Geology of the Carter Lake Region from Lyons to North of Hygiene

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GEOLOGY OF THE GARTER LAKE REGION FROM LYONS TO NORTH OF HYGIENE

By Hamzah All

ProQuest Number: 10781408

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541 i '-j

A thesis submitted to the Faculty and the Board of Trustees of the Colorado School of Mines in partial fulfillment of the requirements for the degree of Master of Science.

Signed: c/1

Golden, Colorado 1950

Approved: ^ \ F. M. Van Tuyl

\

CONTENTS Page Abstract

.....................................

Introduction ..........................................

1 3

Location of the A r e a ..........................

3

Accessibility ...................................

3

Purpose of Investigation

...........

4

.............

4

Previous W o r k ...................................

5

A c know1e d g m e n t s .................................

6

............................................

7

. . . . .

Method of Investigation . . . . .

Geography Relief

.

.....................................

7

D r a i n a g e .......................................... 10 Surface Deposits

...............................

Climate and Vegetation

........................

10 11

C u l t u r e ............................................ 11 G e o l o g y ................................................. 13 Stratigraphy

...................................

13

Regional and Local Relationship ...........

13

Details of Stratigraphie Units

. . . . . .

14

..........................

14

Fre-Cambrian

P e n n s y l v a n i a n .............

14

P e r m i a n ....................................20 Pormo-Tri as s ic

29

Upper Triassic

33

ii

Geology - Continued .................

Jurassic

Unper Cretaceous Quaternary

.........

...............

............ 30

........... 53

Structural Geology ...................... General Statement

...............

.

F o l d s .......................... ..

.

F a u l t s ............................ Historical G e o l o g y ........... ..

. . . . ........... Cl

G g ne r al St at ernen t .................

........... Cl

1re-Cambrian

........... 61

......................

Paleozoic

..........................

Mesozoic

...........

. . . . . . .

C e n o z o i c ................. .. .economic G e o l o g y ............. .. Building Stone Oil and Gas

. . .

. . . . ........... 65

....................

........................

St. Grain Supply Canal

...........

Bibliography . ..........................

ILLUSTRATIONS A panoramic view of the area, showing characteristic topography and structural features ......................................

2

Three hogbacks, that of Tlmpas, top sand of Dakota, and D a k o t a ........... ..

8

A typical exposure of rocks from Lyons to Dakota of Dakota group ....................

8

Typical banding and smooth slope of Foun­ tain formation against dip, with vertical cliffs of Ingleside on top ...............

16

An exposure showing characteristic hogbacks of the foothills. Fountain sandstone slope, Ingleside cliff, Satanka slopes, and hogback of Lyons ..........................

16

Contact of Lyons with arkosic bed, probably a tongue of Fountain ......................

22

Gradational contact between Lyons and Satanka with characteristic pits .........

22

Lamination and cross bedding in Lyons sandstone .................................

24

Contact between Lyons and Lykins

.........

24

Glennon limestone in the Lykins

.........

27

Typical concentric weathering of Glennon l i m e s t o n e .............................. .

27

Contact between Lykins and Jelm

.........

32

...........

32

An exposure showing Jelm, Lntrede, and Morrison contacts ........................

34

Contact between well-bedded Entrada and cross-bedded Jelm . ......................

34

Vegetational pattern developed on Entrada and Jelm, sparse vegetation on Morrison; typical hogback of Dakota conglomerate of Dakota group ..........................

42

Typical cross bedding in Jelm

iv Figure

Page

17

Dakota sandstone boulder, showing cross bedding and lenticular conglomer­ atic l a y e r s ............................... 42

18

Typical weathering of soft sandstone in Dakota formation ........................

44

19

An outcrop of Fuson shales of Dakota group

44

20

An outcrop of top sand of Dakota group . . .

