DEPARTMENT OF THE INTERIOR

UNITED STATES GEOLOGICAL SURVEY

QEOKGE OTIS SMITH, DIRECTOR

BULLETIN 577

GEOLOGY OF THE PHOSPHATE DEPOSITS 

NORTHEAST OF GEORGETOWN, IDAHO

BY

B. W. RICHARDS AND G. R. MANSFIELD

WASHINGTON

GOVERNMENT PRINTING OFFICE

1914

CONTENTS.

Preface, by H. S. Gale..................................................... 7

Introduction.............................................................. 9

Outline of investigation................................................ 9

Location of the area............ '...................................... . 9

Earlier work.......................................................... 10

Geography............................................................... 11

Physiographic features.................................................. 11

Transportation and industries......................................... 13

Geology....................................................... v ......... 14

General features....................................................... 14

Stratigraphy.......................................................... 14

Outline...............................:........................... 14

Carboniferous system.............................................. 17

Mississippian series. ........................................... 17

Madison limestone (lower Mississippian).................... 17

Upper Mississippian limestone............................. 17

Pennsylvanian series.......................................... 18

Wells formation........................................... 18

Permian (?) series.............................................. 22

Phosphoria formation: ....^................................ 22

Triassic system.......'.....................,....................... 29

Woodside shale............................................... 29

Thaynes limestone............................................. 30

Ankareh shale................................................ 31

Jurassic or Triassic rocks...................'........................ 32

Nugget sandstone (Jurassic or Triassic)......................... 32

Jurassic system.................;................................. 32

Twin Creek limestone......................................... 32

' Cretaceous and Jurassic rocks....................................... 33

Beckwith formation.......................................... 33

Tertiary system................................................... 33

Pliocene (?) limestones and conglomerates ......'................ 33

Quaternary system................ '. ................................ 33

Clays.......................................................... 33

Spring deposits and salt....................................... 34

Alluvium.................................................:... 34

Igneous rocks..................................................... 34

Structure......................----....-.-..............------.-...-... 34

General features..................i................................ 34

Bannock overthrust................................................ 35

Characteristic features......................................... 35

Magnitude.................................................... 37

Age.......................-......:---.-........-:...-......... 38

Other faults....................................................... 38

3
4 CONTENTS.

	Page. 

Detailed description of area................................................. 38

Townships examined.................................................. 38

T. 8 S., R. 44 E........................................................ 39

Stratigraphy...................................................... 39

Structure.......................................................... 39

Phosphate deposits................................................. 40

T. 9 S., R. 44E...................................................... 41

Siirvey............^.............................................. 41

Stratigraphy............................................'.......... 41

Structure............-..-....-..----.-..--.....--.................. 43

Phosphate deposits................................................. 44

T. 10 S., R. 44 E........................ : ............................. 46

Survey..;........................................................ 46

Stratigraphy.................. '. ................................... 46

Structure.......................................................... 46

Phosphate deposits................................................. 47

General features............................................... 47

Quality of phosphate rock....................................... 47

Area and tonnage.............................................. 48

Development.................................................. 48

Ownership. -................................................... 48

Accessibility................................................... 49

T. 11 S., R. 44 E....................................................... 49

Survey..................<........................................ 49

Stratigraphy...................................................... 49

Structure.......................................................... 49

Phosphate deposits................................................. 50

South Canyon district......................................... .50

General features........................................... 50

Character of phosphate rock................................. 51

Area and tonnage.......................................... 54

Proposed development.................................... 54

Ownership................................................. 55

Meade Peak district........................................... 55

Quality of the phosphate rock.............................. 55

Area and tonnage.......................................... 55

Development.............................................. 56

T. 8 S., R. 45E...................................;.................... 56

Survey................................................... 1....... 56

Stratigraphy...................................................... 56

Structure.......................................................... 56

Phosphate deposits................................................. 57

Occurrence.................................................... 57

Quality of rock and tonnage.................................... 57

Development.................................................. 58

T. 9 S., R. 45 E........................................................ 58

Survey..............i............................................ 58

Stratigraphy....'.................................................. 58

Structure....................................................;..... v 59

Phosphate deposits................................................. 59
CONTENTS. 5

Detailed description of area Continued. Page.

T. 10 S., R. 45 E................................................... .'.._ 61

Survey............................................................ 61

Stratigraphy...................................................... 61

Structure.......................................................... 61

Phosphate deposits................................................. 62

Occurrence .................................................... 62

Measured sections and quality of phosphate rock................... 62

Area and tonnage.............................................. 63

Development.................................................. 64

Ownership..................................................... 64

Salt deposits....................................................... 64

T. US., R. 45 E........................................................ 65

Survey............... .......................................... 65

Stratigraphy...................................................... 65

Structure.......................................................... 68

Phosphate deposits................................................. 69

General summary of areas examined........................................... 70

Nature and origin of the rock phosphate..................................... 71

General character. .............^.......................................... 71

Original sedimentary deposits........................................... 71

Specific gravity....................................................... 72

Mineral and chemical composition....................................... 72

Determination of phosphoric acid........................................ 73

Enrichment by weathering.............................................. 73

Iron and alumina...................................................... 73

Source of phosphoric acid and problem of its accumulation................ 74

Index.................................................................... 75
ILLUSTRATIONS.

Page. 

PLATE I. Meade Peak and South Canyon from the ridge in center of sec. 12,

T. 11 S., B. 44 E.............................'...............-.. 10

II. A, Hill in sec. 16, T. 9 S., R. 44 E.; B, Ridge, of Rex chert member 

of the Phosphoria formation extending from sec. 14 through sec. 3, . 

T. 8 S.,B. 44 E..............................'...............!.. 12

III. Stereogram of part of the region traversed by the Bannock

overthrust..................................................... 36

IV. A, Panorama from south-pointing spur on hill north of Georgetown 

Canyon; B, Panorama from point near the southeast corner of the 

area shown in Plate III........................................ 38

V. Geologic map and sections, T. 8 S., R. 44 E........................ 40

VI. Geologic map and sections, T. 9 S., R. 44 E........................ 42

VII. A, Cliffs of Wells formation, west side of Slug Valley, in sec. 18, 

T. 9 S., R. 44 E.; B, Ledges of horizontal beds of the Rex chert 

member of the Phosphoria formation, sec. 28, T. 9 S., R. 44 E.... 44

VIII. A, Wells formation, sec. 5, T. 10 S., R. 44 E.; B, Drag fold in under

limestone and phosphate shales in sec. 25, T. 10 S., R. 44 E...... 45

I.. Geologic map and sections, T. 10 S., R. 44 E....................... 46

X. Geologic map and section, T. 11 S., R. 44 E........................ 50

XI. Geologic map and sections, T. 8 S., R. 45 E........................ 56

XII. Geologic map and sections, T. 9 S., R. 45 E......................... 58

XIII. Geologic map and sections, T. 10 S., B. 45 E........................' 62

XIV. Geologic map and sections, T. 11 S., B. 45 E....................... 68

FIGURE 1. Map showing phosphate reserves in Idaho on July 1,1912......... 10

2. Map showing the relative position of the townships in the phosphate area and their general geologic features.................. 15

3. Section showing structural relations along line A-B on Plate III.. 36 

6
PREFACE.

By HOYT S. GALE.

The original discovery of the western phosphate fields is claimed by 

Albert Richter, of Salt Lake City,1 who, according to his own report, 

first recognized the true character of the deposits somewhere in the 

vicinity of La Plata, Cache County, Utah, in 1889, and traced 

the deposits as far as Bear Lake, locating a number of claims and 

excavating discovery pits on them. Richter states that in 1901 

he laid the matter before several of the larger fertilizer manufacturers 

in the Central States, who made analyses of the samples that proved 

them to contain high-grade phosphate, but evidently these firms 

did not at that time deem it worth while to investigate the deposits 

further, probably because of their remoteness from the market.

Later, according to C. C. Jones,2 the deposits were independently 

recognized by R. A. Pidcock, who in the summer of 1897 found some 

old prospects, presumably located for gold, in a soft black formation 

on Twelvemile Creek, a branch of Woodruff Creek in Rich County, 

Utah, and obtained an analysis of the rock which showed it to be 

phosphate. In May, 1903, according to his own statement, Mr. Jones 

examined the deposits on Woodruff Creek* and after studying them 

in the field he succeeded in tracing their outcrops in many places 

throughout southeastern Idaho, southwestern Wyoming, and northeastern Utah. The deposits had previously attracted the attention 

of many prospectors, who "had made locations on them for their 

possible content of the precious metals and because of the superficial 

resemblance of the outcrop to coal blossom. Mr. Jones, however, 

became a pioneer in the first actual development of the field for its 

phosphate, and to him much credit is due for the systematic, scientific 

way in which his field investigations were prosecuted. His papers 

cited above give an account of his methods and fields of work.

Commercial development of 'the fields has undoubtedly been 

retarded by their situation, remote from fertilizer markets in which 

such material might be utilized, which necessitates rail transportation 

at high cost. Without much question, development has also been

1 Western phosphate discovery: Mines and Methods, vol. 2, No. 9, p. 207,1911.

2 Phosphate rock in Utah, Idaho, and Wyoming: Eng. and Min. Jour., vol. 83, pp. 953-955, 1907; The 

discovery and opening of a new phosphate field in the United States: Am. Inst. Min. Eng. Bull. 82, pp. 

2411-2435, October, 1913.

7
8 PHOSPHATE DEPOSITS NORTHEAST OP GEORGETOWN, IDAHO.

more or less impeded by legal difficulties that have arisen in regard 

to the method of location and the titles of these lands. Methods of 

acquiring private ownership of this type of mineral deposit had 

not previously .been specifically provided in the public-land laws. 

However, when the more detailed work of the Geological Survey was 

first undertaken in these fields in 1909, many of the properties more 

readily accessible to existing railroad lines had already passed into 

private control, although a vastly greater area still remained, 

literally unprospected, as a part of the public domain.

The first lands withdrawn in these phosphate fields comprised an 

area of about 7,000 square miles in Idaho, Utah, and Wyoming. 

This withdrawal was made by direction of the Secretary of the 

Interior under date of December 9, 1908. Thus this action preceded specific land examinations for the purpose of accurately 

defining the field. The area withdrawn was outlined by the aid of 

an interpretation of the geology of the region as shown on the 

Hay den Survey map made in 1877. This interpretation was made 

in the light of more recent knowledge of the geologic relations of the 

deposits.

The United States Geological Survey's investigations in the 

western phosphate fields began in 1906. Since 1909 detailed study 

and classification of phosphate and nonphosphate lands' has been 

made a part of each summer's field work. The results of this work 

have been published in the form of progress reports, and references 

to these reports are given in this paper, which forms one of the 

series and which is the first to appear as a separate bulletin.

The type of geologic survey represented in this work is a development of the constantly increasing requirement for detail. The 

delineation of phosphate outcrops in areas beyond the properties 

that have been located and the estimation of the depth, tonnage, and 

quality of the different beds furnish part of the data required for land 

classification. This work has been done by accurate instrumental 

methods, and the mapping has in large part been performed with a 

degree of refinement which it is unfortunately not possible to reproduce on the small scale of the plates in this bulletin.

Special acknowledgment is due to the authors for their important 

contribution to the knowledge of the structural geology of this region, 

through the recognition and the excellent exposition they have given 

of the important fault which has been named the Bannock overthrust. 

A paper on this fault has already been printed elsewhere. 1

i Richards, R. W., and Mansfield, 0. R., The Bannock overthrust, a major fault in southeastern Idaho 

and northeastern Utah: Jour. Geology, vol. 20, pp. 681-709,1912.
GEOLOGY OF THE PHOSPHATE DEPOSITS NORTHEAST 

OF GEORGETOWN, IDAHO.

By R. W. RICHARDS and G. R. MANSFIELD.

INTRODUCTION.

OUTLINE OF INVESTIGATION.

The geologic examination of the western phosphate fields for 

the United States Geological Survey was continued in 1911 by 

the authors of this bulletin in Idaho and by Eliot Blackwelder in 

Wyoming.

The area studied includes a portion of the lands comprising the 

phosphate reserve created by the withdrawals of December, 1908, 

and December, 1909, by the Secretary of the Interior, which were 

ratified, confirmed, and continued by the President under the act of 

June 25, 1910.

This paper is a progress report of the detailed geologic work for 

the year in southeastern Idaho. The authors were assisted in the 

field by E. L. Troxell and E. C. Ragar. The chairman of the landclassification board, W. C. Mendenhall, made a brief inspection of 

the field methods employed by the party and contributed useful 

suggestions on several of the problems. E. H. Finch was detailed 

to the party for the month of August. G. H. Girty, paleontologist, 

was with the party for three weeks in September and made further 

study of the stratigraphy of the Carboniferous and Triassic portions 

of the section. F. B. Van Horn and A. R. Schultz made a short 

visit to the party during the later part of September.

After the close of the detailed work for the year the senior author 

and Mr. Schultz spent two weeks in a reconnaissance of an area 

lying north of the townships described in this report and south of 

Snake River. A report embodying the results of this reconnaissance 

has been published in Bulletin 530.

LOCATION OF THE AREA.

The accompanying map of the phosphate reserves in Idaho (fig. 1) 

shows the area examined in 1911 and its relation to the areas surveyed in the preceding years and described in Bulletins 430 and 470. 

The area discussed in this report comprises portions of Bear Lake

9
10 PHOSPHATE DEPOSITS NOBTHEAST OF GEORGETOWN, IDAHO.

38 39 40' 41 AZ 43 44 45

I JJVUVGI I 16

38 39 4O. 41 42 43 . 44 45 46

FIGURE 1. Map showing phosphate reserves in Idaho on July 

1,1912. Shaded areas indicate phosphate lands. The areas 

surveyed in 1909-1911, inclusive, are indicated (a, reconnaissance; b, detailed survey).

and Bannock counties in 

southeastern Idaho, and 

includes the phosphate 

deposits in Georgetown 

Canyon, which were 

briefly described in the 

report for 1909.1

EARLIER WORK.

The earliest report on 

the geology of the region 

is that of the reconnaissance of 1877 by A. C. 

Peale 2 of the Hayden 

Survey. If the rapidity 

with which this work 

was done is considered, 

it is an excellent summary of the broader 

stratigraphic and structural features.

In 1907 Weeks and 

Ferrier 3 published a general account of the western phosphate fields with 

brief descriptions of several localities, including 

the Georgetown Canyon 

district (T. 10 S., R. 44

E.).

In 1910 H. S. Gale 4 

and the senior author 

of this bulletin pub1 Gale, H. S., and Richards, R. W., 

Preliminary report on the phosphate 

deposits in southeastern Idaho and 

adjacent parts of Wyoming and 

Utah: U. S. Geol. Survey Bull. 430, 

pp. 457-535,1910.

2 Peale, A. C., U. S. Geol. and 

Geog. Survey Terr. Eleventh Ann. 

Kept., pp. 511-644,1879.

3 Weeks, F. B., and Ferrier, W.F., 

Phosphate deposits in western United 

States: U. S. Geol. Survey Bull, 315, 

pp. 449-462,1907.

« Gale, H. S., and Eichards, R. W., 

Preliminary report on the phosphate 

deposits in southeastern Idaho and 

adjacent parts- of Wyoming and 

Utah: U. S. Geol. Survey Bull. 430, 

pp. 483-488,1910.
U. S. GEOLOGICAL SURVEY 

yi *iS

MEAQE PEAK AND SOUTH CANYON.

From ridge in center of sec. 1 2, T. 11 S., R. 44 E. Cl, Mississippian limestone; Cw, Wells formation; Cpa, Rex chert m

Twin Creek limestone.
GEOGRAPHY. 11

lished a more detailed reconnaissance of the Georgetown Canyon 

district, in which the extent and quality of the phosphate deposits 

of the area was first presented.

In the same year C. L. Breger * described the geology of the portion 

of the area that includes Crow Creek and discussed the origin of the 

salt deposits of the vicinity.

In 1911 the writers 2 published a preliminary report of detailed 

geologic work in areas adjacent to the region described in the present 

report and in the paper by Mr. Gale and the senior author.

GEOGRAPHY.

PHYSIOGRAPHIC FEATURES.

The area examined in detail in 1911 comprises eight townships 

lying in the two ranges immediately east of the area surveyed in 1910 

and including Tps. 8 to 11 S., Ks. 44 and 45 E. of the Boise meridian. 

The geographic features of the region therefore form the eastward 

continuation of those described in the report of the work done in 

1910.3

The general topography of the area is marked by a series of curving 

ridges, whose trend varies from a little east of north in the southern 

part of the area to northwest in the northern part. Between the 

ridges are valleys that in the southern part are relatively narrow and 

deeply cut but in the central and northern parts are broadly opened 

basins.

The most pronounced topographic feature of the region is the 

series of ridges that passes northward nearly through the center and 

comprises portions of the Preuss Range, Snowdrift Mountain, and 

Dry Ridge. Meade Peak (Pis. I and IV, A), in the SW. i NW. i 

sec. 6, T. 11 S., R. 45 E., which has an elevation of 9,953 feet, is the 

highest point of the region. Snowdrift Mountain, a ridge 4 or 5 miles 

long, has an elevation of 9,000 to 9,700 feet, and Dry Ridge maintains an elevation of 8,500 to nearly 9,000 feet for a distance of 10 

miles or more. To the east and west the ridges are broader and more 

interrupted.

The lowest elevation, about 5,950 feet, is found in the southwest 

corner of T. 11 S., R. 44 E. The maximum relief is therefore about 

4,000 feet. The larger canyons are cut from 1,000 to 2,500 feet or 

more below their adjacent ridges.

The area lies within two great drainage basins. The southwest 

part is drained by branches of Bear River, one of the main feeders of 

Great Salt Lake. The greater part, however, is contributory to the

1 Breger, C. L., The salt resources of the Idaho-Wyoming border, with notes on the geology: U. S. Geol. 

Survey Bull. 430, pp. 555-569,1910.

* Richards, R. W., and Mansfield, G. R., Preliminary report on a portion of the Idaho phosphate reserve: 

U. S. Geol. Survey Bull. 470, pp. 371-439.1911.

«Idem, pp. 372-374.
12 PHOSPHATE DEPOSITS NORTHEAST OF GEORGETOWN, IDAHO.

Snake-Columbia system and drains into the Pacific Ocean. The 

divide, which thus constitutes a part of the Great Basin and Pacific 

divide, lies along the boundary between Bear Lake and Bannock 

counties and passes westward south of Crow Creek in T. 11 S., R. 

45 E., northward along Snowdrift Mountain in T. 10 S. 3 R. 45 E., 

around the head of Georgetown Canyon, and westward around the 

head of Slug Creek in T. 10 S., R. 44 E.

The topography shows a very close adjustment to structure. The 

region is crossed by a series of narrow folds that pitch gently northward and have the same general trend as the ridges. The great 

longitudinal valleys are strike or subsequent valleys, eroded along 

the outcrop of the softer or weaker members of the strata exposed. 

Dry Valley, the largest depression within the area, is excavated on 

the west flank of an anticline. Its southern part is drained westward 

by transverse streams into Slug Valley. Tne northern part drains 

northward into Blackfoot River. The divide lies in the broad flat 

floor of the valley. . ;

There are numerous small strike valleys, and one is sufficiently 

large and well developed to merit special comment. This valley 

crosses the northeast part of T. 8 S., R. 44 E., and causes Dry Ridge 

to fork into a main ridge.and a well-marked subordinate flanking 

ridge on the west (PI. II, B). This valley lies along the contact 

between the heavy cherts of the Rex chert member of the Phosphoria 

formation on the west and the sandy and shaly limestones of the 

Woodside shale on the east. The Rex chert forms a remarkable dip 

slope along the west side of this valley.

The topography gives evidence of three well-defined cycles of 

erosion. The hill and ridge tops have developed more or less even 

sky lines or gentle slopes, indicating an advanced stage of erosion. 

These older surfaces are cut by the present sharp-featured canyons, 

most of which are young. An intermediate level at an elevation of 

about 7,500 to 7,750 feet is well marked in many places, particularly 

in Georgetown Canyon in T. 10 S., R. 44 E., where rock terraces extend along both sides of the canyon about 2,000 feet below the bordering ridges. These terraces appear to indicate an intermediate, 

maturely developed cycle of erosion, for they occur not only where 

rocks of different character and resistance form the ridge and terrace, 

as in Georgetown Canyon, but also where rocks of the same general 

character and resistance form both ridge and terrace, as along the 

west side of Dry Ridge in T. 9 S., R. 45 E. These intermediate 

terraces seem to lack uniform development, probably because of the 

varying resistance and structure of the rocks involved.

The basins of the region are important topographically and are 

valuable for grazing and agricultural land. Some are apparently of 

structural origin, like the beautiful basin in the southwest corner of
U. S. GEOLOGICAL SURVEY BULLETIN 577 PLATE

Cp

A. HILL IN SEC. 16, T. 9 S., R. 44 E. 

Showing succession from lower part of Wells formation (Cw) to upper part of Phosphoria formation (Cp).

' >" .. S. RIDGE EXTENDING FROM SEC. 14 THROUGH SEC. 3, T. 8 S., R. 44 E. 

Showing strike of Rex chert member (Cp-a); Cp-b, phosphate shales, Phosphoria formation; Cw, Wells formation; Tw, Woodside shale.
GEOGRAPHY. . 13

T. 9 S., R. 44 E. Others, like Slug Valley and Dry Valley, are eroded 

along the strike of upturned beds. In Slug Valley the formation of 

the basin may also have been influenced by the faulting. In other 

portions of the area, as in sees. 10 and 22, T. 9 S., R. 45 E., basins 

have been developed at the intersection of longitudinal and transverse valleys, which now form excellent grazing meadows. The 

slopes of the floors of these basins are so gentle and the drainage is 

so poor that alluvial deposits have accumulated and. have partly 

buried some of the lower rock hills, which now rise like islands above 

the level of the alluvium.

Alluvial fans are formed along the borders of the larger basins, 

particularly along the east side of Dry Valley, a fine example being 

found in sec. 9, T. 8 S., R. 44 E. These fans are now somewhat 

dissected.

Along the top of Snowdrift Mountain in T. 10 S., R. 45 E., a series 

of interesting basins has been formed, probably by the combined 

action of solution and nivation. 1 The exterior walls of the basins 

rise about 30 to 50 feet above the basin floors and, were it not for the 

gaps here and there, which allow views of the adjacent lower country, > 

the traveler passing through these basins would hardly realize that he 

was on the top of a high mountain. The basins are excavated in 

limestones that have sharp anticlinal structure. . Small sink holes 

also occur in places along the top of the ridge.

TRANSPORTATION AND INDUSTRIES.

The region surveyed is touched by the Oregon Short Line Railroad 

at three points in Idaho, namely, Georgetown, Montpelier, and 

Soda Springs. Georgetown, however, is the only village strictly 

within the area here described. The location of the other two 

towns mentioned is shown on the general map (fig. 1, p. 10).

Wagon roads to each of these three towns constitute the principal lines of travel in the area. The Montpelier-Afton (Wyoming) 

stage road is kept open throughout the year, but the roads from 

Georgetown and Soda Springs, although possibly better for summer 

travel, are generally rendered impassable by the heavy snowfall 

of winter.

