale glaciation and deglaciation in the western US: Geology, v. 39, no. 2, p. 171–174.

DESCRIPTION OF MAP UNITS

SURFICIAL DEPOSITS

[Soil classifications from Birkeland (1999)]

ARTIFICIAL FILL AND MINE WASTE

Mine waste/artificial fill (latest Holocene)—Consists of granule- to boulder-size 

fragments of broken and relocated country rock and engineered material used for 

stabilization purposes. Heaps of mine waste are included in the unit and are 

common adjacent to adits and prospects throughout the region. Artificial fill is 

mainly used for dam and roadway construction and for support in the region of 

Turquoise Lake and State highways. Thickness generally 1–20 meters (m) 

ALLUVIAL AND MASS MOVEMENT DEPOSITS

Alluvium (Holocene)—Subangular to well-rounded pebble-, cobble-, and 

boulder-sized clasts interbedded with silt and sand. Primarily along the East Fork 

Arkansas River and forks of Tennessee Creek, along with smaller active streams, 

tributaries, and washes. Unit includes floodplain and lower terrace deposits (less 

than 5 m above active stream channels) generally capped by floodplain deposits 

consisting of fine-grained sands and silts. Soils typically have a weak A/C or 

A/Bw/C profile. Deposits locally include silts and clays accumulated in kettles 

and other depressions formed after the retreat of late Pleistocene glaciers. 

Within Tennessee Park, unit contains peat and bog deposits. Deposits locally 

include minor colluvium, debris-flow deposits, and till. Thickness approximately 

1–5 m

Alluvium and colluvium, undivided (Holocene and late Pleistocene)—Poorly to 

moderately sorted sheetwash alluvium, perennial-stream, colluvial, and talus 

deposits occurring primarily along steep hillslopes and within topographic 

depressions. Unit primarily consists of angular to subrounded clasts in a silty 

sand matrix being derived locally from the surrounding country rock. Clasts 

range in size from pebbles to boulders. Locally, debris-flow, hyperconcentrated 

flow, till, and rock fall deposits are included. Estimated thickness 1–5 m

Landslide deposits (Holocene and late Pleistocene)—Poorly sorted, fine- to 

coarse-grained, angular to subrounded clasts in a silty sand to silty clay matrix. 

Deposits generally lack stratification. Mode of deposition primarily by surface 

creep and earthflow mechanisms. Commonly characterized by hummocky 

topography. Deposits along western flank of Mount Zion and eastern flank of 

Missouri Hill locally include subrounded, deeply weathered Paleozoic rocks 

most likely derived from unit Qtpb. On the western portion of the quadrangle, 

deposits along Porcupine, Long, and Tennessee Creeks are chiefly remobilized 

glacial till of unit Qtp redeposited as landslides due to post-glacial collapse of 

oversteepened lateral moraines. Most of the mapped deposits postdate the Last 

Glacial Maximum (LGM) in the region approximately 22–21 thousand years 

ago (ka) (table 1) (Mason and others, 2011; Coe and others, 2013; Ruleman and 

others, 2013). Estimated thickness ranges from 1 to 10 m

Debris-flow deposits (Holocene and late Pleistocene)—Poorly sorted to unsorted 

deposits consisting of angular to subrounded, pebble- to boulder-sized clasts in a 

sand to clay matrix. Deposits are mostly mapped along the East Fork Arkansas 

River, where late Pleistocene glaciation undercut steep cliffs of easily eroded 

igneous rocks of the White porphyry group (TKw). Most deposits are 

characterized by hummocky microtopography with approximately 1–2 m of 

relief and diagnostic levees trending in the direction of transport. Debris flow 

deposits and associated processes locally occur within units mapped as landslide 

deposits (Qls) and till (Qtp, Qtb, and Qtpb). Estimated thickness 3–5 m

GLACIAL AND GLACIO-FLUVIAL DEPOSITS

Outwash gravel of Pinedale glaciation (late Pleistocene)—Pebble, cobble, and 

boulder gravel in a silty sand matrix, interbedded with sand and sandy 

pebble layers and lenses. Underlies terraces that grade to unit Qtp. Clasts are 

subrounded to rounded and generally <1 m in diameter. Deposits are locally 

clast-supported with little to no matrix. Maximum thickness and aggradation of 

unit is correlated with the LGM (Pinedale glaciation) approximately 22–21 ka 

and higher-energy glacio-fluvial deposition that waned or terminated by 

approximately 14–13 ka (table 1). Pedogenic soils typically have an A/Bw/C 

profile within Tennessee Park and a weak A/Bt/C profile along the East Fork 

Arkansas River, where deposits are more deeply dissected and surfaces are 

abandoned. Clast composition consists of Paleoproterozoic metamorphic to 

Tertiary volcanic rocks derived from the surrounding region. Height of terrace 

treads above active stream channels ranges from 3 to 10 m. Source is primarily 

reworked till of Pinedale glaciation (Qtp) along tributary streams originating in 

the northern Sawatch and Mosquito Ranges. Thickness varies with geomorphic 

location within the basin, but generally ranges from 3 to 15 m

Till of Pinedale glaciation (late Pleistocene)—Subangular to subrounded, 

unconsolidated, pebble- to boulder-sized clasts in a clayey, silty sand matrix. 