21

Contact between top sand of Dakota group and Graneros s h a l e ......................... 46

22

Graneros shale with bentonite b e d s , in section Y - Y 1 of plate 2 ................ 48

23

Three limestone members of the Greenhorn f o r m a t i o n .................................. 43

24

An exposure showing typical Tlmpas hogback, contacts between Apishapa on top and Carlile below, and terrace deposit overlying the three f o r m a t i o n s ................ 50

25

Inoceramus deformis in Tlmpas limestone

26

Terrace deposit overlying top sand of Dakota group .................................

55

27

Silicifled fault zone of Dyons sandstone . .

55

28

Strike fault on the nose of Dowe Pass a n t i c l i n e .................................. 57

29

Small tight folds on western flanks of the major Rabbit Mountain anticline ...........

.

. .

46

50

57

V

Plate 1

Location of A r e a ........................

3a

2

Relation of Geology to Topography

3b

5

General Stratigraphie Column

4

Detailed Stratigraphie Column from Base of Dakota to Top of Lykins ...........

26a

5

General Structural Fabric ...............

56a

6

Geological Cross Section

66b

7

Areal Geologic M a p ........................ Pocket

3

Areal Map of the Carter Lake Reservoir

... *

.........

.

...............

.

13a

66a

ABSTRACT

The area discussed in this paper is a part of the eastern foothills of the Front Range of Colorado, extending from west of Lyons to north of Hygiene.

The area is com­

prised of pre-Cambrian crystalline rocks and sedimentary rocks ranging in age from the Upper Pennsylvanian to the Pierre formation of the Upper Cretaceous.

Flat-lying

Quaternary terrace deposits overlie the eroded surface of Upper Cretaceous formations. The'area is one of considerable relief, marked by echelon folds and numerous faults with the monoclinal dip showing a series of hogbacks as a result of differential erosion.

Major structures trend northwest-southeast and

the smaller ones northeast-southwest

(fig. 1).

2

H* 03

Lyons anticline

A panoramic view of the area looking north from State ing characteristic topogranhy end structural features

$ 1-

Stone Canyon

Lalcota hogback of Indian Mountain

Synclinal valley

Dowe Pass anticline

;

II

Rabbit Mountain anticline Highway 7 , show­ of the area. Table Mountain

3

INTRODUCTION Location of the Area The size of the area mapped is about 32 square m i l e s , and it lies in the eastern foothills of the Front Range of Colorado, between latitudes 40° 1 3 f to 40° 1 5 1 3 0 ” north and longitudes 105° 9 f to 105° 18* west.

It extends east­

ward from a little west of Lyons to due north of the town of Hygiene.

The northern limit is the Boulder-Larimer

County line, and the southern limit Is State Highway 66. Plate I illustrates the location and the highway which passes through the area.

Plate 2 gives the location by

township and the areal geology of

the region.

Accessibility The area is easily accessible by means of east-west State Highway 66 in the extreme southern part of the area. It is connected by three roads running to the north which are well-maintained and can be used throughout the year. Private roads connecting them are

poor during therainy

season.

on plate 7.

The road system is shown

% F T . COLUN

ROCKY n a t v

MTN.

GREELEY

LOVELAND

Pa r k

\

r-

LONGMONL

Cheycnne • • FT. C o l l ins

DENVER ,'//// D €- N V E R

285 COLORADO

C O L O . Sf R I N G

N. M E X

HAMZAH A L l é T H E S I S A R E A

PLATE L O C AT I ON

I OF

AREA

PLATE RELATI ON

OF

2

GEOLOGY

TO

TOPOGRAPHY

4

Purpose of Investigation The field work undertaken in connection with the re­ quirements for the degree of Master of Science at the Colo­ rado School of Mines is an integral part of a program ini­ tiated by the Graduate Committee of the Department of Geol­ ogy, with the view of mapping in detail the sedimentary rocks along the eastern margin of the Front Range and of eventually publishing a complete report on the area. This area is an excellent one for the study of engi­ neering problems as relating to irrigation outlet tunnels and open ditches.

Method of Investigation The field.work was undertaken in the latter part of July, 1049, and was completed early in September of the same year.

To acquaint the writer with the stratigraphy

of the area, several sections were measured with Brunton compass and tape in Big Thompson Valley and the Dry Creek section.