About seven-eighths of the area lies within the Caribou National 

Forest. However, a large portion of that area is not idle, for both 

grazing and lumbering under a system of permits are in operation. 

The sparsely timbered areas are no longer overstocked, as they were 

prior to the establishment of the national forest, and the well-timbered 

areas are utilized with a view to conservation. The attitude of the 

inhabitants of the region toward the national forest is well shown

1 Matthes, F. E., U. S. Geol. Survey Twenty-first Ann.^Rept., pt. 2, pp. 179-185,1900.
14 PHOSPHATE DEPOSITS NORTHEAST OF GEORGETOWN", IDAHO.

by the report that they have petitioned for an extension of the forest, 

to include the unreserved portion of the Montpelier Creek basin.

Except in the vicinity of Georgetown, Crow Creek, and lower 

Slug Creek, the ranches are occupied only during the summer months, 

and the inhabitants are occupied mainly with dairying and sheep 

grazing.

The continued growth of the settlements centering about Afton, 

Wyo., in the. Star Valley, together with the economic value of the 

phosphate, saline, and other deposits of the region, will eventually 

lead to further railroad construction. Several preliminary location 

surveys are reported to have been made, but little is known as to 

which is the most desirable or most likely to be utilized.

GEOLOGY.

GENERAL FEATURES.

The greater part of the area, including that which contains the 

.valuable phosphate deposits, is underlain mainly by stratified rocks 

ranging from early Carboniferous to Lower Triassic age. Besides 

.these rocks small areas of Tertiary and Quaternary rocks, including 

basalt, are present and locally conceal the older formations.

In the southern and eastern part of the area the higher Triassic, 

Jurassic, and basal Cretaceous rocks outcrop. Their presence in 

apparently undisturbed sequence indicates that the - Permian (?) 

phosphate deposits lie too deep for recovery.

All the rocks of the area, except those of late Tertiary and Quaternary time, have been so folded that the areal distribution of any 

formation is determined mainly by the structure of the rocks.

Major and minor faulting in addition to the folding complicates 

the distribution of the several formations, so that certain local areas 

of the Thaynes limestone and Woodside shale are not underlain, 

as they are in most places, by the Permian (?) phosphate, and conversely the strata are in places overturned so that rocks older than the 

phosphate actually overlie it. This complexity of the structure 

justifies a rather extended review of the stratigraphy and the structure 

of the region.

STRATIGRAPHY. 

OUTLINE.

The general characters of the several geologic formations outcropping in the area examined are given in the table (p. 16), and 

further details concerning them are set forth in the following pages.

Figure 2 shows the general geologic relations of the region discussed in this report.
GEOLOGY. 15

R.44 E. R.45 E.

LEGEND

B ,

r,ooo;

5,000,

6,000

FIGURE 2. Map showing the relative position of the townships in the phosphate area and their general geologle

features. Geologic section at bottom.
16 PHOSPHATE DEPOSITS NORTHEAST OF GEORGETOWN, IDAHO.

General section of phosphate area in southeastern Idaho.

System.

Quaternary.

Tertiary.

Cretaceous and Jurassic.

Upper Jurassic.

Jurassic or Triassic.

Lower Triassic.

Carboniferous.

Series.

Pliocene 

(?) 

Permian 

(?).

Pennsylvanian.

Upper Mississ ip - 

pian.

Lower Mississ ip - 

pian.

Formation.

Unconformity. 

Beckwith formation.

Twin Creek limestone.

Nugget sandstone.

Ankareh shale.

Thaynes limestone.

Woodside shale.

Phosphoria formation. 

Unconformity in places.

Wells formation.

Madison limestone.

Thickness 

(feet).

00

00

4,650±

3,500±

1,900

6670

2,000±

c 1,000- 

1,500

315-730

2,400

1,130+

1,000±

General character.

Alluvium, travertine, clays, and 

basalt flows.

White marls, marly limestones, 

calcareous conglomerates; dense, 

nearly lithographic limestones 

near Soda Springs; pea-green 

grits.

Red shale and sandstone for 1,200 

feet, overlain by 250-600 feet of 

greenish-gray sandstone, which is 

overlain by conglomerate succeeded by limestone.

Grayish-white shaly limestone.

Massive red sandstone, with white 

conglomeratic sandstone at base 

and locally white sandstone at 

top. In places silicified to a 

quartzite.

Essentially red shale and mottled 

red and greenish clay and shales, 

with some sandstone and some 

limestone.

Main body of the formation darkblue limestone, in many places 

fossiliferous, weathering to a 

brown muddy color, also including sandy and calcareous shale.

Thin-bedded calcareous shales, 

with intercalated muddy limestones; heavy limestone beds at 

top.

(a) Rex chert member at top, 240-550 

feet. One or more massive 

strata of cherty limestone or 

chert, prominent as a ledge 

maker, grading in part to a purplish cherty or flinty shale. 

(*) Rock phosphate, phosphatic 

shale, sandstone, and minor 

limestone bands.

Massive white calcareous sandstone, weathering with projecting fossil fragments, generally 

with bluish chert bands and in 

some localities with black chert 

in rounded nodules in the lower 

portion. 

White sandstone and quartzite, 

calcareous sandstones, and lightcolored limestones, with variable 

amounts of interbedded quartzites. Light-colored cherty limestone with interbedded sandstones.

Bluish-gray thick-bedded limestones with spherical nodules of 

black chert; gray sandy limestone streaked with calcite and 

specked with siderite; locally 

marked with fossil corals, crinoid 

stems, and brachiopods.

Thick massive blue to gray limestone, generally making high 

mountainous country where 

brought to the surface in mass; 

thinner bedded than overlying 

limestone.

Not measured. 6 Near Montpelier. In the Preuss Range.
GEOLOGY. 17

CARBONIFEROUS SYSTEM.

MISSISSIPPI^ SERIES. 

MADISON LIMESTONE (LOWER MISSISSIPPIAN).

The basal Carboniferous sediments of the area are dark bluish-gray, 

relatively thin-bedded limestones, which resist erosion and form cliffs. 

They are brought to the surface in small areas by the erosion of some 

of the anticlines or by faulting. The base of the formation is not 

exposed but the thickness amounts to 1,000 feet, more or less. The 

fauna collected from these beds includes small cup corals. Syringopora, Loxonema, Productella, Spirifer centronatus, Chonetes, 

Euomphalus, and other fossils. According to G. H. Girty, this fauna 

corresponds to that of the basal portion of the " Wasatch limestone" 

of the Wasatch Mountains of Utah, as described by the early writers.

UPPER MISSISSIPPIAN LIMESTONE.

Above the Madison limestone, apparently in conformable succession, though the base is not exposed, lies about 1,130 feet of massive 

light to dark gray limestones, weathering white to light gray. Locally 

a dark shale zone about 15 feet thick is present near the top. In 

places also chert nodules occur in concentric and irregular forms, together with streaks of chert. The limestones are in places specked 

with siderite and seamed with calcite or aragonite and are abundantly fossiliferous at some horizons. The fauna includes large cup 

corals with many fine septa, Syringopora, Lithostrotion, Martinia, 

and Productus giganteus. The Martinias form a bed near the top of 

the formation.

The formation constitutes much of the»Preuss Range and is well 

exposed in Meade Peak, the culminating point of that range. (See 

Pis. I and IV, A.) No complete section has been measured because 

of structural interruptions, but future studies in the Ross Fork 

locality may afford a more favorable opportunity to obtain the uninterrupted sequence, and the selection of a type locality for the formation is deferred for the present.

The authors are also indebted to G. H. Girty for the following 

faunal list and comments:

An interesting and varied fauna has in places been obtained from the upper part 

of the upper Mississippian. It is shown by the list of forms collected at station 101. 

A short distance below this collection a new species of Martinia was found in countless 

numbers, constituting a bed a foot thick. Very abundant also in local occurrences 

is a small variety of Productus giganteus. Large zaphrentoid corals are likewise a 

feature of the upper Mississippian, being commonly associated with Syringopora and 

one or more species of Lithostrotion. Some of these colonies are of great size. At this 

horizon in some places is also found an assemblage of small forms more or less related 

to the Spergen fauna reported by Meek from Ross Fork. The horizon of all these 

rather strikingly different facies appears to be below that of station 101. 

37002° 14 2
18 PHOSPHATE DEPOSITS NORTHEAST OF GEORGETOWN, IDAHO.

The following fossils were collected at station 101:

Zaphrentis sp. 

Stenopora sp. a. 

Stenoporasp. b. 

Stenopora? sp. 

Batostomella? sp. 

Rhombopora? sp. 

Productus semireticulatus. 

Productus semireticulatus var. 

Productus pileiformis. 

Productus punctatus var. 

Productus aff. longispinus. 

Diaphragmus elegans. 

Camarophoria wortheni. 

Dielasmasp. 

Spirifer striatus? 

Spirifer increbescens? 

Spiriferina sp. 

Composita trinuclea? 

Edmondia sp.

Edmondia? sp. 

Conocardium sp. 

Schizodus sp. 

Sphenotus sp.

Myalina aff. sanctiludovici. 

Leptodesma aff. spergenense. 

Sulcatipinna ludlowi? 

Parallelodon? sp. 

Cypricardinia? sp. 

Aviculipecten sp. a. 

Aviculipecten sp. b. 

Aviculipecten sp. c. 

Pseudomonotis? sp. 

Laevidentalium venustum? 

Naticopsissp. 

Straparollus similis var. 

Bulimorpha aff. elongata. 

Griffithides sp. 

Phillipsia sp.

PENNSYLVANIAN SERIES.

WELLS FORMATION.

The upper Mississippian limestone is succeeded by about 2,400 feet 

of sandy limestones, calcareous sandstones, and quartzites of somewhat variable character. No unconformity has yet been recognized 

between the underlying formation and these rocks in this field, though 

Blackwelder* has observed such a relation between the Mississippian 

and the Pennsylvanian in Utah.

The rocks of this formation occupy the same stratigraphic position 

as that of the Morgan, Weber, and a portion of the Park City formations of Utah. In the Idaho field, however, these rocks show such 

variable lithologic features that it has been found impracticable to 

apply the names Weber and Morgan. Furthermore, Mr. Girty states 

that from the f aunal evidence there is no certainty that these divisions 

as recognized are actually the equivalents of the formations in Weber 

Canyon, Utah. On faunal and structural grounds it has been found 

necessary to include in this formation the calcareous sandstone or 

siliceous limestone that normally underlies the phosphate shales and 

has hitherto been included in the Park City formation.2 To the 

groups of strata thus constituted the name Wells formation has been 

assigned,3 from Wells Canyon, in T. 10 S., R. 45 E., where a detailed

1 Blackwelder, Eliot, New light on the geology of the Wasatch Mountains, Utah: Geol. Soc. America 

Bull., vol. 21, p. 530,1910.

2 Gale, H. S., and Richards, R. W., Preliminary report on the phosphate deposits in southeastern Idaho 

and adjacent parts of Wyoming and Utah: U. S. Geol. Survey Bull. 430, pp. 457-535, 1910. Richards, 

R. W., and Mansfield, G. R., Preliminary report on a portion of the Idaho phosphate reserve: U. S. Geol. 

Survey Bull. 470, pp. 371-439,1911.

a Richards, R. W., and Mansfield, G. R., The Bannock overthrust, a major fault in southeastern Idaho 

and northeastern Utah: Jour. Geology, vol. 20, pp. 681-709,1912.
GEOLOGY. 19

section was measured. The formation here consists of three somewhat variable portions, of which the upper and lower are predominantly calcareous, whereas the middle is mainly sandy.

The lithologic succession above outlined differs from that in Weber 

Canyon, Utah, where the order, as given by Mr. Girty, who has 

recently reviewed that section, is white quartzite at the top, succeeded below by gray calcareous sandstone, and at the base red 

quartzite (Morgan formation).

The following section was measured at the type locality:

Geologic section of beds exposed on north side of Wells Canyon, Idaho.

Wells formation: Feet. 

Limestone, light brownish gray, sandy, containing Squamu- 

. laria or Composita and crinoid stems, possibly Productus.... 5

Chert, bluish gray........................................ 1

Limestone, light brownish gray, sandy...................... 44

Concealed................"................................ 172

Sandstone, gray, calcareous, fine grained, in loose blocks, and 

thin beds of quartzite or chert............................ 150

Concealed.................................................. 50

Sandstone, whitish, soft, in loose blocks; weathers like limestone, and contains small quartz-lined geodes; poorly exposed, and partly represented by sandy soil and small fragments. .................................................. 350

Limestone, light bluish gray, earthy, with considerable dark 

chert......................................'.............. 230

Sandstone, yellowish to red, weathered in large rounded 

blocks................................................. 100 

Sandstone, whitish, rather soft ............................. 150

- Quartzite, white, weathers pink to red, in large loose slabs,

laminated and cross-bedded............................... 200

Limestone, in part clear, in part cherty...................... 200

Limestone, dark gray, with large chert concretions; furnished 

fossil collection No. 45................................... 200

Limestone, sandy, alternating with quartzite and clearer 

limestone............................................... 400

Sandstone, whitish, fine grained, one bed .................... 2

Sandstone, red in part, nearly quartzite, cross-bedded........ 100

Limestone, sandy, with quartz-lined geodes, one bed........ 3

Sandstone, white to reddish, soft; bears abundant Schizophoria and also furnished fossil collections Nos. 28 and 32 

from near-by locality .................................... 35

Sandstone, single bed....................................... 2

Sandstone, thin bedded; furnished fossil collection lOlc...... 6

Total thickness, Wells formation....................... 2, 400

Upper Mississippian:

Limestone, earthy, with chert in irregular concretions and 

streaks parallel to bedding............................... 20

Limestone, light gray to whitish, thin bedded; furnished fossil collection 101........................................ 46

Sandstone, white; calcareous; bears large zaphrentoids........ 14
20 PHOSPHAT^ DEPOSITS NOBTHEAST OF GEORGETOWN, IDAHO.

Upper Mississippian Continued. Feet. 

Limestone, dark gray, crinoidal; includes a Martinia horizon,

about..................................................... 100

Shale and reddish quartzite fragments, about................ 30

Quartzite, whitish, outcrops small and scattered; bears small

zaphrentoids............................................ 270

Concealed................................................ 200

Limestones, gray, in 1 to 3 foot beds; furnished fossil collections. 450 

Base of upper Mississippian not exposed.

Thickness of Upper Mississippian exposed.............. 1,130

Total thickness of section............................ 3,530

The principal variations in the three portions of the Wells formation 

in the area studied are as follows:

\ The upper member ranges from a maximum thickness of 75 feet to 

a mere trace. It consists of dense calcareous sandstone grading into 

siliceous limestone, which weathers into white massive beds that are 

conspicuous cliff makers (PI. II, A, and VII, A, p. 44). Bluish-white 

chert occurs in bands 2 inches to 1 foot thick and locally in ovate 

nodules. Toward the base the chert becomes more nodular and 

darker. Silicified fragments of brachiopods project in little crescents 

from the weathered surface of the limestone.

Locally the upper member is absent and the overlying Phosphoria 

formation rests directly upon the more sandy middle member of the 

Wells formation, which in these places is composed of a breccia of 

chert and quartzite, similar to that described by Blackwelder * as 

occurring under similar conditions, and which apparently represents 

a brief erosion interval at the close of the deposition of the Wells 

formation.

G. H. Girty says in a personal letter:

The upper part of the Wells formation is usually nearly barren of fossils. Locally 

large Product! of the semireticulatus group are found, as at station 49, in the SW. £ SE. £ 

sec. 35, T. 9 S.,-K. 45 E., few of them, however, in identifiable condition. Some 

well-preserved examples obtained at this horizon near Swan Lake, Bannock County, 

show a form closely allied to Productus ivesi. In that region also a small spiriferoid 

is very abundant, occurring as silicified fragments which project from weathered 

surfaces like small arched scales. The specimens of these fossils that can be identified 

belong to a species of Squamularia related to S. perplexa.

The middle portion of the Wells formation comprises 1,700 to 1,800 

feet of sandy limestone, in places containing thin beds of quartzite 

and sandstones. This portion of the formation weathers white, red, 

or yellow and forms smooth slopes with few projecting ledges (PI. I). 

Locally thin limestone beds interstratified with the sandstones have 

become silicified to dense quartzite bands (PI. VIII, A, p. 45). These 

rocks may be sparingly fossiliferous, but no fossils have been found 

in them. Locally a siliceous facies becomes strongly developed and

' Blackwelder, Eliot, Newlight on the geology of the Wasatch Mountains, Utah: Geol. Soc. America Bull., 

vol. 21, p. 532,1910.
GEOLOGY. 21

this portion of the Wells formation is then comparable with the Weber 

quartzite of Utah.

In the section under discussion sandy and cherty limestones with 

thin interbedded sandstones are conspicuous in the lower portion of 

the Wells formation. The maximum observed interval of beds included in this facies is about 750 feet. Within a distance of 2 miles 

to the north the same interval .was found on careful study to comprise only about 100 feet of beds. The cherty limestones are prominent ledge makers and carry a fauna which, according to G. H. Girty, 

is probably similar in age to, although not specifically identical with, 

that found in the Morgan formation of Utah. Blackwelder * has 

described the Morgan formation as composed of red sandstone, shale, 

and thin intercalated limestones, so that lithologically it is wholly 

distinct from the cherty limestones described above. G. H. Girty 

has contributed the following faunal lists of collections from the 

Wells formation and makes the following comments:

At the very base of the Wells formation a Schizophoria is in many places very 

abundant, apparently the same species which White identified in New Mexico as 

S. resupinoides? (lot 10Ic). A short distance above a more varied fauna is usually 

found in which a large variety of Spirifer rockymontani.is, the same which I identified 

in Colorado as S. boonensis, is specially abundant (stations 28 and 32). Large branching Stenoporas related to $. carbonaria are also a feature of this fauna. Another 

phase of the lower Wells fauna is shown in lot 33. In this assemblage of epeciea 

Marginifera splendens is extremely common and large branching Stenoporas are also . 

plentiful

Lot 33. Southwest corner of sec. 22, T. 9 S., R. 45 E. From beds about 500'feet 

above base of Wells formation:

Stenopora wellsiana.

Stenopora gracilis. 

Stenopora idahoensis. 

Stenopora? ep. 

Derbya sp.

Lot 45 (see section): 

Zaphrentis gibsoni. 

Monilipora prosseri. 

Rhombopora lepidodendroides. 

Productus cora.

Lot 28. SE. i sec. 35, T. 9 S., R. 45 E.: 

Spirifer rockymontanus.

Productue cora. 

Productus nebraskensis. 

Productus semireticulatus. 

Marginiiera splendens. 

Spirifer rockymontanus.

Productus Bemireticulatus. 

Spirifer cameratus. 

Composita subtilita. 

Euconospira n. sp.

Aviculipecten sp.

Myalina aff. kansasensis. 

Lot 32. Same locality as lot 28, but from beds about 150 feet lower in the section:

Stenopora idahoensis. 

Stenopora? sp. 

Batostomella? sp. 

Derbya sp.

Productus cora. 

Spirifer rockymoritanus. 

Composita subtilita. 

Myalina ep.

Lot lOlc (see section): Schizophoria resupinoides?

1 Blackwelder, Eliot, Geol. Soc. America Bull., vol. 21, p. 529,1910.
22 PHOSPHATE DEPOSITS 1STOBTHEAST OF GEORGETOWN, IDAHO.

PERMIAN (?) SERIES. 

PHOSPHORIA FORMATION.

The name of the Phosphoria formation is derived from Phosphoria 

Gulch in T. 10 S., R. 44 E., where the formation is typically exposed. 

This gulch joins Georgetown Canyon at a distance of 2£ miles N. 

16° W. of Meade Peak. 1

The name of the Rex chert member, suggested by H. S. Gale, is 

derived from Rex Peak in the Crawford Mountains, Rich County, 

Utah, where the chert forms an anticlinal cap.

The Phosphoria formation is the equivalent of the upper two members of the Park City formation 2 as heretofore mapped in the phosphate districts of Idaho and Utah, namely, the "overlying chert" 

and the phosphate shales. These members have also been recognized in the type section 3 of the Park City "in Cottonwood Canyon 

by H. S. Gale,4 who reviewed the section in 1909, and noted the 

presence of phosphate rock. Gale regards the upper 129 feet of 

Boutwell's section as approximately equivalent to the chert member, 

and the underlying 112 feet as representing the phosphatic shale 

interval.

The remaining 194 feet of Boutwell's section is predominantly 

siliceous, but contains a number of prominent limestone beds and is 

evidently comparable to the underlying siliceous limestone or calcareous sandstone of the phosphate districts.

The Park City formation was first referred by Boutwell to the Pennsylvanian, but in his later work on the district 5 he has referred it as' 

a whole doubtfully to the Permian. The lower portion, which contains the bonanzas for which the Park City district is famous and is 

therefore the important part of the formation, has now, on additional 

faunal evidence, been referred to the Pennsylyanian. Other reasons 

for the separation in the Idaho field of the two upper members of 

the Park City formation from the lowest member are found in the 

pronounced lithologic differences between this member and the overlying phosphate shales and in the fact that in certain areas in southeast Idaho the phosphate shales rest unconformably on the more 

siliceous portion of the Wells formation.

1 Richards, R. W., and Mansfield, G. R., The Bannock overthrust, a major fault in southeastern Idaho 

and northeastern Utah: Jour. Geology, vol. 20, pp. 681-709,1912.

2 Boutwell, J. M., Stratigraphy and structure of the Park City mining district, Utah: Jour. Geology, 

vol. 15, p. 444,1907. Gale, H. S., and Richards, R. W., Preliminary report on the phosphate deposits in 

southeastern Idaho, Wyoming, and Utah: U. S. Geol. Survey Bull. 430, p. 475,1911.

» Boutwell, J. M., loc. cit.

* Personal communication.

6 Boutwell, J. M., Geology and ore deposits of the Park City district, Utah: U. S. Geol. Survey Prof. 

Paper 77,1912.
GEOLOGY. .23

The Phosphoria formation is also correlated with the upper portion 

of the Embar formation of Wyoming 1 and the phosphatic beds above 

the Quadrant formation of certain areas 2 in southwestern Montana.

The Rex chert member is the conspicuous portion of the Phosphoria 

formation, and because .of its superior hardness it forms salient topographic features (Pis. II, B, and VII, B, p. 44). The phosphate shales, 

on the other hand, are comparatively nonresistant and the development of gulches along them is characteristic. The following table 

shows the thickness and character of the Rex chert:

Complete section of Rex chert member in sec. 12, T. 10 8., R. 44 E. of Boise meridian.

Feet. 

Shale, black, cherty, weathers red............................... 80

Chert, brown to purple, in heavily iron stained ledges. ........... 60

Limestone, gray, banded, with ashy gray to black chert........... 100

240

Locally 50 to 75 feet above the base the Rex chert gives way to 

gray limestone, and in other places a dark-gray to black or purplish 

flinty or cherty shale occupies the major portion of the Rex chert 

interval, but more generally the shaly facies is present near the top 

of the section and is in places with difficulty distinguished from, the 

basal portion of the Woodside shale.

