Description of Indicator 

Plants and Methods of 

Botanical Prospecting for 

Uranium Deposits on the 

Colorado Plateau

GEOLOGICAL SURVEY BULLETIN 1030-M

This report concerns work done on behalf 

of the U. S. Atomic Energy Commission 

and is published with the permission of 

the Commission

Description of Indicator 

Plants and Methods of 

Botanical Prospecting for 

Uranium Deposits on the 

Colorado Plateau

By HELEN L. CANNON

A CONTRIBUTION TO THE GEOLOGY OF URANIUM

GEOLOGICAL SURVEY BULLETIN 1 03 0 - M

This report concerns work done on behalf 

of the U. S. Atomic Energy Commission 

and is published with the permission of 

the Commission

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1957
UNITED STATES DEPARTMENT OF THE INTERIOR 

FRED A. SEATON, Secretary

GEOLOGICAL SURVEY 

Thomas B. Nolan, Director

For sale by the Superintendent of Documents, U. S. Government Printing Office 

Washington 25, D. C. - Price 50 cents (paper cover)
CONTENTS

	Page 

Abstract________________________________________________________ 399

Introduction._____________________________________________________ 399

Colorado Plateau soils and ground-water conditions-___________________ 400

Plants in relation to ground water.__________________________________ 401

Plant associations and indicator plants on the Colorado Plateau.________ 402

How to prospect by plant analysis.__________________________________ 405

How to use indicator plants in prospecting.___________________________ 407

Selected bibliography. _____________________________________________ 411

Illustrations and descriptions of indicator plants.______________________ 413

Glossary__ _ _____________________________________________________ 514

Plant index_______________________________________________________ 515

ILLUSTKATIONS

Page 

FIGUKE 74. Dead plants of Astragalus paltersoni useful in fall and

winter in deciding where to drill._________________ 409

75. Index map of part of the Colorado Plateau showing

location of mining districts._____________________ 410

76. 77. Astragalus pattersoni A. Gray, or Patterson poisonvetch___________ _ ________________ 414, 415 

78, 79. Astragalus preussi A. Gray, or Preuss poisonvetch__ 416, 417 

80, 81. Astragalus thompsonae S. Wats., or Thompson loco 418, 419 

82, 83. Astragalus confertiflorus A. Gray, or blue poison vetch. 420, 42] 

84, 85. Astragalus bisulcatus (Hook.) A. Gray, or two-grooved

poisonvetch______________________ 422, 423

86, 87. Astragalus missouriensis Nutt., or Missouri milkvetch. 424, 425 

88, 89. Astragalus lonchocarpus Torr., or long-seeded milkvetch-_-._________________._________________ 426, 427

90, 91. Astragalus dodgianus Jones, or Dodge milkvetch_ __ 428, 429 

92, 93. Astragalus tenellus Pursh, or looseflower milkvetch. 430, 431 

94, 95. Astragalus aculeatus A. Nels., or spiny milkvetch__ 432, 433 

96, 97. Allium acuminatum Hook., or tapertip onion, and related species_________________________________ 434, 435

98, 99. Calochortus nuttalli Torr. & Gr., or Sego lily, mariposa______________________________ 436,437

100, 101. Zigadenus gramineus Rydb., or grassy deathcamas.. 438, 439 

102, 103. Stanleya pinnata (Pursh) Britt., or desert princesplume. 440,

441

104, 105. Lepidium montanum Nutt., or mountain pepperweed._ 442,

443

106,107. Lepidium lasiocarpum Nutt., or hairy-pod pepperweed_ 444,

445

108, 109. Sisymbrium altissimum (L.) Britt., or tumblemustard. 446,

447

ill
IV CONTENTS

Page 

FIGUBE 110, 111. Cryptantha fiava A. Nels., or cryptanth, and related

species._____________________________________ 448, 449

112,113. Oenothera caespitosa Nutt., or tufted evening-primrose. 450,

451

114, 115. Oenothera albicaulis Pursh, or whitestemmed eveningprimrose. ____________________________________ 452, 453

116,117. Eriogonuminflatum Torr.,or deserttrumpet eriogonum- 454,

455 

118, 119. Eriogonum fusiforme Small, or deserttrumpet______ 456, 457

120, 121. Eriogonum ovalifolium Nutt., or silver plant or cushion

eriogonum______________-----_------------__- 458, 459

122, 123. Eriogonum unibellatum Torr., or sulfur eriogonum__ 460,461 

124, 125. Eiymus salina Jones, or salina wildrye_____________ 462, 463

126, 127. Stipa comata Trin. & Rupr., or needleandthread_____ 464, 465

128, 129. Oryzopsis hymenoides (Roem. & Schult.) Ricker, or

Indian ricegrass_______________ _______________ 466, 467

130, 131. Aster venustus Jones, or woody aster_______________ 468,469

132, 133. Townsendia incana Nutt., or hoary townsendia______ 470,471

134,135. Aplopappus armeriodes A. Gray, or goldenweed_ _ _ _ _ 472,473

136, 137. Grindelia sguarrosa (Pursh) Dunal, or curlycup gumweed______________________________________ 474, 475

138, 139. Senecio longilobus Benth., or threadleaf groundsel____ 476,477

140, 141. Euphorbia fendleri Torr. & Gr., or sandmat or fendler

euphorbia and related prostrate species __________ 478, 479

142, 143. Mentzelia multiflora (Nutt.) A. Gray, or desert blazingstar____________________-_______----___-__ 480, 481

144, 145. Solidago petradoria Blake, or rock goldenrod________ 482, 483

146, 147. Tetradymia spinosa Hook. & Arn., or cottonthorn

horsebrush__________________________________ 484, 455

148, 149. Cowania stansburiana Torr., or Stansbury cliflfrose.__ 486, 487 

150, 151. Purshia tridentata (Pursh) DC., or antelope bitterbrush...____________________________________ 488, 489

152, 153. Hedysarum boreale Nutt., or northern sweetvetch_ _ 490, 491 

154, 155. Castilleja integra Gray, or Indian paintbrush or paintedcup____________-____-_----__---------_---_ 492, 493

156,157. Plantago purshi Roem. & Schult., or woolly indianwheat. 494,495 

158, 159. Atriplex confertifolia (Torr.) S. Wats., or shadscale

saltbush__________.__________________________ 496, 497

160, 161. Atriplexcanescens (Pursh) Nutt., or fourwing saltbush__ 498,499 

162, 163. Sarcobatus vermiculatus (Hook.) Torr., or black greasewood.___________________________________ 500, 501

164, 165. Ephedra sp., or jointfir or mormon tea____________ 502, 503

166, 167. Opuntia engelmanni Salm-Dyck, or Engelmann pricklypear, and other species_______________________ 504, 505

168, 169. Mirabilis multiflora A. Gray, or Colorado four-o'clock. 506,507 

170, 171. Fraxinus anomala Torr., or singleleaf ash___________ 508,509

172, 173. Hymenopappus filifolius Hook., or fineleaf hymenopappus____-_________._____ __ 510,511

174, 175. Actinea acaulis (Pursh) Spreng., or stemless actinea__ 512, 513
DESCRIPTION OF INDICATOR PLANTS AND METHODS

OF BOTANICAL PROSPECTING FOR URANIUM DEPOSITS

ON THE COLORADO PLATEAU

By HELEN L.

ABSTRACT

Two methods of botanical prospecting for uraniferous deposits on the Colorado Plateau are useful in semiarid country in prospecting for ore-bearing beds 

at depths as much as 70 feet. By one method, tips of tree branches are sampled 

and analyzed for uranium content. Generally more than 1 part per million of 

uranium in the ash indicates favorable ground for further geologic exploration. 