Deposits generally poorly sorted to unsorted. Clasts range up to 10 m in diameter 

and are competent, with very little weathering. Deposit is characterized by 

steep-crested lateral moraines and undrained hummocky depressions within 

terminal and recessional moraine complexes. Deposited directly by glacial ice. 

Locally has sorted and bedded lenses of sandy gravels deposited by subglacial 

streams. Convoluted and disturbed bedding due to minor glacial advances is 

locally preserved. Soils on deposits are generally characterized by weak to 

moderately developed Bw horizons but locally have weak Bt horizons of stage I 

development. Clasts are chiefly unweathered and competent, except where older 

deposits have been reworked into deposits of Qtp. Ages of deposits are 

constrained by 10Be and 26Al cosmogenic nuclide ages on exposed surface 

boulders that generally range from approximately 22 to 16 ka within the 

quadrangle (table 1). Other studies within the region indicate Pinedale glaciation 

occurred between 30 and 12 ka (Madole, 1986; Nelson and Shroba, 1998; 

Benson and others, 2004, 2005) with the LGM being about 22 ka and a possible 

ice advance or stagnation at approximately 15.5–14.5 ka (Brugger, 2007; 

Briner, 2009; Mason and others, 2011; Young and others, 2011; Ruleman and 

others, 2013). Complete deglaciation of the northern Sawatch Range occurred by 

approximately 14–13 ka (table 1) (Ruleman and others, 2013). Estimated 

thickness is 3–60 m

Outwash gravel of Bull Lake glaciation (late? and late middle Pleistocene)— 

Pebble, cobble, and boulder gravel in a silty sand matrix underlying terraces. 

Grades to unit Qtb. Clasts are subrounded to rounded and consist of 

Paleoproterozoic metamorphic to Tertiary volcanic lithologies derived from the 

surrounding country rock. Height above stream level ranges from 5 m 

in Tennessee Park to 20 m along the East Fork Arkansas River. Soils are 

generally characterized as A/Bt/C profiles with stage I±II pedogenic carbonate 

development. Thickness generally 1–15 m

Younger outwash gravel of Bull Lake glaciation (late? and late middle 

Pleistocene)—Pebble, cobble, and boulder gravel in a silty sand matrix 

underlying terraces at elevations above and below units Qgp and Qgb, 

respectively. Soils are generally characterized as those on unit Qgb. Unit mapped 

on southern margin of quadrangle where younger Bull Lake-age alluvium was 

deflected to the south by the Bull Lake-age glacier emanating from Mount 

Arkansas and Fremont Pass east of the map area. Estimated thickness is 1–15 m 

Till of Bull Lake glaciation (late middle Pleistocene)—Subangular to subrounded, 

unconsolidated, nonsorted and lacking bedding and stratification, pebble to 

boulder gravel in a clay, silt, and sand matrix. Deposits generally lie downvalley 

from Pinedale terminal moraines (unit Qtp). The original depositional surface 

morphology has been eroded and smoothed. Boulders are partially to mostly 

buried on the surface, and clasts are more weathered than those of unit Qtp. 

Boulders in unit Qtb commonly have oxidized weathering rinds 3–5 millimeters 

(mm) in thickness and are readily friable. In this northern region of the upper

Arkansas Valley, soils on these deposits are generally A/Bt/C profiles with a

20–30-centimeter (cm)-thick argillic horizon oxidized to slightly red chromas. To

the south of the quadrangle, soils on deposits of this age commonly have stage II

pedogenic carbonate development, but within the mapped quadrangle, Qtb

deposits typically have stage I carbonate development and locally discontinuous

stage II pedogenic carbonate. Deposits are correlated with those dated in the

adjacent Front Range of Colorado with 10Be and 26Al cosmogenic radionuclide

exposure minimum age estimates of 101±21 ka and 122±26 ka (Schildgen and

others, 2002). Thickness varies based on geomorphic position, but is generally

estimated to be 5–20 m

Outwash gravel of pre-Bull Lake glaciations (middle and early? Pleistocene)— 

Light brownish-gray to light reddish-brown and orangish brown, weakly 

stratified, pebble, cobble, and boulder gravel in a clayey, silty sand matrix 

underlying terraces grading to pre-Bull Lake till (Qtpb). Clasts are subrounded to 

rounded and generally deeply weathered and grussified. Proterozoic granitic and 

metamorphic clasts are especially easy to disaggregate by hand. West of 

Leadville, the unit consists of a few old remnant surfaces preserved on deposits 

that prograded westward from the Mosquito Range. Surfaces generally lack any 

original depositional morphology and are buried by greater than about 1 m of 

loess, leaving few to no boulders and clasts exposed at the surface. Glacial 

outwash of pre-Bull Lake age that emanated from the Sawatch Range into 

Tennessee Park is presumed buried by younger deposits due to continuous 

displacement along the dominantly east-dipping northern Sawatch fault zone. 