In the assigned area, sections X - X f and Y-Y*, as

shown in plate 2, were measured in the Dowe Pass Creek south of the Boulder County line in section 2 , T. 3 N . , R . 70 V/.

The section X-X * represents a stratigraphie col­

umn from Satanka-Ingleside-Fountain undifferentiated to the top sand of the Dakota formation (fig. 3). Field reconnaissance work was done to obtain the re­ gional picture of the major fold and fault pattern of the area.

5

Aerial photographs we re enlarged to 1,000 feet to the inch and on which detailed mapping of individual members of different formations and structural features was done. the area there are two main problems:

In

(1) the complicated

major echelon folds with minor warpings, and (2) the dif­ ferentiation of the Satanka, Ingleside, and Fountain forma­ tions .

To the north, each of these three formations exhi­

bits definite mappable contacts, whereas in the assigned area there is interfingering of these formations.

For this

reason, they were mapped together as an undifferentiated unit. The complete map of the area was transferred by the writer from the photographs to the topographic map of the area which has the same scale as that of the aerial photo­ graphs.

To eliminate the error due to shortening of the

area on the edges of the photographs, section lines, perma­ nent roads, and main drainage features were used as ground controls.

From this base an areal geologic map was pre­

pared on a reduced scale of 2,000 feet to the inch.

Previous V/ork In 1869 F. V. Hayden (10)

first published the geolo­

gic reports on the Loveland area near the Big Thompson Can­ yon.

In 1900 a report on the "Foothills Formations of North­

ern Colorado" was published by Junius Henderson. Numbers refer to "Bibliography," p. 69.

The work

6

of R. M. Butters (1) and L. T. Lee (16) followed. of R. L. Heaton (11) and also M s

Papers

unpublished reports on

Carter Lake Reservoir, prepared for tho United States Bur­ eau of Reclamation, give valuable Information with regard to geologic formations and structure of the area. This report is mainly based' on the observed facts in the field and includes only a partial review of the litera­ ture; this report is in conformation with the previous work done by graduate students north of the assigned area.

Ac knowle dgme nt s Before leaving for the field work, the publications of Victor Ziegler (27), N* M . Fenneman (5), V/. T. Lee (16), and F. V. Hayden (10) were reviewed.

These proved very

useful in the correlation of the geologic formations and structures in and around the thesis area. The writer gratefully acknowledges the assistance of the members of the faculty of the Department of Geology, Colorado School of M i n e s , who have given valuable guidance in carrying out this work.

In particular Drs. F. M . Van

Tuyl, Truman H. Kuhn, and L. Y/. LeRoy (the writer's faculty advisor) have been very helpful. The writer also feels indebted to Mr. Harold Kirchin. Geologist, U. S. Bureau of Reclamation, for discussing the area in the field associated with the Carter Lake Reservoir project.

7

GEOGRAPHY Relief In the area examined, there are three distinct topo­ graphic divisions which have been designated by Fenneman and Johnson (6) as the piedmont physiographic division. (1) the plains area,

section of the Great Plains

These topographic divisions are

(2) the foothills section, and (3) the

mountain front reflected by the crystalline rocks. The plains area extends from the Tlmpas ridge towards the Denver Basin.

The area is of very low relief with max­

imum differential relief usually not exceeding 100 feet. However, near the Tlmpas hogback ridge, there are two gravel-strewn mesas with a relief of over 200 feet.

Beyond

these mesas, toward the east, the Pierre shales, due to lack of resistance and low easterly dip, weather rapidly and present a very low, flat, rolling plain. The foothills section, lying between the Tlmpas hog­ back ridge and the Fountain formation, consists of long and narrow hogbacks of the resistant beds, running north-south or in asymmetrical ridges in wide areas.

The differential

relief is about 800 feet between the Table Mountains on the east and Steamboat Mountain on the west (pi. 2; figs. 1 and

2) . The relief of the area is partly due to structure and

L

Fig.

2.

Fig. 3.