The second method, that of mapping indicator plants, is used in semiarid parts 

of the Plateau at low altitude. The distribution of indicator plants is controlled by the availability of chemical constituents of the ore, such as selenium, 

sulfur, and calcium. Plants of the genus Astragalus are most useful in prospecting for uranium deposits of high selenium content; plants of the genera Allium 

and Eriogonum are most useful as indicators of deposits with a high sulfur 

content. Fifty indicator plants commonly associated with carnotite deposits 

and plants tolerant of mineralized ground are described and illustrated.

INTRODUCTION

Two methods of botanical prospecting for uranium deposits have 

been applied on the Colorado Plateau. One method is based on a 

chemical analysis for the uranium content of deep-rooted plants that 

absorb uranium from the ore bodies; the other is based on distribution 

studies of indicator plants that are commonly associated with uranium 

deposits. A third method, that of determining morphological or 

physiological changes in plants growing in ore deposits, has been discarded in this area. The general principles on which methods of prospecting were developed are described in earlier reports (Cannon, 1952; 

1953).

The first method makes it possible to detect uranium-bearing material through a maximum of 70 feet of barren rock by means of tree 

root-systems, which act as conduits for the upward migration of 

soluble salts to the ground surface. The method is applicable where 

the mineralized bed crops out in a broad, flat bench so that plant 

samples can be collected on a grid pattern to outline mineralized zones 

at depth; and also where the mineralized bed crops out in a sharp cliff 

that is commonly obscured by talus or slump. Here a line traverse

399
400 CONTRIBUTIONS TO THE GEOLOGY OF URANIUM

parallel to the cliff may be desirable. The samples are either analyzed 

in the field by a quick test for uranium or are sent to a chemical laboratory for quantitative assay.

Prospecting by indicator plants is the less expensive of the two 

methods and consists of mapping the areal distribution of key indicator plant species. Indicator plants and also plants tolerant of 

mineralized ground, and therefore common in uranium districts, are 

described, illustrated, and evaluated in this report. The information 

has been compiled not as a key for species identification but as a sorting 

device that will enable geologists and prospectors to identify, in a preliminary way, the plants that may be useful in prospecting an area. 

The information was gathered while botanical prospecting studies 

were being made on the Colorado Plateau by the U. S. Geological 

Survey on behalf of the Division of Eaw Materials of the U. S. 

Atomic Energy Commission.

A part of the section on the use of absorber plants was taken from 

unpublished reports by Albert J. Froelich of the Geological Survey. 

The plants collected during the study were identified by T. H. Kearney, 

formerly of the U. S. Department of Agriculture; A. H. Holmgren, 

Utah State Agricultural College; R. J. Da vis, University of Idaho; 

and E. F. Castetter, University of New Mexico. The line drawings 

were made from pressed plant specimens by Maxine Heyl, Ann Pettigrew, and Catherine B. Hayes. The plants were photographed in the 

field by the writer, with the part-time assistance of Edward Clebsch.

COLORADO PLATEAU SOILS AND GROUND-WATER

CONDITIONS

Plant associations on the Colorado Plateau depend on soil and 

ground-water conditions. Because the climate of the Plateau is semiarid, little residual soil forms except in the mountains and on the 

higher mesas. The sandy and clayey soils are commonly closely related to the alternating beds of sandstone and shale from which they 

are derived (Shreve, 1951, p. 16). The texture and salinity of the 

soil associated with the various stratigraphic Units at lower altitudes 

largely determine the plants that grow in them. The most common 

soluble salts in a desert soil are carbonates, chlorides, and sulfates of 

calcium, magnesium, and sodium (Shreve, 1951, p. 16). Many desert 

plants tolerate large amounts of these compounds.

In the semiarid Colorado Plateau the dependence of plants either 

directly or indirectly on ground water requires a study of the ground 

water in areas where plants are studied. Water beneath the ground 

surface occurs in the zone of saturation and the zone of aeration 

(Meinzer, 1923, p. 29-95). The upper surface of the ground water 

occurring in the zone of saturation is called the water table. Owing 

to capillarity, however, the earth is moist for a distance of several
INDICATOR PLANTS AND METHODS OF BOTANICAL PROSPECTING 401

feet above the water table. The thickness of this capillary fringe 

may range from 8 or 10 feet in fine silt or sand to 3 or 4 feet in coarse 

clean sand. Koots of most phreatophytes terminate in the capillary 

fringe (White, 1932, p. 34). The zone of aeration extends from the 

water table to the surface. Other zones of saturation may occur above 

the main water table where lenses or layers of impermeable material 

prevent movement of water down to the main water table. Such 

zones are termed "perched water tables" and may be temporary or 

permanent.

Perched water tables are common on the Colorado Plateau where 

the ore-bearing sandstone beds are underlain by impervious clay (D. A. 

Phoenix, written communication, 1952). Locally, clay seams may 

prevent the downward movement of ground water and thus prevent 

the oxidation of primary ores even at relatively shallow depths.

PLANTS IN RELATION TO GROUND WATER

Perennial plants that obtain water from the water table, especially 

in arid regions, in contrast to plants that utilize soil moisture above 

the water table are called phreatophytes (Meinzer, 1923, p. 95; 1927, 

p. 1; Robinson, in preparation). Plants that utilize soil moisture 

where it is available in the zone of aeration but can withstand long 

periods of drought are called xerophytes. Many, like the cactus, have 

short roots and thickened stems or leaves that are well protected from 

evaporation and designed for water storage. A third group, called 

ephemeral, endures adverse periods as bulbs or as seeds beneath the 

soil, bursts into bloom suddenly after a period of heavy rainfall, sets 

fruit, and disappears. All three groups grow in uranium districts of 

the Colorado Plateau and are described in this report.

Such phreatophytes as Salix (willow), Tamariw (tamarisk), Gowania (cliffrose), /Shepherdia (buffaloberry), Sarcobatus (greasewood), Clirysothamnus (rabbitbrush), and Hedysarum (sweetvetch) 

are typical indicators of ground water. Normally, on the Colorado 

Plateau juniper and piny on are also phreatophytes and, in areas 

where the ore-bearing bed contains water, are useful for uranium 

analysis.

Generally xerophytes are tolerant of soils that have a high salt 

content, and these are therefore tolerant of and in some cases indicative 

of shallow uranium deposits. Where the water table is below the ore 

zone, Atriplex confertifolia (shadscale), a xerophyte, may be used as 

the sampling medium.

In areas where the capilliary fringe extends nearly to the surface 

and soluble salts from sulfide ore bodies have migrated in large quantities to surface soils, ephemeral indicator plants may flourish and 

become useful in prospecting. For example, wild onions, which are
402 CONTRIBUTIONS TO THE GEOLOGY OF URANIUM

sulfur indicators, have indicated uranium at depths of 20 to 30 feet 

beneath the surface.

PLANT ASSOCIATIONS AND INDICATOR PLANTS ON 

THE COLORADO PLATEAU

The distribution of major plant associations on the Colorado Plateau 

is controlled by many factors including slope, altitude, ground-water 

conditions, and texture and salinity of the soil. Few uranium deposits occur at altitudes of more than 9,000 feet in the spruce-fir and 

alpine life zones. At altitudes of 7,400 to 9,500 feet ponderosa pine 

and Douglas-fir forests predominate. These include the following 

shrubs and trees:

Pinus ponderosa, ponderosa pine 

Abies concolor, white fir 

Pseudotsitffa taxifolia, Douglas fir 

Juniperus scopulonnn, Rocky Mountain juniper 

Popiilns tremuloides, quaking aspen 

Quercus gamtelli, Gambel's oak 

Arctostaphylos pungens, manzanita 

Ceanothus fendleri, buckbrush 

AmelancMer alnifolia, shadbush 

Symphoricarpos oreophilus, snowberry

Lack of sunlight causes a poor distribution of herbaceous plants and 

consequently of indicator plants in this association. Here tree sampling has been used successfully as a method of prospecting.