The Rex chert is generally nonfossiliferous but locally contains 

spicules and casts of crinoid stems. G. H. Girty lists the following 

vas the most characteristic species:

Productus multistriatus. 

Productus subhorridus.

Spiriferina pulchra. 

Composita subtilita var.

Spirifer aff. cameratus.

At a locality on Deer Creek in the Preuss Range Mr. Girty obtained 

the following fauna from the limestone facies of the Rex chert:

Amphoporella laminaria. 

Productus nevadensis.

Productus multistriatus (?). 

Camarophoria n. sp.

Productus eucharis.

The Rex chert shows considerable range in thickness, so that the 

width of.its outcrop as mapped is not wholly dependent on the inclination of its beds. It ranges from a minimum thickness of about 240 

feet in T. 10 S., R. 44 E., to a maximum of about 550 feet in T. 9 S., 

R. 45 E.

The Rex chert locally contains a thin bed of rock phosphate, which 

is in most places less than 6 inches in thickness.

1 Carton, N. H., Paleozoic and Mesozoic of central Wyoming: Bun. Geol. Soc. America, vol. 19, p. 416, 

1908. Blackwelder, Eliot, A reconnaissance of the phosphate deposits in western Wyoming: U. S. Geol. 

Survey Bull. 470, p. 459,1911.

2 Gale, H. S., Rock phosphate near Melrose, Mont.: U. S. Geoi. Survey Bull. 470, pp. 440-451, 191L 

Blackwelder, Eliot, New light on the geology of the Wasatch Mountains, Utah: Geol. Soc. America Bun., 

vol. 21, pp. 517-532, 1910.
24 PHOSPHATE DEPOSITS NORTHEAST OF GEORGETOWN, IDAHO.

The remaining portion of the Phosphoria formation, the basal 

division, consists of 75 to 180 feet of yellowish to brown phosphatic 

sandstones and shales, with one to three important beds of oolitic 

rock phosphate and in some places dark-colored fetid limestones in 

beds and lenses. The limestones are from 3 inches to 2 feet thick.

The fauna of the phosphate shales is extensive and has.been studied 

by G. H. Girty, who has selected the following characteristic list from 

his bulletin 1 on the subject:

Lingula carbonaria (?). 

Lingulidiscina missouriensis. 

Chonetes ostiolatus. 

Productus geniculatus. 

Productus eucharis. 

Productus montpelierensis.

Pugnax osagensis var. occidentalis. 

Ambocoelia arcuata. 

Leda obesa. 

Plagioglypta canna. 

Omphalotrochus ferrieri. 

Omphalotrochus conoideus. 

Productus phosphaticus. Hollina emaciata var. occidentalis.

Pugnax weeksi.

The following section of the phosphate shales, measured in 1909 in 

Georgetown Canyon, is on the whole the most satisfactory one obtained 

in the western fields and shows the maximum phosphate content, 

both in high-grade and low-grade material.

Section of basal portion of Phosphoria formation in Georgetown Canyon (SE. J NW. \

sec. 30, T. 10 S., R. 45 E. of the Boise meridian), Idaho.

[Land lines theoretical.]

Field 

No. of specimen.

144-A 

144-B 

144-C

144-D 

144-E

144-F 

144-G

144-E 

144-1

Shale, calcareous, or muddy limestone, brown, weathering

Phosphate rock, oolitic, weathering brown or gray; effervesShale, hard, brown, calcareous at the top; effervesces vigorouslv

Phosphate rock, coarsely oolitics gray; effervesces vigorously. 

Shale, brownish, earthy, containing 6 laches of phosphate;

Phosphate rock, including Ft. in. 

Phosphate rock, oolitic, hard, gray, calcareous. .... 7

(Sample shows considerable effervescence.) 

Phosphate rock, including 

Phosphate rock, coarsely oolitic, gray, brittle. ..... 1 2 

Phosphate rock, finely oolitic, brownish gray. ..... 4

Phosphate rock, finely oolitic, brownish pray. ..... 4

(Sample effervesces slightly.) 

Phosphate rock, including 

Phosphate rock, medium to finely oolitic, brownish

Shale, phosphatic, brownish, somewhat oolitic .... 10 

Phosphate rock, coarsely oolitic ................... 2

Phosphate rock, including 

Phosphate rock, coarsely oolitic, brownish-black

(Sample effervesces considerably.)

P2 06 .a

Per cent. 

3.5

35.8

Trace. 

37.6

10.0 

I 21.9

33.3

29.3 

i 34.7

Equivalent to 

Cas(P04)2.

Per cent.

7.7

78.4

82.1 

21.9

48.0 

72.7

65.3 

'75.8

Thickness.

Ft. in. 

25 .6

6

1 

2 11

1 0 

1 5

4 2

1 10 

4 10

a Phosphoric acid determinations by W. H. Waggaman, Bureau of Soils, U. S. Dept. Agr; , 1909.

i Girty, G. H., The fauna of the phosphate beds of the Park City formation in Idaho, Wyoming, and 

Utah: U. S. Geol. Survey Bull. 436,1910.
GEOLOGY.

Section of basal portion of Phosphoria formation in Georgetown Canyon (SE. 

sec. 30, T.10.S.,R. 45 E. of the Boise meridian), Idaho Continued.

25

NW.l

Field 

No. of specimen.

144-K

144-M

144-N

144-0

144-P

144-Q

144-R

144-S

144-T

Shale, brownish to black, earthy composition, thin bedded,

Shale, including Ft. in.

Concealed, not included in sample (probably same

RVinlp Vilflf»lr pnrtVnr* pffprvpcppQ diofTrHv

Shale, black and dark brown, calcareous, earthy; effervesces

Shale, black and dark brown, calcareous, earthy; eServesces

Limestone, shaly, brownish gray; effervesces vigorously. ....

Phosphate rock, main bed prospected, coarse to medium, 

oolitic, gray; contains two or more minor streaks of shaly

Limestone, massive, underlying the phosphatic series.

PS06 .<*

Per cent. 

24.2

11.7

[ 15.1

1

19.9

1

21.2

25.8

24.6

17.8

36.8

3 7

Equivalent to 

CaaCPOOz.

Per cent.

cq n

25.6

33.1

43.6

46.4

56.3

53.9

39.0

80.4

8.1

Thicl 

ness

Ft. 

8

12

17

12

12

6

12

4

2

6

139

cfn.'

0

0

n

0

fl

0

10

n

 3

4

11

About 2£ miles north along the same outcrop of the Phosphoria 

formation another detailed section was measured in 1911. Samples 

for.the determination of phosphoric acid were taken from the upper 

portion only, as it appeared to afford a better exposure of that part 

of the formation than had been obtained in the preceding section. It 

will be noted that this section contains about 40 feet more of the 

phosphate-bearing beds. The phosphate content of that part of the 

section from which .no samples were taken is inferred from visual 

examination to be about the same as that found in the section given 

above.

Section of basal portion of Phosphoria formation in SE. -J- sec. 7, T. 10 S., R. 45 E. of

the Boise meridian, Idaho.

[Land lines theoretical.]

Field

No. of

sample.

M 20-1

M 20-2

Shale, dark brown, weathers light brown, not fetid. ..........

Phosphate rock, gray, coarsely oolitic, with large pebbles, 

fossils, or oolites near base, the largest being 2 inches in

Phosphate rock, gray, coarsely oolitic pebbles or oolites, the

Shale, brown, weathers gray, in part finely oolitic ............

Clay, yellow, weathered sandy, largest concretions one-fourth 

inch in diameter; grades into the shale above. ..............

P205 .

Per cent.

36.3

36.7

Equivalent

to

Ca3 (P04) 2 .

Per cent.

79.3

30.1

ness.

Ft. in. 1 0

1 0

5

Ql

94

8
26 PHOSPHATE DEPOSITS NORTHEAST OP GEORGETOWN", IDAHO.

Section of basal portion of Phosphoria formation in SE. J sec. 7, T. 10 S., R. 45 E. of 

the Boise meridian, Idaho Continued.

Field 

No. of 

sample.

M 20-3 

M 20-4

M 20-5 

M20-6

M 20-7

M20-8 

M 20-9

M 20-10 

M 20-11

Shale, dark brown, phosphatic. . .............................

Phosphatic rock, dark brown, weathers gray, medium oolitic,

Shale, brown, sandy with concretions, the largest 1 inch in

Phosphate rock, coarsely oolitic..............................

Shale, brown, sandy .........................................

Phosphate rock, medium oolitic. .............................

Shale, brown, weathers gray with bluish tinge, finely oolitic. .

Phosphate rock, gray, coarse to finely oolitic. ................

Phosphate rock, brown, medium oolitic ......................

Shale, brown, with one-fourth inch streak of oolitic rock near 

base ....................................................

Phosphate rock, dark brown, coarse to finely oolitic, shaly in

Phosphate rock, gray, coarsely oolitic; includes half an inch

Shale, brown, weathers gray. ................................

Shale, brown. ................................................

Phosphate rock, dark gray, coarsely oolitic, with several shaly 

. partings less than one-eighth inch thick ....................

Shale, black, in part finely oolitic ............................

Shale, black, pnosphatic, in part finely oolitic ................

Shale, brown, witn concretions, the largest 2 inches in diameter .........................................................

Shale, rusty brown to yellow, with a few concretions, the largShale, dark brown, with thin pebbly or concretionary bed at 

top . phosphatic in places ...................................

Pebbly or concretionary bed, with concretions, the largest 2 

inchesin diameter. ............................... .

Shale, brown..........................:......................

Shale, black to dark brown. ..................................

Pebbly or concretionary layer, phosphatic. ...................

Shale, black, slightly oolitic. . .............................

Shale, with pebbles or concretions, the largest 2 inches in 

diameter ...................................................

Shale . brown, weathers to ocherous soil ......................

Pebbly or concretionary bed.................................

Pebbly or concretionary bed, phosphatic? .... ; ...............

Shale, brown, phosphatic. ...................................

Shale, black, thin bedded.. ........................:.........

Clay, ocherous...............................................

 Shale, brown. ................................................

Shale, black to light brown, slightly phosphatic ..............

Limestone, broken and intermixed with shale ...............

Shale, broken, and weathered, only slightly phosphatic. .....

Shale, brown, weathers yellow, concretionary ................

Limestone, purplish drab, lenticular. ...................... .

Shales, dark, broken and weathered..... ....... ..............

Soil, black, fetid.... .........................................

Shale, black, phosphatic, finely oolitic. .....................'..

Limestone, dark, fetid .......................................

Shale, brown, somewhat phosphatic, contorted. ..............

Limestone, dark gray, dense ("cap lime" fossils) .............

Phosphate rock, dark brown, medium, oolitic, soft, broken, 

apparently high grade (corresponds to 144-S of section to

Limestone, white, weathers buff, sandy, not measured.

PiOe.

Per cent. 

35.3

29.4

35.9

35.9

33.2

33.2 

37.0

30.0

26.1

*

Equivalent 

to 

Ca3(P04)2.

Per cent. 

77.1

64.2'

78.4

78.4

72.5

72.5 

80.8

65.5

57.0

o40±

Thickness.

Ft. in. 

5 

2

5

5 

1 2 

3 

4 

1

I*

2 

4 

1 

2 

11 

3 

4

6 

9

1 1 

5 

3 

9 

2 

3

10 

10 

9 8 

3 0 

1 8 

6 6

10 

1 8 

16 6

4 

1 2 

9 

3

7

6 

3 4 

4 

2 3 

1 0 

2 6 

6 

10 

1 0 

11 0 

6 0 

21 0 

5 6 

1 0 

8 

15 0 

3 0 

9 0 

5 6 

6 

15 0 

3 0

7 0 

- 1 0

175 2§

a Estimated.
GEOLOGY. 27

Prior to this examination by the United States Geological Survey 

no prospecting had been done on the phosphate beds north of the 

above section. In the course of this investigation cuts were made 

across the main phosphate-bearing portion of the Phosphoria formation at two localities, namely, in sec. 16, T. 9 S.y R. 44 E., and sec. 14, 

T. 8 S., R. 44 E. The sections follow:

Section of lower and phosphate-bearing strata of Phosphoria formation in the NW. J 

NE. i sec. 16, T. 9 S., R: 44 E. of the Boise meridian, Idaho.

Field 

No. of specimen.

M 256-8 

M 256-7

M 256-6 

M 256-5

M 256-4 

M 256-3

M 256-2 

M 256-1

,

Sandy and clayey broken zone, yellow .......................

Phosphatic rock, gray, dense, medium oolitic. ................

Clayey and calcareous, yellow, probably . weathered from 

earthy limestone ...........................................

Phosphate rock, gray, coarsely oolitic; interrupted by 6-inch 

shaly band and 2-J-inch limestone lens. .....................

Clay, yellow and brown, 2 inches; phosphatic rock 4 inches; 

sandy clay 4 inches. ........................................

Phosphatic rock, brown to gray, coarsely to medium oolitic;

Weathered sandy zone .......................................

Phosphatic rock, brown, medium to finely oolitic, broken. . . .

Shales, brown to black, earthy, micaceous; poorly preserved 

lamellibranchs andbrachiopods near base; in places nodules 

of dense black limestone ?, feet in diameter. .................

Limestones and sandstones, broken and poorly exposed,

Shale, brown, earthy, darker toward base and somewhat

Broken contorted zone of phosphate shales and thin limePhosphaticrock, brown, weathers gray; fine to medium oolitic;

Limestone, brown, dense, somewhat earthy and slightly fetid.

PsOs.

Per cent.

28.4

33.5

24.5

23.5

27.1

19.1

27.8

Equivalent 

to 

Ca3 (P04 )2.

Per cent.

62.0

73.2

53.5

51.3

58.5

59.2

60.7

'

Thickness.

Ft. in. 

4 4 

6 

1 0

1 0 

2 6 

10

2 0 

5 

1 10 

1 6

3 4 

40 0

3 0 

1 5 

3 

3 8 

2 

2 6

3 0

2 0 

7 

1 4 

6 

1 2 

1 10 

7 

1 2 

3 

4J

83 J
28 PHOSPHATE DEPOSITS NORTHEAST OF GEORGETOWN, IDAHO.

Nearly complete section of phosphate shales of Phosphoria formation in the SW. 

sec. 14, T. 8 S., R. 44 E. of the Boise meridian, Idaho.

SE.

Field 

No. 

of specimen.

M 307-7

M 307-6

M 307-5 

M 307-4

M 307-3 

M 307-2 

M 307-1

Phosphate rock, dark gray, coarsely oolitic, dense; possible 

evidence of dislocation ....................................

Shale, with thin intercalated sandstones, limestones, and 

very thin beds of phosphate rock, probably none as much 

as one-fourth inch thick ....................................

Shale, with thin intercalated limestone and sandstone and

P206 .

Per cent.

36.0

28.4

29.7 

31.5

31.5 

32.6 

31.0

Equivalent to 

Ca3(P04 ) 2.

Per cent.

78.6

62.0

64.9 

68.8

68.8 

71.2 

67.7

Thickness.

Ft. in. 

10± 

8 0 

6

1 8 

6

122 0 

1 10

21 0 

3 0 

2 5 

8 4 

2 7 

3 0 

3 0 

5 2 

3

193 3

A comparison of these sections with the two preceding sections 

shows in some respects a marked similarity but in others a pronounced .difference. The higher-grade beds lie near the bottom and 

near the top of the lower portion of the Phosphoria formation. There 

is, however, a variation both in thickness of beds and quality of the 

rock phosphate. It appears that a bed not over 3 feet thick generally 

occurs near the top of the phosphate shales, whereas at the base, 

according to the best exposure, that of the section last given, the bed 

may well be expected on further exposure to contain as much as 

8 feet of rock containing about 70 per cent tricalcium phosphate. 

The minimum thickness (4£ inches), found in the section given on 

page 27, is regarded as partial and as being due to the cutting out of 

the upper portion of the bed by a slight local slip, a disturbance 

which is indicated by the broken condition of the overlying shale.

In 1909 another section was measured on a small tributary of Slug 

Greek near the west boundary of T. 8 S., R. 44 E.
GEOLOGY. 29

Complete section of phosphate-bearing strata of Phosphoria formation on tributary of Slug 

Greek (in the SW. J SW. i sec. 7, T. 8 S., R. 44 E. of the Boise meridian], Idaho.

Field 

No. 

of specimen.

R 378-6

R 378-5

R 378-4

R 378-3

R 378-2 

R 378-la

R 378-1

Sandstone, white, fine grained; weathers brown. .............

Shale, brown, sandy, with limestone lenses. . .................

Limestone, grayish black, fine grained, compact, fetid ........

Phosphatic rock, black, coarsely oolitic. ......................

Limestone, grayish black, fine grained, compact, fetid. . ......

Limestone, grayish black, fine grained, compact, fetid. .......

Shale, brown, with some oolitic streaks. ......................

Shale, brown, thin bedded, slightly oolitic ...................

Phosphatic rock, brownish black, finely to coarsely oolitic. . . . 

Phosphate rock, brownish black, shaly ......................

Phosphate rock, brownish black, finely oolitic. ...............

P206 .

Per cent.

26.3

33.5

6.6

29.4 

17.2

27.5

Equivalent to 

Ca3(PO4) 2 .

Per cent.

57.5

73.2

14.4

64.3 

37.6

60.1

Thickness.

Ft: in. 

10 0

47 0

5 0

1 0

6

1 0

1 6

1 0

6

1 0

10

8

2 0

4

1 7 

1 4

1 4

76 7

Of the sections measured this one is by far the poorest in phosphatic material, but the richer sections to the west and east indicate 

that the variation is a local rather than a general change in the character of the deposits.

The Phosphoria formation, so far as at present known, occurs only 

in portions of southeastern Idaho, northeastern Utah, and southwestern Montana.

TRIASSIC SYSTEM. 

WOODSIDE SHALE.

The Woodside shale, which immediately overlies the Phosphoria 

formation, is so called by correlation with the section in the Park 

City mining district, Utah. It is composed mainly of thin-bedded, 

platy, somewhat sandy shale with intercalated sandy limestones, and 

it contains heavy beds of limestone at the top. Unlike the Woodside 

shale of the Utah section, the formation within this area does not 

contain red beds. The great mass consists of the thin beds above 

mentioned, which have yellowish to olive-greenish tints and firm 

texture. The rock is hard enough when fresh to ring under the 

hammer and weathers to yellowish or brownish colors.

The base of the Woodside is in most places quite distinct, for the 

Rex chert member of the underlying Phosphoria formation is generally represented by massive chert ledges topographically prominent. 

But even where the ledges are absent the chert fragments below can 

on close examination be distinguished from the Woodside shale 

fragments above.

The limestone at the top of the Woodside shale closely resembles 

the overlying Thaynes limestone. The upper limit of the Woodside
30 PHOSPHATE DEPOSITS NORTHEAST OF GEORGETOWN", IDAHO.

has been somewhat arbitrarily placed at the layer immediately below 

the Meekoceras zone. This delimitation seems desirable, because 

without subdivision the combined Woodside and Thaynes formations 

would be nearly 4,000 feet thick and because the Meekoceras zone 

marks the entry of the first ammonites recognized in the faunas of 

these formations. Minor lithologic differences also exist between the 

rocks of the Meekoceras zone and those below. The upper part of 

the Woodside is composed of heavy ledges of whitish to gray massive 

limestones, which in some zones are crowded with fossils, principally 

species of Myalina. These limestones make fine ledges that form 

pronounced gateways in some of the canyons. The uppermost members of the heavy-bedded limestones pass into those containing Meekoceras with no perceptible stratigraphic break. The thickness of the 

Woodside shale ranges from about 1,000 to 1,800 feet.

Topographically the Woodside shale is generally marked by smooth, 

rounded hills with few ledges, except where the upper members are 

exposed.

THAYNES LIMESTONE.

The Thaynes limestone, which overlies conformably the Woodside 

shale, takes its name from Thaynes Canyon, near Park City, Utah. 

It contains marine fossil shells at many horizons and from the occurrence of certain ammonoids (Meekoceras fauna) at its base it has 

been assigned by Hyatt and Smith to the Lower Triassic.1 The 

"Meekoceras beds," where recognized by the Hayden Survey, were 

referred to the Triassic.

The Meekoceras zone at the base of the formation consists of whitish to gray limestones 10 to 25 feet thick, crowded with ammonites, 

whose chambered shells are conspicuous on the weathered surfaces 

of the rock. This zone, though not apparently continuous, is fairly 

constant in the portions of the area occupied by the Thaynes limestone within the region considered in this report. Two other important ammonite horizons, the Tirolites and Columbites zones, have 

been recognized by Smith in the Thaynes limestone in Paris Canyon, 

Idaho, a part of the region described in the report for 1910. The 

Tirolites zone is included in gray calcareous shales carrying forms 

listed under the Tirolites fauna about 250 feet above the Meekoceras 

zone. The Columbites zone lies about 25 feet above the Tirolites 

zone and occurs in a thin bed of brownish bituminous limestone containing the Columbites fauna.2 In the region considered in this 

report the Tirolites and Columbites zones have not been definitely

i Hyatt, Alpheus, and Smith, J. P., The Triassic cephalopod genera of America: U. S. Geol. Survey Prof. 

Paper 40,"pp. 17 et seq., 1905. 

»Smith, J. P., The distribution of Lower Triassic faunas: Jour. Geology, vol. 20, p. 17,1912.
GEOLOGY. 31

recognized, but at two localities", in the SE. | sec. 1, T. 8. S., R. 44 E., 

and in the SE. f sec. 3, T. 9 S., R. 45 E., ammonites were found which 

may prove to' be representatives of these horizons. In the locality 

in township 9 the ammonites occurred in dark nodular masses of 

limestone in light calcareous shales similar to those of the Paris Canyon section.

The lithology of the Thaynes limestone in most of the area described 

in this report is much like that of the limestones at the top of the 

Woodside, but for 200 feet or more above the base the rocks are less 

sandy and more clayey and have a well-defined grayish color, different from the yellowish and greenish tints of the Woodside. This 

feature is a helpful indicator where the Meekoceras zone ismot well 

developed. The limestones contain much clay and sand, so that on. 

weathering they assume a sandy or muddy aspect, which makes it 

difficult in many places to distinguish them from sandstones except 

on fresh fractures. No complete section of the Thaynes limestone 

has been found in this region, but at Raymond Canyon, Wyo., and in 

Montpelier Canyon it has a thickness of about 2,000 feet.

ANKAREH SHALE.

The Ankareh shale, which overlies the Thaynes limestone with 

apparent conformity elsewhere in Idaho, Wyoming, and Utah, has 

not been definitely recognized in this area. Possibly, however, certain beds in T. 11 S., R. 45 E., which are assigned to the Nugget in 

this report, may be referable to the Ankareh. As originally described 

from the Park City section, exposed in Big Cottonwood Canyon, near 

Salt Lake City, it consists chiefly of clay shale of deep maroon or 

chocolate color, massive where fresh but commonly breaking down 

after exposure into thinner-bedded shaly material. It includes also 

some pale-greenish clayey and sandy strata, beds of mottled green 

and maroon shale, and harder layers of red or greenish sandstone 

and limy strata, and in the Montpelier district is defined at the top 

, and bottom by massive limestones. The limestone or calcareous 

shale at the top distinguishes the Ankareh to the south from the 

massive sandstones and red sandy shales of the Nugget sandstone. 