Three hogbacks, that of Tlmpas (T) , top sand (TS) of Dakota, and Dakota (L ) , looking northeast from the Dakota formation.

A typical exposure, showing rocks from the Lyons to the Dakota formations. Looking west from Dowe Pass ridge.

partly due to difference in resistance of various forma­ tions exhibiting homoclinal dip.

Rabbit Mountain, Dowe

Pass hill, and the hill west of Stone Canyon are anticlinal hills (fig. 1).

Those hills are capped by highly resistant

sandstone beds of Dakota and Lyons formations.

There are

two valleys of major synclines; one lies between Rabbit ^ Mountain

and Indian Mountain, and theother is occupied by

the town

of Lyons and the area to the north.

There are four resistant formations

(Timpas limestone,

top sand and Dakota sand of the Dakota formation,

and Lyons

sandstone), which form prominent hogbacks and are useful for determining local geologic structure and for facilitat­ ing mapping work.

From east to west, they:

first, the low

Timpas hogback which can easily be traced, indicating the intricate folding on the western flanks of Rabbit Mountain (pi. 2).

To the west of the Timpas hogback Is the second

hogback formed by the top sand member of the Dakota forma­ tion.

Next to the Dakota (basal conglomerate sand of the

Dakota formation) producing the higher hogbacks of Rabbit Mountain

and Indian Mountain (fig. 2)

hogbacks

referred to above.

than that of the two

The Lyons sandstone forms the

highest hogback with a maximum relief of 700 feet as shown by the Steamboat Mountain and Beech Hill on the extreme western foothills section of the area (fig. 5). The third topographic division— the mountain front-consists of the pre-Cambrian rocks.

In this area the moun­

tains rise abruptly to the west above the foothills and

10

and show exceedingly irregular and considerably dissected topography.

Drainage There are two perennial streams, the Little Thompson River to the north and St. Vrain Creek to the south, and all intermittent streams are tributaries to these streams. These two perennial streams cut almost at right angles through the structure and flow easterly.

The St. Vrain

Creek cuts through the nose of the Indian Mountain anti­ cline, and Little Thompson cuts through the Dowe Pass anti­ cline.

In the foothills area these rivers exhibit a youth­

ful stage; upon emerging onto the plains, several meanders are evident and point to the mature stage.

Many of the

smaller and intermittent streams are subsequent and flow in strike valleys between successive ridges.

These intermit­

tent streams show trellis or dendritic drainage patterns in the strike valleys, such as around Rabbit Mountain in the extreme southeast of the area.

There are a few shallow

structural basins forming lakes, such as McCall Lake. These are now fed by the irrigation ditches.

Surface Deposits Due to high relief, most of the area is barren and rocky. ' Fairly rich soils occur in the synclinal valley b e ­ tween Rabbit Mountain and Indian Mountain and in Stone Can-

11

yon.

Wide areas are covered by thick alluvium in the

plains area near the

Table Mountains. St.

flanked by low gravel terraces. the top of the Lyons Mountains.

Vrain Creek is

Pin© sand locally covers

hogback of Beech Hill and Steamboat

This sand is probably a regolith or wind-born

deposit.

Climate and Vegetation The area lies in the northern part of Colorado and is climatically similar to the Great Central plains of Colo­ rado.

The temperature ranges from sub-zero in winter to

high temperatures of mid-summer.

The rainfall is about 14

inches annually, and it occurs in spring and early summer. Vegetation is very sparse on barren dip slopes of the rocks.

It consists of grasses, sage brush, willows, and

cottonwood, especially along the flanks of the streams. Pine trees flourish well on the Lyons formation.

Vast

plains and synclinal valleys, covered with thick fertile alluvium, are under irrigation and produce sugar beets, alfalfa, and grains.

Culture Farming and quarrying of building stone are the only industries in the area.

North of Lyons and in Stone Canyon

there are numerous quarries for building stone.

The Lyons

formation, because of cross bedding and easy splitting, gives big slabs and flags which are used both for walling and pavement.