From 5,000 to 7,400 feet pinyon and juniper forests predominate on 

foothill pediments and on mesas capped with sandstone that contains 

sufficient water. The shrubs that occur in or near the fringes of these 

forests prefer a light sandy soil and water of low salt content. They 

include:

Cowania stansimriana, cliffrose 

Cercocarpus montanus, mountain mahogany 

Epliedra viridis, Mormon tea 

Malionia fremontii, hollygrape 

Rhus trilobata, skunkbush

They also include low growth of Gambel's oak. The herbs in this 

altitude range include many of the plants described in this report. 

Pinyon and juniper have been used commonly in plant analysis 

prospecting.

From altitudes of 3,500 to 5,000 feet the plants are characteristic of 

the northern desert flora and are divided into two major groups; 

namely, those that are tolerant of alkali soils and those that are not. 

In loose soils of low-salt content, sagebrush predominates. Sagebrush is frequently associated with or replaced in drier areas by:
INDICATOR PLANTS AND METHODS OF BOTANICAL PROSPECTING 403

Atriplex canescens, saltbush 

Grayia spinosa, hopsage , 

Coleogyne ramosissima, blackbrush 

Chrysothamnus puberulus, little rabbitbrush

The sagebrush association is common on pediments and alluvial fans 

at the base of mountains and is the characteristic flora in areas underlain by the Dakota sandstone.

In low areas of drier soils and of higher salt content within this 

altitude range, the shadscale association is dominant. Atriplex confertifolia, or shadscale, is shallow rooted and depends upon moisture 

in the surface soils for its water supply. Woody plants belonging to 

the association include:

Tetradymia spinosa, horsebrush 

Artemisia spinescens, budsage 

Gutierresia sarothrae, snakeweed 

Eurotia lanata, winterfat.

The shadscale association is characteristic of sandstone exposures of 

the Summerville, Chinle, and Mancos formation at lower altitudes. 

In heavy saline soils of high moisture content, an association of Sarcobatus vermiculatus, or greasewood, prevails. The association is 

generally restricted to low, poorly drained salt flats, and the presence 

of greasewood indicates saline ground water at depths of not much 

more than 15 feet. In areas where the water table is at or near the 

surface, seepweed or pickleweed may be the only plants able to grow 

in tl|e highly alkaline environment.

The importance of these associations in prospecting lies not in 

their normal association with a given geologic formation of the Colorado Plateau but in their abnormal occurrences as island communities 

indicative of greater or less soil salt or moisture content than the 

endemic association. On the higher benches where ground water of 

low alkali content is available in the sandstone, little change in the 

general appearance of the juniper-pinyon flora can be seen around 

carnotite deposits. In drier areas at lower altitude, however, the 

general appearance of the flora in the carnotite districts is commonly 

similar to the flora of a salt flat. Instead of an association in which 

sagebrush (Artemisia tridentata}, hop sage (Grayia spinosa}, or 

saltbush (Atriplex canescens} is dominant, it is largely a shadscale 

(Atriplex con ferti folia} association capable of growing in soils of 

high salt content.

Patches of indicator plants, controlled in distribution by the availability of specific chemical elements, are commonly found within 

areas of shadescale and snakeweed. These plants that indicate mineralized ground are not all controlled by the same chemical element
404 CONTRIBUTIONS TO THE GEOLOGY OF URANIUM

and are usually common weeds rather than unusual plants. The 

control of the species may be pH variations; a change in the availability of phosphorus, calcium, or other major constituent necessary 

for plant growth; or a true dependence on a minor element, such as 

selenium or sulfur.

Selenium-indicator plants are the only group definitely known to be 

completely dependent on the presence or absence of a single element. 

The selenium indicators described by Trelease and Beath (1949) include a tribe of Astragalus species, Stanleya, Aster venustus, Oryzopsisj and several other plants. These indicators absorb large amounts 

of selenium, sufficient to poison sheep and cattle. Because selenium 

is present in many uranium ores, these plants are in some places useful 

guides to the location of uranium deposits.

The distribution of many sulfur and calcium-absorbing plants reflect the presence of gypsum in the soil. Plants that require large 

amounts of these elements for their growth include the lily and mustard families, at least a part of the buckwheat family, and various 

isolated genera. Because uranium ores commonly contain sulfides 

from which gypsum may be produced in the surface soils, gypsumindicators may also be found in the vicinity of uranium deposits.

Both selenium and sulfur occur in all sedimentary rocks, but the 

concentration varies greatly between different stratigraphic units and 

in different regions. For instance, the selenium content of western 

shales of Cretaceous age is high and remains relatively constant in 

particular beds or strata for several hundred miles. Both elements 

may also be concentrated in tuff, coal, or sulfide ore deposits. The occurrence of selenium and sulfur, on the other hand, in amounts less 

than 10 ppm in barren sandstones of Triassic and Jurassic age contrasts sharply with concentrations of 100 to 1,000 ppm in ore deposits 

in the same formations, For this reason, the distribution of indicator 

plants along the outcrops of these sandstones forms conspicuous 

patterns.

Besides an increase in total selenium in carnotite ore, experimentalplot studies indicate that the proportion of water-soluble selenium 

is increased in the presence of carnotite. This results in a marked 

tendency for the Astragalus group to grow in the vicinity of ore 

deposits where it is possible for them to absorb selenium in concentrations of several hundreds or perhaps thousands of parts per million 

from ground containing only 2 ppm total selenium. Stanleya, however, appears to substitute selenium for sulfur in the plant metabolism 

and is capable of extracting and concentrating large quantities of 

selenium from gypsum containing only small amounts, but it is not
INDICATOR PLANTS AND METHODS OF BOTANICAL PROSPECTING 405

capable of extracting large amounts of selenium from a carnotite ore. 

For this reason Stanley a is not a primary indicator of seleniferous 

uranium, ore but may be used in some areas as a secondary indicator of 

mineralized ground water.

Many of the other plants found near uranium deposits probably 

reflect changes in acidity and in the availability of major plant nutrients. Experimental studies show that larger amounts of calcium and 

phosphorus are available to plants in the vicinity of carnotite deposits 

than in barren ground. This favors an increase in the number of the 

calcium absorbers, Mentzelia, Cryptantlia, and Oenothera, around ore 

deposits. The phosphorus absorbers, Eriogonum, AUium, Oalochortus, and mustards, are encouraged by the increase in available phosphorus and sulfur as indicators of uranium ore.

In addition to those plants that act as indicators of mineralized 

ground or can be used in alluvial prospecting, many plants are tolerant 

of mineralized ground. Sixteen of these plants are described in this 

report. In general, the plants best adapted to soils of high mineral 

content are those having an acid cell sap that enables the plant to 

absorb and neutralize alkali elements. For example, shadscale absorbs large quantities of salts without harm to the plant growth. 

Plants of the goosefoot, rose, and cactus families are also tolerant of 

highly mineralized ground on the Colorado Plateau.

