18.4 19.6 22.1 24.7 17.7...
TRANSCRIPT
PETROLOGIC, TECTONIC, AND GEOMORPHIC FEATURES OF CENTRAL COLORADO
R. C. EpisColorado School of MinesGolden, Colorado 80401
G. R. Scott, R. B. Taylor, W. N. SharpU. S. Geological SurveyDenver, Colorado 80225
Road Log
Mileage
0.0
0.2
3.0
4.8
8.8
17.7
Hilton Hotel, 16th St. and Court
Place, Denver. Proceed on Court
Place to 15th St.; turn left on
15th St. and proceed to Broadway
Blvd.
Turn right (south) on Broadway
Blvd.
Turn left to 1-25 (Valley
Highway) south.
University of Denver on right.
Front Range, forming skyline on
right (west), is composed mostly
of Precambrian granitic rocks
and associated schists and
gneisses. High peak at 3:00,
Mt. Evans (elev. 14,264 ft.;
4,346 m.), rises above general
level. Southward, the range is
truncated by a relatively smooth
surface of late Eocene age. On
east flank of range, broad
channels in the late Eocene sur-
face can be recognized. Some
boulder alluvium is preserved in
modified segments of these
channels, and is probably best
correlated with the Ogallala
Formation (Miocene-Pliocene) of
the plains.
Waviness of pavement for several
miles is result of swelling clays
in Denver Formation and in B
horizons of pre-Bull Lake soils
on pediments.
Mileage
18.4
19.6
22.1
24.7
28.6
Southern outcrops of Denver
Formation (Late Cretaceous-
Paleocene) overlain by northern
exposures of Castle Rock
Conglomerate (Oligocene).
Dawson Arkose (Late Cretaceous-
Paleocene) near here intertongues
with andesitic Denver Formation.
Outcrops of Denver Formation 1
mi. (1.6 km) to the west contain
the southernmost known andesitic
mudflow detritus.
Red weathered soil zone at top
of tongue of Denver Formation
overlain by Dawson Arkose in
roadcut on left.
Pikes Peak (elev. 14,109 ft.;
4,298.5 m.) straight ahead on
skyline at 1:00.
Smooth surface on skyline to
right, on top of Rampart Range,
is a late Eocene erosion surface.
Devil's Head is an erosional
remnant that rises above the sur-
face. Surface is cut on Pre-
cambrian Pikes Peak Granite
(1.05 b.y.) which generally
exhibits a deeply weathered,
disaggregated zone of grus.
Castle Rock. The small butte
northeast of the town is the
type locality for the Castle
Rock Conglomerate. The Castle
Rock Conglomerate contains frag-
'gS?J3-y&£\viMtSSl' v-*'_/««cI.
COLORADOSPRINGS
-39'
-38'
Figure 1. Composite of Army Map Service plastic relief maps (2-degree quadrangles) showingroute of field trip. Numbers refer to stops indicated in road log. (See also fig. 1» P1(j0.)and others, paper 25, this volume, for names of major geomorphic elements of central Colors
302
Time Formation
Holocene
Pleistocene
Pliocene
Miocene
Oligocene
Paleocene
Cretaceous
Jurassic
Iria.q.q i r-
Permian
Pinedale
Bull LakeIllinoian or SangamonYarmouth or Kansan
Aftonian or Nebraskan
Late Cretaceous
Early Cretaceous
Late Jurassic
Pennsylvanian
Mississippi an
Qrdovician
Cambrian
Precambrian
1.05 b.y.
1.45 b.y.
1.72 b.y.
> 1.72 b.y.
Post-Piney Creek alluviumPiney Creek Alluvium
Broadway AlluviumLoessLouviers AlluviumSlocum AlluviumVerdos AlluviumRocky Flats AlluviumNussbaum Alluvium
Gravel at Divide
Castle Rock ConglomerateWall Mountain Tuff
Denver Formation _. „ . , , , .Arapahoe Formation Dawson ̂ °™̂ lon (Arkose>
2. t 0 0 0Laramie Formation 250'Fox Hills Sandstone 250'Pierre Shale 3,150 - 4,800'Niobrara Formation 550'Carlile' Shale ~\Greenhorn Limestone \ 300'Graneros Shale — /Dakota Sandstone 100'Purgatoire Formation 200'Morrison Formation 225'Ralston Creek Formation 20'Lykins Formation 180'Lyons Sandstone 700 - 800'Fountain Formation 4,400"Glen Eyrie Shale Member
Leadville Limestone 130'Williams Canyon LimestoneManitou Limestone 185'Peerless Dolomite 40'Sandstone dikesSawatch Sandstone 25'
Pikes Peak GraniteSyenogabbro
Cripple Creek Granite
Boulder Creek Granodiorite
Feldspathic gneiss
Figure 2. Generalized stratigraphy of central Colorado.
Mileage
30.7
Figure 3. Generalized composite stratigraphyof the Thirtynine Mile volcanic field.
ments of the Wall Mountain Tuff
(35-36 m.y.) and various por-
phyritic volcanic rocks of inter-
mediate composition that were
probably derived from the Thirty-
nine Mile volcanic field. A
remnant of the ash-flow tuff
also is on the Rampart Range
about 3 mi. (5 km) south of the
South Platte River, and several
outcrops occur south of Devil's
Head.
Most of mesas at 10-12:00 are
capped by a silicic ash-flow
tuff dated at 34.8+1.1 m.y.
(Izett, and others, 1969). The
I06'00'
Sedimentary rock* of Pliocene to early Miocene age
Volcanic and intrusive rock* of early Miocene to Ollgocene *|«
Sedimentary and igneou* rock* of Eocene to Ordovlcian •»«
Crystalline rock> of Cambrian and Preeambrian age
Contact
Faul t—Sol id where JUeogene movement can be demonstrated; do"where concealed. Bar and ball on downthrown .id*
Folds—Solid where Neogene can be demonstratedAntic l ine
Sync l ine
POINTS OF REFERENCE
1. 1C* Pasa fault2. Manltou Park graben3. Divide4. Cripple Creek5. Cuffey6. Thirtyone Mile Mountain7. Currant Creek fault6. De Weese Plateau9. Tanner Peak10. Locke Park
11. Uixaon Divide12. Greenhorn Mountain13. Promontory Divide
14.15.It.17.18.19.20.21.
UtsUciMcCAlvCotPonH»rFour
cllfft f"""clifltu c Mount»ln
r do f«ul'B wood P«»k
Figure 4. Geologic map showing rocks and Neogene structural features of central Co ^Compiled from mapping by R. B. Taylor, G. R. Scott, R. C. Epis, R; A. Wobus and rrolished sources (after Taylor 1975).
304
Mileage
33.6
34.0
37.8
40.7
42.6
45.0
48.2
49.4
tuff probably is the distal end
of the Wall Mountain Tuff of the
Thirtynine Mile field, west of
the Rampart Range, (for strati-
graphy, see fig. 3.)
Dawson Butte, type locality of
Dawson Formation at 2:00.