13

GEOLOGY

Stratigraphy Regional and Local Relationship In the area treated, work was concentrated in the sedimentary-rock section that involves strata ranging from Upper Paleozoic to Tertiary.

The pre-Cambrian rocks gen­

erally consist of gneisses and schists intruded by granitic phases.

These rocks were studied cursorily near the Foun­

tain contact.

The Paleozoic rocks consist of a group of

formations formerly known as "Red beds" and include the Fountain, Ingleside, Satanka, and Lyons formations.

The

Mesozoic rocks, in the order of their succession, are Ly­ kins, Jelm, Entrada, Dakota, Benton, Niobrara, and Pierre formations. hills.

These rocks are well-exposed along the foot­

On the erosion surface of the easterly dipping Up­

per Cretaceous

rocks, from the Dakota to the Pierre, Quater­

nary boulder conglomerates have been deposited, forming flat hills on the eastern portion of the area.

Plate 3

shows the succession, thicknesses of rock types, and formational relationships within the area.

PLATE

g e n e ra l

0 too'

3

s t r a t i g r a p h i c c o lu m n P IERR E

COLOR SYMBOLS ARSHAPA

200' T IM P A S CAR LILE

GRAY RED

400' PINK W H ITE

GRANEROS

TOP SANA MEMBER

F U S O N s i® MEMBER ?

LA K O TA M E M B ER

MORRISON

E N TR A D A JE LM

LY K IN S G LE N N O N

LYO NS

S ATANKA

IN G LE S ID E

FOUNTAIN

PRE-CAMBRIAN

Details of Stratigraphie Units Pre-Cambrian The work was confined mainly to sedimentary forma­ tions ; and the main features of the pre-Cambrian rocks, the basement rocks which rise rapidly to several thousand feet above the foothills, were examined only near the basal con­ tact of the Fountain formation. At the lower Fountain contact, mostly pink, coarse granites with their associated pegmatites and quartz veins are exposed.

Mica and hornblende gneisses occur as b an ds ,

lenses, or irregular masses. rocks is northwest.

The general strike of these

These basement rocks appear to have

been eroded to a comparatively plane surface prior to depo­ sition of the Paleozoic sediments.

Pennsylvanian Fountain Location of Typical Exposure.--The Fountain formation forms the major portion of the western slopes of Beech Hill and Steamboat Mountain and extends north of the Boulder County line and south of North St. Vrain Creek.

The forma­

tion is cross-bedded, but the general dip of beds is about 10 degrees east. History.--F. V. Hayden (10) first described the Foun­ tain formation of the Loveland area as red sands of Triassic age.

C. V/. Cross (4) , while describing red sandstones

15

and conglomerates of Fountain Greek, south of Manitou Springs, Colorado, assigned them to the Fountain formation. On the diagnostic fossil evidence found in 1907 to the north of Fort Collins (13) , the formation is relegated to the Upper Pennsylvanian. Thickness.--The poorly exposed contact of the Fountain with the basement rocks, may be observed in the gullies near the Boulder-Larimer County line.

The upper contact is

not definite, as the Ingleside and Satanka formations show Interfingering with the Fountain due to facies change. From the cross-bedded nature of the Fountain formation, it is difficult to obtain accurate dips of the b ed s.

Assuming

about 10 degrees dip of some of the persistant beds, and the width of the sloping outcrop between the base of Ingle­ side cliff and the contact with the basement rocks, the thickness of the formation is estimated to be 800 fe et . Llthology.--The Fountain formation is irregularly bed­ ded, showing alternate red and white lenticular layers. The white layers are mostly arkose and conglomeratic sand­ stone.

The deep red beds generally consist of fine silt-

stone.

This feature is most conspicuous in the middle part

of the section (fig. 4), and also in this part of the sec­ tion occasional lenticular limestone beds occur.

The lime­

stone is impure, fine-grained, and brecciated, and it wea­ thers Into concretionary nodules. Stratigraphie Relationships.--The Fountain formation rests uneonformably on the pre-Cambrian rocks.

North of

15 Ingleside

Fig. 4.