HOW TO PROSPECT BY PLANT ANALYSIS

Trees or shrubs of extensive root habit may be analyzed for uranium 

content to denote areas of mineralized ground. Basic information 

on the rate of absorption of uranium by plants must be gathered for 

control in the area to be prospected. Commonly a collection of 

samples from a variety of species in close proximity is made in an area 

that is known to be mineralized from drill-hole data or surface outcrop 

but is uncontaminated by surface workings. This collection is compared with similar collections in an area known by past exploration 

to be unmineralized.

In general, uranium is best absorbed by plants with a fairly acid 

cell sap and high cation exchange capacity in the root. Experimental 

work shows that plants belonging to this category absorb large 

amounts of calcium, selenium, and (or) sulfur along with uranium, but 

very little potassium. Conversely, potassium absorbers absorb only 

small amounts of uranium. Plants that have been used in sampling 

programs belong largely to the rose and pine families.
406 CONTRIBUTIONS TO THE GEOLOGY OF URANIUM

The trees and shrubs commonly sampled on the Colorado Plateau 

are as follows:

Altitude

(feet) 

Pinus ponderosa Dougl. (ponderosa pine)______________

Pseudotsuffa taxifolia Britt. (Douglas fir)___________ 7Ann_onnn 

Abies concolor Lindl. (white fir)_______________ 7,000-9,000 

Shepherdia rotundifolia Parry (buffaloherry)___________

Pinus edulis Englm. (pinyon) .

T * ,-r. ,,,-,... s f OjUUU i,UUU Jumperus scopulorum Sarg. (Rocky Mountain juniper)___]

utahensis Sarg. (Utah juniper)_____________

monosperma Engelm. (oneseed juniper)____________

Coivania stansTyiiriana Torr. (cliffrose)__________ 

Atriplex confertifolia (T. & F.) S. Wats (shadscale)- 

4,000-6,000

The sampling medium and sampling interval are determined after 

a study is made of the extent of mineralized outcrop, size, and habits 

of the known ore bodies, and the relation of the ore-bearing bed to 

the water table and to plant roots. A plant species that has an extensive root system which penetrates to the ore horizon is chosen as the 

sampling medium. If information concerning the absorption of 

uranium by that species is not available, preliminary samples are collected to determine the lowest value indicative of mineralized ground. 

Several trees are also selected for periodic sampling to test the consistency of laboratory results and seasonal variation. Branches on a 

given side of the tree are connected directly with roots on that side of 

the tree; thus the uranium content may vary greatly from one side of 

the tree to the other. To obtain the most representative sample, 

therefore, it is recommended that branch tips be collected from all 

sides of the tree. The method is applicable where the uranium-bearing bed is not more than 70 feet beneath the surface.

The sampling interval depends in part upon the objective of the 

project. On a broad flat bench a grid-pattern spacing adequate to 

detect either ore bodies or mineralized halos is desirable. The resulting values may be contoured to show areas favorable for geologic 

exploration. An initial sampling program on a 200- to 250-foot spacing is usually adequate. Later fill-in samples on a 50-foot spacing 

may be collected in anomalous areas. A short interval of 15 to 30 

feet is recommended for sampling across talus-covered outcrop.

In the fluorimetric laboratory procedure, pint samples (about 75 

grams) of material are required for an analysis. Samples are shipped 

to a well-equipped, uncontaminated laboratory for analysis. Two 

fluorimetric methods of analysis for small amounts of uranium in 

plant ash have been developed by the Geological Survey laboratories 

(Grimaldi and others, 1952 and 1954). By the direct fluorimetric 

method the plant ash is mixed with a fluoride-carbonate flux and the
INDICATOR PLANTS AND METHODS OF BOTANICAL PROSPECTING 407

amount of fluorescence of the bead or button is measured photoelectrically by a transmission fluorimeter. This method is satisfactory 

for samples that contain little or no manganese or other elements that 

may act as a quencher and reduce the amount of fluorescence of the 

uranium bead. When quenching elements are present in quantity, 

the extraction-fluorimetric method is employed. By this method the 

uranium is separated chemically from interfering elements before the 

button is made. The procedure is considerably longer and more expensive than the direct fluorimetric method. Analytical results are 

stated in terms of parts per million of uranium in the plant ash. The 

precision to be expected from the laboratory for values from 0.3 to 

5.0 ppm of uranium is a standard deviation of 0.5 ppm. A chromatographic field test by which many more analyses may be made in a 

day has also been developed in the Survey laboratory.

The detection of radioactivity in plant ash by alpha count has been 

used by Anderson and Kurtz (1955) in prospecting for pitchblende 

vein deposits. It is possible by this method to detect variations in 

uranium content above 10 ppm. Interferences from natural radioactivity due to other elements in the plant ash apparently mask radioactivity due to uranium below this amount. Therefore, the method 

is probably not applicable to prospecting for carnotite-type deposits.

Although the average amount of uranium absorbed by plants rooted 

in ore varies slightly, depending on the type of ore and degree of oxidation and also on the species collected, an average figure of 1 ppm 

in the ash has been used in many areas sampled as an arbitrary cutoff. 

Contents of uranium above this amount are considered anomalous 

and indicate favorable and possibly mineralized ground.

In places where grid sampling is used, isograms of the assay data can 

be drawn on base maps. Where rim-sampling is employed, areas of 

favorable rim can be indicated for back-from-rim drilling. The 

anomalies, however, delimit only areas of unusual uranium content in 

the vegetation cover. They do not show a positive correlation between 

the amount absorbed by the plants and the grade of the ore or the depth 

to ore. The interpretation of the data depends on the validity of the 

laboratory analysis, the size of sample interval, and the studies that 

are made of geologic and topographic field relations. Much depends 

on the comprehension by the prospector of the geologic environment. 

Plant analysis is an additional prospecting tool to be used with geologic interpretation in the search for ore.

HOW TO USE INDICATOR PLANTS IN PROSPECTING

The use of a plant as an indicator in prospecting for uranium is 

based on the assumption that its distribution is affected by the avail-
408 CONTRIBUTIONS TO THE GEOLOGY OF URANIUM

ability of the chemical constituents of the ore. The first step, then, 

in a new area is to study the plants growing in ground known to be 

mineralized. The information on indicator plants included in this 

report was established by marking off 10- by 5-foot areas over known 

ore bodies in a number of districts, and similar areas over unmineralized parts of the same bed with similar exposure and slope. Complete 

lists of plants in each plot were made, and final lists of indicator and 

tolerant plants were derived from them. When any of the plants 

illustrated in this report are observed in a new area, a careful study 

of their distribution should be made to determine whether and how 

they can be used in prospecting.

After such studies have been made, similar plant associations may 

be sought along the outcrop of an ore-bearing bed through reconnaissance prospecting. Caution must be exercised because the plants 

tare, of course, all common weeds and may be found in places where 

no uranium occurs. Selenium plants, for example, grow wherever 

there is a small amount of selenium in the soil. Sulfur plants may 

grow wherever gypsum is present. The plant species described in 

this report, nevertheless, have been noted repeatedly in close association with uranium ore deposits on the Colorado Plateau and have been 

used successfully in uranium prospecting.

Indicator plants are best studied and mapped when in bloom. For 

this reason, the approximate blooming date has been given for plants 

growing at an altitude of 4,500 feet and near the 39th parallel. The 

blooming time for a given plant would be somewhat earlier farther 

south or at lower altitudes, and later farther north or at higher altitudes. In general, ephemeral plants such as the lily family are available for study only in the spring or early summer. Although many 

of the Astragalus species bloom in April, they can be recognized from 

the dead seed pods and stalks and can be used in prospecting throughout most of the year (fig. 74). Stanley a and other mustards bloom 

throughout most of the summer. Many Composites, Plantago, and 

Mentzelia bloom in the late summer and fall.