Yellowish Broadway Alluvium of
Pinedale age on left in terrace
scoured by 1965 flood.
Torrential rainfall in 1965
caused the light-colored washouts
seen at 9:00. Channel of Plum
Creek was flooded and deeply
scoured; the flood caused major
damage from Castle Rock north-
ward through Denver. Sandstone
cap of mesa is Dawson Arkose,
overlain by Wall Mountain Tuff.
Good outcrops of Dawson Arkose
in roadcuts to east.
At 3:00, good view on skyline of
late Eocene surface on Rampart
Range. At 3-5:00, red stained
Pikes Peak Granite along Rampart
Range fault.
Dawson Arkose in roadcuts on
west; view of Pikes Peak at 1:00
late Eocene surface is clearly
defined on Rampart Range below
peak. (fig. 5)
Air Force Academy at 12:00;
Cheyenne Mountain at 11:00;
pediments of three ages extend
eastward from Rampart Range;
highest is capped by Rocky Flats
Alluvium, intermediate by Verdos
Alluvium, and lowest by Slocum
Alluvium.
Salmon colored monuments of
Dawson Arkose at 3:00 are fault-
ed against Pikes Peak Granite
along Rampart Range fault.
Townsite of Monument is at this
locality.
White sandstone butte at 3:00 is
Cathedral Rock, composed of
Dawson. Large treeless flatiron
Figure 5. Oblique aerial view southwardalong east frontal fault-line scarp of theRampart Range, showing Pikes Peak (rightskyline) and the flat, late Eocene surfaceon the Rampart Range uplifted from the gen-eral learel of the western Great Plains (left)The surface on the Rampart Range is overlainby patches of Wall Mountain Tuff and thegravel of Divide.
Mileage
55.0
56.5
58.0
above it is a sliver of Manitou
and Sawatch Formations along
Rampart Range fault. Black
Forest, on skyline on left, is
underlain by Dawson Arkose.
Fine-grained pediment gravel on
both sides of 1-25 is Slocum
Alluvium reworked from Dawson
Arkose. Dawson Arkose, in turn,
was derived from Pikes Peak
Granite. Pikes Peak Granite
produces few stones larger than
1 in. (2.5 cm) in diameter.
Highway follows Monument Creek
for many miles.
North entrance to Air Force
Academy; academic area and chapel
at 3:00.
Air Force Academy stadium at
3:00. Rampart Range fault bounds
east front of Rampart Range,
bringing Dawson Arkose against
Pikes Peak Granite for a long
distance. Fault cuts Verdos
Alluvium of Kansan or Yarmouth
age at south end of Academy.
Valley of West Monument Creek at
:. .VsSsft'J
Mileage Mileage
59.4
60.7
62.0
62.6
63.4
63.8
64.6
3:00. Streams depositing gravel
at Divide followed this valley
to plains in Miocene-Pliocene (?)
time.
The two conspicuous scars on the
mountain front are two quarries
in lower Paleozoic limestone
that is used for concrete ag-
gregate. The northern is the
Pikeview quarry, chiefly in
Williams Canyon Limestone; the
southern is the Castle quarry,
chiefly in Manitou Limestone.
Sand dunes among trees on left;
some large barchans are develop-
ed here. The valleys in the
Academy contain ventifacts.
Light gray Dawson Arkose bed
along Monument Creek, low in
right middle ground, is same as
arkosic sandstone at Pulpit Rock
to south.
Junction of south entrance to
Air Force Academy with 1-25.
For several miles, highway tra-
verses Slocum Alluvium of
Illinoisan or Sangamon age.
Pediments on right, capped by a
housing development, are covered
by Verdos Alluvium.
Good outcrops of lower andesitic
part of Dawson Arkose (Cretaceous)
on left.
Pulpit Rock at 10:00. Outcrop
of Cretaceous and Paleocene
arkosic Dawson overlying
Cretaceous andesitic Dawson,
which in turn overlies Laramie
Formation.
Monument Creek.
Outcrop of Laramie in roadcut on
right; good view of Cheyenne
Mountain and late Eocene surface
on top at 11:30. Cheyenne
Mountain houses a large under-
ground NORAD installation; Ute
Pass reverse fault trends along
66.1
68.5
69.5
70.2
71.0
71.9
73.0-73.4
73.7
74.0
74.5
its eastern base with dips as
low as 30° to the west. A large
rockfall, probably triggered by
an earthquake in Yarmouth time,
covers about 3 sq. mi. (7.5 km^)
of Pierre Shale at the east base
of the mountain.
Large pediment remnant, "The
Mesa," on right, is covered by
Verdos Alluvium of Kansan or
Yarmouth age.
Colorado College on left.
Center of Colorado Springs on
left. Downtown area lies on
Louviers Alluvium of Bull Lake
age .which overlies Cretaceous
Pierre Shale.
Turn west at exit 60, bypass to
Manitou Springs, U.S. Hwy. 24.
Tailings dump of former Golden
Cycle Gold Mill at 9:00; tail-
ings are now being eroded and
transported into Fountain Creek;
former millsite is at chimney.
Old one-half, round house of
Colorado Midland RR; now houses
Van Briggle Pottery.
Permian Lyons Sandstone; Permian
and Triassic(?) Lykins Formation;
Jurassic Ralston Creek Formation;
Morrison Formation^ Cretaceous
Dakota Sandstone; Graneros Shale;
Greenhorn Limestone; Carlile
Shale; and Fort Hays Limestone;
and Smoky Hill Shale Members of
Niobrara Formation on left. Beds
are vertical or overturned owing
to Rampart Range fault which
trends south-southeast through
Smoky Hill Shale Member.
Permian Lyons Sandstone flatirons
in Garden of the Gods at 3:00.
Grassy patch on skyline at 1:00
is Nussbaum Alluvium, oldest
Quaternary alluvium in area.
Cross Fountain Creek; type area
of Fountain Formation (Permian
I
Mileage Mileage
and Pennsylvanian) ahead.
75.2 Fountain Formation, faulted
against Precambrian rocks along
Ute Pass fault at about 9:00;
Precambrian rocks are Boulder
Creek Granodiorite and meta-
sedimentary gneiss in the fault
zone and Pikes Peak Granite
across the fault to the south-
west. Miarolitic cavities in
the Pikes Peak at Crystal Park
have produced beautiful crystals
of smoky quartz, amazonstone,
and rare minerals. Cliff dwell- 83.3
ings on right in Fountain
Formation.
75.7 Williams Canyon cut in Williams
Canyon Limestone, Peerless
Dolomite, Manitou Limestone, 84.0
Sawatch Sandstone, and Pre-
cambrian gn5iss. 84.3
76.3 View of unconformity between
Sawatch Sandstone (Cambrian) and
Pikes Peak Granite on both sides 84.6
of highway. Sawatch dips steep-
ly off southeast flank of 85.5
Rampart Range into Manitou
embayment. Manitou Limestone
contains numerous collapse 86.2
structures due to solution re-
moval of rock north and west of
Manitou Springs.