Exposure From western slopes of Steamboat Moun­ tain, exhibiting the banded nature and the smooth slope across the dip of Fountain formation, the vertical cliffs of the Ingleside on top, and a section of river gravel in the foreground.

F i g . 5.

Southern end of Steamboat Mountain, showing Foun­ tain sandstone slope (F), Ingleside cliff (I), Satanka, and Lyons hogback.

17

the Boulder-Larimer County line, this contact in the gul­ lies is marked by basal conglomerates.

The upper contact

is not definite, as the Ingleside and Satanka formations interfinger with the latter.

The relationship is quite

common along the Beech Hill and Steamboat Mountain ridges and also in the Dowe Pass section. Paleontology and A g e .--Fossile were not observed in the Fountain formation in this area; however, from fossil evidence found north of Fort Collins, the Fountain is of Upper Pennsylvanian age. Environment of Deposition.— There is no definite con­ clusion as to the environment of deposition of the Fountain formation.

The typical cross bedding indicates a fluvia-

tile deposit and high content of feldspar in the sedimen­ tary rocks, according to F. j. PettiJohn (21), is due to high relief and rapid erosion as a result of diastrophism. . The ferruginous nature exhibited in the red beds shows subarid to humid climate with seasonal rainfall at the time of deposition.

Probably the Fountain formation was laid down

at a rapid rate from the material supplied by highlands of high relief by the action of rivers and in a semiarid to humid climate. Correlation.--The thickness of the Fountain formation is variable.

It thins out to the north and is correlated

with the Casper formation in Wyoming (25).

South of Colo­

rado Springs, it Increases and at De adman Canyon, El Paso County, it is about 2,000 feet thick.

18

Ingleside Location of Typical Exposure.— The Ingleside formation forms the vertical cliff of Steamboat Mountain. and 5 illustrate the nature of the deposit.

Figures 4

In the Dowe

Pass area (pi. 2) the Ingleside Is interstratifled with the Fountain formation. History.--Butters (1) named the rocks between the Lyons and the top of the Fountain as Ingleside, from the type locality at the town of Ingleside, Colorado. Thickness.--The correct thickness of the Ingleside formation in this area is difficult to determine because of the lack of a definite separable contact due to interfingeripg with the Fountain and also because of its cross­ bedded nature.

Roughly, it is a little less than 100 feet.

A thickness of 93 feet was found when the writer, with E. E. Rue (24), measured the formation in the middle part of the letter’s thesis area. Lithology.--The Ingleside is a compact, massive, cross­ bedded, light pink sandstone consisting of fine, well-sort­ ed, _subrounded grains of quartz.

Fine mica flakes are less

abundant than in the Fountain formation.

Due to the uni­

form nature, the sandstone resists erosion well and forms vertical cliffs (figs. 4 and 5). Stratigraphie Relationships.--The Ingleside in this area shows gradational contacts, both at the base and at the top.

Toward the b a s e , the arkosic sandstone 1nterfIn­

ge rs with the Ingleside, and on the top when not in contact

19

with the Satanka, the Ingleside merges Into the conspicu­ ously cross-bedded Lyons formation.

Its light pink color

and uniform massive nature are the only criteria in the field to distinguish it from the underlying Fountain and the overlying Satanka end Lyons formations. Paleontology and A g e .--No fossils were found in the Ingleside in this area, but fossils were found by earlier workers.

According to Johnson (14), the Ingleside is Penn­

sylvanian in age. Environment of Deposition.--The uniform nature and cross bedding of the sandstone indicate a shallow marine environment.

Heaton (11) believes that the Ingleside, in

view of thickening to the north and thinning to the south, is in part the marine equivalent of the Fountain. Correlation.--The Ingleside, due to the gradational contact along the slopes of Steamboat Mountain and in Dowe Pass, has been mapped as an undifferentiated member of the Upper Pennsylvanian. Cutter (2) and Rue

To the north, in the thesis areas of

(24), this formation shows a strong dis-

conformity at the base, which is supported by L e e ’s view (16) that the Ingleside is of much later age than the Foun­ tain.