The plants shown in this report (figs. 76-175) are given in order of 

their importance in prospecting. Those that have aided directly in 

the location of uranium ore have been marked primary indicators; 

those that occur in plant associations known to indicate favorable 

ground are listed as secondary indicators; and common plants known 

to be very tolera/it of mineralized ground are included last. It is not 

necessary to identify species of many genera because all species may 

act as indicator plants. Species identification of these genera has not 

been given. Common and scientific names of most species are spelled 

in accordance with Kelsey and Dayton (1942). Descriptions have
INDICATOR PLANTS AND METHODS OF BOTANICAL PROSPECTING 409

FIGURE 74. Dead plants of Astragalus pattersoni useful in fall and winter in deciding

where to drill.

been written as simply as possible; the technical terms are listed in a 

glossary. All information of interest in the use of these plants has 

been compiled from the references listed. Mining districts (fig. 75) 

in which these plants have been observed are given as a general guide 

to their areal distribution.
410 CONTRIBUTIONS TO THE GEOLOGY OF URANIUM

MINING DISTRICTS

1 Poison Basin

2 Uinta Basin

3 Meeker

4 Rifle

5 San Rafael

6 Green River

7 Thompson

8 Moab 

	Gateway

10 Paradox

11 Uravan

12 Bull Canyon

13 Gypsum Valley

14 Placerville

15 Rico

16 La Plata

17 Cortez

18 Slick Rock

19 Monticello

20 White Canyon

21 Circle Cliffs

22 Henry Mountains

23 Kaiparowits

24 Monument Valley

25 Ship Rock

26 Chilchinbito

27 Chuska

28 Defiance

29 Little Colorado

30 Grants

31 La Ventana

FIGURE 75. Index map of part of the Colorado Plateau showing location of mining districts.
INDICATOR PLANTS AND METHODS OF BOTANICAL PROSPECTING 411

SELECTED BIBLIOGRAPHY

Abrams, Le Roy, 1940, Illustrated flora of the Pacific States: 4 v., Stanford Univ.

Press. 

Anderson, R. Y., and Kurtz, E. B., Jr., 1955, Biogeochemical reconnaissance of

the Annie Laurie uranium prospect, Santa Cruz County, Ariz.: Econ. Geology,

v. 50, p. 227-232. 

Benson, L., and Darrow, R. A., 1944, A manual of southwestern desert trees and

shrubs: Ariz. Univ. Bull., v. 15, no. 2, 411 p. 

Cannon, H. L., 1952, The effect of uranium-vanadium deposits on the vegetation

of the Colorado Plateau : Am. Jour. Sci., v. 250, p. 735-770.

 1953, Geobotanical reconnaissance near Grants, N. Mex.: U. S. Geol.

Survey Circ. 264, 8 p. 

Cannon, W. A., 1911, Root habits of desert plants: Carnegie Inst. Washington

Pub. 131, 96 p. 

Dayton, W. A., 1937, Range plant handbook: U. S. Forest Service, U. S. Dept.

Agriculture. 

Grimaldi, F. S., May, Irving, and Fletcher, M. H., 1952, U. S'. Geological Survey

fiuorimetric methods of uranium analysis: U. S. Geol. Survey Circ. 199, 20 p. 

Grimaldi, F. S., May, Irving, Fletcher, M. H., and Titcomb, Jane, 1954, Collected

papers on methods of analysis for uranium and thorium: U. S. Geol. Survey

Bull. 1006, 184 p. 

Harrington, H. D., 1954, Manual of the plants of Colorado: Denver, Colo.,

Sage Books. 

Kearney, T. H., and Peebles, R. H., 1951, Arizona flora: Calif. Univ. Press,

1069 p. 

Kelsey, H. P., and Dayton, W. A., 1942, Standardized plant names: Compiled

for American Joint Committee on Horticultural Nomenclature, McFarland

Co., Harrisburg, Pa., 673 p. 

Meinzer, O. E., 1923, Occurrence of ground water in the United States: U. S.

Geol. Survey Water-Supply Paper 489, 320 p.

 1927, Plants as indicators of ground water: U. S. Geol. Survey WaterSupply Paper 577, 95 p.

Muenscher, W. C., 1951, Poisonous plants in the United States: 277 p. New 

York, The Macmillan Co.

Patraw, Pauline M., 1951, Flowers of the Southwest mesas: SW Monuments 

Assoc. Popular Ser. no. 5, U. S. Natl. Park Service, 112 p.

Robinson, T. W., 1957, Phreatophytes: U. S. Geol. Survey Water-Supply Paper 

1423. In press.

Rydberg, P. A., 1917, Flora of the Rocky Mountains and adjacent plains: Published by author, New York, 1110 p.

Shreve, Forrest, 1951, Vegetation of the Sonoran Desert: Carnegie Inst. Washington Pub. 591, v. 1, 192 p.

Trelease, S. F., and Beath, O. A., 1949, Selenium; its geological occurrence and 

its biological effects in relation to botany, chemistry, agriculture, nutrition, 

and medicine. Published by the authors, Box 42, Schermerhorn Hall, 

Columbia Univ., New York.

White, W. N., 1932, A method of estimating ground-water supplies based on 

discharge by plants and evaporation from soil: U. S. Geol. Survey WaterSupply Paper 659-A, p. 1-107.

Wooton, E. O., and Stanley, P. C., 1915, Flora of New Mexico: U. S. Natl. Herbarium Contrib., v. 19, 800 p.

421588 57 2

ILLUSTRATIONS AND DESCRIPTIONS 

OF INDICATOR PLANTS

The plants shown on the facing pages that follow are the same 

species, the scientific name being given on the left-hand page 

and the common name on the right-hand page.
414 CONTRIBUTIONS TO THE GEOLOGY OF URANIUM

INCHES 

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FIGUKE 76. Astragalus pattersoni A. Gray.

Family: Pea, Leguniinosae.

Subgenus: Jonesiella.

Flowers: Cream-colored irregular flowers with purple dot on keel, growing in

tall clusters which extend beyond the foliage. Blooms in April

and May.

Leaves : Pinnate with numerous oval leaflets. 

Fruit: Fat pods mounted on short stem. Seeds rattle in pod when dry (then

called rattleweed).

Root: Very long taproot, commonly 30 feet or more in length. 

Plant: Perennial, 1-4 feet high. Garliclike odor common to foliage owing

to presence of selenium.
INDICATOR PLANTS AND METHODS OF BOTANICAL PROSPECTING 415 

Primary indicator Control: selenium

FIGURE 77. Patterson poisonvetch.

Altitude: 4,500-7,500 feet.

Occurrence: Best selenium-indicator plant in uranium districts of the Colorado Plateau because requirements and absorption of selenium 

are very high. Commonly absorbs several thousand parts per 

million of selenium and several hundred parts per million of 

molybdenum from ore bodies. Plot experiments suggest 

growth stimulated in vicinity of carnotite deposits by increased solubility of selenium and molybdenum but inhibited 

by excesses of calcium sulf ate.

Districts noted: San Raf ael, Thompson, Green River, Monticello and Circle Cliffs, 

Utah; Ship Rock, in Arizona; Slick Rock and Gypsum Valley, 

Colo.; Grants and Pojoaque, N. Mex.
416 CONTRIBUTIONS TO THE GEOLOGY OF URANIUM

INCHES 

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Family: 

Subgenus' 

Flowers:

Leaves: 

Fruit: 

Plant:

Dark calyx

FIGURE 78. Astragalus preussi A. Gray.

Pea, Leguminosae.

 Jonesiella.