78.2-79.2 Large Quaternary landslide on 87.1
left. Slide came from Pikes
Peak Granite in southwest valley 88.7
wall and forced Fountain Creek
against its north valley wall,
where it cut a new channel into
Pikes Peak Granite. Note large
boulders of Pikes Peak Granite 89.1
which possibly were corestones
before slide. Highway follows
Fountain Creek for several miles. 89.3
80.0 Cascade. Junction with road to
North Pole and Pikes Peak. Stay 89.5
on U. S. Hwy. 24.
60.5 Fan gravel in cuts on right
apparently was deposited behind
a dam created by a large land-
slide; gravel is underlain by
Pikes Peak Granite. Ute Pass
fault parallels this valley.
The steep slopes along the sides
of the valley pose a possible
future landslide problem,
especially in the event of an
earthquake. The valley walls
are less stable than typical
granite because of crushing
along the fault.
Another large Quaternary land-
slide on right. It also probably
dammed Fountain Creek and caused
the accumulation of fan gravel
and lake silt.
Valley fill dammed behind large
landslide.
Turnoff to Green Mountain Falls
and Chipita Park; stay on U. S.
Hwy. 24.
Sharp ridge at 12:00 is large
sandstone dike.
Enter Teller County. This is
southeast end of Ute Pass-
Manitou Park graben.
Ordovician Manitou Limestone
quarry on valley wall at 3:00.
Heavily forested ridge on left
is Pikes Peak Granite.
Fountain Formation on right in
roadcuts.
Woodland Park. Late Eocene
erosion surface below Pikes Peak
along tree-covered flat in lower
middle ground to left is cut on
Pikes Peak Granite.(fig. 6)
Junction of Colo. Hwy. 67 with
U. S. Hwy. 24. Stay on U. S.
Hwy. 24.
Fountain overlain by Quaternary
fan gravel in roadcut on right.
Fault contact between crushed
and altered Pikes Peak Granite
and Pennsylvanian and Permian
307
Figure 6. Oblique aerial view northeastwardof Miocene(?) alluvium (gravel of Divide)along grassy area in paleochannel on upthrowneast side of Manitou Park graben east ofWoodland Park. Paleochannel was incised onlyseveral to a few tens of meters below border-ing, tree-covered late Eocene surface to leftand right.
Mileage
90.0
90.3
90.6
91.8
93.0
Fountain Formation along Ute
Pass fault zone.
Crushed and altered horst-like
block of Pikes Peak Granite in
Ute Pass fault zone. Fault
trends southeastward. At 12:00
late Eocene surface visible on
skyline.
Cambrian sandstone dike on left
and right in Ute pass fault zone.
Good exposure of gravel at
Divide (Miocene-Pliocene) in
roadcuts.
View at 4:00 of Devil's Head,
which stands above the late
Eocene surface on Rampart Range
and is composed of Pikes Peak
Granite; grassy area in fore-
ground is gravel at Divide,
(fig. 7)
STOP 1. Fault between Pikes
Peak Granite and gravel at
Divide. Gravel is largely com-
posed of andesite and other
rocks from Thirtynine Mile
volcanic field and phonolite
from Cripple Creek volcanic
center. It also contains frag-
ments of Wall Mountain Tuff and
Precambrian rocks, especially
Figure 7. View northwestward near Divide ofthe late Eocene surface overlain by thinunits of gravel of Divide in the smooth,grassy areas.
Mileage
94.6
95.6
96.1
96.5
97.0
Pikes Peak Granite. Stones are
somewhat weathered. Fault extends
about 1 mi. (1.6 km) east and
west from this outcrop. Phono-
lite at Cripple Creek was dated
by Obradovish (U.S.G.S.) as
27.3-29.3 m.y.
Clayey facies of gravel at
Divide.
On left is depot of the Colorado
Midland RR labeled "Murray's
Junction."
Divide. Junction U. S. Hwy. 2*
and Colo. Hwy. 67. Turn left.
Colo. Hwy. 67 stays on gravel at
Divide for about 3 mi. (5 km)•
At Divide the north-trending Oil
Creek fault (up on the east)
dammed the stream carrying the
gravel and caused the gravel to
spread widely to the north and
south.
Excellent view of Sawatch Range
to the west.
View of the late Eocene
at 4:30. Small knob at 4:30
Signal Butte, a rhyodacite
protruding through the surf»c
Devil's Head, composed of PI
Peak Granite, rises above the
308
Mileage
99.0
99.7
100.0
100.3
101.6
102.1
10S.S
late Eocene surface that caps
the Rampart Range, on skyline at
6-8:00. The southern segment of
the surface on the Rampart Range
is faulted up about 1,000 ft.
(306 m.) by the Ute Pass fault.
Good outcrops of gravel at
Divide in roadcuts contain
phonolite. Rhyolite Mountain at
12:00 is composed of phonolite
of Cripple Creek.
South end of gravel at Divide.
Large quarry in grus of Pikes
Peak Granite.
Oil Creek fault shows well in
roadcut on right. For the next
8 mi. (13.3 km) highway is in
Pikes Peak Granite, which for
much of the distance is badly
sheared and altered along a
major fault zone extending south-
southeastward from Fourmile
Creek. The late Eocene surface
has been faulted up along this
and other subparallel faults
from the general level of Divide
to the level of Gillett, a dis-
placement of about 1,000 ft.
(306 m). Additional faults to
the west drop the late Eocene
surface down another 400-500 ft.
(122.4-153 m.) to the general
level of the Florissant Basin.
Highway crosses Fourmile Creek
and follows one branch of fault
zone southward.
Roadcuts through sheared and
altered Pikes Peak Granite along
fault zone. Good view of north
shoulder of Pikes Peak at 12:00.
Old railroad tunnel. Road fol-
lows old railroad bed for most
of distance from Divide to
Cripple Creek. This was one of
three railroads serving Cripple
Creek and Victor. The others
came up Phantom Canyon from
Mileage
106.5
107.1
107.7
108.2
108.5
109.5
109.8
111.1
111.6
111.9
Florence, and up the Corley
Mountain Highway (Gold Camp Road)
from Colorado Springs.
STOP 2. Quarry in Pikes Peak
Granite showing grus and core-
stones .
Late Eocene surface across valley
to right.
Coarse colluvium on slopes of
Pikes Peak on left.
Cross large Oil Creek fault.
Valley of Oil Creek, under
highway, was glaciated. Pikes
Peak had about 10 glaciers on it
during Bull Lake and Pinedale
times.
Highway comes out on late Eocene
surface. Small phonolite plug
cutting Pikes Peak Granite at
9:00.
On left is large Bull Lake
terminal moraine. During a
torrential rain in 1965, a dam
for a water-supply lake for
Cripple Creek broke, distributing
huge boulders for many miles
down West Beaver Creek and
damaging a siphon in the
Colorado Springs water-supply
system. The dam was founded on
loose till. Trachyte Knob
southeast of curve is another
phonolite plug with associated
dike.
Old townsite of Gillett on late
Eocene surface (9,935 ft.;
2,980 m.). Stay on Colo. Hwy.