Based on drill hole data of Tweto (1974), deposits of unit Qgpb appear to lie 

unconformably on the Dry Union Formation and Malta Gravel of Tweto (1961) 

and mark a dramatic shift in depositional systems at the contact from deposits 

related to lower-energy, episodic depositional systems (for example, debris flow 

and alluvial fan deposition) below to weakly bedded and stratified, subrounded to 

rounded, and sorted glacio-fluvial gravels above. Pedogenic carbonate 

development is not consistently preserved in these deposits within the 

quadrangle, but carbonate accumulation and cementation within the gravels is 

noted to be locally pervasive in adjacent areas (Behre, 1953). Richmond (1983) 

places the Malta Gravel above and younger than the Lava Creek B ask bed 

(approximately 640 ka, Lanphere and others, 2002) and older than Bull Lake 

moraine (approximately 200–130 ka), making these the first definitively 

recognized glaciogenic deposits in the upper Arkansas River valley to be middle 

Pleistocene (788–132 ka; Richmond and Fullerton, 1986), not early Pleistocene 

(2.59 Ma–788 ka; Richmond and Fullerton, 1986). Where the East Fork Arkansas 

River enters Tennessee Park, Tweto (1974) described older pre-Bull Lake till 

buried beneath pre-Bull Lake outwash by several meters at most (see geologic 

map). Thickness varies, but may be as much as 20 m

Till of pre-Bull Lake glaciations (middle and early? Pleistocene)—Unsorted, 

unstratified, deeply weathered boulder gravel in a clayey, silty sand matrix 

lacking original depositional morphology. Surface clasts are typically absent on 

the landform and, where exposed, are deeply weathered and easily pulverized in 

the hand. Mapped at Leadville along the East Fork Arkansas River extending 

beyond both Pinedale and Bull Lake glacial limits. Deposits mapped at and 

proximal to Tennessee Pass are interpreted as older till and differentiated from 

unit Qd to the south based on the geomorphic position to Mount Zion and 

glaciated No Name Gulch. Minor drainages south of No Name Gulch and north 

of the East Fork Arkansas River appear to be unglaciated and associated older 

pre-Bull Lake deposits (unit Qd) adjacent to the range front are interpreted as 

debris-flow deposits. Thickness varies from 1 to 40 m

Diamicton (middle and early? Pleistocene)—Unsorted, unstratified boulder gravel 

in a clayey, silty sand matrix. Deposits are deeply weathered with almost 

complete erosion of original depositional landform. Depositional process 

unknown, but deposits resemble pre-Bull Lake till deposits within the 

quadrangle. Two possible explanations for the deposits exist. The sediments 

were either deposited by glaciers emanating from Mt. Zion and the northern 

Sawatch Range, as part of a previously unrecognized, more regionally extensive 

ice field, or by debris flows shed off the western flank of Mount Zion within 

unglaciated drainages. If these deposits are sourced from the west, then 

displacement along the northern Sawatch fault zone has downdropped and buried 

these deposits with younger glacial and glacio-fluvial deposits below Tennessee 

Park, as noted by Tweto (1974) (see unit Qgpb description). Estimated thickness 

3–30 m

PLIOCENE TO LATE CRETACEOUS 

INTRUSIVE ROCKS

Rhyolite (Pliocene? or Miocene?)—White to light-gray, fine-grained rhyolite with 

minor amounts of black vitrophyre. Unit associated with rhyolite breccia in the 

Leadville region and was emplaced at very shallow depths. The only definitively 

recognized Tr dikes within the quadrangle lie approximately 1 kilometer (km) 

east of downtown Leadville on the western flank of Canterbury Hill. Regionally, 

dikes tend to be found along the northern Sawatch fault zone and other 

range-bounding faults

Rhyolite porphyry (Oligocene?)—Light-yellow to pinkish-brown, fine-grained 

rhyolite porphyry with abundant, large (>5 mm) quartz phenocrysts. Secondary 

phenocrysts consist of sanidine, potassium feldspar, and biotite. Unit is exposed 