Purple irregular flowers with darker calyx, arising from creeping

root stalks. Blooms in April and May. 

Smooth pinnate with 11-15 elliptic leaflets. 

Fat smooth oblong pod slightly curved, with short stem. 

Perennial. Many stems less than a foot high arising from a woody

base. Garliclike odor of foliage is due to presence of selenium.
INDICATOR PLANTS AND METHODS OF BOTANICAL PROSPECTING 417 

Primary indicator Control: selenium

FIGUBE 79. Preuss poisonvetch.

Altitude: 3,300-6,000 feet.

Occurrence: Common on mine dumps and along outcrops of ore-bearing beds 

where selenium and vanadium are available. Mineralized 

ground under these plants in Yellow Cat area, Utah, at an 

average depth of 41 feet. One of the best selenium indicator 

plants in uranium districts on the Colorado Plateau. Commonly absorbs large amounts of selenium and vanadium from 

the ores.

Districts noted: Ship Hock, in Arizona ; Slick Rock, TJravan, and Gypsum Valley, 

Colo.; Thompson, San Raf ael, Henry Mountains, Green River, 

and Moab, Utah.
418 CONTRIBUTIONS TO THE GEOLOGY OF URANIUM

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Family: 

Subgenus: 

Flowers:

Leaves:

Fruit:

Plant:

FIGURE 80. Astragalus thompsonae S. Wats.

Pea, Leguminosae.

Euastragalus.

Very showy, pinkish-lavender irregular flowers in clusters on long

stems. Blooms in April and May. 

Leaves all basal, pinnate, with 10 or more pairs of ovate leaflets which

become progressively smaller toward apex. Hairy, but hairs not

alined in any particular direction; spreading. 

Fat, erect, two-celled, slightly curved, hairy pods with thick walls

which become woody. No stem. 

Rosette type of perennial 6-12 inches across, with all leaves basal.

Plant and pods covered with soft, silvery hairs.
INDICATOR PLANTS AND METHODS OF BOTANICAL PROSPECTING 419 

Primary indicator Control: selenium

FIGURE 81. Thompson loco.

Altitude: 4,700-7,500 feet.

Occurrence: On seleniferous sandy soils and rocks. Often grows directly on

rock outcrop, but difficult to distinguish except in bloom. 

Districts noted: Ship Rock, in Arizona; Thompson, San Raf ael, White Canyon,

Monticello, and Uinta Basin, Utah; Gypsum Valley, Bull

Canyon, and Paradox Valley, Colo.
420 CONTRIBUTIONS TO THE GEOLOGY OF URANIUM

FIGURE 82. Astragalus confertiflorus A. Gray.

Family: Pea, Leguminosae.

Subgenus: Cnemidophacos.

Flowers: Cream-colored, irregular flowers in dense inflorescence. Blooms in

May.

Leaves: Pinnate, with 11 to 15 linear leaflets. Silvery hairs. 

Fruit: Erect one-celled pod from stalk, not inflated, and with no individual

stem. Woody. 

Plant: Perennial; about 8 inches; has erect stems and bluish foilage.
INDICATOR PLANTS AND METHODS OF BOTANICAL PROSPECTING 421 

Primary indicator Control: selenium

FIGURE 83. Blue poison vetch.

Altitude: 

Occurrence:

5,000-6,000 feet.

Restricted to seleniferous clay which commonly underlies ore

deposits. 

Districts noted: Thompson, Henry Mountains, Monticello, and Uinta Basin,

Utah, Grants, N. Mex.
422 CONTRIBUTIONS TO THE GEOLOGY OF URANIUM

Calyx deep purple

Two-grooved seed pod

Cross section enlarged

FIGURE 84. Astragalus Usulcatus (Hook.) A. Gray.

Family: Pea, Leguminosae.

Subgenus: Diholcos.

Flowers: Deep purple, irregular flowers in dense elongated spikelike inflorescence which extends above the foilage. Blooms in June and July.

Leaves: Smooth pinnate with oval or oblong leaflets.

Fruit: Linear one-celled pod with two deep grooves on the upper side. Pod 

with stem extends from calyx.

Plant: Stout, erect. Perennial.
INDICATOR PLANTS AND METHODS OF BOTANICAL PROSPECTING 423 

Primary indicator Control: selenium

 ^ _awrwiif^i: -' ~~ s~' $*

FIGURE 85. Two-grooved poisonvetch.

Altitude: 

Occurrence:

3,500 to 8,000 feet.

Dry meadows and sandy soil. This species absorbs large

amounts of selenium and molybdenum and is very poisonous

to stock. 

Districts noted: Powder River Basin, Wyo.; Huerf ano, Colo.
424 CONTRIBUTIONS TO THE GEOLOGY OF URANIUM

FIGUBE 86. Astragalus missouriensis Nutt.

Family: Pea, Leguminosae.

Subgenus: Xylophacos.

Flowers: Irregular, large, rose-purple pealike flowers in open cluster. Blooms

in May. 

Leaves: Pinnate, with 9-15 broad leaflets. Hairs oppressed, not spreading,

some pick-shaped or attached below the middle. 

Fruit: Pods 1 inch, 4-angled, 1-celled, beaked, curved slightly upward, and

woody. No stem. 

Plant: Low perennial, with basal resetted leaves and large flowers on many

erect flowering stems.
INDICATOR PLANTS AND METHODS OF BOTANICAL PROSPECTING 425 

Secondary indicator Control: selenium

FIGURE 87. Missouri milkvetch.

Altitude: 

Occurrence:

3,500-8,000 feet.

Dry sandy soils. Replaced on mesas by closely related A.

shortianus Nutt. with inflated seed pods and deep pink

flowers. 

Districts noted: Thompson and Monticello, Utah; Paradox, Colo.; Ship Rock,

in Arizona.
426 CONTRIBUTIONS TO THE GEOLOGY OF URANIUM

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FIGURE 88. Astragalus lonchocarpus Torr.

Family: Pea, Leguminosae.

Subgenus: Lonchophaca.

Flowers: Irregular creamy white, pea-shaped flowers, % to % inch long, in

elongate spreading clusters. Blooms in June. 

Leaves: Pinnate with three to nine linear or threadlike leaflets. Terminal

leaflet much longer than the others. 

Fruit: Linear pod with long stem exceeding calyx, tapering at both ends,

1% inches long. Thin, 1-celled, dorsally flattened, with prominent

sutures. Pods pendulous. 

Plant: Tall rushlike perennials with 1-2 foot stems arising from woody

base.
INDICATOR PLANTS AND METHODS OF BOTANICAL PROSPECTING 427 

Secondary indicator Control: selenium

FIGURE 89. Long-seeded milkvetcll.

Altitude: 4,000-7,500 feet

Occurrence: Dry, sandy, or clayey soil.

Districts noted: Paradox, Colo.; Cuba, N. Mex.

421588 57-
428 CONTRIBUTIONS TO THE GEOLOGY OF URANIUM

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FIGURE 90. Astragalus dodgianus Jones.

Family: Pea, Leguminosae.

Subgenus: Homalobus.

Flowers: Irregular, white, pealike flowers with purple-tipped keel. % inch.

Black hairs on calyx which has triangular teeth. Blooms in May. 

Leaves: Odd pinnate with 9 to 11 linear leaflets % inch long. 

Fruit: Linear pod 1-celled with short stem. Flattened, with both sutures

prominent and lower suture straight. 

Plant: Sparingly hairy perennial with slender lax stems and woody root

stalk.
INDICATOR PLANTS AND METHODS OF BOTANICAL PROSPECTING 429 

Secondary indicator Control: selenium

FIGUEE 91. Dodge milkvetch.