67, which makes a sharp curve to
right.
Rhyolite Mountain at 3:00 is
composed of breccia and phonolite
of Cripple Creek.
Pits in grus of Pikes Peak
Granite on right side of road.
Approach contact of Pikes Peak
Granite and andesitic breccia of
Cripple Creek (mid-Tertiary).
309
Mileage
112.0
112.7
113.9
114 .9
115.4
Mileage
Intense hydrothermally altered
granite can be seen in roadcuts
on left.
Contact of breccia of Cripple
Creek and Pikes Peak Granite.
Turn left on gravel Range View
Road to Victor; view of Cripple
Creek townsite below to right.
Junction with road to Colorado
Springs; stay right. South
flank of Pikes Peak at 8-9:00 is
cut by glaciated valleys.
Contact of Boulder Creek
Granodiorite within breccia of
Cripple Creek.
STOP 3. Observation point on
Range View Road (alt. 10,500 ft.;
3,150 m.). Excellent panoramic
view north, west, and south of a
large part of the southern Rocky
Mountains. From north to south
on skyline, we see: Mount Evans
in the Front Range; Mosquito
Range and South Park; Sawatch
Range; Sangre de Cristo Range;
Wet Mountain Valley; Greenhorn
Mountain and the Wet Mountains.
In immediate foreground are seg-
ments of the Cripple Creek
volcanic pile, including pro-
minent phonolite plug of Mount
Pisgah due west. Principal
eruptive centers of the Thirty-
nine Mile volcanic field (Guffey,
Thirtyone Mile Mountain, and
Waugh Mountain) and associated
layered volcanic rocks lie in
the middle distance. Excellent
view of the late Eocene-pre-
volcanic surface beneath Badger
Flats; South Park; ThirtynineMile volcanic field; Cripple
Creek volcanic pile; Wet Mount-
ain Valley; and along the crest
of the Wet Mountains. View
illustrates faulting of the
erosion surface upward on east
116.8
117.8
118.2
118.6
119.3
120.3
121.3
side of Fourmile Creek from be-
neath the Thirtynine Mile
volcanic field to the base of
Mount Pisgah. Continue south-
ward on Range View Road. Over
the next 2.4 mi. (4 km), Range
View Road passes by the Inde-
pendence, Portland, and Ajax
mines, among the largest in the
Cripple Creek district, (fig.8)
Old townsite of Goldfield at
lower left. Nipple Mountain,
conical peak of phonolite at
12:00, rises above the late
Eocene surface. Greenhorn
Mountain, at top of Wet Mount-
ains, is visible on skyline just
left of Nipple Mountain.
Enter Victor (alt. 9,693 ft.;
2,908 m.), the home of Lowell
Thomas! Junction with Colo. Hwy.
67. Turn right 2 blocks, then
left, then right, on highway to
Cripple Creek.
Coarsely porphyroblastic grano-
diorite of Boulder Creek type
(1.72 b.y.). Straub and Grouse
Mountains in middle distance to
the southwest contain Wall
Mountain Tuff, Tallahassee Creek
Conglomerate and ThirtvnineMile Andesite, interlayered with
phonolite and faulted up about
1,500 ft. (450 m.) from the gen-
eral level of High Park to the
west.
Mount Pisgah straight ahead.
Contact between Boulder Creek
and breccia of Cripple Creek-
Over the next 1.6 mi. (2-6 km:t
the road winds back and forth
across the contact of thebreccia and the Boulder CreeV
Granodiorite.Carlton Gold Mill of Golden
Cycle Corp.
tI{•f•r-
!-,
Contact between CrippleCreek
310
Mileage Mileage
121.9
Quartz Monzonite (1.45 b.y.) and
Boulder Creek Granodiorite. Road
winds back into breccia of
Cripple Creek one more time.
STOP 4. Contact of Cripple
Creek Quartz Monzonite and
breccia of Cripple Creek at west
123.0
margin of the Cripple Creek
volcanic center. Note intense
hydrothermally altered rock of
quartz monzonite and breccia.
Cripple Creek Quartz Monzonite
on right side of road. Granite
locally intruded by phonolite
BM TM
Figure 8. Olbique aerial view of the Guffey volcanic center of the Thirtynine Mile volcanicfield looking west-northwest along upper West Fourmile Creek (WFC). Outward-dipping lavas ofthe upper member of the Thirtynine Mile Andesite underlie Black Mountain (BM); ThirtynineMile Mountain (TM); Saddle Mountain (SM); The Castle (C) ; Mclntyre Mountain (MM); WitcherMountain (WM) ; and Cover Mountain (CM) and mark the remnant flanks of the Guffey compositeVolcano. Thin veneer of the lower member of the Thirtynine Mile Andesite covers the late5fn*» pre-volcanic surface in foreground. Distance between Black Mountain and The Castle" mi. (26.̂ > km), distance between Cover Mountain and Thirtynine Mile Mountain is 10 mi.
Jon). High peaks of the Sawatch Range are dimly visible on the far skyline. View isto that from Observation Point on Range View Road above Cripple Creek.
Mileage
123.3
124.0
124.3
125.1
125.5
125.8
126.0
126.6
127.4
128.3129.5
131.2
132.0
132.2
dikes. Both rocks exhibit con-
siderable alteration.
Contact between Cripple Creek
Quartz Monzonite and feldspathic
gneiss.
Downtown Cripple Creek; turn
left at stop sign on road to
Florissant.
Turn right on Teller Cty. 1 and,
after one block, turn left and
follow signs to Florissant.
Pavement ends .
Mount Pisgah, a phonolite plug
at 11:00.
STOP 5. Cripple Creek Quartz
Monzonite on left.
Late Eocene surface at 3:00.
Road begins to descend from the
late Eocene surface east of a
fault along Fourmile Creek to
the down-dropped late Eocene
surface near Florissant. Offset
is about 1,500 ft. (450 m.).
Contact between Cripple Creek
Quartz Monzonite and syenogabbro
of Pikes Peak Granite.
STOP 6. Syenogabbro in large
well-jointed exposure on left
side of road. Syenogabbro is a
differentiate of Pikes Peak
Granite batholith.
Contact between syenogabbro and
granite. Good outcrops of Pikes
Peak Granite for next 4.6 mi.
(7.6 km).
Cripple Creek Mountain Estates.
Late Eocene surface on wooded
Precambrian rocks straight ahead.
Puma Hills in background. Valley
of Fourmile Creek at foot of
this grade contains laharic
breccias of Thirtynine Mile
Andesite.
Large exfoliation domes of Pikes
Peak Granite at 3:00.
Contact between Pikes Peak
Granite and Thirtynine Mile
Andesite
Cross Fourmile Creek.
Mileage
132.6
132.8
STOP 7. Roadcuts expose laharic
breccia of the Thirtynine Mile
Andesite. Pavement begins.
Junction with Teller Cty. 11;
turn left and stay on Teller Cty.
11. Road follows valley of Four-
mile Creek southward and is most-
ly cut in andesitic laharic
breccias of the lower member of
the Thirtynine Mile Andesite.