However, according to Heaton (11) as pointed out

above, the Ingleside is contemporaneous in age with the Fountain.

7/. 0. Thompson (25, in fig. 2, p. 57) also shows

that the Ingleside is the tongue of the Casper formation of Wyoming.

20 Permian Satanka Location of Typical Exposure.--The Satanka is exposed in the Steamboat Mountain ridge.

It occurs as thin-bedded

sandstone and silty shales between the cliff-forming Ingle­ side and the top hogback of the Lyons (fig. 5).

In the

Dowe Pass section, this formation shows typical even bedding, which distinguishes it from the cross-bedded Lyons above. History.--N. H. Darton (3) first distinguished and de­ fined the Satanka from the type exposures which are a few miles south of Laramie, Wyoming. Thickness.--The Satanka formation, like the Ingleside, shows intertonguing with the Fountain and is mapped .toge­ ther with the Ingleside and the Fountain. quite variable.

Its thickness is

Estimating from the top of the Ingleside

cliff to the bottom of the Lyons, the Satanka has a thick­ ness of about 100 feet. Llthology.--The Satanka consists of deep red, thinbedded

silts tones, shales, and fine-grained sandstones.

These beds are micaceous and intercalated with lenticular arkose and conglomeratic sandstones, probably the tongues of the Fountain. Stratigraphie Relationships.--In the Dowe Pass area, where the section X - X 1 was measured,

the Satanka contains a

deep red, highly pitted, ferruginous, micaceous bed on the

•

top which grades downward into light buff-colored and wellbedded sandstones.

In this bed mica diminishes gradually

upward in the Lyons (fig. 7).

The same feature was ob­

served in the middle part of R u e ?s thesis area (24).

The

lower contact with the Ingleside is lithologie and struc­ tural.

The Satanka is thin-bedded, micaceous, and arkosic,

and the Ingleside is massive and cross-bedded; however, interstratifieation of the latter with the Fountain gives no sharp contact between the Ingleside and Satanka. Paleontology and A g e .--No fossils were discovered in this area.

Earlier writers have included this formation in

the Permian period (25, pp. 56-57). Environment of Deposition.--The Satanks beds are red, thin-bedded, slightly arkosic, and thus indicate shore-line deposition in a warm, dry climate. Correlation.--The Satanka is gradational toward the top, and has been mapped with the underlying undifferen­ tiated Ingleside and Fountain formations.

Thompson (25)

has referred to it as "lower Satanka tongue" which separ­ ates the Lyons from the underlying "Ingleside tongue" of the Casper formation.

To the north, in R u e ’s (24) and

C utte r’s (2) thesis areas, however, the Satanka thickens and shows definite contacts, whereas to the south, near Boulder, the Satanka beds are totally absent and the Lyons overlaps on the Fountain. L yons. Location of Typical Exposure.--The Lyons is very re-

Fig. 6.

Contact of Lyons with arkosic conglomerate, pro­ bably of Fountain, in the St. Vrain Greek; look­ ing east.

F i g . 7.

Eastern limb of the anticline in Dowe Pass Creek, showing typical pitted and gradational contact between Lyons (L) and Satanka (S).

23

sistant to weathering and forms excellent hogbacks north of Lyons and for the same reason are persistent on the major anticlines of Indian Mountain and Dowe Pass (pi. 5; figs. 1, 3, and 5). History.--The early workers included "Lyons sandstone" in the red beds that consisted of formations from the Foun­ tain to the Lykins, inclusive.

In 1905 Fenneman (5) first

named the thick cross-bedded sandstone overlying the Foun­ tain formation in type locality of Lyons, Colorado.

But­

ters (1) subdivided the section and the formation between the Lyons and Fountain as Ingleside.

Lee (10) finally sep­

arated the upper typically m a ssive, cross-bedded sandstones. The Lyons formation was mapped in this area as defined by Lee. Thickness.--From the section measured along X - X 1 in the Dowe Pass Creek (pi. 2), the thickness of the Lyons formation is 60 feet. Llthology.--The Lyons sandstone is light red to pink in color, hard, compact, and fine-grained.