Altitude: 4,000-7,500 feet.

Districts noted: Rocky slopes.

Occurrence: Paradox, Colo.
430 CONTRIBUTIONS TO THE GEOLOGY OF URANIUM

FIGUBE 92. Astragalus tenellus Pursh.

Family: Pea, Leguminosae.

Subgenus: Homalobus.

Flowers: Irregular, %-inch cream to pale-lavender flowers with purple tip on

keel generally hidden in the foliage. Blooms in June. 

Leaves: Pinnate with 7 to 21 linear smooth leaflets. 

Fruit: Pods 1-celled, % inch long, laterally flattened with both sutures

prominent. Pods pendulous with short stem exceeding calyx. 

Plant: Perennial with woody root stalk. Stems 8 to 20 inches tall and leafy.

Foliage blackens when dried.
INDICATOR PLANTS AND METHODS OF BOTANICAL PROSPECTING 431 

Secondary indicator Control: selenium

FIGUEE 93. Looseflower milkvetch.

Altitude: 5,000-11,000 feet.

Occurrence: Moist alkaline soils.

Districts noted: Poison Basin, Wyo.
432 CONTRIBUTIONS TO THE GEOLOGY OF URANIUM

FIGUEE 94. Astragalus aculeatus A. Nels.

Family: Pea, Leguminosae.

Subgenus: Kentrophyta.

Flowers: Irregular, small purple pea-shaped flowers about 4 mm long, in axils

of leaves. Blooms in July.

Leaves: Pinnate, with 5 stiff spine-tipped leaflets % inch long. 

Fruit: Pods with 2 prominent sutures 1-celled, ovoid, % inch long. 

Plant: Perennial, with strong taproot, branches sprawling or erect, so

densely covered with prickly leaves as to appear clublike.
INDICATOR PLANTS AND METHODS OF BOTANICAL PROSPECTING 433 

Secondary indicator Control: selenium

FIGTJKE 95. Spiny milkvetch.

Altitude: 4,500-9,000 feet.

Occurrence: Dry mesas.

Districts noted: Pojoaque, and Grants, N. Mex.
434

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FIGURE 96. Allium acuminatum Hook, and related species.

Family: Lily, Liliaceae.

Flowers: Umbrellalike cluster of small pink flowers at end of long stalk. Each

petal has a middle line of deep pink. Blooms in April and May. 

Leaves: Two linear leaves about 6 inches long from bulb at base. Leaves are

shorter than flower stem. 

Fruit: Three-lobed capsule. 

Plant: Spring ephemeral. Bulb with outer covering. Strong odor of crushed

plant characteristic.
INDICATOR PLANTS AND METHODS OF BOTANICAL PROSPECTING 435 

Primary indicator Control: sulfur, phosphorus

FIGURE 97. Tapertip onion.

Altitude: 4,000-7,500 feet.

Occurrence: Grows in large patches around gypsiferous ore deposits and on 

sulfur-rich shale, but inhibited by highly seleniferous ores. 

Encouraged by increased availability of phosphate in carnotite environment. Roots are shallow, but in Thompson district it is found growing over carnotite deposits lying as much 

as 25 feet below the surface.

Districts noted: Thompson, Moab, and Green River, Utah; Slick Rock, Colo.; 

Chilchinbeto, Ariz.
436 CONTRIBUTIONS TO THE GEOLOGY OF UKANTUM

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FIGTJEE 98. Calochortus nuttalli Torr. & Gr.

Family: Lily, Liliaceae.

Flowers: Three large white petals marked yellow and purple at base. Gland

with hairs at base of petal. One to five flowers on stalk. Blooms

in April and May. 

Leaves: Several alternate grasslike leaves about 6 inches long, trough-shaped

in cross section. Onionlike bulb. 

Fruit: Three-angled capsule. 

Plant: Spring ephemeral. Grasslike leaves arising from bulb.
INDICATOR PLANTS AND METHODS OF BOTANICAL PROSPECTING 437 

Secondary indicator Control: sulfur, phosphorus

FIGUEE 99. Sego lily, mariposa.

Altitude: 5,000-8,000 feet

Occurrence. Dry sandy soil. A good indicator in early spring.

Districts noted : Thompson, Utah; Slick Rock, Colo.; Poison Basin, Wyo.
438 CONTRIBUTIONS TO THE GEOLOGY OF URANIUM

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FIGUBE 100. Zigadenus gramineus Rydb.

Family: Lily, Liliaceae.

Flowers: Inconspicuous greenish-white flowers with 6 "petals" which grow in

a raceme on flower stalk about 8 inches high. Gland near the base

of the petal. Blooms in April.

Leaves: Smooth, narrow, grasslike leaves arising from bulb. 

Fruit: Three-celled capsule. 

Plant: Spring ephemeral. Bulb with membranous covering.
INDICATOR PLANTS AND METHODS OF BOTANICAL PROSPECTING 439

Secondary indicator Control: sulfur, phosphorus

FIGURE 101. Grassy deathcamas.

Altitude: As high as 12,000 feet.

Occurrence: In sulfur-rich soils, from wet sandy seashore to dry desert 

sandstone. Poisonous to sheep owing to toxic alkaloids.

Districts noted: Thompson, Utah; Slick Rock and Paradox Valley, Colo.; Monument Valley, Ariz.
440 CONTRIBUTIONS TO THE GEOLOGY OF URANIUM

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FIGURE 102. Stanley a pinnata (Pursh) Britt.

Family: Mustard, Cruciferae.

Flowers: Golden yellow, with four clawed petals on tall stalk; through the 

summer months the stalks show a progression from buds to flowers 

to seeds. Stamens unequal, with anthers curled at maturity.

Leaves: Pale green, alternate; variable in shape and size, often lyre-shaped 

or entire.

Fruit: Long thin capsule containing many seeds.

Plant: Coarse perennial with thick erect stalk, 1-3 feet high, and woody root.
INDICATOR PLANTS AND METHODS OF BOTANICAL PROSPECTING 441 

Secondary indicator Control: selenium, sulfur

FIGURE 103. Desert princesplume.

Altitude: 2,500-7,000 feet.

Occurrence: Along rims and water courses draining gypsiferous areas. All 

species of this genus require both selenium and sulfur, but 

plot experiments indicate intolerance of highly mineralized 

ground. Therefore useful along drainage courses and in 

prospecting rims.

Districts noted: Ship Rock, Chilchinbeto, in Arizona; Slick Rock, Gypsum 

Valley, and Paradox Valley, Colo.; Thompson, San Rafael, 

Marysvale, White Canyon, Monticello, Green River, Henry 

Mountains, Moab, and Circle Cliffs, Utah; La Ventana, 

N. Mex.
442 CONTRIBUTIONS TO THE GEOLOGY OF URANIUM

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FIGURE 104. Lepidium montanum Nutt.

Family: Mustard, Cruciferae.

Flowers: Dense cluster of white flowers. Four clawed petals one-fourth inch

long which form a cross. Blooms from April to September. 

Leaves: Basal leaves finely divided, several inches long. Upper leaves simple

and smooth edged; do not clasp the stem. 

Fruit: Small round disk-shaped capsules that are not inflated. Narrowly

winged and obscurely notched at the apex. 

Plant: Bushy perennial 1 to 2 feet high. Stems not woody. Several stems

from same root.
INDICATOR PLANTS AND METHODS OF BOTANICAL PROSPECTING 443 

Secondary indicator Control: sulfur, phosphorus

FIGURE 105. Mountain pepperweed.

Altitude: 3,000-7,000 feet.