The general course of Fourmile
Creek was used repeatedly for
the transport of fluvial and
volcanic rocks during late
Eocene and early Oligocene time.
About 1 mi. (1.6 km) north
of this road junction, breccias
and lavas of the lower member of
the Thirtynine Mile Andesite
filled the drainage and created
a dam, behind which Lake
Florissant extended approximately
12 mi. (20 km) northward and
northwestward to the vicinity of
the town of Lake George. The
famous Florissant Lake Beds
accumulated in this lake.
Congress authorized the
formation of the Florissant Fos-
sil Beds National Monument on
August 20, 1969. The action was
prompted by concern over rapidly
expanding real estate subdivisions
within the Florissant area. The
national monument consists of
6,000 acres lying immediately
south of Florissant.
The Florissant deposits
consist dominantly of volcanic
detritus and are less than 150
ft. (45.9 m.) thick. Tuffaceous
shales and mudstones, near the
middle of the sequence, contain
most of the delicately preserve
fossil plant and insect remain*-
andesitic tuffs and mudflow*petri"
i
underlying them preserve
fied stumps and logs of g1
Sequoia trees. Judging
ianttn»
312
Mileage
133.1
133.6
135.7
135.9
136.4
nature of the sediments and their
enclosed flora and fauna,
MacGinitie (1953) concluded that
ancient Lake Florissant existed
under climatic conditions that
were warm, perhaps even sub-
tropical. Recent K/Ar age de-
terminations by Obradovich
(U.S.G.S.) indicate that the
lake existed during early
Oligocene time, about 34 m.y.
ago.
Contact of Pikes Peak Granite
and Cripple Creek Quart;
Monzonite buried beneath
alluvium and andesite breccias.
Wright's Reservoir at 11:00.
Exhumed late Eocene surface is
visible atop low hills of
Cripple Creek Quartz Monzonite
on right (west). To the east
(left), the same surface is
faulted up to the level of
Cripple Creek townsite along Oil
Creek fault zone. The fault
scarp generally bounds the east
side of Fourmile Creek for many
miles~ to the south.
Contact of andesite breccias of
the lower member of the Thirty-
nine Mile Andesite with the old-
er Tallahassee Creek Conglomer-
ate. The conglomerate consists
of clasts of porphyritic volcanic
rock, lesser dense quartzite,
and Wall Mountain Tuff. It
occupies paleovalleys that were
entrenched into the late Eocene
surface after deposition of the
Wall Mountain Tuff in early
Oligocene time.
Good outcrops of Tallahassee
Creek Conglomerate on left.
Mt. Pisgah at 9:00. Enter valley
of West Fourmile Creek after
crossing terrace alluvium of
Bull Lake age. Hills on skyline
at 2:00 form the eastern part of
the Guffey volcanic center.
Mileage
136.9
137.0
138.3
138.7
138.8
140.9
Cross West Fourmile Creek.
Junction of Teller Cty. 11 and
112. Turn left. Exposures of
Tallahassee Creek Conglomerate
in roadcuts.
Contact of Tallahassee Creek
Conglomerate and Cripple Creek
Quartz Monzonite.
Enter High Park. Road crosses
High Park fault zone, which
trends northeastward and along
which High Park is downfaulted
relative to its northwestern rim.
Bare Hills at 12:00.
Sharp bend to right in road.
Partly wooded hill on left con-
tains Wall Mountain Tuff, over-
lain by Tallahassee Creek
Conglomerate and phonolite.
These units and the late Eocene
surface they rest on are faulted
up about 1,500 ft. (450 m.) to
the level of Straub and Grouse
Mountains south of Cripple Creek
by movement along the Oil Creek
fault zone. (fig. 9)
-• .- -
Figure 9. View northeastward from High Parkacross the late Eocene surface covered byTallahassee Creek Conglomerate. The rathersmooth, late Eocene surface beneath theCripple Creek volcanic field can be seenalong the skyline, above which protrudes theconical phonolite plug of Mt. Pisgah (left).The surface at Cripple Creek has been fault-ed up about 1500 ft. (450 m.) from its gen-eral level in High Park along the Oil Creekfault zone.
313
Mileage
141.6
142.0
Grassy hills in immediate
foreground are underlain by the
Tallahassee Creek Conglomerate.
This conglomerate and the Echo
Park Alluvium are host rocks for
uranium mineralization in the
southern and eastern parts of
the Thirtynine Mile volcanic
field. Exploration for uranium
deposits began in High Park in
the early 1950's and has contin-
ued sporadically ever since.
Renewed drilling activity was in
progress in the spring of 1976.
Ledge-forming outcrop on left is
welded zone of the Wall Mountain
Tuff.
STOP 8. Wall Mountain Tuff left
of road. The tuff weathers red-
dish-brown to yellowish-buff and
forms clifflike outcrops. It
exhibits moderate to dense weld-
ing and distinct eutaxitic
structure imparted by flattened
and stretched pumice lapilli and
by partings that reflect laminar
flowage. The tuff is commonly
devitrified and contains micro-
crystalline alkali feldspar and
silica-minerals of vapor-phase
origin. Fresh, glassy-clear
sanidine and fresh-to-argillized
andesine are the principal
phenocrysts. Small amounts of
biolite and opaque oxides and
traces of pyroxene also are
present. Chemically, the tuff is
a rhyolite. The Wall Mountain
Tuff is the most widespread
formation in the Thirtynine
Mile volcanic field. It is
important because it marks the
onset of volcanism in earliest
Oligocene time, preserves and
dates the regional post-Laramide
erosion surface, and serves as
a datum for determining the
Mileage
142.6
143.4
143.8
147.1
149.7
150.3
151.4
152.0
location and magnitude of middle
to late Cenozoic block faulting.
STOP 9. Tallahassee Creek Con-
glomerate resting on Precambrian
Cripple Creek Quartz Monzonite.
Bare Hills, straight ahead, a
local, relatively thick pile of
Tallahassee Creek Conglomerate
and lower member of the Thirty-
nine Mile Andesite.
For the next several miles,
the road is in older Precambrian
(>1.72 b.y.) pink to tan biotite-
microcline-quartz-plagioclase
migmatitic gneiss. The gneiss
is surrounded by very large areas
of younger (1.45 b.y.) Cripple
Creek Quartz Monzonite.
Enter Fremont County.
Small sliver of Morrison For-
mation caught up in northeast-
trending fault zone.
Morrison Formation, in roadcut
on right, overlain by Dakota
Sandstone. Locally, the Morrison
rests on Cripple Creek Quartz
Monzonite.
Rolling, subdued topography on
the late Eocene surface on the
right is overlain by layered
rocks of the Thirtynine Mile
volcanic field at the southern
extension of Cap Rock Ridge.
Here the Wall Mountain Tuff and
Tallahassee Creek Conglomerate
overlie the Morrison and Dakota
and, in turn, are overlain by
the lower and upper members of
the Thirtynine Mile Andesite.
Cap Rock Ridge is capped with
andesite flows of the upper
member that were erupted from
the Guffey volcano about I- nu'
(20 km) to the northwest.