along the southwest side of Tennessee Pass and farther to the north, off the 

quadrangle. Unit is only exposed within and proximal to normal faults and 

sheared zones interpreted to be associated with regional extension. Trp is 

correlated with the approximately 29 million years ago (Ma) Chalk Mountain 

Porphyry (McCalpin and others, 2012) based on texture and composition in hand 

specimen, and thus correlative herein. Crosscutting relationships and age 

constraints in the adjacent Climax, Colo., 7.5' quadrangle (McCalpin and others, 

2012) demonstrate that unit is younger than Cretaceous to Eocene igneous 

intrusive rocks. Close proximity of exposures to rift-related normal faults within 

the quadrangle and to the north within the Camp Hale region further supports an 

Oligocene age and rift-related emplacement. Due to structural and hydrothermal 

alteration, exposures of unit within quadrangle are not optimal for dating or 

chemical analyses 

Hornblende latite porphyry (Eocene?)—Pink-gray to dark greenish-gray, 

porphyritic granodiorite sills and dikes mapped on the southwestern ridge of 

Mount Zion. Based on composition, unit correlated with the Eagle River 

Porphyry and assigned an Eocene age. However, no absolute age has been 

determined and the Gray porphyry group (Tg) is intruded by Thl, suggesting unit 

Thl could be as young as Oligocene

Gray porphyry group (Eocene)—Includes the Evans Gulch, Johnson Gulch, and 

Mount Zion Porphyries of Emmons and others (1927) and Behre (1953) and the 

Sacramento Gulch and Eagle River Porphyries of Tweto (1974). Widely exposed 

along the western flank of Mount Zion as a domed laccolith and accompanying 

sills within the Minturn Formation (m). All of these porphyries are generally 

gray to greenish-gray, and locally bluish-gray, porphyritic monzogranite or 

granodiorite with phenocrysts of plagioclase, quartz, and biotite <10 mm in 

diameter in a microcrystalline groundmass. Locally contains large hornblende 

phenocrysts <5 mm. Generally weathers as plates and slabs that are light 

yellowish brown to grayish white in color. The youngest pluton of this sequence, 

the Johnson Gulch Porphyry, has a zircon fission-track age of 43.1±4.3 Ma 

(Thompson and Arehart, 1990) and a recent U-Pb zircon age of 39.5±0.6 Ma 

(Kellogg and others, 2017) from adjacent areas outside the quadrangle. Previous 

work separated these individual stocks and plutons based on geographic location 

and local minor variations in petrology and appearance. Herein, these units are 

combined to illustrate the local extent of late Eocene magmatic activity 

expressed as sills and laccoliths intruded into the Paleozoic country rocks. Tweto 

(1974) originally described the Sacramento Gulch Porphyry as being cut by the 

Lincoln Porphyry (Tl), but crosscutting relationships east of Tennessee Pass 

demonstrate that the Lincoln Porphyry is older. Locally contains inclusions of 

White porphyry group (TKw) and Lincoln Porphyry (Tl), which further 

complicates the interpretation of structural and intrusive relationships. Similar 

approximately 40 Ma biotite K-Ar and zircon-sphene-apatite fission-track ages 

have been documented to the east, at the northern end of South Park (Bryant and 

Naeser, 1980; Bryant and others, 1981; Ruleman and others, 2011) 

Lincoln Porphyry (Eocene)—Exposed as a main sill body on Cooper Hill and the 

western flank of Buckeye Peak and Chicago Ridge in northeastern part of 

quadrangle. Gray to light pinkish-gray porphyritic monzogranite with 

phenocrysts of mainly orthoclase and quartz <1 cm long and rare biotite and 

hornblende (Behre, 1953). Unit is crosscut by the Gray porphyry group (Tg), but 

the age is problematic. Earlier biotite K-Ar ages of 62 Ma (Pearson and others, 

1962) and 64.6 Ma (McCalpin and others, 2012) are in conflict with a more 

recent biotite K-Ar age of 44.1±1.6 Ma (Marvin and others, 1989) and 

fission-track dates of 36.7±3.9 Ma and 48.6±6.6 Ma on apatite and 40.1±3.9 Ma 

and 41.5±3.7 Ma on zircon (Mach, 1992) on rocks of very similar composition 

and appearance. Based on geologic mapping by Tweto (1974) and the complex 

intrusive history of the region, which leads to difficulty in differentiating units, 

we interpret the older Paleocene ages as measurements of xenolithic bodies and 

inclusions of the older White porphyry group (TKw) within the Lincoln 

Porphyry. Region stippled on the west flank of Buckeye Peak indicates where 

strong secondary, shallow fluid-rock, deuteric alteration occurred

Undivided porphyries (Paleocene and Upper Cretaceous)—Generally white, red, 

yellow, and brown, highly altered and sheared porphyries of varying 

composition. Unit exposed within shear zones and faults associated with Late 

Cretaceous and Paleocene deformation along the western flank of Missouri Hill 

and within a dike along the southern flank of Mount Zion

White porphyry group (Paleocene and Upper Cretaceous)—White to yellowish 

brown, cryptocrystalline to aphanitic porphyritic rhyolite and monzogranite. 