The limestone at the base of this "red bed" formation is the uppermost of the massive beds that constitute the more prominent part of 

the Thaynes limestone. The total thickness of the Ankareh as measured in the Montpelier district is about 670 feet, including the limestone at the top, but excluding the massive underlying sandstone 

strata more properly classed with the main body of the Thaynes. 

The thickness in this area is probably about the same as in the Montpelier district.
32 PHOSPHATE DEPOSITS NORTHEAST OF GEORGETOWN", IDAHO.

JURASSIC OR TRIASSIC ROCKS. 

NUGGET SANDSTONE.

As described in a previous report,1 the Nugget sandstone, which 

overlies the Ankareh shale in areas where the Ankareh is present, is 

composed chiefly of massive reddish sandstone, locally deeply colored 

and in places much cross-bedded. The Nugget sandstone includes 

also intervals of sandy shale, which are generally obscured by talus 

of the more massive strata. At its base lies a white conglomeratic 

sandstone, and hi some areas several hundred feet of white sandstone 

form the upper part. In this area the base of the formation is not 

exposed. The_ sandstone as a whole is fairly uniform in color and 

texture and is more or less silicified to quartzite. In Tps. 10 and 11, 

R. 44 E.y the upper part of the formation is marked by deep-red 

sandy and shaly beds with two or more massive beds of gray limestone. Owing to its massive resistant character, the Nugget sandstone forms high ridges with broad rounded slopes or in exposures it 

is marked by heavy talus of brown or black weathering blocks. Its 

thickness has not been measured in this area. In Raymond Canyon 

a thickness of 1,900 feet was observed.

fro fossils have been found in the Nugget sandstone, but as it lies 

below the marine Jurassic of the Twin Creek limestone and above the 

beds from which the Triassic ammonoids of Hyatt and Smith were 

obtained, its position leads to the conclusion that it is either Triassic 

or Lower Jurassic. It is thought to be in greater part the stratigraphic equivalent of the White Cliff and Vermilion Cliff sandstones 

of the Uinta Mountains, and if so there is some probability that at 

least its upper part may be Jurassic.

JURASSIC SYSTEM. 

TWIN CREEK LIMESTONE.

The Twin Creek limestone, which overlies the Nugget sandstone, 

consists principally of grayish-white shaly limestones that form steep 

slopes covered by a veneer of chippy and splintery weathered pieces. 

In some places -the limestone is less shaly and the beds are more 

massive. Fossiliferous strata here and there show that the formation 

is marine and of Jurassic age. The base and the top of the formation 

are bounded by red beds and are well defined. No continuous section suitable for measurement has been found, but the total thickness 

in this area is probably 3,000 feet or more. Characteristic exposures 

of the Twin Creek limestone are shown in Plate IV (p. 38).

No occurrence of phosphate rock in this formation other than that 

discovered by -Gale and noted in the report 2 published in Bulletin

1 Gale, H. S., and Richards, R. W., Preliminary report on the phosphate deposits in southeastern Idaho 

and adjacent parts of Wyoming and Utah: U. S. Geol. Survey Bull. 430, p. 480,1910. 

» U. S. Geol. Survey Bull. 430, p. 508,1910.
GEOLOGY. 33

430 has been observed. The base of the Twin Creek limestone, 

according to measurements recorded in that report, lies about 6,500 

feet above the Paleozoic phosphate beds, so that when this and later 

formations occupy the surface in normal and unfaulted positions 

the phosphate lies too deep for recovery under present conditions.

CEETACEOUS AND JURASSIC ROCKS. 

BECKWITH FOKMATION.

The Beckwith formation overlies the Twin Creek limestone and is 

extensively exposed in the southeastern and eastern parts of the area. 

The boundary between the two formations is in part at least a fault. 

The lower members of the formation are sandstones of a reddish or 

chocolate-brown color with some whitish or grayish beds. Above 

these lie red conglomerates with heavy ridge-making layers. The 

upper part of the formation is not present in the area discussed in 

this report and no measurements of the section were made. According to Breger 1 the lower .1,200 feet consist of red sandstones and 

shales without conglomerates. These rocks are overlain by greenishgray calcareous sandstones 250 to 600 feet thick. These sandstones 

are succeeded by 850 feet of red conglomerates, and these in turn by 

a massive gray limestone 100 feet or less in thickness. The formation is well exposed in Red Mountain just east of T. 11 S., R. 45 E.

TERTIARY SYSTEM. 

PLIOCENE (V) LIMESTONES AND CONGLOMERATES.

Marls, marly limestones, calcareous grits, and calcareous conglomerates, of probable Pliocene age, which were included in the Salt 

Lake group of Hayden 2 and Peale,3 locally cover the older rocks. 

The principal area of these deposits is found in the foothills north 

and east of Georgetown. On the west side of Slug Creek in T. 9 S., 

R. 44 E., and in the northeast corner of T. 11 S., R. 45 E., other 

fairly large areas of these rocks are present. Small patches were 

also noted in T. 10 S., R. 44 E.

These Pliocene (?) deposits have been disturbed in the deformation 

of the region and locally dip nearly 60°.

QUATERNARY SYSTEM. 

CLAYS.

On the east side of Crow Creek in T. 10 S., R. 45 E., red stony 

clays make up a terrace-like area. The clays have been described 

by Breger,4 who regards them as probably of Pleistocene age. This 

view is tentatively accepted in this report.

1 Breger, C. L., Salt resources of Idaho-Wyoming border: U. S. Geol. Survey Bull. 430, pp. 562-563,1909.

2 Hayden, F. V., U. S. Geol. and Geog. Survey Terr. Fifth Ann. Kept., pp. 154,155,1872. 

' Peale, A. C., U. S. Geol. and Geog. Survey Terr. Eleventh Ann. Kept.,.pp. 588, 640,1879. 

< Breger, C. L., op. clt.

37002° 14 3
34 PHOSPHATE DEPOSITS NORTHEAST OF GEORGETOWN, IDAHO, 

SPRING DEPOSITS AND SALT.

Deposits of travertine and numerous springs are found in the 

southeastern portion of the area, in the valley of Crow Creek and 

along the trace of the Bannock overthrust. The water of some of 

these springs is heavily charged with sodium chloride (common salt). 

The origin and value of these saline deposits has been discussed by 

Breger. 1 The writers are inclined to think that the surface of the 

overthrust has played an important part in the localization of the 

salines, but they can not in this paper enter into a detailed discussion 

of the problem. . ALLUVIUM.

The floors of the several basins are concealed at unknown depths 

by the cover of alluvium. In the larger basins, as Slug Creek valley 

and Dry Valley, where the alluvial filling is thick and the underlying 

structure complicated by folds or faults, the alluvial deposits render 

the character and position of the phosphate beds problematical. 

The fan deposits along the sides of the larger valleys are included 

with the alluvium, the fans on the east side of Dry Valley being 

particularly well developed.

IGNEOUS ROOKS.

A small body of basalt along the boundary between Tps. 9 and 10 

S., R. 44 E., is the only igneous rock observed within the area examined. The rock is somewhat vesicular, dark colored, and fine 

grained and weathers brown. Its mineralogic constitution is not 

wholly apparent to the naked eye. However, a few inconspicuous 

phenocrysts of augite and olivine are seen with difficulty. In thin 

section the groundmass is found- to consist mainly of glass inclosing plagioclase, augite, olivine, and magnetite.

The area appears to represent an outlier of the extensive flows 

which lie to the north and west. The rock is believed to be of late 

Pliocene or early Pleistocene age, judging from its relations to the 

Pliocene (?) limestone and conglomerate.

STRUCTURE. 

GENERAL FEATURES.

The area surveyed comprises two folded and discordantly related 

structural units, which originally were distant portions of the same 

folded sedimentary complex. The present discordance between the 

units is due to major overthrust faulting, which is believed to have 

transposed the mass of Carboniferous rocks containing the valuable 

phosphate deposits eastward over beds which are normally, from 

6,000 to 12,000 feet higher in the geologic column.

1 Bregcr, C. L., op. cit.
GEOLOGY. 35

The effect of this great crustal readjustment extends beyond the 

area described in this report.

BANNOCK OVERTHRUST. 1 

CHARACTERISTIC FEATURES.

The fault produced by the crustal readjustment has been named 

the "Bannock overthrust" from its typical development in Bannock 

County, Idaho. From the north fork of Georgetown Canyon (left 

fork of Twin Creek), where the fault emerges from beneath the late 

conglomerates, its sinuous course was followed across the Preuss 

Range into Crow Creek as far as the mouth of Sage Creek (Pis. I, 

III, and IV), a distance of approximately 35 miles, beyond which 

it appears to continue northward.

The sinuosity, of the fault trace is due not only to erosion but also 

to deformation. In the north fork of Georgetown Canyon an anticlinal axis has arched the thrust surface or plane, so that it has been 

partly removed, and the underlying Nugget and Twin Creek formations are exposed in the valley, though long strips of heavy Mississippian limestone reach down the spurs of .the ridges (PL III). A synclinal axis depresses the thrust surface where it passes beneath the 

Preuss Eange in the headwaters of Montpelier Creek. In this region 

there is a marked contrast between the massive castellated Mississippian limestones that constitute the upper part of the ridge and the 

chippy and shaly limestones of the Twin Creek formation that are 

exposed along the lower slopes of the valley side.

The structural relations produced by the Bannock overthrust are 

illustrated in the structure section A-B (fig. 3 and PL III). The 

profile and distances shown in the section are based on the topographic 

map rather than on the stereogram.

In Georgetown Canyon and southeast across the Preuss Range the 

relations are the same. The underlying Twin Creek strata are 

folded, so that the stratigraphic throw can not be measured with 

accuracy, but the missing formations, including Pennsylvanian to 

Triassic rocks (Nugget), represent a minimum vertical displacement 

of about 8,500 feet. Eastward the throw apparently diminishes, 

partly on account of branching faults and partly on account .of the 

folded structure of the rocks in the upper block.

The general trend of the trace of the fault appears to be a few 

degrees west of north and the direction of thrust a little north of 

east. The dip of the fault surface gives little aid in determining the 

direction of movement because of its present deformed condition. 

The older rocks, however, lie to the west and the thickness of the thrust 

block appears to increase in that direction.

1 Richards, R. W., and Mansfield, G. R.,,The Bannock overthrust, a major fault in southeastern Idaho 

and northeastern Utah: Jour. Geology, vol. 20, pp. 681-709,1912.
36 PHOSPHATE DEPOSITS NORTHEAST OP GEORGETOWN, IDAHO.

The distance, perpendicular to the general trend, between the 

westernmost observed portion of the fault trace in Georgetown

Canyon and the easternmost portion 

of that trace in Crow Creek is about 

12 miles. It appears, therefore, 

that the heave may be equal at 

least to that distance.

In the ridge west of Slug Creek 

an elongate area apparently surrounded by a fault boundary is interpreted as an anticlinal portion of 

the main thrust or .of a subordinate 

thrust, unroofed by erosion so that 

the underlying block is exposed 

through a "window" or "fenster" 

(PI. III). The position of this window 

with reference to the anticline in the 

north fork of Georgetown Canyon is 

favorable to this interpretation.

This discussion of the structure is 

naturally divided into two parts, 

namely, the discussion of the overlying or overthrust block, and that 

of the basal or underlying block.

The underlying block is exposed 

in the southern half of the area and 

is made up at the surface of the 

Nugget sandstone, the Twin Creek 

limestone, and the Beckwith formation. The oldest of these. forma- 

 tions, the Nugget sandstone, is exposed only along anticlinal crests, 

whereas the two younger formations 

are included in the synclinal folds 

(PI. IV, B). The folded beds are 

overturned toward the east, and the 

folds are complex rather than as 

simple as suggested by the omission 

of lithologic details in the structure 

sections accompanying the geologic 

maps (Pis. V, VI, IX-XIV).

The constitution of the unexposed 

portion of the underlying block 

beneath three-fourths of the entire area surveyed is of necessity a 

matter of inference from the character of the block as exposed along 

the eroded margins of the overthrust. For this region a statement
U. S. GEOLOGICAL SURVEY BULLETIN 577 PLATE

STEREOGRAM OF TPS. 9-11 S., RS. 43-45 E., OF REGION TRAVERSED BY BANNOCK OVERTHRUST.

Movement was in general from west to east. Note deformation of thrust plane. A-B, Line of section shown in figure 3, page 36.
GEOLOGY. 37

has already been made, and for the area lying to the east and north 

data are included in the reconnaissance report by Schultz and Richards.1 The formations here exposed range from the Ankareh shale 

to -the Beckwith formation. It appears, on the whole then, that these 

higher formations are most apt to make up the surface of the underlying block at its concealed contact with the overthrust block. It is 

suggested, however, that irregularities in the pitch of the folds may 

locally bring the lower rocks up to the fault plane, and it is thought 

that an example of this phenomenon is found in the peculiarly shaped 

fault-bounded outcrop of the sandy limestones and quartzites of the. 

Wells formation, in sees. 17, 20, 21, and 28, T. 9 S., R. 44 E. The 

possibility that this effect is produced by the outcrop of a branch of 

the main thrust which has transgressed into the upper fault block 

offers a satisfactory alternative explanation of the relations shown in 

the field.

The structure of the overlying block is of particular importance 

because it determines to a large extent the distribution of the phosphate beds. The abundance of data regarding the outcrop renders the 

interpretation of the structure of this block much easier and more 

certain than that of the block previously discussed.

The rocks outcropping in the overthrust block are mainly sedimentary, ranging from the Madison limestone nearly to the top of the 

Thaynes limestone, and to the 6north of the area some rocks as high as 

the Beckwith formation are included. A small area of basaltic rocks 

is present in sees. 33 and 34, T. 9 S., R. 44 E., and sees. 3 and 4, T. 

10 S., R. 44 E.

The broader structural features comprise a series of anticlinal and 

synclinal folds whose trend curves from> approximately N. 20° E. in 

the southern part of the block to nearly N. 45° W. at the north 

boundary. The eroded and faulted remnants of four synclines and 

five anticlines represent the larger folds. In general the anticlines are 

smaller and sharper than the intervening synclines. The comparative widths of the anticlines and synclines are due mainly to the 

general attitude of the folds; as the folds plunge toward the north 

the synclines become broader, and as they rise toward the south the 

synclines become narrower and the older rocks which form the remnants of the anticlines, occupy the greater part of the area.

MAGNITUDE OF THE BANNOCK OVERTHRTTST.

In the above description only a portion of the Bannock overthrust 

has been considered. The study of the great fault within the area 

discussed in this report has led to the view that several thrust faults 

discovered in 1909 and 1910 are really parts of one great fault that 

may extend for 270 miles with sinuous course from Woodruff, Utah,

1 Schultz, A. R., and Richards, R. W., A geologic reconnaissance In southeastern Idaho: U. S. Geol. 

Survey Bull. 530, pp. 267-284,1913.
38 PHOSPHATE DEPOSITS NORTHEAST OF GEORGETOWN; IDAHO.

to John Grays Lake and the Blackfoot Range. The minimum horizontal, displacement produced by this great fault, based on a structure section constructed across the Montpelier quadrangle, from the 

southeast corner T. 11 S., R. 43 E.; to the northeast corner T. 11 S., 

R. 45 E., normal to the fault trace, is 12 miles. The maximum 

displacement in the region, based on the shortest distance between a 

line connecting the westernmost known points on the fault trace 

and a tangent to the east margin of the fault, is 35 miles.

AGE OF THE BANNOCK OVERTHRUST.

The oldest rocks involved in the faulting are sandstones of the 

Beckwith formation, which may in part be of early Cretaceous age. 

The youngest rocks which, have been found concealing its trac^e are 

the conglomerate of the Almy formation,1 which represents the basal 

division of the Wasatch group (Eocene) as defined by Veatch.

The possible range of age is, then, from late Cretaceous to early 

Eocene, and it is probable that the faulting may have occurred 

during the interval represented by the unconformity between the 

AdavUle 2 and Evanston 3 formations of Veatch.

OTHER FAULTS.

Minor overthrusts are present, some of which are subsidiary 

branches of the main thrust; others, which may have originated at 

the same time and from the same general cause," apparently have no 

direct connection with the major fault.

Normal faults occur within the area but are few in number and 

so far as known of slight importance.

DETAILED DESCRIPTION OF AREA.

TOWNSHIPS EXAMINED.

The area examined in 1911 comprises eight townships in Rs. 44 

and 45 E. of the Boise meridian. These townships were included in 

whole or in part in the phosphate reserves as originally constituted 

by the withdrawals of December, 1908, and December, 1909. All 

the eight townships contained phosphate deposits and the rocks 

immediately associated with them, both normally above and below, 

and also other rocks which normally lie well above them in the geologic column but which are now found in discordant relation beneath 

them. The areas of these rocks were complicated by folding and 

faulting, so that detailed geologic mapping was essential to the study 

of the deposits. 

1 Veatch, A. C., Geography and geology of a portion of southwestern Wyoming: U. S. Geol. Survey Prof. 

Paper 56, p. 89,1907. 

5 Idem, p. 72. 

B Idem, p. 76.
U. S. GEOLOGICAL SURVEY BULLETIN 577 PLATE IV

A. PANORAMA FROM SOUTH-POINTING SPUR ON HILL NORTH OF GEORGETOWN CANYON. 

Looking northeast to south. Cl, Mississippian limestone; Cw, Wells formation; Tsn, Nugget sandstone; Jtc, Twin Creek limestone; JKb, Beckwith formation.

B. PANORAMA FROM POINT NEAR THE SOUTHEAST CORNER OF AREA SHOWN IN PLATE

Looking northwest. Showing southern tip of uneroded part of the overthrust block and position of subordinate branch fault. Cl, Mississippian limestone; ~Rt, Thaynes limestone; "En, Nugget sandstone; Jtc, Twin Creek limestone. Parallel syncline and anticlines in foreground.
DETAILED DESCRIPTION OF AREA. 39

T. 8 S., R. 44 E. 

STRATIGRAPHY.

The rocks of T. 8 S., R. 44 E., are all sedimentary and range in age 

from Carboniferous to Triassic. They comprise the Wells formation, 

Phosphoria formation (including the Rex chert member), Woodside 

shale, and Thaynes limestone, which are described in detail on pages 

18-31. The alluvial deposits are intentionally omitted, as they generally have no significant bearing on the phosphate deposits.

STRUCTURE. ,

The rocks of this township have been folded and faulted on a large 

scale and the structure is relatively simple. The southwest half is 

almost entirely occupied by a syncline that enters the area from the 

township to the south. The west side of this syncline is broken by 

a fault, interpreted as a thrust with westerly hade, apparently the 

continuation of the thrust shown in the western part of the township 

to the south. This fault brings'the Rex chert against Pennsylvanian 

limestones and quartzites in the SW. | SE. £ sec. 3.1. From this 

point it extends to the NW. J NW. J sec. 19, where it appears to die 

out in the axis of a small anticline. The big syncline is apparently 

normal and upright and grows narrower toward the northwest. It 

forms part of a canoe-shaped fold, the northern tip of which lies in 

the township to the northwest.

East of the above-mentioned syncline is a somewhat narrower 

anticline, the axis of which lies in the west flank of Dry Ridge. This 

anticline also appears to be normal and upright, but on account of 

the absence of 'upper Mississippian rocks in the axial region of the 

fold it is presumed that the apparent unusual thickness of the Pennsylvanian strata is clue to subordinate folding, and such folds have 

been represented in sections A-B and C-D on the map (PI. V).

The northeast part of the township, including Dry Ridge, is occupied by a part of another large syncline that enters this township 

from the township to the east (PL II, B, p. 12). The axis of this 

syncline probably crosses sec. 1 near the center, with a northwest 

trend. From the SE.-J NE. \ sec. 25 to the SW. J SE. J sec.. 14 this 

syncline is bordered by a fault that dies out in sec. 14. The course 

of this fault through two deeply cut strike or subsequent valleys 

indicates that its hade is nearly vertical. The effect of the fault is 

to cut out parts of the Phosphoria formation and in the NE. | SW. \ 

sec. 24 to cut out this formation entirely.

The great Bannock thrust fault is believed to pass beneath this 

township but at depths too great to affect the phosphate shales.

The structural relations above described are shown in the sections 

on the map of the township (PI. V).
40 PHOSPHATE DEPOSITS NORTHEAST OF GEOBGETOWN, IDAHO. 

PHOSPHATE DEPOSITS.

Previous to the examination by the Survey no prospecting had 

been done in this township. In 1910 the Survey party, in connection 

with the examination of the adjacent township on the west, made a 

shallow opening in the phosphate shales in the SW. £ SW. I sec. 7. 

The section thus obtained.and the analyses of the samples taken 

were published in the report for 1910,1 and are reprinted in this paper 

for the sake of comparison. (See p. 29.) They seem to show an 

unusually lean portion of the phosphate shales.. The phosphate beds 

are unusually thin and the content of phosphoric acid is unusually 

low.

In 1911 the Survey party made an opening in the naturally exposed 

phosphate shales in the SW. f SE. | sec. 14. Three pits were opened 

and offset in such a manner as to cover nearly the entire thickness of 

the shales. The measurements of the section and the phosphate content of samples are given in the table on page 28.

The table shows that the thickness of high-grade phosphate rock 

near the base of the shales is unusually great, amounting to 14 (?) 

feet, and that another bed of high-grade rock, whose. thickness is 

not definitely known, occurs near the top of the shales, only a few 

feet below the chert. It may be noted from the map that both the 

sections referred to are. in close proximity to zones of minor folding 

or faulting. Thus the unusually thin and lean character of the one 

exposure and the unusually thick and rich character of the other may 

in some measure be connected with these minor movements. It seetos 

fair, then, to assume that the phosphate deposits do not differ widely 

in average thickness and character from those of the neighboring 

townships, and that an average thickness of 6 feet of workable phosphate may safely be inferred.

The phosphate beds underlie 16,000 acres in this township at a 

depth probably nowhere greater than about 4,000 feet. The greatest 

depth occurs in the northeast corner of the township near the center 

of sec. 1. The dip of the beds varies but is generally not less than 

20°, though in some places it is as much as 40°, and in a few localities considerably more. It is doubtless safe to assume an average 

dip of 30°.

On the assumption, then, that a 6-foot bed of phosphate underlies 

16,000 acres of land and dips on an average 30°, and that the weight 

of a cubic foot of high-grade phosphate rock is 180 pounds, there are 

within this township approximately 386,400,000 long tons of phosphate. Much of this rock is easily accessible from points of entry 

in Slug Valley and Dry Valley.