Cap Rock Ridge at 2:00.
Road is in small paleovalle)' ̂
carved into Cripple Creek Quflr
314
Mileage
152.7
156.0
156.2
157.0
158.9
1S9.2
160.1
Monzonite and filled with patches
of Wall Mountain Tuff, overlain
by Tallahassee Creek Conglomer-
ate. Road begins moderately
steep descent to Currant Creek
along Miner Gulch, which is in
a shear zone in the Cripple
Creek Quartz Monzonite.
Waugh Mountain in the southern
part of the Thirtynine Mile
volcanic field is on skyline at
12:00. Waugh Mountain is a
rhyolitic to andesitic volcanic
center that is younger (19 m.y.)
than the main Guffey center
(34 m.y.). High peaks on sky-
line to left (south) of Waugh
Mountain are in the Sangre de
Cristo Range.
Enter valley of Currant Creek.
Roadcuts, across creek to the
west, expose intensely sheared
Precambrian rocks in the large
Currant Creek fault zone that
extends northwestward 35 mi.
(58.3 km) to the vicinity of
Hartsel and southeastward 16 mi.
(26.6 km) to join the Ilse
fault of the Wet Mountains.
Bridge across Currant Creek.
Junction with Colo. Hwy. 9.
Turn left. Road follows Currant
Creek shear zone in granodiorite
of Boulder Creek age (1.72 b.y.)
southward to Twelvemile Park.
Late Eocene erosion surface on
skyline at 12:00.
Enter Twelvemile Park; outcrops
of Dakota Sandstone and Purgat-
oire Formation on right.
Fort Hays Limestone and Smoky
Hill Shale members of the
Niobrara Formation on right
dipping steeply eastward into
the Twelvemile Park graben.
At 3:00, high pediment is capped
by Verdos Alluvium containing
Mileage
type 0 Pearlette Ash. Sharp
ridge at 9:00 is nearly vertical
Dakota.
1.60.4 Outcrops of Pierre Shale in
roadcuts.
162.0 Fort Hays Limestone and Codell
Sandstone on left.
163.2 High gravel here is considered
equivalent to Nussbaum Alluvium
of earliest Quaternary age.164.0 Bridge Creek Limestone Member
of Greenhorn Limestone on left.
164.2 Lower part of Greenhorn Lime-
stone and dark gray Graneros
Shale on left.
165.1 Junction with U. S. Hwy. 50.
Turn left toward Canon City.
165.4 High gravel on left is Nussbaum
Alluvium.
165.6 Dakota Sandstone occurs along
ridge on right.
166.3 Road to Royal Gorge of the
Arkansas River on right. Pro-
ceed straight to Canon City.
End of first day. Stay over-
night in Canon City.
Second Day, Rewind Odometer
0.0 At canon City junction of 4th
Street viaduct and U. S. Hwy. 50;
turn left (south) and cross
Arkansas River.
0.6 Jog left.
1.0 Jog left, then right.
1.5 Turn right at Forge Road.
Smelter at right was operated by
New Jersey Zinc to refine the
Gilman ores.
3.9 Road forks; stay right, on dirt
and park.
STOP 10. Aqua-colored
water tank perches on small hill
underlain by pyroxene-olivine
basalt intrusive. Basalt dike
cuts Pierre Shale at base of
hill, Cribbles Park Tuff (29 m.y.)
and mudflows. Clasts of syenite
as large as boulders, from the
315
Mileage
McClure Mountain complex (15 mi.
(25 km) to the southwest) occur
in the mudflows and identify this
deposit as a part of the ancient
drainage system that deposited
alluvium at the top of Tanner
Mileage
5.9
6.6
Peak, 3,650 ft, (1,095 m.) higher.
Turn around and retrace route to
U. S. Hwy. 50.
U. S. Hwy. 50. Turn left (west).
Cross hogback underlain by Dakota
Sandstone. Strike valley, west
Figure 10. Oblique aerial view from above Canon City, northward along Oil Creek. T ~-j'Eocene surface has been faulted up from its general level (left skyline) west of the ICreek fault zone to the level beneath Mt. Pisgah, the conical peak (middle skyline) 11?<;c;,Cripple Creek volcanic field. The surface has been tilted westward by faulting and ri- -toward Pikes Peak (right skyline). The surface remnant along the high western sn°ul° toPikes Peak is interpreted as a segment of the late Eocene surface that was faulted up ̂east above its general level at Cripple Creek. Prominent hogback (middle of picture ̂ stDakota Sandstone, overlain by lesser hogbacks of Greenhorn Limestone and Fort Hays >•• * i.Member of the Niobrara Formation, dipping eastward into the Canon City-Florence b*s,joWedbuildings in lower right are part of Colorado State Penitentiary. U.S. Hwy. 50, r°field trip route, is partly obscured in shadows to left of Dakota hogback.
|«as.
Mileage
10.5
11.8
13.7
16.2
of Dakota rim, is underlain by
Fountain, Ralston Creek, andMorrison beds. Many small
remnants of Slocum and VerdosAlluviums lie in the valley,
(fig. 10)View of folded and faultedPaleozoic limestone in TwinMountains. Travertine quarry is
in beds formed by solution and
redeposition of carbonate from
the Paleozoic section.
STOP 11. Unconformity. OrdovicianManitou Limestone is exposed in
roadcut; the Manitou lies on Pre-
cambrian Boulder Creek Granodiorite.Granodiorite in this outcrop is
part of the core of a zoned pluton
with quartz diorite borders. Rockhas been called Pikes Peak Granite,
but has 1.7 b.y. age (Hedge,written commun., 1971).
Junction, turn left towards Royal
Gorge. Surface here is the pre-Morrison unconformity cut in
Boulder Creek Granodiorite. This
surface was exhumed by streams
in Tertiary time and may wellhave been the surface over whichthe debris that formed theOgallala Formation was trans-
ported. The Royal Gorge bridgecan be seen to the southeast.
(fig. IDBear left on dirt road, and stop
at chain.Pegmatite boulders here
came from Mica pegmatite mine,
mined for feldspar and mica, and
containing small quantities ofrare-earth minerals. Pegmatitesof the Royal Gorge and MclntyreGulch areas to the west arelocated near the contact betweenthis Boulder Creek pluton and
the enclosing gneisses. Turnaround and return to U. S. Hwy.
50.
.-317
Figure 11. Oblique aerial view of the RoyalGorge of the Arkansas River looking north-westward, west of Canon City, showing excel-lent Pre-Mesozoic surface largely strippedof former cover of Morrison Formation. Pre-cipitous canyon was cut in Pliocene time.Highest mountains on skyline are TableMountain (left); Waugh Mountain (center) ;and Black Mountain (right center) in theThirtynine Mile volcanic field.