Composed primarily of visible quartz and biotite <2 mm in a fine-grained 

groundmass of quartz, biotite, and plagioclase. Common accessory minerals 

include magnetite, zircon, apatite, and hornblende (Cappa and Bartos, 2007). 

Exposed along the western flank of Mount Zion as sills subparallel to bedding 

within the Minturn Formation (m). Intrusive body thickens to the southsoutheast into domed sills and small stocks in the Mount Sherman quadrangle 

(Bohannon and Ruleman, 2013). Unit includes the Pando Porphyry of 

Tweto (1951, 1974) with biotite K-Ar ages of 70 Ma (Pearson and others, 1962) 

and 71.8 Ma (Cunningham and others, 1994) and a more recent U-Pb zircon age 

of 64.1±0.9 Ma (Kellogg and others, 2017). 

PALEOZOIC SEDIMENTARY ROCKS

The Paleozoic section of sedimentary rocks crops out in the eastern part of the quadrangle. Most 

exposures are very limited except in the northeastern area within the Eagle River drainage and the 

western flank of Chicago Ridge and Mount Zion. Much of the detailed bedrock mapping is based 

on float on colluvial slopes and adit, prospect, and shaft data (see geologic map for locations) 

collected by Ogden Tweto during the years 1948–1953. Descriptions of units are from local 

exposures of units and extrapolated from concealed subsurface exposures (Tweto, 1974) and 

adjacent regions where exposure is more extensive (McCalpin and others, 2012; Bohannon and 

Ruleman, 2013)

Minturn Formation (Middle Pennsylvanian)—Predominantly light-gray to 

grayish-brown, fine- to coarse-grained arkosic sandstone interbedded with 

pebble-cobble conglomerate and calcareous shale. Calcareous shale and thin 

limestone beds occur towards the base of the formation. Weathers grayish-brown 

to reddish brown. Clasts in conglomerate are predominantly quartzite and chert. 

Section of the Minturn within quadrangle is mainly that of the “gray-brown 

facies” of Bohannon and Ruleman (2013), a section named for its diagnostic 

weathering and (or) alteration color around the Mount Sherman area to the east, 

but not diagnostic within this quadrangle. Tweto (1974) subdivided eight 

limestone members within the formation. Some of these members higher in the 

stratigraphic section are not within the quadrangle, but have been mapped in 

adjacent regions (Widmann and others, 2004, 2005; Widmann and others, 2006; 

McCalpin and others, 2012). The base of the Minturn Formation is defined as a 

coarse-grained sandstone and pebble conglomerate overlying the Belden 

Formation (b) black shale sequence. This coarsening upward sequence in the 

Minturn Formation, above the Belden Formation, was originally called the 

Weber Formation by Emmons (1886) and Behre (1953). In the northeast 

quadrant of the map, the 1–2 m-thick Jack 8 dolomite bed (J8) (Tweto, 1974) is 

a red-, green-, and light brown-mottled, coarse-grained dolomite with abundant 

chert and jasper grains occurring approximately 150 m above the base of the 

Minturn in the region. Thickness of the Minturn Formation is estimated to range 

from approximately 1,000 to 1,200 m within the quadrangle, but is unknown due 

to the profuse intrusive history and magmatic inflation of the region

Belden Formation (Middle and Lower Pennsylvanian)—Dark gray to black, 

laminated to massively bedded shale interbedded with thin-bedded gray to dark 

gray limestone and dolomite. Shale is commonly calcareous and (or) carbonaceous within the quadrangle. Limestone beds are locally fossiliferous and 

contain layers of fossil hash. Contains minor amounts of interbedded light gray 

to olive-gray, fine-grained, arkosic sandstone. Locally, shale layers contain plant 

fragments and petrified wood. Formation generally forms a subtle swale in 

topography within the stratigraphic section. Lies unconformably above the 

Mississippian Leadville Limestone (Ml) on an irregular, karst-erosional surface 

(Tweto, 1974) with moderate pre-existing topographic relief (<10 m), which 

contributes to the irregular thickness of the formation. Within the quadrangle, 

thickness varies due to extensive replacement and remobilization of shales during 

the Paleocene to Oligocene intrusive sequence, but is generally 20–30 m. The 

Belden Formation thickens substantially to the east and southeast to as much as 

360 m in the Jones Hill 7.5' quadrangle (Widmann and others, 2011) and 230 m 

in the Fairplay West 7.5' quadrangle (Widmann and others, 2006). Within the 

Climax 7.5' quadrangle (McCalpin and others, 2012), the Minturn and Belden 

Formations were mapped as a single unit

Leadville Limestone (Lower Mississippian)—Medium-gray, micritic limestone and 

pitted dolomite grading down section into bluish-black, fine-grained dolomite 

containing abundant well-rounded and fragmented black chert pebbles and 

cobbles. Bedding is generally massive and irregular. Brecciated zones are found 

throughout the unit and are interpreted as evidence for paleokarst activity 

(Maslyn, 1977; Beaty and others, 1990). Grades down section to a basal 

yellowish-brown to white, thin-bedded, discontinuous-bedded sandstone and 

quartzite with limestone rip-up clasts called the Gilman Sandstone member of the 

Chaffee Group (Tweto and Lovering, 1977; Kirkham and others, 2012). 