'.Richards, R. W., and Mansfield, G. R., Preliminary report on a portion of the Idaho phosphate reserve: 

U. S. Geol. Survey Bull. 470, p. 389,1911.
U. S. GEOLOGICAL SURVEY BULLETIN 577 PLATE V

Topography from Slug Creek sheet

LEGEND

limestone

Fault

Concealed, fault 

(Covered-by later sediments)

Strike and dip

x

Irospcct

land comer fouiui

Contour interval 250feet 

(s mean sea leveZ 

1914

GEOLOGIC MAP AND SECTIONS OF T. 8 S., R. 44 E.
DETAILED DESCRIPTION OF AREA. 41 

T. 9 S., R. 44 E. 

SURVEY.

The ^detailed geologic examination of T. 9 S., R. 44 E. ; was made 

during the early part of July, 1911. A brief inspection of portions 

of this township was made later in the same season by W. C. Mendenhall, F. B. Van Horn, and A. R. Schultz, of the Survey. The 

work was done mainly with plane table over the topographic base 

prepared by Albert Pike during the preceding summer.

The accompanying map (PL VI) is a reproduction on a smaller 

scale of the field map with portions of the original detail omitted.

Only" a partial survey of the township has been made by the Gen- 

. eral Land Office, but a theoretical net has been projected over the 

remainder of the township for convenience in reference.

0 STRATIGRAPHY.

The rocks of this township range in age from Carboniferous to 

Pliocene or Pleistocene and include both sedimentary and igneous 

types. The various formations are fully considered on pages 14-33 

of this report, but a brief description of them is given here, together 

with an account of their distribution.

The Carboniferous rocks include upper Mississippian limestone, the 

Wells formation (Pennsylvanian), and the Phosphoria formation 

(Permian?). The Madison limestone has not been observed. The 

rocks below the Phosphoria formation were not differentiated in the 

field, but it is probable that most if not all of them should be assigned 

to the sandy limestones and quartzites of the Wells formation. They 

occupy most of the southeastern part of the township and underlie 

most of sees. 1, 12, 13, 30, 31, and 32, and a strip along the west 

border of the township. The topmost part of the formation, which 

underlies the phosphate beds (the underlying limestone of the report 

for 1910), is well developed in many places and forms fine cliffs in 

sees. 16 and 18.

The Phosphoria formation underlies the valley just east of the 

ridge that extends from sec. 32 to sec. 19. It also spreads around 

a lower intervening ridge and appears on the west side of Slug Valley 

from sec. 28 to sec. 17. Farther north it appears in a belt extending 

north from the NE. £ sec. 7 through sec. 6. Southeast of the Schmid 

ran'ch the formation extends from the NE. \ sec. 8 obliquely across 

the broad range east of Slug Valley, through sees. 9, 16, 15, and 14, 

where it plunges beneath the alluvium in Dry Valley. It reappears in 

the eastern half, of sec. 2. In the NE. £ SW. J sec. 28 the Rex chert 

member is horizontal and has a pseudocolumnar jointing resembling 

basalt (PL VII, B}. The. lower or phosphate-bearing portion Is not 

exposed but may be traced by float in characteristic position between
42 PHOSPHATE DEPOSITS NORTHEAST OF GEORGETOWN, IDAHO.

the underlying limestone and the chert. This portion of the formation finds topographic expression in the line of depressions or saddles 

that runs parallel to the heavy chert ledges of the upper member of 

the 'formation, as is particularly well shown in sees. 32 and 29. The 

Rex chert member is marked by heavy chert layers, which locally, 

as in sec. 2, constitute the entire member and form great ledges. 

Elsewhere, as in sec. 20, this member is more largely composed of 

the chippy and flinty shale facies, which weathers into smooth 

slopes, with few or only subordinate ledges. No fossils were observed 

in either facies.

The Woodside shale occupies two areas in this township. It 

forms a belt a quarter to half a mile wide along the east flank of 

the ridge west of Slug Valley from sec. 21 to sec. 7. It also underlies 

the entire range between Slug Valley and Dry Valley in the northern 

part of the township, including the area north of a line extending 

northwest from sec. 14'to sec. 5. In the western belt only the 

lower half of the formation is exposed the thin-bedded sandy 

limestones and yellowish and greenish shales. In the eastern area 

the entire thickness of the .formation is present, and the heavy 

limestones of the upper portion, some of which are crowded with 

pelecypod shells,, form pronounced ledges on the hilltops.

The Thaynes limestone appears only in a small area, including 

parts of sees. 2, 3, and 4. The basal member or Meekoceras zone 

is readily identified and traced, though it is not uniformly developed. 

The rocks above the base closely resemble the shaly members of the 

Woodside formation below, so that without the basal member the 

identification of the formation is difficult. The Thaynes limestone 

and the limestones of the upper part of the Woodside shale form 

smooth, high hills, in many places heavily wooded with aspen. Comparatively few ledges are seen. Fine exposures of both rocks are 

found on the north side of the road in the NW. £ SE. £ sec. 3. The 

other Mesozoic formations are not represented in this township.

The Pliocene (?) deposits form a nearly continuous band from a 

quarter of a mile to a mile or more wide along the west side of Slug 

Valley, extending from the SE. % SE. £ sec. 7 to the northern part 

of sees. 33 and 34. These beds consist of marls, grits, and conglomerates or breccias, which contain fragments of local sedimentary 

rocks only. They form hill slopes and ridges whose greatest elevations are 250 feet or more above the bottom of Slug Valley. One 

isolated patch in the NW. i NW. £ sec. 33 and adjoining portions of 

sec. 32 lies at" an altitude of 7,241 feet or nearly 700 feet above the 

level of Slug Valley. The beds are not horizontal. The dips range 

from 18° to 58°, indicating that the beds have been disturbed by 

orogenic movements since their deposition, for inclined deposition 

could not account for dips so great.
U. S. GEOLOGICAL SURVEY BULLETIN 577 PLATE VI

Concealed fault 

Covered, by later sediments

x

Prospect

L and corner found,

5000

Scale 62,soo 2 Miles

Contour interval 250feet

Datum is mean sect, level

191*

GEOLOGIC MAP AND SECTIONS OF T. 9 S., R. 44 E.
. DETAILED DESCRIPTION OF AREA. 43

Basalt covers a little more than a square mile in sees. 33 and 34. 

The rock is dark, somewhat vesicular, and weathers brown. It has 

few outcrops and weathers into bowlders ranging from a few inches 

to 2 or 3 feet in diameter. It appears to overlie the Pliocene (?) 

beds and is not definitely represented in the conglomerates of those 

beds. Bowlders of the basalt occur within the area mapped as 

Pliocene (?) in the NW. £ NW. | sec. 34, but it is believed that 

these bowlders have been carried downstream from the basalt hills 

and do not represent bowlders weathered from the Pliocene (?) 

deposits. The basalt appears from its relation to the supposed 

Pliocene marls and conglomerates to be of late Pliocene or early 

Pleistocene age. The hills that it now caps have shared in the 

general erosion of the region and have acquired forms comparable 

to those developed in the neighboring earlier sediments.

STRUCTURE.

The main structural features of the phosphate deposits in this 

township are two synclines, more or less broken, that form southern 

extensions of a larger syncline which occupies the west half of the 

adjoining township on the north. Between the two synclines an 

anticline plunges gently northwest and is broken by a fault with 

downthrow on the west, so that rocks of Lower Triassic age (Woodside shale) are probably brought into contact with lower Pennsylvanian rocks. The fault is concealed beneath the alluvium of Slug 

Creek, and between the two rock formations lies the band of Pliocene (?) marls, grits, and conglomerates. The absence of these supposed Pliocene beds on what appears to be the upthrown side of the 

fault, together with, the steep dips in these beds already noted, suggests that this fault is associated with a later period of disturbance 

than that which developed the main structural features of the district. According to this view the Pliocene (?) beds may have been 

deposited on the east side of Slug Creek as well as on the west, but if 

so they have been removed by erosion.

The western syncline extends from the north-central part of sec. 

4, T. 10 S., R. 44 E., in a northwesterly direction through T. 9 S., 

R. 44 E., as far as sees. 17 and 18. The west limb is fairly straight. 

In the SW. £ SW. I sec. 33 the rocks dip about 45° E., but from 

the SE. \ SE. I sec. 29 throughout the remainder of this limb the 

dips are reversed and become westerly, the angles ranging from 

22° to 65°. The syncline as a whole is therefore strongly inclined 

eastward. The east side of the syncline is partly obscured by basalt 

and Pliocene (?) deposits, but from the center of sec. 28 northwestward its boundary is marked by a fault that brings the upper part 

of the Phosphoria formation (upper part of the Rex chert member) 

against the lower part of the Wells formation. East of this fault
44 PHOSPHATE DEPOSITS NORTHEAST OF GEORGETOWN, IDAHO.

lies a somewhat irregular area of sandy limestones and quartzites of 

the Wells formation. The eastern boundary of this area is also 

formed partly by a fault that seems to be a continuation of the same 

fault that marks its western boundary. The dips of the rocks lying 

east and west of this lower Pennsylvanian area, as well as some of the 

dips within the area itself, indicate a general anticlinal structure.

'The interpretation offered for the appearance of this area, made 

up of the beds of the Wells formation and largely bounded by faults, 

within the general syncline of the Phosphoria formation has already 

been given on page 37.

The eastern border of the area of rocks of the Phosphoria formation 

in sees. 17, 20, and 21 has been crumpled by minor folds. From the 

NW. | sec. 20 through sees. 17,18, and 7, and northwestward there is 

a fault, interpreted as a subsidiary thrust, that brings the Woodside 

shale and the Rex chert member of the Phosphoria formation against 

lower Pennsylvanian sandy limestones and quartzites (Wells formation), with the younger rocks on the east (PI. VII, A).

The foregoing structural features are shown on the sections drawn 

along the lines A-B and C-D, accompanying the map (PI. VI).

The eastern syncline is apparently normal and upright, though the 

axis lies nearer the east than the west.side. The southeast portion 

of the syncline is concealed beneath the alluvium of Dry Valley. 

The limits of the concealed portion have been shown on the map 

as calculated from the thickness and dips of the formations involved. 

The structural features of this syncline are indicated in the section 

drawn along the line E-F.

PHOSPHATE DEPOSITS.

The phosphate beds are not naturally exposed in this township, 

and previous to the summer of 1911 no openings in the beds had been 

made. In the NW. £ NE. I, sec. 16 the Survey party in July, 1911, 

opened a trench 450 feet long that had a maximum depth of about 10 

feet. This trench traversed the formation from the overlying chert 

to the underlying limestone (PI. Ill, p. 36). The character of the 

formation as there exposed is given, together with phosphate content of samples of the more important phosphate beds, on pages 

27-28.

The formation in this township contains two important phosphatebearing zones, near the top and the bottom, respectively, with a broad 

barren zone between. Each of the phosphate-bearing zones consists of several members and includes narrow bands of lean or barren 

material. The upper zone contains an aggregate of 4 feet 6 inches of 

phosphate rock averaging 60 per cent or more tricalcium phosphate 

and an additional .band, 1 foot 10 inches thick, averaging nearly 50
U. S. GEOLOGICAL SURVEY BULLETIN 577 PLATE VII

A. CLIFFS OF WELLS FORMATION, WEST SIDE OF SLUG VALLEY, SEC. 18, T. 9 S., R. 44 E.

Down-faulted Triassic rocks on left; Carboniferous rocks in distance. The phosphate shales have been largely 

eroded from the top of the Wells formation.

LEDGES OF HORIZONTAL BEDS OF THE REX CKERT MEMBER OF THE PHOSPHORIA FORMATION, SEC. 28, T. 9 S, R. 44 E.

Pseudo-basaltic appearance is due to jointing and weathering of the chert,
U. S. GEOLOGICAL SURVEY BULLETIN 577 PLATE VIM

A. WELLS FORMATION, SEC. 5. T. 10 S., R. 44 E. 

Showing characteristic interbedding of sandstone and cherty limestone (largely siltcified).

£. DRAG FOLD IN UNDER LIMESTONE AND PHOSPHATE SHALES, IN NW. > SW. J- SEC 25 T 10

S., R. 44 E.
DETAILED DESCRIPTION OF ABBA. 45

per cent tricalcium phosphate. The lower zone has two beds aggregating 3 feet 5 inches of phosphate rock that averages nearly 60 per 

cent tricalcium phosphate. The rock from which sample No. 2 was 

collected lies immediately beneath a broken and contorted zone of 

phosphate shales and thin limestones. The position of this bed corresponds to that of the main bed in the townships to the west and 

south. The main bed in Georgetown Canyon is 6 feet 4 inches thick. 

These facts, together with the general uniformity of thickness of the 

main bed elsewhere, tend to show that in this section part of the bed 

has probably been cut out. -

The phosphate beds where exposed by trenching were rather deeply 

covered by weathered surface drift, and the inclination of the beds 

was such that dirt could be washed into the phosphate rock by percolating waters. It was found impracticable to deepen the ditch sufficiently to secure wholly clean material for analysis, hence it is probable that .the given figures are somewhat low. As it is, the trench 

shows a total thickness of workable phosphate rock amounting to 

about 8 feet, with an average content of about 60 per cent tricalcium 

phosphate.

The phosphate beds underlie 10,000 acres in this township, at a 

depth probably nowhere greater than 1,800 feet. The dip of the 

beds varies and locally is quite steep, but these steep dips do not 

in all probability descend to depths greater than 500 or 600 feet. The 

great bulk of the deposit appears to dip 10° to 20°, and perhaps 15° 

may be taken as a fair average.

If only the upper bed, 4 feet 6 inches thick, is considered, and the 

dip is taken as 15°, and if the weight of a cubic foot of phosphate rock 

is taken at 180 pounds, there are within this township, in the upper 

bed alone, 164,600,000 long tons in round numbers of phosphate rock 

averaging 60 per cent or more tricalcium phosphate. If the lower 

bed, 3 feet 5 inches thick, is added under the same conditions, the 

total tonnage will be approximately 289,839,500 long toils.

The entire region underlain by phosphate rock is believed to be a 

part of the great thrust block previously referred to (see p. 35), and 

hence it is perhaps underlain by a great thrust fault. The depth of 

the supposed fault beneath the surface is not known. It is doubtful 

if it is high enough in this township to cut out much if any of the phosphate-bearing formation, yet in the absence of definite information 

such as that given by drill records it is perhaps wiser to make ample 

allowance for that possibility. Thus the smaller figure given above 

should fall well within the limits of probability.

Both the eastern and western areas are accessible from valley bottoms and much of the rock is probably above ground-water level.
46 PHOSPHATE DEPOSITS NORTHEAST OF GEORGETOWN, IDAHO.

T. 10 8., R. 44 E. 

SURVEY.

The eastern part of T. 10 S., R. 44 E., was surveyed by Gale in 1909, 

and discussed in a preliminary report on the Georgetown district.1 

A topographic map on the scale of 1:31,680 was made by Albert Pike 

in 1910. This was used as the base for the geologic work during the 

following summer.

STRATIGRAPHY.

The earlier Carboniferous rocks occupy the greater portion of the 

township, but in the south-central part a somewhat triangular area 

of Jurassic limestone and sandstone underlies limestones of Carboniferous age, older than the phosphate rocks.

The phosphate deposits have been so folded in the synclines as to 

present a full section of the Woodside shale, and locally the.basal portions of the Thaynes limestone are also exposed. Tertiary marls and 

conglomerates cover a considerable area in the southwestern corner 

of the township and are also present in minor patches to the north.

Igneous rocks are represented by a small area of cellular basalt in 

sees. 3 and 4.

STRUCTURE.

Two independent structural complexes exist in this township. 

These two units bear an abnormal stratigraphic relation to each other 

in that the overlying unit is made up in general of the older rocks. 

This abnormal relation is a result of the Bannock overthrust, which 

has been referred to on page 35. The area of Jurassic rocks in the 

south-central part of the township is a portion of the underlying 

block which has been uncovered by erosion. The surface or plane of 

the Bannock thrust was probably originally nearly horizontal, but it 

has been subsequently deformed and in this township shows welldeveloped folds. , . The structure of the superimposed block comprises a series of 

anticlinal and synclinal folds whose axes have a trend slightly east of 

north. The structural details are not clear west of the high ridge in 

the eastern part of the township, as the distribution of the several 

formations older than the phosphate rocks has. not been mapped. 

This ridge, however, is known to be roughly paralleled by a strike 

fault whose trace swings locally from one side to the other of the 

ridge.

The structure of the underlying block is characterized by the presence of somewhat broader folds than those of the upper block, and" 

the axes-apparently have a nearly parallel trend.

» Gale, H. S., and Richards, R. W., U. S. Geol. Survey Bull. 430, pp. 483-488,1910.
U. S. GEOLOGICAL SURVEY BULLETIN 577 PLATE IX

LEGEND

Topography from Slug Creek sheet

Conceale'dfaiit 

(Covered bylaterdeposits)

Strike anddrp

X

Strike and,verticaiarp

Beds neadyhorizontal

® 

Hbrizontalbed.

l^w W) \,m \\ T ^ ^^^ -s^

undifferentiatfcd \\V^!1-^ ^-^ 

^ »,. < ^fcsSSs===«Baa

fiSSlLaSSjiUjrust

-9000

-esoo'

-eooo'

-7SOO*

-7000*

-6soo' 

^6000'

^SSQC/ 900'

T\mnel

x 

Proi?pect

o

Landcomer 

found

 

House

.2l£les

Contour interval250feet 

JDaftan is mean sea level

GEOLOGIC MAP AND SECTIONS OF T. 10 S., R. 44 E.
DETAILED DESCRIPTION" OF AREA. 47

PHOSPHATE DEPOSITS. 

GENERAL FEATURES.

The phosphate deposits lie in a synclinal trough which is situated 

mainly in sees. 12, 13, and 24. The fold is modified slightly by the 

presence of minor folds (PI. VIII, B] and at least one fault. The 

southern tip of another phosphate-bearing area enters the township 

in sec. 4. The phosphate shales here, as elsewhere in this general 

region, are inclosed between an underlying light-colored sandy limestone and an overlying dark-colored chert, which in nearly all attitudes makes salient topographic features.

The main phosphate area forms a rather lenticular patch, about 3 

miles long and 1 mile wide, in the eastern tier of sections. In a 

graphic projection it would appear like the somewhat distorted bow 

of a canoe. In reality it constitutes only the southern tip of a long 

boatlike fold, which extends far to the north, as will be seen by reference to the general map (fig. 2, p. 15). The margin of this area is 

crenulated by subordinate folds.

The other phosphate areas are much smaller but have a similar 

structure and shape.

In most places the outcrop is best marked by prominent ledgesupported ridges of the overlying chert, but in other places the underlying limestone makes either a well-defined cliff, a salient knoll, or a 

ridge. The shales are more easily eroded and are generally characterized by the development along them of minor gullies, many of which 

are too small to be shown on the field scale of mapping.

QUALITY OF PHOSPHATE ROCK.

Many shallow openings have been made along the outcrop of the 

phosphate shales in the course of the assessment and patent work 

incidental to the mineral claims of the Utah Fertilizer & Chemical 

Manufacturing Co. At the time of examination by the United States 

Geological Survey, however, nearly all the sections had been obscured 

by caving, and information was cniefly gained from the more extensive 

cuts in the township to the east. A better-exposed section is described 

on pages 24-25, and another, which supplements it somewhat, on 

pages 25-26. A prospect in the NE. | SE. f sec. 25 showed a section of the main bed measuring 6 feet 6 inches, and a sample collected 

here contained 37 per cent phosphoric acid, equivalent to 80.8 per 

cent tricalcium phosphate. The outcrop of the shale contains abundant pieces of high-grade phosphate rock, and similar pieces are also 

found' on the dumps of many of tha caved openings. The field evidence appears to indicate that this area contains rock which will 

run 70 per cent or over in tricalcium phosphate, probably in beds 

comparable in thickness to those of the section given on pages 24-25.
48 PHOSPHATE DEPOSITS NORTHEAST OF GEORGETOWN", IDAHO.

AREA AND TONNAGE.

The main phosphate area comprises about 1,920 acres and the minor 

tracts contain about 80 acres. The area of the main phosphate 

bed under these lands is greater than their' surface area because 

of the folding, which is indicated in the structure sections A-B and 

C-D on Plate IX. This folding is estimated to add 25 per cent to 

the area and thus the main lower bed is estimated to occupy about 

2,500 acres. The bed-is assumed to average 6 feet in thickness 

throughout this extent. The content of such a bed of phosphate 

rock weighing 180 pounds to the cubic foot is 52,000,000 long tons.

DEVELOPMENT.

Little has been accomplished in the actual development of this 

area. Two tunnels, both of which have a southeasterly trend, have 

been put in by the Utah Fertilizer & Chemical Manufacturing Co. 

on the Superior Extension claim. One of the tunnels is about 125 

feet long, but the other is less than 30 feet. The longer tunnel 

terminates in the limestone which underlies the phosphate shales. 

The shorter one is in low-grade shales. A third tunnel about 50 

feet in length on the Highland No. 2 claim shows mainly low-grade 

shales with a minor amount of high-grade rock. The direction of 

all these workings has been determined by minor folds, which complicate the laying out of a general plan of mining development for 

the district.

The plan selected will undoubtedly depend mainly on the desired 

rate of production. If-the production is to be moderate, an advantageous procedure for immediate utilization will be to extend the lowest 

of the present tunnels along the general strike of the main phosphate 

bed as an outlet for the overhead tonnage. If, however, the demand 

is large, and a long-lived plan of operations is to be outimed, the 

economic possibilities of a main tunnel on the principal phosphate 

bed along the anticlinal crest, with workings inclined toward the 

west and the east, should be compared with the cost of a series of 

similarly located surface installations operating by means of inclines 

from the canyon level. In either system of operations the working 

tunnels will lie along the synclinal, troughs, and the mining practice 

adopted will involve either a chamber, a caving long wall, or overhead 

stoping, as the inclination of the phosphate bed and the character 

of the roof makes advisable.

OWNERSHIP.

The phosphate lands in this township belong in part to the United 

States Government and in part to the Utah Fertilizer & Chemical 

Manufacturing Co. The company has claims amounting to about 

250 acres on the lands described under this township which have been
DETAILED DESCRIPTION" OF AREA. 49

surveyed for patent, and it also holds additional areas amounting to 

about 480 acres. The remaining area, about 1,190 acres, is public 

land, all within the Caribou National Forest.

ACCESSIBILITY.

Georgetown Canyon oilers a natural outlet for the ph.osph.ate rock 

in this township. It is reported that a location survey for a spur to 

connect with the Oregon Short Line Railroad has been made, but 

there appears to be little probability that this line will be constructed 

in the near future.

T. 11 S., R. 44 E. 

SURVEY.

The detailed geologic survey of T. 11 S., R. 44 E., was made in 

June, 1911, the topographic base being obtained by the enlargement 

of the corresponding portion of the map of the Montpelier quadrangle, 

which was made by A. E. Murlin and Albert Pike in 1909. The general geologic survey of the township was made on scale of 1:31,680, 

but a small area of especially complicated geologic structure which 

contains phosphate was mapped on a larger scale.

STRATIGRAPHY.

The rocks of the Phosphoria formation with the included phosphate 

deposits are found only in the northeast corner of the township. 