Mileage18.7
20.4
21.3
21.5
Junction U. S. Hwy. 50; turn
left (west).Cross beds of Morrison and
Dakota, which are steeply dipping,faulted, and folded, and a partof the structure of TwelvemilePark, a down-dropped remnant of
Mesozoic beds, surrounded bytopographically higher mountains
of Precambrian rocks.STOP 12. Turnout. Black, sub-horizontal dikes of diabase cut
reddened rocks of Boulder Creek
Granodiorite. To the south, in
Temple Canyon Park, similar dikes
are unconformably overlain byOrdovician Harding Sandstone.These dikes are probably Cambrianand are related to the alkalicgabbro-syenite complexes locatedabout 10 mi. (16.6 km) to the
southwest, and dated at 515-520
m.y.Webster Park, a complexly-folded
Mileage
22.9
26.5
31.4
graben, bounded by walls of Pre-
cambrian rock; eolian sand in
cuts beside road. Mills across
Arkansas River are at Fink; they
processed pegmatite materials
from several districts.
Cross Use fault; Mesozoic sedi-
mentary rocks on eastern side
are downdropped against Boulder
Creek Quartz Diorite. Use fault
is a major fault that first moved
in Precambrian time before intru-
sion of the Boulder Creek Grano-
diorite; it reactivated at many
different times, and in Neogene
time was the locus of major
vertical uplift to the south and
less displacement to the north.
Pinedale outwash on right. Walls
of the canyon of the Arkansas
River for the next 4 mi. (6.6 km)
are in Boulder Creek Quartz Dio-
rite, part of the border of the
differentiated pluton previously
seen at STOP 11.
Contact of Boulder Creek Quartz
Diorite with metamorphic geneisses
crosses highway; gneisses consist
of interlayered feldspathic units,
hornblende-rich units, and local
mica-cordierite interlayers.
Echo Park to north, across river.
The valley is cut into a graben,
bordered by Precambrian gneiss
and granite. The Echo Park
Alluvium lies in the graben,
which formed in part during de-
position of the Echo Park Allu-
vium; the alluvium is overlain
by Oligocene and Miocene
volcanic rocks of the Thirtynine
Mile field. Although not precise-
ly dated, the alluvium probably
is correlative with the Huerfano
Formation (Eocene). Quaternary
alluvium now covers much of the
park. Uranium occurs in the park
and suggests that the park is an
extension of the Tallahassee
318
Mileage
32.8
34.3
35.3
35.4
36.2
36.9
37.8
Creek district to the north,
(fig. 12)
Silvery-gray gneiss and schist
on the south side of the road is
a muscovite-rich rock that con-
tains porphyroblasts of cordier-
ite several inches long. Sills
of pegmatite in canyon walls to
the north follow bedding of the
gneisses; most are related to
the Boulder Creek pluton, but
some may be related to a Silver
Plume pluton that is just west
of the Echo Park graben.
Contact of metamorphic gneisses
to east and Boulder Creek Grano-
diorite to west. The Boulder
Creek is part of a batholith
that forms the walls of the
Arkansas canyon for about 10 mi.
(16.6 km) to the west; the lobe
here is separated from the main
mass by displacement on the Texas
Creek fault and is evidence for
about 10,000 ft. (2,999.7 m.) of
vertical movement on this fault,
with the east side up.
Texas Creek fault; gouge to south,
covered in part with Verdos All"'
vium. Pinedale outwash occurs on
north side of Arkansas River.
Junction; turn left (south) on
Colo. Hwy. 69 towards Westcliffe-
South of the junction, Texas
Creek cuts through the margin
Silver Plume pluton, which here
contains intermixed gneiss and
is cut by northeast-trending
faults.
Cuts to left and right are seS"
ments of old Texas Creek rail*"0*
grade built to connect Canon C»*.
with Westcliffe after washout*
destroyed prior route in Graff
Creek.Verdos(?) Alluvium, cemented
caliche, covers Texas Creek
fault zone.Sheared rocks of Texas Cree
of
WMCM CR
Figure 12. Oblique aerial view northward into the head of Echo Park from above the canyon ofthe Arkansas River (lower right). The smooth prevolcanic surface is shown by the dashed line.A prevolcanic paleovalley in Precambrian rocks, filled with Echo Park Alluvium, is extensive-ly exhumed (right of center). The Wall Mountain Tuff and the lower member of the ThirtynineMile Andesite rest on Precambrian rocks and Echo Park Alluvium. Cliffs of the Cribbles ParkTuff and overlying andesite of Waugh Mountain form the rim of Echo Park. Eastern WaughMountain (WM); Dicks Peak (DP); Thirtynine Mile Mountain (TM); and Cover Mountain (CM) arevolcanic constructional features of the Thirtynine Mile volcanic field. Caprock Ridge (CR)is a thin sheet that consists of Wall Mountain Tuff, Tallahassee Creek Conglomerate, andThirtynine Mile Andesite, resting on the prevolcanic surface. Length of dashed linerepresents about 7 mi. (11.6 km).
Mileage
40.3
Mileage
fault are exposed at the divide,
on both sides of road. To south,
fault is covered by alluvial fill.
Main break on fault leaves valley
bottom about 2 mi. (3.3 km) south
on west side of valley. Bouldery
hills to west are part of Silver
Plume pluton; flat tops of these
hills are pediment surface
(Eocene?) capped by Santa Fe(?)
gravels.
Road Gulch; turn left on dirt
road. After turn, Lookout
Mountain is seen at 11:00. Look-
out Mountain is made up of Boulder
Creek rocks forming a complex,
semiconcordant pluton. Road
Gulch follows an east-northeast-
trending fault zone and affords
many good views of sheared rocks.
Most of these rocks are migmatitic
gneiss, but some are Boulder
Creek Granodiorite.
Road is on late Eocene surface,
which is partly covered by tan
to gray alluvial Santa Fe(?)
46.9
48.8
gravels. Mountains on skyline
include Tanner Peak (11:30) and
Curley Peak (12:30). The surface
is evident on these summits, and
is identifiable in eroded terrain
at 10:00 beneath outcropping
Cribbles Park Tuff. Contact of
Precambrian rocks with Cambrian
syenite of McClure Mountain com-
plex is concealed beneath Santa
Fe(?); hills to south are made
up of biotite-hornblende syenite,
(fig. 13)Road junction; turn right (south).
Rocks on both sides of road are
McClure Mountain syenite.
STOP 13. Copper Gulch divide.
Variants of nepheline syenite,
exposed in road cuts, are
characteristic of contaminated
zones in McClure complex. Rocks
to west are nepheline syenite
and hornblende gabbro in complex
reaction zone. To south, grass-
covered flats are covered in part
by Santa Fe(?) beds.
319
Figure 13. Use fault escarpment near Locke Park. Fault-line scarp along the Use faultdivides segments of the late Eocene surface on the Wet Mountains (skyline) from equivalentsurface on the De Weese Plateau (middle distance). Modern drainage of Grape Creek (foregroundcuts deep, steep-walled canyon below late Eocene surface. Timber-covered ridges on the DeWeese Plateau are upheld by resistant layers of metamorphic rock and stand above generalsurface level.