Formation unconformably overlies the Devonian Chaffee Group (Dc). 

Thickness ranges from 40 to 50 m

Chaffee Group, undivided (Upper Devonian)—Includes the Dyer Dolomite and 

Parting Sandstone of Chronic (1964) described below. Units mapped as a group 

where exposure and structural relationships obscure the stratigraphy. Total 

thickness ranges from 30 to 50 m

Dyer Dolomite—Fine-grained, sparry, thin- to massive-bedded dolomite. 

Generally, unit grades from light gray to dark gray and weathers to a mottled 

yellowish-gray to brownish-gray color. Locally contains thin lenses (<5 mm) of 

shale and (or) chert. Considered part of the “Blue Limestone” at Leadville by 

Tweto (1974). Conformably grades from the underlying Parting Sandstone (Dcp) 

(Chronic, 1964). Thickness 20–30 m

Parting Sandstone—White to light-gray, fine- to medium-grained, well-rounded, 

well-sorted quartzite and sandstone with minor interbeds of dolomitic sandstone. 

Finer-grained dolomitic sandstone beds weather a reddish-yellow brown and 

quartzite layers weather bright white. Typically contains a coarse pebble 

conglomerate at the base. Locally contains thin layers and lenses of shale and 

(or) chert. Thickness varies, but is generally 10–20 m

Manitou Dolomite (Lower Ordovician)—Light-yellowish-gray to dark-gray, thin- to 

thick-bedded sandy dolomite and dolomite. Weathers yellowish- to 

reddish-brown and commonly has rough, angular surfaces (Tweto, 1974). 

Commonly contains whitish-gray to black laminated chert nodules, blebs, and 

stringers. The lowermost 1–3 m have been called the “red cast beds” (Emmons, 

1886) and were formerly considered the upper member of the Peerless Formation 

(Behre, 1953). However, more recent paleontologic investigations place these 

beds within the Taylor Pass Member of the Manitou Dolomite (Myrow and 

others, 2003). The Taylor Pass Member section is characterized by thick (about 

1 m), tabular dolomite beds with oxidized red spots that are <0.5 cm in diameter. 

Locally contains crinoids, gastropods, echinoderms, nautiloids, and trilobite 

fragments (Houck and others, 2012). The Manitou Dolomite pinches out to the 

north towards Tennessee Pass where it is unconformably overlain by the 

Devonian Chaffee Group (Dc). Thickness averages between 30 and 40 m

Dotsero Formation (Upper Cambrian)—Interbedded fine- to medium-grained 

sandstone grading upward to dolomitic sandstone and silty, sandy dolomite. 

Generally weathers to a reddish-brown and purple-brown color. Formerly 

mapped as the Peerless Formation (Behre, 1953; Tweto, 1974). Beds within the 

lower, more quartzose section are tabular and typically 0.5–1.0 m in thickness. 

Beds thin upwards into the more dolomitic section and are generally wavy, 

subparallel, and range from a few centimeters to 25 cm in thickness. Overall 

thickness is 20–30 m

Sawatch Quartzite (Upper Cambrian)—Fine- to coarse-grained, medium- to 

thick-bedded, white, light-yellowish-brown, and reddish-brown quartzite and 

finer-grained sandstone unconformably overlying Mesoproterozoic and 

Paleoproterozoic rocks on a planar to low-relief surface (Tweto, 1974). 

Sandstone is locally glauconitic. Generally moderately to well-sorted, and grains 

are subrounded to rounded. Typically has a 10 cm–1 m-thick basal conglomerate 

with well-rounded, quartz-pebble clasts. Beds range in thickness from 1 cm to 

1 m and are distinguished by variations in resistance and color. Thickness ranges 

from 30 to 40 m

PROTEROZOIC IGNEOUS 

AND METAMORPHIC ROCKS

Hornblende diorite dike (Mesoproterozoic?)—Gray to dark gray to green, 

medium-grained, hornblende-rich diorite dikes on the north side of Missouri Hill. 