The formations that outcrop in the remainder of the township are 

the Beckwith formation, the Twin Creek limestone, the Nugget 

sandstone, the upper Mississippian limestone, the Tertiary lake 

beds (presumably Pliocene), and the alluvial deposits of the portion 

of Bear River valley included in the southwestern part of the township. The lake beds and the alluvial deposits conceal the geology of 

the older rocks, so that little can be inferred concerning the presence 

or absence of phosphate in the areas covered by them.

STRUCTURE.

The presence of phosphate in sees. 1 and 12 is due solely to the 

geologic structure, as the area that includes the Permian (?) and 

Triassic rocks has been thrown out of ordinary sequence and lies 

above rocks of much later age. The great thrust fault which has 

accomplished this result is described, together with its general effects, 

on pages 35-38. The local effect of this fault is to place upper Mississippian limestone over Jurassic limestone. The plane of the thrust 

in this township is nowhere exposed in horizontal position but dips 

steeply both east and west, subsequent deformation having been 

marked.

37002° 14 i
50- PHOSPHATE DEPOSITS NORTHEAST OP GEORGETOWN, IDAHO.

The structure of the underlying block, or the base on which the 

thrust rests, consists of broad anticlinal and synclinal folds involving 

rocks of at least Triassic and Jurassic ages. The adjacent structure 

to the west is concealed by the Tertiary beds and the alluvium. A 

strong suggestion of recent fault movement along the eastern margin 

of the valley was noted and the position of the fault plane is indicated in sees. 16 and 21 on the map (PI. X).

The structure of the overlying block,' which comprises beds ranging 

in age from upper Mississippian to Triassic, is complicated both by 

close folding and by subordinate faulting. The synclinal folds 

which hold the phosphate deposits are truncated by these faults. 

The attitude of the faults is by no means simple but is so variable 

that it must doubtless be due in greater part to warping or folding.

PHOSPHATE DEPOSITS.

The phosphate deposits of the township form two distinct areas, 

the larger of which, situated in South Canyon, will be first described, 

and the smaller, described by Gale and Richards * in 1910, which 

.lies on the western slope of Meade Peak, will afterward be reviewed 

briefly.

SOUTH CANYON DISTRICT.

GENERAL FEATURES.

The topographic features of this district are shown in Plate I 

(p. 10).

The prominent, natural exposures of the dark-colored phosphate 

shales in the gulch on the south side of South Canyon near the present 

mine openings led to the original discovery, but the strong outcrop 

of the persistent overlying Rex chert member of the Phosphoria 

formation is a more useful marker of the geologic horizon. The 

underlying limestone is present but is not .prominent enough to 

serve as a marker. The phosphate deposits outcrop in two places in 

South Canyon, one of which lies in the township under discussion 

and one just east of the township line. The western outcrop has 

been known for some time and upon it the local prospecting has 

centered. The eastern outcrop was apparently unknown prior to 

the examination by the United States Geological Survey. It will be 

considered briefly here because of its bearing on the deposit in sec. 12. 

The eastern outcrop is marked by an equally prominent ledge of the 

Rex chert. Float phosphate rock was also found in considerable abundance along the trace of this outcrop. The rocks in the area between 

the western and eastern chert ledges, although poorly exposed, 

clearly consist of the iron-stained calcareous shales of the Woodside 

shale.

i U. S. Geol. Survey Bull. 430, pp. 457-535,1910.
U. S. GEOLOGICAL SURVEY BULLETIN 577 PLATE X

Concealed fawlt 

( Covered bylcuterdeposits')

landcomerfoxmd,

 <, 

Tbmiel

 

House

Topography from Montp.elier sheet, 

Sligtftly modified in region of South 

Canyon,by R.W. Richards

Scale 62,5oo.

Contour interval 250 feet 

DatumismeansealeveL '

GEOLOGIC MAP AND SECTION OF T. 11 S., R. 44 E.
DETAILED DESCRIPTION OF AREA. 51

The shape of the deposit is revealed on the east and west by the 

distribution of the outcrops of the phosphate shales and on the north 

and south by the presence of areas of rocks older than those containing the phosphate (Mississippian limestone and Wells formation), which have presumably come into their present relation to 

the phosphate and the overlying rocks by faulting. The exact 

position of the fault planes is known in only a few places because of 

the scarcity of ledges and their irregular distribution. This much, 

however, appears clear, namely, that the faults are bverthrusts 

whose planes have been subsequently folded* These faults are 

doubtless closely related to the Bannock over thrust (PI. I, p. 10).

The areal distribution of the several formations together with the 

inclination of the chert ledges leads to the conclusion that the phosphate deposits lie in a synclinal basin which comprises a portion of 

the overthrust block. A diagrammatic cross section of this basin is 

included in the structure section on Plate X. Future mining development will probably demonstrate that the fold is complex rather than 

simple, as represented, and that it comprises a number of smaller

folds.

CHARACTER OP PHOSPHATE ROCK.

A number of prospect openings have been made on the phosphate 

shales by the Utah Fertilizer & Chemical Manufacturing Co. These 

were somewhat caved when examined by the members of the Survey 

party, so that the information obtained is incomplete. The principal exposures are described in the order of the numbers which have 

been assigned to them on the map (PL X).

Near locality 1, in sec. 1, within a few feet of ledges of Mississippian 

limestone, two pits were found. One of them exposed about 3 feet 

of the basal or main phosphate bed immediately above the underlying 

limestone. The rock appeared on visual examination to be of 

excellent quality, and no' samples were taken for analysis. The 

second pit is several feet higher in the shales of the Phosphoria 

formation, and exposed 2 feet of limestone underlain by about 10 feet 

of brown, phosphatic shales containing a few 2 or 3 inch streaks of 

higher-grade oolitic rock about 3 feet from the base of the exposed 

section.

At locality 2 (a prospect) the following section was measured:

Section of phosphate bed in the SE. $ S W. £ sec. 1 (unsurveyed), T. 11 S., R. 44 E. of the

Boise meridian, Idaho.

Field 

No, of 

sample.

M 70-1

Limestone, dark gray ("cap lime" with characteristic fossils). 

Phosphate rock, dark brown, fine to medium oolitic, someP205 .Per cent. 

33.4

Ca3 (PO<) a .

Per cent, 

72.3

Thickness.

Ft. in. 

4 0

2 8

030

a Exposed.
52 PHOSPHATE DEPOSITS NORTHEAST OF GEORGETOWN", IDAHO.

The presence of the "cap lime" as well as the basal position of the 

bed makes fairly certain the correlation of this bed with that which 

has been developed rather extensively in the Montpelier district and 

described by Gale and Richards.1

The broken condition of the "cap lime" together with the unusual 

thinness of the phosphate bed makes it doubful if the entire bed is 

present at this locality.

The tunnel prospect at locality 3 on the north side of South Canyon shows a section of about 4 feet of medium oolitic brown rock. 

The local structure is complicated, so that about 50 feet from the 

entrance the underlying limestone is encountered, and the tunnel 

makes a sharp bend at nearly right angles to the right for about 30 

feet. It then resumes its original trend, about N. 23° W. At the 

time of the examination the tunnel terminated about 30 feet from 

the last turn. The geologic structure, which is roughly followed by 

the tunnel, may bear two interpretations. It may be either a slight 

fault or a sharp drag fold (PI. VIII, B, p. 45). The latter view seems 

to better satisfy the conditions observed.

The rocks cut by the tunnel at the offset and beyond are so finely 

broken and slickensided that the oolitic texture has largely disappeared from the phosphate rock. A sample of this material tested 

qualitatively contains a high percentage of phosphoric acid, but no 

quantitative examination has been made because of the lack of 

definite information concerning the thickness of the bed.

Another tunnel, locality 4, has been opened on the south side of the 

canyon, and this affords the best information obtained concerning the 

mam. bed in this district. The entrance of the tunnel is located in the 

phosphate shales, and the tunnel extends westerly across the strike 

about 30 feet until it cuts the basal phosphate bed and terminates on 

the underlying brown shale. From this point a drift extends southerly along the strike for about 30 feet. The bed ranges from 5 feet 4 

inches to 5 feet 10 inches in thickness. The following section was 

measured in the face of the drift:

Section of phosphate bed from tunnel of Utah Fertilizer & Chemical Manufacturing Co., 

in sec. 12, T. 11 S., R. 44 E. of the Boise meridian, Idaho.

Field 

No. of 

sample.

R 117-1

R 117-2

R 117-3

R 117-4

Limestone ("cap lime") fossils.

P2 06 .

Per cent. 

32.1

34.8

035.8

32.1

Ca3 (P04 )2 .

Per cent. 

70.1

76.0

78.2

70.1

Thickness.

Ft. in. 

2 0

. 2 0

1 7

5 10

a The phosphate content of R 117-3 has been lowered slightly by the inclusion of the underlying shaly 

bench.

i U. S. Geol. Survey Bull. 430, pp. 457-535,1910.
DETAILED DESCRIPTION OP AREA. 53

The average phosphoric acid content for the full section is about 

34.5 per cent phosphoric acid, which is equivalent theoretically to 

75.1 tricalcium phosphate.

The following excellent natural exposure of the upper portion of the 

phosphate shale was measured in the gulch south of the tunnel:

Section of the upper portion of phosphatic shales in sec. 12, T. 11 S., R. 44 E.

Cherty limestone (base of overlying chert). . Ft. in. 

Shale, dark brown........................................... 17 0

Phosphate rock, brown, medium oolitic, thin bedded; includes 

local limestone lenses and about 6 inches of coarsely oolitic 

phosphate............................................... 1 2

Phosphate rock, brown, coarsely oolitic; weathers gray....... 6

Phosphate rock, gray, coarsely oolitic........................ 9

Phosphate rock, brown, medium oolitic...................... 2

Limestone, brown, shaly at top and bottom.................. 1 0

Phosphate rock, gray, coarsely oolitic or pisolitic, some of the 

pisolites being nearly 2 inches in diameter................ 7

Shale, brown............................!.................... . 2

Phosphate rock, medium oolitic, grading to finely oolitic at

base....................;................................. 2

Shale, brown................................................ 2

Limestone lens, maximum thickness................"......... 4

Phosphate rock, gray, coarsely oolitic........................ 3-6

Shale, brown................................................ 2

Phosphate rock, gray, coarsely oolitic........................ 3

Shale, brown................................................ 1 1

Phosphate rock, gray, coarsely oolitic........................ 6-12

Shale, dark brown, with a few oolitic streaks................1

Concealed................................................[

Phosphate rock, brown, medium oolitic, shaly................ 5± 0

Shale, brown, not measured.

60 7±

About one-sixth of the section is composed of phosphate rock which 

contains more than 32 per cent phosphoric acid, or about 70 per cent 

of tricalcium phosphate. The shale which practically comprises the 

remainder, by comparison with similar shales which have been analyzed, is estimated to contain about 25 per cent of phosphoric acid, 

equivalent to 54 per cent bone phosphate. The average content of 

the 60 feet measured (eliminating the limestone lenses and lentils) 

would be about 57 per cent tricalcium phosphate. Such material as 

this, although undoubtedly of too low grade to be utilized by present 

practice of superphosphate manufacture, ought eventually to be of 

value as a source of finely ground phosphate rock meal or "floats," 

or possibly it could be utilized in some cement-manufacturing process 

with recovery of the phosphoric acid as a by-product.

About 750 feet south of the natural exposure and some 200 feet 

higher, at locality 5, two short tunnels were visited. The more easterly is shown on the map and is located in the phosphate shales, but
54 PHOSPHATE DEPOSITS NORTHEAST OP GEORGETOWN, IDAHO.

was so filled by caving that it was inaccessible. The other tunnel is 

about 100 feet to the west in a siliceous, somewhat porous limestone, 

lower in the Pennsylvanian portion of the section than the "under 

lime." Abundant specimens of banded travertine were seen, which 

is probably to be interpreted as evidence of faulting.

The mapping of the phosphate shales from this point south to the 

ridge top, where they disappear under Mississippian limestone, is 

based mainly on the tracing of the accompanying overlying chert to 

that point by means of abundant float fragments.

AREA AND TONNAGE.

The area of phosphate land in this district can not be regarded as 

coextensive with the area of outcrop of the normally overlying chert 

and Woodside shale, because the surface or plane of the Bannock thrust underlies the area and truncates the synclinal fold, somewhat as indicated in the diagrammatic cross section shown on Plate X. 

This plane is estimated to cut the phosphate shales about 1,200 feet 

down the dip.from the level of the tunnels near the canyon bottom. The length of the outcrop from the trace of the fault termination on the north side to that on the south side is about 3,500 feet. 

The best exposure of the main phosphate bed indicates that it is 

somewhat over 5 feet in thickness. However, that-figure may be 

taken as the basis for a conservative estimate of its contents.

The total tonnage of the basal phosphate bed included within the 

three faults and the surface is estimated on the basis noted above at 

about 1,968,000 long tons of high-grade phosphate rock. The portion of this tonnage lying about the present tunnel (No. 4) level and 

the south limit of the deposit is 37,000 long tons.

The complete section contains more high-grade rock than is taken 

for the basis of the calculation, but the data at hand do not warrant 

more accurate estimates. If the fault plane lies in a position different from the one considered in the estimate, the actual tonnage will 

decrease or increase as the fault plane rises higher into .or falls below 

the curve described by the phosphate bed in the fold.

PROPOSED DEVELOPMENT.

The Utah Fertilizer & Chemical Manufacturing Co. plan early 

development of these deposits. A start was made in the fall of 1911, 

but the work was interrupted by the, heavy snowfall. The company is said to contemplate the erection of surface equipment capable 

of handling 1,000 tons or more a month, and it is probable that the 

high-grade rock lying about the present tunnel, No. 4, will be the 

first removed. Slight difficulty should be encountered in carrying 

out this plan, although several minor faults offset the phosphate bed 

toward the west for distances ranging from a few feet to a maximum
DETAILED DESCRIPTION OF AREA. . * 55

of perhaps 150 feet. The first fault of this series will be cut at about 

490 feet from the present tunnel.

The heavy snowfall and avalanches in the vicinity of these openings will make operations during the winter rather expensive and 

possibly somewhat dangerous. This difficulty would be obviated and 

at the same time a larger portion of the body of phosphate rock 

would be made easily minable, by a horizontal tunnel about 5,000 

feet in length from about the 6,900-foot level eastward along the 

line of the geologic section. In offering this suggestion, however, it 

is not intended to imply that details of costs of construction under 

this and other plans have been estimated. The total quantity of 

ro.ck which could be removed through such a tunnel can not be 

safely estimated at over 196,800 long tons.

OWNERSHIP.

The boundaries of the Great Producer and Great Deposit claims, 

held by the Utah Fertilizer & Chemical Manufacturing Co., are shown 

on the accompanying map (PL X). It will be noted that owing to 

.the peculiar structure these claims contain practically all of the 

.phosphate rock included in the part of this district lying in T. 11 S., 

R. 44 E.

MEADE PEAK DISTRICT.

The northwestern slopes of Meade Peak consist of rocks older than 

the phosphate-bearing rocks except in a small tract comprising 

about 6 acres in the NW. £ sec. 1. In this tract the phosphate shales are bent into a sharp syncline which is apparently 

overturned toward the southeast. This structure is truncated on the 

south by a fault which is regarded by the writers as a thrust of 

subordinate order but which is probably a branch of the major thrust,

QUALITY OP THE PHOSPHATE ROCK.

The lower main bed was sampled in 1909 at the breast of the main 

tunnel on the claim at this locality. The thickness of the bed at this 

point is 6 feet and the samples were found to contain 35.7 per cent 

phosphoric acid, which is equivalent to 78 per cent bone phosphate.

AREA AND TONNAGE.

The area of the outcrop of the phosphate shales, as above noted, is 

about 6 acres, but the surface area of the phosphate bed is probably 

at least one-third in excess of this, owing to the compression of the 

bed in a rather sharp fold. The assumption that a single 6-foot bed 

of phosphate underlies an area equivalent to 10 acres of flat-lying 

beds gives about 200,000 long tons of phosphate rock for the main 

bed. The higher beds in this area in all probability do not carry a 

sufficient quantity of phosphate to be considered in the tonnage 

estimate.
56 PHOSPHATE DEPOSITS NORTHEAST OF GEORGETOWN, IDAHO.

DEVELOPMENT.

The company which, preceded the Utah Fertilizer & Chemical 

Manufacturing Co. in the ownership of this claim began the development. Near the northeast corner of the deposit a tunnel about 90 

feet in length runs in about 60 feet S. 70° W. and then turns southward, following the bedding or the strike for about 30 feet more. A 

more favorable location for this tunnel would have been 150 feet 

lower and about 400 feet slightly west of north of the present location. The suggested location is on the axis of the syncline and at the 

lowest point on the phosphate bed, and would therefore serve in 

mining out both limbs of the fold.

A tramway about 3,000 feet in length was built from the elbow of 

Georgetown Canyon to this phosphate area. The uppeV end of the 

tramway is about 1,000 feet above its lower terminal, but it has not 

been completed.

T. 8 S., R. 45 E. 

SURVEY.

The examination of T. 8 S., R. 45 E., was made by the writers during the field season of 1911, after the mapping of the topography by 

Albert Pike. The township has not been surveyed by the General 

Land Office, but a theoretic land net has been added to the accompanying map (PI. XI) for convenience in reference. The area is 

included in the Caribou National Forest.

STRATIGRAPHY.

The rocks in this township range in age from Pennsylvanian to 

Lower Triassic. Quaternary alluvial deposits are also present. 

The older formations are the Wells formation, the Phosphoria 

formation (including at the top the Rex chert member), the Woodside 

shale, and the Thaynes limestone.

STRUCTURE.

The geologic structure, as interpreted from the data furnished by 

the outcropping formations, is fairly simple, the principal features 

being two synclines separated by a narrower anticline. The axes of 

the folds have a slightly curving trend and pitch gently about N. 25° 

W. This structure is represented graphically in the diagrammatic 

cross sections on Plate XI. A study of the surrounding region, however, makes it clear that this simple structure does not extend to 

great depths, but that it is interrupted by the Bannock overthrust 

(pp. 35-38), the plane or surface of which was originally almost 

horizontal, though now considerably deformed. Below this fault
U. S. GEOLOGICAL SURVEY BULLETIN 577 PLATE XI

Topography from Crow Creek sheet

sooo'

Overthrust

i Scale 62,500

2Miles

OHitourintervalZSOfeet 

7ne t 

1914

GEOLOGIC MAP AND SECTIONS OF T. 8 S., R. 45 E.
DETAILED DESCRIPTION OF AREA. 57

surface, whose depth is mainly a matter of conjecture, the geologic 

structure differs from that above, and the rock formations in general 

are of later geologic age.

The principal economic interest in the overthrust involves the 

question whether or not the bottoms of the phosphate-bearing 

synclines are truncated by it. The writers are of the opinion that 

undoubtedly these synclines are cut by the overthrust in some places. 

It is impossible, however, to verify this opinion without drilling.

PHOSPHATE DEPOSITS. 

OCCURRENCE.

All the township except about 2 square miles is underlain by phosphate rock, all of which is regarded as ultimately recoverable from 

favorable points of entry. The phosphate here as elsewhere in this 

general region occurs in rocks of Permian (?) age and is overlain by 

dark resistant cherts, which are succeeded by 4,000 to 5,000 feet of 

limestones, in part shaly, of Lower Triassic age. The whole series of 

rock, including the underlying sandy limestones, sandstones, and 

limestones, has been bent up into large folds. The phosphate shales 

outcrop along the sides and around the tips of the anticlines. The 

area is unique in that it contains the largest body of phosphate rock 

included in any township yet examined.

QUALITY OF ROCK AND TONNAGE.

No prospecting has been done on the phosphate deposits of this 

township and the nearest section from which information is available 

concerning the thickness of the phosphate beds and the quality of the 

rock is exposed in a trench made by the survey party in sec. 14, T. 8 

S.y R. 44 E. This section is given on page 28 of this bulletin, and 

from it the writers consider that the phosphate shales in this township can be reasonably estimated to contain at least a 6-foot bed of 

rock which averages 32 per cent phosphoric acid, equivalent to about 

70 per cent tricalcium phosphate.

The area of lands made up of the rocks of the formations which 

normally overlie the phosphate in this township is estimated at 

21,900 acres.

In estimating the tonnage of the mam phosphate bed two factors 

have to be considered the increase of area due to folding and also a 

possible decrease due to the removal of phosphate by truncation of 

the synclines by the thrust fault. The increase can be approximated 

with a fair approach to accuracy, but the decrease, quantitatively at 

least, is so purely a matter of conjecture that it is practically useless 

to introduce it, although it must diminish the actual tonnage of phos-
58 PHOSPHATE DEPOSITS NOETHEAST OF GEORGETOWN, IDAHO.

phate to some extent. Theoretically, perhaps, the two factors may 

be regarded as equivalent, although when actually determined they 

may be found to vary widely. The assumption that 21,900 acres is 

underlain by a horizontal 6-foot bed of phosphate rock weighing 180 

pounds to the cubic foot gives a total of 459,900,000 long tons.

The depth of the main phosphate bed in the township ranges from 

the outcrop at the surface- to a maximum probably not much in 

excess of 2,000 feet from favorable points of entry.

DEVELOPMENT.

The phosphate deposits of this township were entirely unprospected 

prior to this investigation. Their economic development will of. 

necessity depend on the construction of railroads into this district. 

The natural lines to be followed in the development of the phosphate 

will be along Diamond Creek to the northwest or (if a railroad is built 

in Star Valley) along the southern forks of Stump Creek, Smoky 

Canyon, and the unnamed canyon in sec. 31, T. 8 S., R. 46 E.

The points of entry which are regarded as most favorable are 

situated in sec. 21, T. 8 S., R. 45 E., and in sec. 19, T. 8 S., R. 46 E., 

on the tips of the anticlines. These points of entry permit the construction of main haulage tunnels northwestward along the anticlinal 

crests. A system of lateral inclines at favorable grades, connecting 

the main working tunnels along the synclinal troughs, appears to 

offer ideal facilities for large-scale extraction of the rock phosphate.

T. 9 S., R. 45 E. 

SURVEY.

The geologic examination of T. 9 S., R. 45 E., was made by the

writers immediately after the completion of the topographic map by 

Albert Pike. The township has not been surveyed by the General 

Land Office, but a theoretic land net has been superimposed on the 

accompanying map (PI. XII) to facilitate reference. The township 

is included in the Caribou National Forest.

STRATIGRAPHY.

The rocks of the township are all sedimentary and belong to the 

formations included in the stratigraphic interval from the upper Mississippian limestone to the Thaynes limestone (LowerTriassic). They 

are, in ascending order, the Wells formation, the Phosphoria formation (including the Rex chert member), and the Woodside shale. 

Within half a mile of the southeast corner, rocks of Jurassic or Cretaceous age appear on the east side of a great thrust fault.
U. S. GEOLOGICAL SURVEY BULLETIN 577 PLATE XII

Thaynes limestorie

 Topography from Crow Creek sheet

R-45E.jR.46E 

I

Beckwith formation and 

Twin Creek limestone

Beckyi/ith formation 

and Twin Creek limestone

Scale 62,500

Coniirarinterval 250 feet 

Jfdeum is mean &ea level

GEOLOGIC MAP AND SECTIONS OF T. 9 S. R. 45 E.
DETAILED DESCRIPTION OP AREA. 59 

STRUCTURE.