Mileage
52.3
54.6
STOP 14. Road junction; take
right fork (straight ahead) to
Gem Park. Stop is on Eocene
surface, covered by Santa Fe beds
Volcanic clasts within Santa Fe
are derived from exposures east
of Hillside, and include flows
of local sources and Cribbles
Park Tuff. Quarry on DemocratMountain to southwest exploits
epidotized gneiss for a crushed
ornamental aggregate. Gem Park
complex is just west of Democrat
Mountain.Road crosses contact between Pre-
cambrian gneiss and Cambrian Gem
Mileage
55.3
56.2
Park mafic-ultramafic complex
STOP 15. Gem Park; quarry fvermiculite in metasomatized
(basic fenite equivalent)and pyroxenite. Bronze zonesthe quarry wall are vermicul'«f •
blue sodic amphibole and whlt'natrolite are also exposed.
<• i
veinlets on southwest
tain small amounts of luc?
fersmite, and natroniobitc •
to east expose bluish
ites, containing PYT°
Southwest edge of Gem
plex. West edge is P
ed by volcanic rocks
t «?
320
Mileage Mileage
57.6
64.3
66.9
67.5
68.8
Creek-Hillside paleovalley; bedded
volcanic sedimentary rocks west
of the road probably are corre-
lative with the Antero Formation
(Oligocene) of South Park.
Paved road; turn left. Roadcuts
are in biotite latite; this is
part of an extensive flow that
seems to be derived from dike
feeders underlying it.
Cross Grape Creek. Numerous
silver prospects and mines are
visible on White Hills at 10:00.
The rocks of White Hills belong
to the Silver Cliff volcanic
center.
Turn right and stop on east side
of Grape Creek. Gravel pit in
V'erdos Alluvium. White layer is
Pearlette ash layer 0, about
600,000 years old and derived
from Yellowstone Park. Although
the Verdos lies about 250 ft.
(76.5 m.) above modern streams on
the plains, the abnormal base
levels of the mountains bring it
here to within 25 ft. (7.5 m.) of
Grape Creek. Turn around and
return to highway; turn right.
Turn left on road to Lake De
Weese. Road lies west of White
Hills at the fringe of the
volcanic center. Mines on Ben
West hill include the Song Bird
(Pasaflora) on mineralized ring
fractures that produced silver,
gold, and lead from sulfide ores.
Dirt road; turn right. Road goes
through Copper Flats, underlain
by a porphyritic quartz monzonite
stock, about 30 m.y. old, that
fills the throat of an eroded
volcano. Hills to right are
coarse volcanic breccia, fringing
the throat.
Nearby mines (to left) belong to
the Reveille group. The Lady
Franklin is on the hill to the
right. Both are on mineralized
71.6
71.9
72.5
radial fractures in Precambrian
gneisses. Dark hills at 10:00
are the Blue Hills, underlain by
a Precambrian gabbro pluton. At
the south edge of the hills, mine
buildings mark the Bull Domingo
pipe, a major lead-zinc producer.
Junction; bear right. Sharp hill
at 10:00 is Round Mountain, one
of several rhyolite domes ringing
the east side of the subsidence
block of the Silver Cliff center.
Other rhyolite domes are low cones
on ridge to right. Some of these
cones have alunitized core zones.
Behind Round Mountain, in the
distance, are the Rosita Hills,
the companion stratovolcano to
Silver Cliff. The hummocky hills
near Rosita are subvolcanic ande-
site plutons and extensive ring
fault-controlled rhyolite domes
and flows.
STOP 16. Rhyolites and glass
flows of Silver Cliff volcano.
Flow-banded rhyolite and glass
from several vents cover a major
volcano-tectonic depression, more
than 2,000 ft. (589 m.) deep,
filled with rhyolitic fragmental
rocks. During subsidence, these
volcanic rocks were fractured and
mineralized. The fractures were
filled with Fe-Mn-carbonate veins
and metal sulfide minerals. The
weathering of these carbonate
veins produced black manganese
coatings and veins in near-surface
rocks; some veins carry substant-
ial silver.
Old silver mines to west include
the quarry of Racine Boy and ad-
joining Silver Cliff mine. The
Silver Cliff mine is in black,
manganese-laced rhyolite, con-
taining silver chloride and bro-
mide. A breccia pipe is the
mineralizing conduit at this site.
Road junction; turn left on paved
Mileage
74.0
76.9
79.0
82.2
86.1
86.7
road (Colo. Hwy. 96).
Oligocene boulder alluvium in
cuts to right; most of the allu-vial cover in this area is Santa
Fe(?), but the upper part hasbeen somewhat reworked.
Roadcuts expose ash-flow tufffrom Rosita field (south), over-
lying an alluvium almost entirelycomposed of Precambrian rocks.Volcanic-rich alluvium coversboth units to the south. Pre-
cambrian rocks at 12:00 are gneissintruded by San Isabel Quartz
Monzonite (1.45 b.y.), a medium-to coarse-grained rock of Silver
Plume age'. The Rosita volcano
is exposed in the hills to the
right. Some prospecting pits
are visible. The famous BassickMine is located in this volcano.
Peridotite and gabbro sills ingneisses exposed here are weath-
ered to hydrobiotite and havebeen prospected for vermiculite.
Most rocks are Precambrian, but
Cambrian intrusive rocks may
also be present.
Deeply weathered gneiss lies
beneath these grassy flats. Theflats are underlain by the lateEocene erosion surface. Hill to
left is underlain by Bear Mount-
ain pluton of San Isabel Quartz
Monzonite. To east, valleys arestrike valleys, following easilyeroded layers in banded, isoclin-
ally folded gneiss.
Prospect pits (to left) are in the
Wet Mountain thorium district.Veins were mined both for thoriumand for barite, the major non-metallic mineral. Veins are pro-bably Cambrian and are related tosyenite intrusive rocks.
Numerous fractures and prominentiron-stained fault gouge mark the
trace of Use fault zone.
Mileage
87.3
88.6
90,392.3
93.8
94.8
95.6
96.9
Junction; bear left on Colo. Hwy.
96 along Hardscrabble Creek.
Roadcuts expose banded migmatizedfeldspathic and biotite gneiss.
At this location, a small apliticpluton, probably quartz monzonite
of Boulder Creek age, has fedseveral sills in the gneiss.
Smith Creek Picnic Ground.Mouth of Hardscrabble Canyon,underlain by Dakota Sandstone;major fault occurs in coveredarea between Dakota beds andPrecambrian rock.Landslides cover must of mountainfront to left; largest came fromdepression in Precambrian rocks
behind ridged topography.Road crosses axis of north-trendin.
anticline; rimmed by Dakota ridge.'
to south. Complex folds in sedi-
mentary rocks lie just east ofthe major faults bounding the Ket
Mountain uplift.Flat-topped hill west of Wetmorc
capped by remnant of Nussbaum
Alluvium.Road junction at Wetmore; turn
left. Road follows levels of
Slocum and Verdos Alluviums;small remnants of Rocky Flats
alluvium rise above. Old oilwells are at southern end of *ht
Florence oil field, the second
oldest field in the United
States. End of road log.Return to Hilton Hotel,
Denver.
322