Truncates Paleoproterozoic host-rock foliations. Hosts metalamprophyres and 

St. Kevin batholith within the Homestake Reservoir region to the west

St. Kevin Granite (Mesoproterozoic)—Medium- to coarse-grained, gray to 

light-pinkish-gray and pinkish-brown, euhedral equigranular to porphyritic, 

massive to locally weakly foliated biotite-muscovite monzogranite, with local 

gradational and facies changes to granodiorite and other textural variations 

(Pearson and others, 1962; Tweto and Pearson, 1964; Tweto, 1974, 1987). The 

main batholith is characterized by a central region of coarse-grained trachtytic 

monzogranite grading outward into medium-grained monzogranite and 

eventually to fine-grained, foliated monzogranite and granodiorite with 

seriate-to-porphyritic texture commonly having Carlsbad twinning in aligned 

microcline phenocrysts. Within the map area, medium-grained, euhedral 

monzogranite is the common phase of the main plutonic body. Batholith has been 

previously assigned to the Silver Plume intrusive event (Stark and Barnes, 1935; 

Behre, 1953). Rb-Sr isochron age is 1,390±60 Ma (Pearson and others, 1962), 

and a more recent U-Pb age from outside the quadrangle is 1,444±15 Ma 

(Moscati and others, 2012) 

Pegmatite and aplite (Mesoproterozoic? and Paleoproterozoic?)—Fine- to 

coarse-grained to megacrystalline, white to light-pink and red, inequigranular 

quartz-feldspar-biotite-muscovite rock that intrudes all metamorphic and igneous 

Proterozoic rocks in the quadrangle. Biotite is the predominant mica. Forms 

zoned, linear dikes and veins typically with fine-grained, “chilled,” aplitic 

textures formed towards the margins and within latest-phase intrusions. Also 

forms concentrated blebs, pods, and stringers as much as 10 m in width. 

Pegmatites within and proximal to the St. Kevin batholith generally contain 

sparse black tourmaline and beryl (Tweto, 1974). Pegmatite and aplite are 

similar in composition, but aplite is generally light pinkish-brown to gray, fineto medium-grained, and leucocratic, which can be similar in appearance to 

Mesoproterozoic St. Kevin Granite (Ygs)-associated rocks, especially the 

finer-grained, marginal phases. Crosscutting relationships indicate that pegmatite 

and aplite are associated with late-stage intrusive processes and occur within 

both the Paleoproterozoic Routt Plutonic Suite (about 1,700 Ma) and 

Mesoproterozoic Berthoud Plutonic Suite (about 1,400 Ma) of Tweto (1987). 

Pegmatite and aplite rocks mapped within the quadrangle appear to be undeformed

Monzogranite, granodiorite, biotite gneiss and schist, and pegmatite, undivided 

(Mesoproterozoic and Paleoproterozoic)—Medium-gray to black, 

grayish-pink, light-pinkish-brown to light-brown, fine- to coarse-grained biotite 

gneiss and schist profusely intruded by phases of predominantly units Ygs and 

YXp. Mineralogy is generally consistent with the parent rock and younger 

intrusive complexes consisting of biotite, hornblende, plagioclase, microcline, 

and quartz. Unit is mapped around the peripheries of the St. Kevin batholith and 

associated stocks and other textural and (or) gradational phases where the 

intrusive component and country rock are in relatively equal volumetric 

proportions. Exposures show complicated intrusive relationships and assimilation 

of country rock, which consists predominantly of unit Xb in this region. 

Ptygmatic folding, boudinage, and sigmoidal structures are commonly found. 

Xenolithic bodies have diffuse boundaries and locally internal, intense ptygmatic 

folding. Unit was mapped in adjacent regions to distinguish profusely intruded 

country rock from areas of more distinct metamorphic and igneous rocks 

(Ruleman and others, 2011; Bohannon and Ruleman, 2013). Due to complex 

intrusive and petrologic relationships associated with plutonic metamorphism 

and assimilation of the country rock, unit is commonly confused with other 

“migmatitic” rocks in the region that were formed by older regional, burial 

dynamothermal metamorphism

Biotite gneiss (Paleoproterozoic)—Light-gray to black, fine- to coarse-grained, 

weakly foliated to strongly foliated and layered gneiss and schist. Mineralogy 

composed chiefly of quartz, plagioclase, microcline, biotite, and hornblende. 

Sillimanite is common. Common accessory minerals include rutile, sphene, 

apatite, garnet, and zircon. Locally, garnets are as much as 1 cm in diameter. 