The structural features of the township are developed on a largescale and are relatively simple. An anticline, normal and upright or 

'only slightly inclined eastward, passes through the central part from 

south to north. On both sides of the anticline are synclines that 

broaden and pitch gently north. Beyond the synclines, near the east 

and west margins of the township, are other anticlinal axes. The 

outlines of the folds are fairly simple, though they have been modified 

locally by faulting.

The western syncline is relatively deep and narrow and is overturned 

eastward. The eastern syncline is broader and is also inclined 

toward the east. Minor folds within the greater synclines are indicated by the small infolded areas of Thaynes limestone.

Two minor thrust faults occur in the NE. { sec. 32 and in the 

western half of sec'. 27, respectively. The east border of the eastern 

syncline is modified by a thrust fault of small displacement that 

begins about the center of sec. 24 and extends somewhat irregularly 

through the southeast corner of sec. 1. A small outlying thrust 

block, produced by this fault and now detached by erosion, overlies 

the border of the SE. I sec. 13 and the NE. | sec. 24.

East of the township, extending from the NE. \ sec. 5 to the NW. \ 

sec. 30, T. 9 S., R. 46 E., lies the west limb of another syncline that 

is broken on the east by the Bannock overthrust fault, which brings 

rocks of Carboniferous age over Jurassic and Cretaceous formations.

The northward projection of the great thrust fault from the townships to the south and southwest cuts off a portion of the bottom of 

the deep western syncline, and thus cuts out some of the phosphate 

shales. This interpretation, together with other details of structure, 

is shown in sections A-B and C-D on the map (PI. XII).

PHOSPHATE DEPOSITS.

The phosphate deposits lie in two north-south belts across the township. The western belt has a constant width of about a mile, whereas 

the eastern belt ranges in width from about 2^ miles at the northern to 

half a mile at the southern boundary. The phosphate deposits are 

included in the Phosphoria formation, of supposed Permian age, as 

elsewhere in this general region.

Previous to 1911 no prospecting .had been done in the phosphate 

shales. Members of the Survey party explored the natural exposure 

in the NW. | SE. £ sec. 34 and obtained a partial section about 10 

feet above the underlying limestone. The table following gives the 

measurements thus obtained and the results of the analyses of the 

samples taken:
60 PHOSPHATE DEPOSITS NORTHEAST OF GEORGETOWN, IDAHO.

Partial section of phosphate shales in the NW. J SE. J sec. 84, T. 98., R. 45 E. of the

Boise meridian, Idaho.

Field 

No. of specimen.

E446....

(3)......

(2)......

(1)......

.....do............................ ........................

Shale. ........................................................

Limestone.

PiO».

Per cent.

32.0

29.6

4.4

Equivalent to 

Ca3(P04)2,

Per cent.

69.9

64.6

Thickness.

Ft. in. 1 4

1 11

2 2

5

10 0

The above section shows a bed about 4 feet thick, represented by 

samples 2 and 3, that averages 65 per cent or more tricalcium phosphate. These figures are somewhat lower, both as regards thickness 

and quality, than those for the phosphate beds in adjoining townships to the northwest and southwest.

The upper portion of the shales, near the overlying chert, has not 

been explored, and there may be, as in Tps. 8 to 10 S., R. 44 E., beds 

of high-grade phosphate at that horizon. However, at this time it is 

safe to assume only the presence of the 4-foot bed measured.

On the supposition that the Bannock overthrust, which is believed 

to underlie the township, cuts off a portion of the bottom of the 

western syncline, as shown in the sections accompanying the map 

(PI. XII), some of the phosphate deposits may have been destroyed. 

If a fail- allowance is made for this loss, and the average dip is assumed 

to be 60°, the western syncline contains about 4,400 acres underlain 

by phosphate deposits. The eastern syncline, with an assumed average dip of 30°, contains about 8,160 acres, ancl thus the total is 

approximately 12,560 acres. As a cubic foot, of phosphate rock 

weighs 180 pounds, the 4-foot bed of phosphate rock that underlies 

this township is estimated at 171,400,000 long tons.

In T. 9 S., R. 46 E., these deposits extend under an area estimated 

at 1,460 acres with an approximate tonnage of 20,442,000 long tons.

The deposits of the western syncline are accessible from the road 

in Diamond Creek, built by the Forest Service in 1911. The east 

side of the eastern syncline may be reached with little difficulty by 

the trails in the forks of Sage Creek. The interior of the eastern 

syncline and the west side of the western syncline lie in relatively 

high country to which there is no available means of access' at the 

present time. However, several deeply cut canyons extend far back 

into the ridges and in these roads can be constructed without much 

difficulty. Trails used by sheep outfits are now found in most of 

the larger canyons.
DETAILED-DESCRIPTION OF ABE A. 61 

T. 10 S., R. 45 E. 

SURVEY.

The portion.of T. 10 S., R. 45 E., lying west of the part of the 

Preuss Range locally known, as Snowdrift Mountain was examined 

in a preliminary way by the Geological Survey in 1909. In 1910 the 

topography was mapped by Albert Pike in connection with the survey of the township to the west, and the base map of the remaining 

portion to the east was completed early in 1911. The detailed geologic survey by the writers immediately followed the topographic 

work.

STRATIGRAPHY.

The geologic age of the several formations which outcrop in the 

township ranges from upper Mississippian to Quaternary. Limestone and sandstones of Pennsylvanian age cover nearly half.of the 

township, and the following formations listed in decreasing order of 

area, cover the remainder: Beckwith formation, Woodside shale, 

upper Mississippian limestone, Twin Creek limestone, Phosphoria 

formation (including at the top the Rex chert member), with minor 

areas of alluvium, Pleistocene clay, Nugget sandstone, and Thaynes 

limestone.

STRUCTURE.

Ill this township two masses of folded sedimentary rocks lie one 

above the other as a result of the Preuss Range overthrust. The 

underlying mass at its top is in general composed of younger rocks 

than are now included in the overlying block.

The character and distribution of the folds in the upper block 

determine the distribution of the phosphate deposits. These folds 

are shown in several cross sections on Plate XIII. They comprise 

a series of unsymmetrical anticlinal and synclinal folds of considerable magnitude. The major synclines are two in number and have 

the same distribution as that of the phosphate deposits described 

above. The principal anticlines are also two in number. The axis 

of the western fold practically coincides with the crest of Snowdrift 

Mountain; that of the eastern anticline lies along Crow Creek at the 

margin of the overthrust block.

Faulting has caused several modifications within the upper block. 

A thrust which is regarded as a branch of the main thrust has truncated the south end of the eastern syncline. Other faults occur in 

the northwestern part of the township, either marginal or medial to 

the western syncline. These faults apparently have greater vertical 

than horizontal components and probably should be classed as 

normal.
62 PHOSPHATE DEPOSITS NORTHEAST OF GEORGETOWN, IDAHO.

The structure of the underlying block in this township is apparently 

somewhat more complex than that of the overthrust block. The 

exposure of the underlying block in the eastern part of the township, 

although narrow, shows clearly the existence of a series of compound 

folds with local faulting developed along the boundary between the 

Beckwith formation and the Twin Creek limestone. The structure of 

the greater portion of this underlying block is, however, undetermined.

The narrow area of the Kex chert member of the Phosphoria- formation and the Woodside shale in the eastern part of the township 

is regarded as included between the main thrust and a branch thrust. 

The planes of the two faults probably coalesce westward at no great 

distance. The presence of valuable phosphate deposits between the 

two fault planes is doubtful.

PHOSPHATE DEPOSITS. 

OCCURRENCE.

The phosphate deposits lie in parallel belts in the western and 

central parts of this township. Each belt has a western and eastern 

line of outcrop, and the two belts, are separated by a high mountain 

mass of rocks older than the phosphate-bearing formation, which 

here as elsewhere in this region is of probable Permian age. The 

belts are the uneroded synclinal remnants of a rock series which 

undoubtedly at some early geologic period extended over the intervening anticlinal area. The western belt of deposits has been known 

for some time, and mineral claims were filed along both lines of 

outcrop following the "discovery. The extreme eastern portion of 

the township undoubtedly contains the same phosphate deposits but.

at unrecoverable depths.

MEASURED SECTIONS AND QUALITY OF PHOSPHATE ROCK.

The phosphate deposits of this township have been prospected 

along only one of the four lines of outcrop, namely, that on the west 

flank of Snowdrift Mountain. Many openings, mostly shallow 

trenches, have been made by the Utah Fertilizer & Chemical Manufacturing Co. in the course of its assessment and patent work. Many 

of these openings show the character of the main basal bed, whereas 

others are superficial and do not penetrate to bedrock. Two cuts are 

especially complete and expose practically the entire section of the 

phosphate shales. The sections given on pages 24-26,were measured 

at these localities and are thought to give a representative view of the 

quality and quantity of phosphatic materials which would be found 

in the unprospected portions of this township. Nearly all the strata 

appear to be highly phosphatic and include several high-grade beds. 

In considering these analyses it is well to bear in mind that the samples
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DETAILED DESCRIPTION OF AEEA. 63

were taken near the surface and from beds nearly in vertical position. 

If enrichment along the outcrop has occurred these samples are above 

the average. Though the study of thin sections has not made it 

clear that concentration has taken place, yet theoretically it appears 

that the surficial leaching of - the calcium carbonate would tend to 

cause local enrichment along the weathered zones. The inclusion of 

soil along the numerous minute surficial joints tends to act in the 

opposite direction and renders the deposits leaner 'on the outcrop 

than beneath the surface. It may well be considered, however, that 

in this particular locality the two processes about balance and that 

the results are characteristic of the deposits as a whole.

The main bed, as in the Montpelier district,1 occurs at the base of 

the phosphate section. It varies in thickness but appears to average 

about 6 feet in places where it has been fully opened. Therock phosphate is of'high grade, carrying about 37 per cent phosphoric acid, 

equivalent to about 80 per cent tricalcium phosphate, as shown by 

the analyses. It is medium to coarse oolitic in texture and of dark 

grayish-brown color, almost black when fresh, and contains little 

foreign matter in the form of partings. It is capped by a single 

2-foot stratum of dark fine-grained fossiliferous limestone.

AREA AND TONNAGE.

The area in this township which is underlain by the phosphate 

deposits is estimated to be 3,967 acres. Of this amount about 2,336 

acres lie on the syncline west of the range and the remaining 1,631 

acres on the eastern fold. The surface area of the main phosphate 

bed as bent up on the western fold is approximately two-fifths greater 

than that of the surface area of the land, so that the main basal bed 

comprises about 3,889 acres. The difference between the area of 

the overlying lands and the extent of the main bed is much less in 

the eastern fold, where the area of the bed is estimated to exceed 

that of the lands by one-eighth. A deduction has been made in this 

estimate for the area of phosphate which probably has been displaced 

by the subordinate thrust from its position under the normally overlying chert and Woodside shale in sees. 28 and 29.

The total area of the main basal bed is thus about 4,236- acres. 

On the assumption that the average thickness of the bed throughout 

this extent is 6 feet, the contained tonnage of high-grade phosphate 

rock is 88,900,000 long tons. All the high-grade rock included in 

this estimate is ultimately available, as the greatest depth from 

favorable points of entry is less than 2,000 feet. 

- The phosphate content of the entire section of the phosphate 

shales is probably several times the above estimate that is, in highgrade rock alone and an enormous tonnage of low-grade material is. 

present which may at some future date prove of great value.

i Gale, H. S., and Richards, R. W., TJ. S. Geol. Survey BulL 430, pp. 488-495,1910.-
64 PHOSPHATE DEPOSITS NORTHEAST OF GEORGETOWN, IDAHO.

DEVELOPMENT.

Practically none of the exploratory work which has been done 

by the Utah Fertilizer & Chemical Manufacturing Co. can be utilized 

in the actual mining, of the deposits, with the possible exception of 

the tunnel in the southeast corner of the Hillside claim. This tunnel 

by bearing due east will cut the phosphate shales at a distance of 

about 1,000 feet. The last 500 feet would penetrate the overlying 

chert. It is possible that the portions of the three beds, 144 G, I, 

and S (pp. 24-25), above the level of this tunnel and for a distance 

of 2,000 feet in both directions along the outcrop, can be feasibly 

removed through it. The capacity of this tunnel is in round numbers 660,000 long tons of rock of over 70 per cent tricalcium phosphate. The cost of proper equipment for transporting this tonnage to the main line of outlet in Georgetown Canyon, a distance 

of three-fourths mile, should be compared with a scheme of underground haulage to that point through a system of workings at lower 

levels with a higher total capacity.

Any general scheme of development of the western phosphate 

area will of necessity have to be worked out in connection with the 

natural extension of this area in the township to the west.

The development of the eastern syncline will naturally start at 

the eastern margin and will be' dependent on the construction of a 

railroad in the valley of Crow Creek. The most favorable points of 

entry are situated on Deer Creek, immediately north of the township line, and on the unnamed creek which runs easterly across sees. 

21 and 22. Short tunnels transverse to the axis of the fold with 

extraction drifts paralleling the axis will permit the easiest movement of the rock and present undoubtedly the most economical mining procedure for large-scale operation.

OWNERSHIP.

The title to about 2,767 acres of the total area of phosphate land 

in this township is vested in the United States Government. The 

Utah Fertilizer & Chemical Manufacturing Co., under claims filed 

under the provisions of the mineral-land laws, holds 780 acres. The 

State school land in sec. 16 includes about 405 acres bearing phosphate.

SALT DEPOSITS.

The marginal region of the great thrust on Crow Creek bears salt 

deposits which give rise to saline springs. The only one of the 

springs which has been utilized as a source for brine is located in sec. 

14. The origin, distribution, and economic bearing of these deposits have been discussed by C. L. Breger.1

1 Breger, C. L., The salt resources of the Idaho-Wyoming border, with notes on the geology: U. S. 

Geol. Survey Bull. 430, pp. 555-569,1910.
DETAILED DESCRIPTION OF AEEA. 65 

T. 11 S., R. 45 E. 

SURVEY.

A detailed geologic survey was made of the entire township 

except sees. 24, 25, and 36, which are underlain by the southward 

continuation of the Beckwith formation, examined farther north, 

which lies high above the phosphate. In the northwest corner of 

the township, where the phosphate beds outcrop, the survey was 

made with plane table and alidade. Elsewhere locations were determined by pocket compass sights, which were considered sufficiently 

accurate.

The field sheet of the Montpelier quadrangle, enlarged from a scale 

of 1:96,000 to the scale of 1:31,680, was used for the topographic 

base and the geologic work was done on the latter scale.

Collections from the Carboniferous rocks of the northwest part of 

the township were made by G. H. Girty. E. H. Finch, of the Survey, spent three days in examining parts of the township.

The land net as given on the Montpelier sheet was accepted and 

used in the geologic survey.

STRATIGRAPHY.

The rocks of the township range from early Carboniferous to Pliocene (?), the oldest rocks lying in the northwest part and the youngest 

in the east .and southeast parts.

The Madison limestone has been recognized at only two localities 

in this township, namely, in the NW. i sec. 17 and the NE. \ sec. 19, 

where it appears in an eroded anticline or anticlines in the upper 

Mississippian limestones. The formation appears in normal facies 

with characteristic fossils.

The upper Mississippian limestones form the ridge that extends 

from sec. 20 to the northwest corner of the township and culminates 

in Meade Peak (9,953 feet in altitude) in the SW. I NW. | sec. 6, 

the highest point within 'the area described in this report. The 

limestone is characteristically developed and locally well supplied 

with fossils. It is marked by rough craggy ledges and rugged topography and forms picturesque mountain scenery.

The-lower Pennsylvanian sandy limestones, sandstones, and quartzites of the Wells formation occur in two general areas. The smaller 

area lies about the head of the south fork of Georgetown Canyon in 

sees. 7 and 18. The larger area occupies .a part of sees. 4, 5, and 6. 

These localities are marked by somewhat smoothed and rounded 

topographic forms with abundance of sandy float, which weathers 

white or dull red, but outcrops are comparatively rare. Even the

37002° 14 5 ...
66 PHOSPHATE DEPOSITS NORTHEAST OF GEORGETOWN, IDAHO.

limestone that comprises the top of the formation and underlies the 

phosphate beds is here less well marked as a cliff maker than is the 

rule farther north, and it has few outcrops.

The Phosphoria formation is well developed in two localities 

bordering the formation just described and extends also into the 

northern part of sec. 8. The lower or phosphate-bearing portion is 

not actually exposed by open cuts or prospects in this township, 

but its presence may readily be determined by float along the line 

where it approaches the surface. Topographically it is represented 

by depressions or saddles on the ridges, and by valleys. In sees. 4 

and 5 it occurs in a small canyon tributary to the Crow Creek system. 

Tne Rex chert member is well represented in both localities and, 

so far as observed, consists solely of heavy chert layers without 

fossils. In sees. 4 and 8 and 3 and 9 the chert forms remarkably 

fine dip slopes of bare rock along the north side of Crow Creek.

The Woodside shale occupies a belt from a quarter to half a mile 

wide, extending from the middle of sec. 8 northeast through sec. 3. 

In this belt the rock is rather massively bedded, though still retaining its sandy character and its yellowish and greenish tints. A particularly fine exposure of a portion of these beds occurs on a knob 

above Crow Creek in the SE. £ SE. | sec. 4, where fine ledges descend 

nearly 800 feet to the bottom of the creek. Another smaller area 

forms a narrow band extending from the northern part of sec. 18 

through sec. 7 into sec. 12, T. 11 S., R. 44 E., where it expands and 

underlies a large part of the south fork of Georgetown Canyon.

The limestones and shaly limestones of the Thaynes formation 

occupy a large district from half a mile to 2 miles wide, extending 

from the. NE. £ sec. 20 northeast through sec. 3. Topographically, 

the formation is represented by high hills with smoothed slopes and 

few outcrops. The basal member or Meekoceras zone is readily identified and traced. Much of the region underlain by this formation 

is difficult of access because, of brush, timber, and windfalls. The 

Meekoceras and associated fossiliferous zones are well exposed along 

the ridge south of Crow Creek in sees. 8 and 9.

The Ankareh shale has not been definitely recognized in this township. Some red sandy and shaly beds, however, occur along the east 

border of the Thaynes limestone just described. In some localities, 

particularly in the SW. \ SE. \ sec. 10, gray limestone bands (and 

some anhydrite?) are interbedded with the red shales and sandstones, so that the whole strongly suggests the Ankareh shale. But 

.the relation of these beds to the Twin Creek limestone on the east, 

the well-developed Nugget facies of the red sandstones in this same 

band in the township to the north, together with the fact that similar calcareous and shaly bands occur at the top of the Nugget sand-
DETAILED DESCRIPTION OF AREA. 67

stone in Dunns Canyon in sec. 10, T.U.S., R. 44 E., all point to the 

view that the red beds here mentioned belong in the upper part of 

the Nugget sandstone rather than in the Ankareh shale, and they are 

so interpreted. It is possible that the Ankareh may occur at the 

bottom of the canyon in the SW. i sec. 32 within the Nugget sand" 

stone area there shown, but this point has not been determined.

The main occurrence in this township of the Nugget sandstone, 

which is made up chiefly of sandstones and quartzites, has just been 

described. These beds also occupy most of the SW. | sec. 32 and 

a small portion of sec. 31. Here the typical reddish, whitish, and buffcolored sandstones, with dark iron-stained weathered float, are present. The formation constitutes the core of an anticline that enters 

the township from the southeast.

The Twin Creek limestone includes most of the southwest quarter 

of the township and extends in a broad band from sec. 22 northeast 

through sec. 2. So far as observed this formation is here repre^ 

sented almost entirely by the chippy, shaly whitish-gray limestone 

f acies. The rock maintains steep slopes covered with little chippy 

fragments. The west side of Montpelier Creek from sec. 19 southeast 

gives an excellent example of such a slope. The country underlain 

by this formation supports little vegetation and presents a dreary 

aspect.

The Beckwith formation of red sandstones, shales, and conglomerates underlies the entire eastern tier of sections and a considerable 

portion of the second tier. The predominant color is red, though 

some of the sandstones of the formation contain bands of brown, 

gray, or white. In the northeast part of the township this formation is largely conglomeratic and makes ridges and knobs. Red 

Mountain, bordering sec. 12 and extending into the adjoining township, is the most conspicuous topographic feature of this formation 

in this township.

The Pliocene (?) is represented in this township by a belt of strata 

about a quarter of a mile wide, lying hi a depression in the Beckwith 

formation from sec. 1 to sec. 13. In the northern part the beds are 

well-defined white marly grits and conglomerates. Farther south 

they are more influenced by the red material from the adjacent red 

beds and their boundaries are less well defined.

A somewhat crescent-shaped area of travertine is found in portions 

of sees. 3 and 10. In some places, notably on the spur above Crow 

Creek in the north part of sec. 10, the rock contains pebbles of other 

rock and resembles to some degree the marly beds of the supposed 

Pliocene. Elsewhere the banded calcareous material bears evidence 

of deposition from springs, and the resemblance to the Pliocene (?) 

deposits is not close.
68 PHOSPHATE DEPOSITS NORTHEAST OF GEORGETOWN, IDAHO.

STRUCTURE.

In this township faulting has occurred on a considerable scale and 

folding has also taken place in probably two epochs at least. An area 

including somewhat more than the northwest quarter of the township 

constitutes part of a great thrust block that comprises rocks varying 

hi age from the Madison limestone to the Thaynes. These rocks are 

folded into anticlines and synclines that were doubtless formed in the 

earlier period of folding and may have been intensified or modified 

by the later folding.

Meade Peak appears to form part of a closely folded anticlinorial 

ridge which lies between two broken synclines that contain the phosphate deposits of the township. North of Meade Peak the ridge 

 trends northeast, but southward it trends southeast and south. The 

two phosphate-bearing areas appear to be portions of larger synclines to the north, which have been detached by faulting.

The Bannock overthrust, which enters the township in the NW. £ 

sec. 19, branches in the eastern part of sec. 20. The western branch 

separates the Carboniferous from the Triassic (Thaynes limestone), 

and the eastern branch separates the higher portions of the Thaynes 

limestone from the top of the Nugget sandstone. The western branch 

diminishes northward in stratigraphic throw and dies out hi the 

southern part of the adjoining township on the north. The eastern 

branch continues northward with increasing throw and becomes the 

dominant thrust in regions to the north. > The relations of the thrust 

block to the underlying rocks may be very clearly seen on the north 

side of the upper canyon of Montpelier Creek in sees. 19 and 20, where 

rocks of Madison and upper Mississippian age, marked by rough 

craggy topography, overlie- the splintery shaly limestones of the 

Twin Creek formation. The topographic contrast is very striking, 

and the contact may easily be traced along the sides of the valley. 

The stratigraphic displacement here amounts probably to not less 

than 8,500 feet.