It is mainly

composed of quartz grains cemented with silica.

In this

area, the arkosic lenses or beds that are found below the quartz sandstone are included by the writer in the under­ lying undifferentiated Satanka-Ingleside-Fountain (fig. 6), and Thompson considers them as channel deposits in the Lyons formation.

The sand grains are subangular to sub­

rounded, and equidimensional.

The Lyons sandstone shows

parallelism of laminations which in places persists 20 to

*

ig. 8.

Lamination and cross bedding in Lyons sandstone exposed in St. Vrain Canyon,west side of the town of Lyons.

ig. 9.

Contact between Lyons and Lykins in Dowe Pass Creek; Lyons (Ly), well-bedded; Lykins (Lk), earthy and shaly.

25

30 fe ot .

In individual laminae, the grain size remains

uniform but from laminae to laminae it changes.

Y/here the

parallelism is lacking, cross lamination becomes persistent (fig. 8).

The cross laminations are often wedge-shaped.

The sandstone along the partings shows typical dendritic growth of manganese oxide and circular raindrop impressions. Stratigraphie Relationships.— Laminations and cross laminations are distinctive characteristics.

The massive

cross bedding and the prominent hogbacks in the Lyons formation easily distinguish it from underlying undiffer­ entiated members and the overlying Lykins.

In Dowe Pass

Creek and north of the area, the Lyons shows a gradational contact with the Satanka and characteristic intercalation of dark red pitted beds (fig. 7).

In St. Vrain Creek near

and west of the town of L y on s, the Lyons sandstone overlies arkosic conglomerate

(fig. 6).

The upper surface is con­

formable with the overlying Lykins formation (fig. 9). Paleontology and A g e .--In this area in tho Lyons sand­ stone, fossils are absent.

One of the quarrymen informed

the writer that he recovered a stone 8 feet in length with impressions of an animal track (probably an amphibian track) . Environment of Deposit ion.--In the Lyons sandstone, excellent lamination, wedge-shaped cross lamination, trun­ cation of surfaces, and well-sorted grains are features characteristic of shore processes by the action of waves and currents.

Thompson (25) also believes similarly, but

26 at the same time includes arkosic lenses and bods which are probably of fluviatile origin. Correlation.--The Lyons sandstone contains no fossils from which the age of the Lyons may be specifically deter­ mined.

The Lyons formation in other areas is interstrati­

fied with fossiliferous beds, and according to Thompson (25) its age is Middle Permian.

Detailed Section l--From base of Dakota to base of Lykins (see plate 4) Section measured in Dowe Pass Creek miles north of State Highway 66, Sec. 4, T. 3 N., R. 70 W . , Boulder County, Colo­ rado. Measured by Ham aah All and R. E. Hudson, July 1949. Line of section shown as X-X* in plate 2. Morrison -------Entrada 15. 14. 13.

Thickness (Feet)

Interbedded dark greenish gray marlstone and shale with two right-angle joint systems.....

5.0

Dark gray marlstone with orange-red lime­ stone, chalcedony along partings and joints...

1.4

Interbedded dark gray shales and limestones with secondary calcite.........................

0.0

12.

Light gray, fine-grained sandstone............. 10.6

11.

Thin fissile Vermillion shales with thin beds of marlstone............

8.0

10.

Dark gray marlstone interbedded with shales...

25.3

9.

Thin, fissile, vermillion shales...............

26.7

8.

Dark gray silty marlstone.......

7.

Vermillion shales.........................

6.

Vermillion to gray shales with thin marlstone. 41.3

5.

Dark gray marlstone with thin partings of shales..................

1.0 14.0

30.7

PLATE 4 DETAILED STRATIGRAPHIC COLUMN

26a

BASE OF DAKOTA TO TOP OF LYKINS

COLOR SYMBOLS

GREENISH GREY

VERMILION

MORRISON

ENTRADA

JELM