Petrographic Study of Miocene Basalts Near Granby, Colorado

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A THESIS StmOMED to

THE BOARD OP TRUSTEES, PRESIDENT AND FAOD&œ OF TBE OO&ORABO aOBOGL OF MIMES IB PARTIAL FULFTLLBERT OP TBE REQ#IBEKE8T& FOR BEE DEGREE OF MASTER OF GEOLOGICAL ERGIKEERIMG

By Myers aden, Colorado April IB, 1940

ProQ uest N u m b e r: 10781344

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PBTROGRAPMIG STUDY OF MIOCENE BASALTS NEAR GRANBY, COLORADO

t# O, Jay Myera

TABLE OF CONTENTS

Page INTRODUCTION

1

STATEMENT OF PROBLEM

2

LOCATION OF AREA

4

PHYSIOGRAPHY AND CLIMATIC CONDITIONS

5

PREVIOUS WORK ,

5

FIELD METHODS

6

STRATIGRAPHY

7

Pre-Cambrian

7

Cretaceous

7

Tertiary

8

THE MIOCENE BASALTS

IS

MICROSCOPIC PETROGRAPHY

15

Sections D-! to D-9, Inclusive

16-25

Sections II-1, M-2,

1-5

25-30

Sections ^1—1#

*e^—4# Q—5*14—6# 0,-7* Q—8

30—35

CONCLUSIONS

35

BIBLIOGRAPHY

3704

AOKBOWLEDGMBBTS

The writer wishes to acknowledge M s appreciation to Dr. John C. Haff, imder whose supervision this work was carried out, for his help and Inspiration» Thanks are also due to llss Johanna Lyon for kindly criticism end help in the preparation of the manu­ script »

PETROGRAPHIC STUD% OF MIOCENE BASALTS BEAR GBAjmar, coLoamo

IÎTTRODUGTIOB Muoli detailed geologic work undertaken in Colo­ rado has been confined to areas of potential economic Im­ portance •

In accordance with this trend* the Granby anti-

oline in Middle Park, Grand County, Colorado* waa mapped by T.

s.

hovering in 1988#

This project was one of several

cooperative Investigations which have been made by the United States Geological Survey in conjunction with the Colorado Metal Mining Association,

the petroleum possibili­

ties suggested by discovery of this structure caused an in­ flux of geologists Into this area shortly after publication of Levering*® report♦

According to Levering# "its struc-

tural features and the probable character of the rocks Involved in It appear to warrant its exploration for oil and gas." (Levering# 1930, p. 75).

In 1955# the Colorado Oil

Refining Company drilled a well in Sec. 13, T. 1 H., R. 77 W.

This well struck granite at 8560 feet. During the summer of 1939, the writer assisted John

0. Haff* Assistant Professor of Geology, Colorado School of lines. In field reconnaissane© of northeastern Middle Park.

L O C A T IO N O F THESIS AREA

0f*»CK TU tit IPS

C*(kN Rio Bcm/vco

/0QULOM.

IYUMA —1

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^ /

P

If E/BERr

Kir CARSON E YF N N F

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SAGUACWF 'cuSTEk! Pug Biol

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I S ON

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L o v e n n rj

3c ale: tzyooo

A re a included, in A irp la n e P h o to g ra p h 0. (3 M / 9^

/49-/24f -J rjfj^o

Other Tertiary Sedim ents

Wy Terrace

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/(7

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Colorado R iv e r

G LO L O C r/C M A P S u p e r im p o s e d A /r p la n e ' .'

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1•Fraser

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on

P h o to 9-38

P lig h t F lo w n : 10-24-38

S c a le : / T IN : R

77

W ;

F/aure

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-/05 fee!

4

the scattered, slumped, talus-covered exposures *

Effect­

ive reconstruction of the geology has required, therefore, exceedingly detailed work in both field and laboratory*

LOCATIOR OF AREA The area covered by this report Is in Middle Park, Grand County, Colorado (Fig* 1) *

It is In the north-

central part of Colorado and approximately eighty miles northeast of Denver via 0. S* Highway 40*

The lava flows

studied crop out about two miles north of Granby and extend from section 24, T. 2 H*, R. 77 W«, through sections IB and 19, T. 2 W*, R* 76 W., to sections 17 and 20, T* 2 R., R* 76 #, (Fig* 2).

The most conspicuous, abundant, and

workable outcrops occur along Willow Creek and on the north bank of the Colorado River*

A good view of the characteris­

tic lava-capped hogbacks may be seen from points south of Table Mountain (Fig* 2) where they occur on both the Church and Horn ranches * The area is easily accessible and may be reached from any part of the state via ïï. S* Highways 40 and 34* The Denver and Salt Lake Railroad crosses the area examined near the junction of the Colorado and Fraser Rivers (Fig* 3) •

5

PHYSIOGRAPHY AND CLIMATIC CONDITIONS Middle Park Is drained by the Colorado (formerly called the "Grand") and Fraser Rivers.

In T. S N#, B, 76

and 77 W«, Willow Greek and Stillwater Creek# running south­ west into the Colorado River# are the two main tributaries • Trail Greek# which empties into Willow Creek about five miles above the junction of the latter with the Colorado liver# is also an important concentration of secondary runoff.

Both the Colorado and the Fraaer Rivera have a moder-

ate flow even during the dry season# as the annual average precipitation is ten Inches• Most of Middle Park Is at elevations of about 7600 feet.

The bottom of the valleys lie at about 7000 feet#

and the ridge tops rise to about 9500 feet.

The terrain is

rough and usually not well wooded except near cultivated lands along the main streams*

Willows predominate# but aspen#

cedar, juniper# and cottonwood occur on slopes more favorable to vegetation*

On the steeper slopes at higher altitudes

brush may be so dense as to make plane table and stadia map­ ping difficult# tedious# and sometimes impossible•

PREVIOUS WORK The most complete geological reconnaissance of Middle Park was made by A* R. Marvin© of the Hayden Survey

6

In 1873 (Hayden (Harvine), 1874, pp. 154-158).

Since then,

no detailed work on the area has been published other than the local contribution of Dr. Love ring, mentioned earlier. An engineering digest issued by the United States Bureau of Reclamation (Bunger, 1937, pp. 21-34)• a reconnaissance report by L. B. Spook (Spook, 1928, pp. 177-261); and an article by Ross L. Heaton on the geological aspects of the Colorado-Big-Thompson Project (Heaton, 1940, pp. 305-306), all of restricted nature, have also appeared.

FIELD METHODS During the summer of 1939, the writer spent six weeks in detailed field work.

In preparation for mapping,

a triangulation net was set up and checked by transit traverse.

A line of levels was then run fros a Colorado State

Highway benchmark; the elevations of some triangulation points established.

Detailed plane table and stadia mapping,

geologic and topographic, was then carried out on the Church ranch (T. 1 H., R. 77 W., Section 30).

This mapping was on

a 1/500 scale, a ten foot contour being used.

Structural

features of the terrain were carefully considered, and some fault zones studied in attempt at correlation.

Parts of the

general area were mapped on United States Forest Service air­ plane photographs (Fig. 3).

Several critical stratigraphie

sections were measured and hand leveled (Figs. 4, 5).

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