The thrust block itself was probably contemporaneous with the 

earlier folding and represents a great eastward movement of the 

older rocks from the west over the younger formations to the east. 

Subsequently it seems to have suffered compression from the east, 

for the eastern branch of the fault now. has a steep westerly hade, 

whereas the western branch in sec. 8 has an easterly hade of about 

42°. It seems clear, nevertheless, that this western branch is really 

a part of the thrust fault and not an independent normal fault, 

because it may .easily be traced along the saddles at the base of the 

ridge into the thrust fault in Montpelier Canyon, and the hade changes 

from east to west as the branching point is approached. This later 

folding is also shown by a subsidiary thrust that marks off the phosphate basin in<secs. 18 and 7. Here, too, the fault plane has been
Z 

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Mississifpiccn Pennsylvamom

CARBONIFEF?OUS

LOWER TRIASSIC TRIASSIC JURASSIC JURASSIC TERTIARY QUATERN

OB JURASSIC AND

CRETACEOUS
DETAILED DESCRIPTION OF AREA. 69

folded, and from the unequal thicknesses of the existing portions of 

the formations that accompany the phosphate it is inferred that the 

bottom portion of the phosphate syncline has been truncated by the 

fault. The relations above outlined are indicated in the sections 

drawn along the lines A-B, C-D, and E-F on Plate XIV.

The boundary between the Twin Creek limestone and the Beckwith 

formation is marked locally by slight faulting, particularly in sees. 2; 

II, and 22. The two formations, with discordant dips, occupy 

opposite sides of deeply cut valleys, and varicolored clays, suggestive 

of fault clay, are exposed here and there along the general contact 

line. To the north the fault plane is steep and apparently normal, 

with the downthrow on the east. Farther south the contact between 

the formations is less regular and has a much more gentle inclination. 

The faulty appear to die out in both directions.

The SW. J sec. 35 is occupied by the southern apex of an eroded 

cigar-shaped anticline in the Twin Creek limestone, the axis of which 

extends northwest into sec. 22. The form of the fold is preserved in 

spite of the erosion that the region has undergone and is so clear 

as to be almost diagrammatic. To the west lie other axes, both 

synclinal and anticlinal. The eastward dips are steeper than the 

westward dips, giving unsymmetrical folds inclined eastward.

In sees. 31 and 32 the Nugget sandstone appears as the core of 

another anticlinal fold that enters the township from the southeast. 

This fold is also unsymmetrical and is overturned toward the east.

PHOSPHATE DEPOSITS.

Phosphate rock comes to the surface only in sees. 3, 4, 5, 7, 8, and 

18, but it probably underlies most of the rest of the township, except 

the areas of Carboniferous rocks older than the phosphate rogk, at 

depths too great to make it available. No openings have thus far 

been made in the phosphate beds in this township, so that the character of the rock can be determined only by the fragments of float 

on the surface, which seem to indicate deposits comparable in nature 

and thickness with the neighboring deposits in Georgetown Canyon 

to the northwest, where numerous prospect pits have been opened.

The estimated -area underlain by phosphate rock at depths not 

greater than 2,500 feet, bounded at the surface by the Meekoceras 

zone or base of the Thaynes limestone, is 1,260 acres, or nearly 2 

square miles. On the assumption that the high-grade phosphate bed 

is 5 feet thick, a reasonable assumption in view of the known thicknesses in neighboring townships, and that the weight of a cubic foot 

of high-grade rock is 180 pounds, this area would. contain over 

22,000,000 long tons if the rocks were horizontal. The dips within 

the district are somewhat variable, but perhaps 40° may be taken 

as a fair average. On this basis the above estimate would be 

increased 30 per cent. If the estimate were made to include rock as
70 PHOSPHATE DEPOSITS NORTHEAST OP GEORGETOWN, IDAHO.

much as 3,000 to 3,500 feet below the surface there would be added 

the area underlain by the Thaynes limestone, which would add a 

little more than 2 square miles to the total already mentioned, and 

would more than double the estimated tonnage.

It should be remembered, however, that this entire area constitutes 

part of a great thrust block and is underlain in all probability by a 

fault plane, which may cut out much or all of the deeper portions of 

the deposit. In the absence of drill records it is impossible to state 

with certainty the depth at which the fault plane lies. It is possible 

too that the assumed thickness of the phosphate bed may be greater 

than the actual thickness, although this seems unlikely. In view of 

these circumstances it seems wiser to submit the estimate as first 

given namely, 22,000,000 long tons, which is surely conservative.

The phosphate deposits are accessible through the valleys of Crow 

Creek and the south fork of Georgetown Canyon respectively. Much 

of the phosphate rock is above water level.

GENERAL SUMMARY OF AREAS EXAMINED.

The tonnage estimates included with the township descriptions 

accompanying this report cover only the area examined in detail in 

1911 and are additional to the estimates for 1909 and 1910. Although 

these estimates are approximate, they are derived from the most 

complete data available at the present time. Emphasis should be 

placed on the fact that all these estimates, like those of the previous 

years, are based to some extent on assumptions which are, however, 

carefully explained in the accompanying text. All the estimates 

made are intended to be moderate. They are confined to the content 

of the main bed, which lies in the greater part of this area near the 

base f>i the phosphate shales, and no attempt is made to estimate 

the vast tonnage of the intermediate or low-grade rock.

Estimates of phosphate rock available in the townships reviewed in this report.

	Long tons. 

T. 8 S., B. 44 E..................................... 386,400,000

T. 9 S., B. 44 E..................................... 164, 600,000

T. 10 S., B. 44 E.................................... 52,000,000

T.11S.,B.44E.................................... 2,170,000

T. 8 S., R. 45 E................................1.... 459,900,000

T. 9 S., B. -45 E..................................... 171, 400,000

T. 10 S., R. 45 E.................................... 88,900,000

T. 11 S., R. 45 E.................................... 22, OOP, OOQTotal for area examined in 1911.................. 1> 347,370,000

Total for area examined in 1910.................. 1,158, 970,000

Total for area examined in 1909 minus 90,000,000 

tons, estimate for Georgetown district, which is 

duplicated in the total for 1911. v .............. 156,950,000

Total tonnage for area covered with detailed surveys to date................................. 2, 663,290,000
PHOSPHATE DEPOSITS NORTHEAST OF GEORGETOWN, IDAHO. 71 

NATURE AND ORIGIN OF THE ROCK PHOSPHATE. 

GENERAL CHARACTER.

The rock phosphate is characterized by an oolitic texture, which, 

however, may be lacking when the grain of the rock has been destroyed 

by pressure or by shearing. The ovules or oolites are rounded grains 

built up in roughly concentric structure and range in size from 

extremely minute specks to bodies half an inch or more in diameter. 

Many of these oolitic bodies are irregularly flattened, suggesting 

that they have actually existed as pebbles and been worn by attrition 

upon one another. The ovules are in general darker than the matrix 

and a few of them possess a black, shiny coating which is similar in 

appearance to desert varnish.

The rock when fresh usually possesses a dark-brown color, but 

the weathered material found on the outcrop is predominately a light 

bluish gray. The rock that has lost its oolitic texture through 

metamorphism by pressure appears to retain the darker original 

color even after long exposure. The bluish-gray coating (somewhat 

like chalcedony in appearance) has a tendency to concentrate along 

lines in a netlike pattern. These lines are very apparent on the 

darker-colored rock and are of assistance in following scattered float 

along the phosphate beds which lie near the surface.

The phosphate rock and the limestone closely associated with it 

yield when struck a characteristic fetid odor which is described by 

some as bituminous and by others as more nearly sulphurous. One 

feature on which all agree is that the odor, though not particularly 

disagreeable, is exceedingly penetrating. The intensity of the odor 

given off by the rock when struck is by no means an indication of its 

phosphatic content.

ORIGINAL SEDIMENTARY DEPOSITS.

The rock-phosphate deposits of the Idaho, Utah, and Wyoming 

fields are original sedimentary formations Jaid down at a time when 

that part of the earth's surface was largely covered by water. Since 

the time in which the phosphatic strata were deposited other rockforming sediments have been accumulated, so that many thousands 

of feet of subsequent strata have overlain or succeeded them. Deformation of the earth's crust has tilted, folded2 and in many places 

broken these strata, which originally lay flat. Uplift of the land or 

recession of the sea has subjected the rock in its disturbed position 

to stream erosion and the action of atmospheric agencies, so that 

great bodies of the more elevated parts have been removed entirely 

and the truncated edges of the rock strata are now exposed at the 

surface. The occurrence of the rock phosphate at the surface of the 

ground now depends on the geologic structure and more or less acci-
72 PHOSPHATE DEPOSITS NORTHEAST OF GEORGETOWN, IDAHO.

dental relationships, such as absence of masking cover or later 

deposits, depth of erosion, and many minor factors.

The rock-phosphate deposits are thus more properly analogous to 

coal and limestone and especially to the Clinton iron ores of the 

Appalachian region than they are to ore deposits such as veins or 

lodes or to alluvial deposits of the placer type.

SPECIFIC GRAVITY.

A series of experimental determinations of the density of the rock 

phosphate was made in the laboratory of the United States Geological 

Survey and is described in detail in the report for 1909.* The average 

specific gravity of rock containing 70 per cent tricalcium phosphate 

was found to be about 2.9. No further data on this subject have 

been collected and this -figure has been used in the tonnage calculations of the present report.

MINERAL AND CHEMICAL COMPOSITION.

The mineral composition of the western rock phosphate is not yet 

completely ascertained, and the problem is difficult of solution, owing 

to the mode of occurrence of the constituent minerals. Thin sections 

of the richest oolitic ore show under the microscope that the rock 

consists mainly of ovules or concretions of a cryptocrystalline substance which, in some concretions, is surrounded by banded zones of 

crystalline fibers with local isotropic bands, all having the same average index of refraction (about 1.60) and apparently representing the 

phosphatic substance. In some places the interstices are filled with 

calcite and in others with an isotropic material which appears to be 

identical with the substance that forms the cores of the concretions. 

The extinction of the double-refracting mineral is parallel to the elongation of the fibers, but the optical character of this mineral can not 

be determined because of the absence of cleavage or crystal faces.

The isotropic substance probably represents collophanite,

z(Ca3 (P04 ) 2 ) or z((CaF2 )Ca8PO4 ) 6 + yCaC03 + zH2O,

and the double-refracting substance is possibly quercyite. Quercyite 

comprises a variable mixture of the series of lime-phosphate minerals, 

including collophanite, described by Lacroix 2 from the French phosphorites.

The ovules include minute curly, hairlike, and branching plant 

fragments, whose appearance strongly suggests that they represent 

fungi.

» U. S. Geol. Survey Bull. 430, pp. 463-464,1910.

* Lacroix, A., Sur la constitution mine'ralogique des phosphorites frangais: Compt. Rend., vol. 150, p. 1213, 

1910; Min6ralogie de la France, vol. 4, pt. 2, p. 555,1910.
NATURE AND ORIGIN OF THE ROCK PHOSPHATE. 73

Chemical analyses of the rock phosphate of the western field are 

published in the report for 1909.1 No additional complete analyses 

have been made.

DETERMINATION OF PHOSPHORIC ACID.

The phosphoric acid determinations published in this report were 

made by John G. Fairchild in the chemical laboratory of the United 

States Geological Survey after improved methods which have been 

. developed by him.2

ENRICHMENT BY WEATHERING.

A tendency toward enrichment of the content of phosphoric acid is 

shown in the weathered outcrops of the rock-phosphate beds. As 

this would naturally be expected from the chemical and mineralogical 

composition of this material, no extensive examination has been 

undertaken to verify this conclusion. An average sample of the main 

bed, taken at the surface at Montpelier in 1909, ran 4 per cent higher 

in phosphoric acid than the average samples taken in the same year at 

the Waterloo mine, and J. J. Taylor, the superintendent of the property, reports that a still lower content was found in the bed as cut by 

a bore hole at comparatively shallow depth. This evidence is probably insufficient on which to base general conclusions, but the mining 

operations in other parts of the field seem to demonstrate that fresh 

clean rock from the thicker workable beds usually maintains an average content exceeding 32 per cent of phosphoric acid.

Positive information about the character of these deposits at greater 

depth is needed, as it must be admitted that all the data collected at 

present have come practically from the outcrop, and only theoretic 

foundation exists for statements concerning the character of the 

greater volume of the rock included in the tonnage estimates.

The importance of the phosphate deposits still in public ownership 

is greatly enhanced if only the outcrop of these deposits is of present 

commercial value, and it is therefore imperative that a study of the 

quality of these deposits under cover should be conducted by systematic drilling prior to their disposal and development.

IRON AND ALUMINA.

Iron and alumina in phosphate rock in excess of 3 to 4.5 per cent 

in the eastern fields are considered as placing the ore below foreign 

contract standards. These substances are supposed to produce in 

the present process of superphosphate manufacture deliquescent salts 

which render the drying and shipment of the product difficult. In

i U. S. Geol. Survey Bull. 430, p. 465,1910.

s Fairchild, J. G., The accurate volumetric determination of phosphoric acid in phosphate rock: Jour. 

Ind. and Eng. Chemistry, vol. 4, pp. 520-522,1912.
74 PHOSPHATE DEPOSITS NORTHEAST OF GEORGETOWN, IDAHO.

all samples from these fields that have been tested in the laboratory 

of the Geological Survey less than 1 per cent of either radicle computed in the oxide form was found. The manufacturers of superphosphate using the rock from the western field agree that the 

amounts of these substances present are too small to be considered 

objectionable.

SOURCE OF PHOSPHORIC ACID AND PROBLEM OF ITS 

ACCUMULATION.

An adequate explanation of the accumulation of the enormous 

amount of phosphoric acid locked up in the phosphate deposits of 

the western fields has not been given. The ultimate source of the 

phosphoric acid clearly must have been the phosphate-bearing minerals of the igneous rocks, of which apatite is the most abundant.

Whether or not the concentration of the acid and its combination 

into a lime phosphate has been accomplished largely through the 

action of life agencies rather than through purely chemical and 

physical means is a mooted question. Shells of Lingulidiscina, a 

phosphate-secreting brachiopod, are associated in great abundance 

with the phosphate in portions of the Wyoming field, but are generally absent from the greater portion of the phosphate areas studied, 

and the rocks contain no other fossils representing known phosphatesecreting forms. It seems scarcely probable that such fossils would 

have been completely destroyed in the processes of deposition. The 

absence of these fossils and the fact that the rocks immediately associated with the beds of rock phosphate are shales that represent conditions somewhat unfavorable to the abundant animal life tend to cast 

doubt on the theory that the phosphate was concentrated by means 

of living organisms.

It seems to the writers to be a suggestive coincidence that water 

charged with carbon dioxide is the best natural solvent of the mineral apatite, so far as known, and that according to a rather prevalent 

assumption the atmosphere of Pennsylvanian time was rich in that 

gas, though the recent decision that the phosphate deposits are of later 

age (probably Permian) appears to weaken the significance of such a 

coincidence. Possibly, however, though the solution and accumulation may have occurred while the atmosphere was rich in carbon 

dioxide, the concentration and deposition may have taken place 

largely during a subsequent period of decrease in the quantity of that 

gas in the atmosphere.

It is apparent, however, that too little is known at present concerning the land and marine conditions that prevailed during the 

process of formation of the phosphate deposits to permit the formulation of a satisfactory hypothesis. It is hoped that further light on 

this question will be obtained before the investigation of the western 

phosphate fields is completed.
INDEX:

A. Page. 

Access, means of .................*...... 7-8,14,49

Alluvium, occurrence and character of....... 34

Ankareh shale, distribution and character

of............................. 16,31,66

B.

Bannock overthrust, age of.................. 38

features of............................... 35-37

magnitude of......... '. ................... 37-38

section of................................ 36

stereogram showing............... 36 (PI. Ill)

Basins, distribution and character of......... 12-13

Beckwith formation, occurrence and character

of............................. 16,33,67

Blackwelder, Eliot, work of................ 9,20,21

Boutwell, J. M.,cited........................ 22

Breger, C. L., work of....................... 11

C.

Carboniferous system, fossils of.............. I7

occurrence and character of........ 16-29,42,46

Clays, occurrence and character of........... 33

Cretaceous system, occurrence and character

of................................ 16,33

D. 

Drainage, description of..................... 11-12

E.

Enrichment, processes of. 

Erosion, cycles of.........

F.

Fairchild, J. G., work of.....................

Fans, alluvial; distribution of...............

Ferrier, W. F., and Weeks, F. B., work of... 

Field work, extent of.........................

Finch, E.H., work of.......................

G.

Gale, H.S., work of................. 9Ct. 10-11,22

Geography, account of....................... 11-14

Geological Survey, U. S., investigation by... 8 

Georgetown Canyon, section in.............. 24-25

view of....:....................... 37 (PI. IV)

Girty, G. H., fossils determined by.......... 17-

18,20,21,23,24 

on age of rocks........................... 18,19

work of.................................. 9

I.

Igneous rocks, occurrence and character of... 34,43 

Industries, character of...................... 13-14

J. Page.

Jones, C. C., on phosphate discovery ........ 7

Jurassic system, occurrence and character of.. 16,

32-33 

M.

Madison limestone, distribution and character

of............................. 16,17,65

fossils of................................. 17

Mansfield, G. R., acknowledgments to....... 8

work of.................................. 9,11

Map of phosphate reserves................... 10

of townships.. ............................ IS

See also particular townships. 

Map, geologic, of townships.................. 15

Meade Peak, elevation of.................... 11

view of............................. 10 (PI. I)

Meade Peak district, phosphate rock of...... 55-56

Mendenhall, W. C., aid of.................... 9

Mineral laws, omission in.................... 8

Mississippian series, fossils from.............. 17-18

occurrence and character of.............. 16-18

N.

Nugget sandstone, distribution and character

of.......................... 16,32,66-67

0.

Overthrust. See Bannock overtbrust. 

P.

Panorama............................. 38 (PI. IV)

Peale, A. C., work of......................... 10

Pennsylvanian series, distribution and character of...................:. 16,18-21,65

fossils of.................................20,21

Permian series, fossils of..................... 23,24

occurrence and character of........... 16,22-29

Phosphate lands, acquisition of.............. 7-8

investigation of.......................... 8

map of................................... 10

withdrawals of.......................... 8,9

See also particular townships. 

Phosphate rock, alumina in.................. 73^-74

amounts available of..................... 70

character of.............................. 71

chemical composition of................. 72-73

1 enrichment of-.......................... 73

foldin........................... 45 (PI. VIII)

ironin................................... 73,74

mineral composition of.................. 72

occurrence of............................ 24-29

origin of................................. 71-72

specific gravity of........................ 72-

75
76 INDEX.

Phosphoria formation, correlation of......... 22-23

distribution and character of.... 16,22-29,41-42

fossils of................................. 23,24

phosphorus in........................... 24-29

sections of............................... 24-29

view of........................... 44 (PI. VII)

Phosphoric acid, source of................... . 74

Phosphorus, amounts available of........... 70

' occurrence of............................ 24-29

See also particular townships. 

Physiography, description of................ 11-13

Pidcock, R. A., discovery by................ 7

Pliocene series, occurrence and character of. 10,

33,42,67

Q.

Quaternary system, occurrence and character of......................... 16,33-34

R.

Ragar,E. C., work of........................ 9

Railroads, construction of................... 14

Rex chert member, distribution and character of....................... 16,22,23,66

fossils of................................. 23

section of................................ 23

view of........................... 44 (PI. VII)

Richards, R. W., acknowledgments to....... 8

work of.................................. 9,11

Richter, Albert, discovery by............... 7

Salt, occurrence and character of............. 34

Schultz,A. R., work of....................... 9

Section, general, in phosphate area........... 16

Slug Valley, description of................... 13

section in................................ 29

view in........................... 44 (PI. VII)

Snowdrift Mountain, elevation of............ 11

South Canyon, view of.................. 10 (PI. I)

South Canyon district, phosphate rock of.... 50-55

phosphate rock of, character of........... 51

sections of........................' 51,52,53

Specific gravity of phosphate rock............ 72

Spring deposits, occurrence and character of.. 34 

Stereogram, showing Bannock overthrust............................ 36 (PI. Ill)

Stratigraphy, details of...................... 17-34

outline of...........:.................... 14-16

Structure, description of..................... 34-38

topography adjusted to.................. 12

T.

Terraces, distribution of..................... 12

Tertiary system, occurrence and character

of.................:........... 16,33,46

Thaynes limestone, distribution and character of................... 30,31,42,46,66

fossils of................................. 30

T. 8S.,R.44 E., geology of.................. 39

map of............................. 40 (PI. V)

phosphate deposits of................. 39-40,70

sections in.......................... 40 (PI. V)

T. 8 S., R. 45 E., geology of................. 56^57

mapof............................ 56 (PI. XI)

phosphate deposits of................ 57-58,70

sections in......................... 56 (PI. XI)

survey of................................ 56

T. 9 S., R. 44 E., geology of.................. 41-42'

mapof...:........................ 42 (PI. VI)

phosphate deposits of................. 44-45,70

sections in......................... 42 (PI. VI)

T. 9S..R. 45 E., geology of.................. 5S-E9

mapof........................... 58 (PI. XII)

phosphate deposits of................. 59-60,70

sections in....................... 58 (PI.XII)

survey of................................ 58

T. 10 S., R. 44 E., geology of,................ 46

mapof....:....................... 46 (PI. IX)

phosphate deposits of................. 47-49,70

sections in......................... 46 (PI. IX)

survey of................................ 46

T. 10 S.,R. 45 E., geology of................. 61-62

mapof.......................... 62 (PI. XIII)

phosphate desposits of................ 62-64,70

salt deposits of.......................... 64

sections in........................ 62 (PI. XIII)

survey of................................ 61

T. 11S.,R. 44 E., geology of................. 49-50

map of.............................. 50 (PI. X)

phosphate deposits of................. 50-56,70

section of......................'..... 50 (PI. X)

survey of................................ 49

T. 11 S., R. 45 E., geology of................. 65-69

mapof........................... 68 (PI. XIV)

phosphate deposits of.................... 69-70

sections of....................... 68 (PI. XIV)

survey of...'............................. 65

Townships, detailed descriptions of.......... 38-70

geologic map of.......................... 15

See also particular townships.

Transportation, means of.................... 13

Travertine, occurrence and character of...... 34

Triassic system, fossils of.................... 30

occurrence and character of........... 16,29-32

Troxell, E. L., work of...................... 9

Twin Creek limestone, distribution and character of....................... 16,32-33

U.

Upper Mississippian limestone, distribution

and character of........... 16,17-18,65

fossils from.............................. 17-18

1 V. 

Valleys, description of....................... 12-13

Van Horn, F. B., work of................... 9

W.

Weeks, F. B., and Ferrier, W. F., work of... 10 

Wells Canyon, section'in..................... 19-20

Wells formation, fossils from................ 20,21

distribution and character of... '. 16,18-21,65-66 

section of................................ 19-20

views of............ 44 (PI. VII), 45 (PI. Virj)

Woodruff Creek, Utah, phosphate on........ 7

Woodside shale, distribution and character

of....................... 29-30,42,46,66

fossils of................................. 30

o