Unit Xb contains minor amounts of interlayered amphibolite, hornblende gneiss, 

quartzite, and calc-silicate rock, especially within the northwest part of the 

quadrangle. Rocks are predominantly of metasedimentary and metavolcanic 

origin (Tweto, 1987). Correlated with similar metasedimentary rocks within the 

adjacent Gore and Front Ranges, with detrital zircon U-Pb ages ranging from 

approximately 1,785 to 1,750 Ma (Kellogg and others, 2008, 2011). Wallace (1993) 

concluded that the rocks were deposited between 1,770 and 1,700 Ma and 

metamorphosed between 1,750 and 1,670 Ma

Qgb

Qgby

Qtb

Qgpb

Qtpb

Qd

Thl

Tr

Trp

Tg

TKu

TKw

m

J8

b

Ml

Dc

Dcd

Dcp

Om

d

s

Yhd

Ygs

YXp

YXmr

Xb

af

Qa

Qac

Qls

Qdf

Qgp

Qtp

SCALE 1: 24 000

1 1/ 2 0 1 MILE

1000 0 1000 2000 3000 4000 5000 6000 7000 FEET

1 .5 0 1 KILOMETER

Base from U.S. Geological Survey, Leadville North, Colo., 1994

North American Datum 1927 (NAD 27). Projection and 10,000-foot ticks:

Colorado coordinate system, central zone (Lambert conformal conic)

1,000-meter Universal Transverse Mercator ticks, zone 13

Surficial geology mapped by Cal Ruleman 2011−2014. Bedrock geology and

concealed structure based on Tweto (1974). Sample collection was with Marc W. 

Caffee and Cody M. Mason during 2011 and 2014 field seasons

Dark gray tunnels, prospects, and mine shaft locations modified from Tweto (1974)

GIS database and digital cartography by T.R. Brandt

Publishing support provided by Denver Publishing Service Center

Edit and cartographic layout by Anya V. Hess and L.J. Binder

Manuscript approved for publication February 23, 2018

CONTOUR INTERVAL 40 FEET

NATIONAL GEODETIC VERTICAL DATUM 1929

COLORADO

MAP LOCATION APPROXIMATE MEAN

DECLINATION, 2017 TRUE NORTH

MAGNETIC NORTH

9°

U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigations Map 3400

Geologic Map of the Leadville North 7.5' Quadrangle, Eagle and Lake Counties, Colorado

By

Chester A. Ruleman,1

 Theodore R. Brandt,1 Marc W. Caffee,2 and Brent M. Goehring2 

2018 1

U.S. Geological Survey 

2

Purdue University, Lafayette, Indiana

ISSN 2329-132X (online)

https://doi.org/10.3133/sim3400

For more information concerning this publication, contact

Center Director, USGS Geosciences and Environmental Change Science Center

Box 25046, Mail Stop 980

(303) 236-5344

ScienceBase GIS files available at https://doi.org/10.5066/F7DR2TRG

Report digital files available at https://doi.org/10.3133/sim3400 or https://pubs.usgs.gov/sim/3400

Suggested citation: Rulman, C.A., Brandt, T.R., Caffee, M.W., and Goehring, B.M., 2018, Geologic map 

of the Leadville North 7.5’ quadrangle, Eagle and Lake Counties, Colorado: U.S. Geological Survey 

Scientific Investigations Map 3400, 1:24,000, https://doi.org/10.3133/sim3400

This map or plate is offered as an online-only, digital publication. Users should be aware 

that, because of differences in rendering processes and pixel resolution, some slight 

distortion of scale may occur when viewing it on a computer screen or when printing it on 

an electronic plotter, even when it is viewed or printed at its intended publication scale.

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 may 

contain copyrighted materials as noted in the text. Permission to reproduce copyrighted 

items must be secured from the copyright owner.

This database, identified as SIM 3400, has been approved for release and publication by the 

U.S. Geological Survey (USGS). Although this database has been subjected to rigorous 

review and is substantially complete, the USGS reserves the right to revise the data 

pursuant to further analysis and review. Furthermore, it is released on condition that neither 

the USGS nor the U.S. Government may be held liable for any damages resulting from its 

authorized or unauthorized use.

Although these data have been processed successfully on a computer system at the U.S. 

Geological Survey (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.

Divisions of Quaternary, Neogene, and Paleogene time

used in this report1

Period or

subperiod

Epoch Age

Quaternary

Holocene 0–11.5 ka

late 11.5–132 ka

Pleistocene middle 132–788 ka

early 788 ka–2.588 Ma

Neogene

Pliocene 2.588–5.332 Ma

Miocene 5.332–23.03 Ma

Oligocene 23.03–33.9 Ma

Paleogene Eocene 33.9–55.8 Ma

Paleocene 55.8–65.5 Ma

1

Ages of time boundaries are those of the U.S. Geological Survey Geologic Names 

Committee (2010) except those for the late-middle Pleistocene boundary and middleearly Pleistocene boundary, which are those of Richmond and Fullerton (1986). Ages 

are expressed in ka for kilo-annum (thousand years) and Ma for mega-annum 

(million years).

International System of Units to U.S. customary units 

CONVERSION FACTORS

Multiply By To obtain

0.03937 inches (in)

3.281 foot (ft)

0.6214 mile (mi)

Length

millimeter (mm)

meter (m)

kilometer (km)

U.S. customary units to International System of Units

Multiply By To obtain

0.3048 meter (m)

Length

foot (ft)

A

A'