Occurrence: Common around shallow uranium deposits where sulfur is available in surface soil. Very high absorption of uranium. Common on gypsum dunes of White Sands, N. Mex.

Districts noted: Thompson, White Canyon, and Green River, and Uinta Basin. 

Utah.

421588 57-
444 CONTRIBUTIONS TO THE GEOLOGY OF URANIUM

Seeds

INCHES

r2

Flowers 

(enlarged)

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FIGURE 106. Lepidium lasiocarpum Nutt.

Family: Mustard, Cruciferae.

Flowers : Not conspicuous, may be obsolete. Blooms from January to April. 

Leaves: Small simple rounded leaves. Basal leaves incised. 

Fruit: Notched round disk-shaped capsules.

Plant: Tiny hairy annual, 2 inches high, branched from the base and not 

woody.
INDICATOR PLANTS AND METHODS OF BOTANICAL PROSPECTING 445 

Secondary indicator Control: sulfur, phosphorus

FIGUKE 107. Hairy-pod pepperweed.

Altitude: 3,000-4,500 feet.

Occurrence: Sandy soil where sulf ates are present in surface soil.

Districts noted: Thompson and San Rafael, Utah; Ship Bock, in Arizona.
446 CONTRIBUTIONS TO THE GEOLOGY OF URANIUM

Capsule

FIGTJEE 108. Kisymbrium altissimum (L.) Britt.

Family: Mustard, Cruciferae.

Flowers: Four creamy, flat, one-fourth inch petals which form a cross. Blooms 

from May to July.

Leaves: Upper leaves threadlike, lower leaves divided and not clasping the 

stem.

Fruit: Thin linear capsules, more than 2 inches long. Divergent.

Root: Tap root, but with fine long laterals ; root system extensive.

Plant: Coarse erect annual 2 to 4 feet high with smooth stems, freely branching. An introduced European adventive weed both tolerant and indicative of soils containing sulf ate.
INDICATOR PLANTS AND METHODS OF BOTANICAL PROSPECTING 447 

Secondary indicator Control: sulfur, phosphorus

FIGURE 109. Tumblemustard.

Altitude: 5,000-7,000 feet

Occurrence: Around ore deposits on higher mesas. High absorption of

uranium. 

Districts noted: Slick Hock, Gypsum Valley, Paradox Valley, and Rifle, Colo.;

White Canyon and San Kafael, Utah.
448 CONTRIBUTIONS TO THE GEOLOGY OF URANIUM

FIGURE 110. CryptantJia flava A. Nels. and related species.

Family: Borage, Boraginaceae.

Flowers: Pale-yellow, tubular flowers one-fourth inch long in small congested,

densely hairy heads. Blooms in spring and summer. 

Leaves: Rough, simple, linear, and mostly basal. 

Fruit: Smooth oval nutlet. 

Plant: Stout, pale-green, hairy perennial 4 to 12 inches high, growing from

woody base.
INDICATOR PLANTS AND METHODS OF BOTANICAL PROSPECTING 449 

Secondary indicator Control: calcium

FIGUEE 111. Cryptanth.

Altitude: 5,000-7,000 feet.

Occurrence: Prefers dry sandy or limestone soil. Localized around gypsif erous uranium deposits in many districts. The controlling factor is probably available calcium. Common on gypsum dunes 

at White Sands, N. Mex., and on limestone and calcium-rich 

vein deposits in Arizona.

Districts noted : Thompson, Green River, White Canyon, and Circle Cliffs, Utah; 

Grants, N. Mex.; Ship Rock, Defiance, in Arizona; Gypsum 

Valley, Bull Canyon, and Paradox Valley, Colo.; Poison Basin, 

Wyo.
450 CONTRIBUTIONS TO THE GEOLOGY OF URANIUM 

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Family: 

Flowers:

Leaves:

Fruit: 

Plant:

Seed

FIGTJKE 112. OenotJiera caespitosa Nutt.

Primrose, Onagraceae.

Large fragrant white flower with 4 heart-shaped petals on a long

slender calyx tube which rises directly from the ground for about

4 to 5 inches. Flowers open in the evening and turn pink with age.

Fragrant. Blooms in May and June. 

Strap leaves in a basal rosette. Smooth-margined or toothed, on

winged stems.

Oval capsule with rounded tubercles on the angles. 

Perennial.
INDICATOR PLANTS AND METHODS OF BOTANICAL PROSPECTING 451 

Primary indicator Control: calcium

FIGURE 113. Tufted evening-primrose.

Altitude: 

Occurrence

3,000-7,500 feet.

Common associate of uranium-indicator plants. The distribution of this plant suggests that it is an indicator of available 

calcium. Listed in flora of White Sands, N. Mex., and common 

on volcanic beds of Arizona.

Districts noted: Grants, N. Mex; Thompson, San Raf ael, Green River, and White 

Canyon, Utah; Ship Rock, in Arizona.
452 CONTRIBUTIONS TO THE GEOLOGY OF URANIUM

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Seed pod

L-O

FIGURE 114. Oenothera albicaulis Pursh.

Family: Primrose, Onagraceae.

Flowers: Four large white lobes resembling petals at end of tube 1 inch long.

Blooms from May to July. 

Leaves: Basal leaves, blunt, spatulate, toothed. Stem leaves, 2 to 5 inches

long, deeply divided.

Fruit: Pod, % to 2 inches long, % inch thick. 

Plant: Annual or biennial, 4 to 12 inches high, branched at the base.
INDICATOR PLANTS AND METHODS OF BOTANICAL PROSPECTING 453 

Secondary indicator Control: calcium

FIGURE 115. Whitestemmed evening-primrose.

Altitude: 2,400-7,500 feet.

Occurrence: Gypsum-bearing sandy soil.

Districts noted: Thompson and San Rafael, Utah.
454 CONTEIBUTIONS TO THE GEOLOGY OF URANIUM

Flowers

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FIGURE 116. Eriogonum inflatum Torr.

Family: Buckwheat, Polygonaceae.

Flowers: Clusters of 10 to 20 tiny yellow flowers on much-branched mass of

fine stems. Blooms from March to July. 

Leaves: Rounded leaves in rosette at base of plant. 

Seeds: Three-angled dry seed. 

Plant: Bluish-green tubular stems with hollow, inflated, trumpetlike parts

before divisions. Stem divides in threes, 1 to 2 feet high perennial,

with woody base.
INDICATOR PLANTS AND METHODS OF BOTANICAL PROSPECTING 455 

Primary indicator Control: sulfur, phosphorus

Altitude: 

Occurrence:

FIGURE 117. Deserttrumpet eriogonum.

As high as 4,500 feet.

Common on sulfur-rich soils and gypsiferous ore deposits. 

Turns Mancos shale yellow when in bloom. High phosphorus 

content.

Districts noted: Ship Rock, in Arizona; Thompson, San Raf ael, Henry Mountains, Green River, Monticello, and Circle Cliffs, Utah.
456 CONTRIBUTIONS TO THE GEOLOGY OF URANIUM

INCHES 

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Family: 

Flowers:

Leaves: 

Stem: 

Fruit: 

Plant:

Flowers 

(enlarged)

FIGURE 118. Eriogonum fusiforme Small.

Buckwheat, Polygonaceae.

Tiny white or yellowish flowers in diffusely branching inflorescence

Blooms in June and July.

Basal, rounded or kidney-shaped in outline, scattered hairs. 

Inflated part above the middle of stem. 

Dry, small, smooth. 

Annual, with flower stalk extending from basal rosette.
INDICATOR PLANTS AND METHODS OF BOTANICAL PROSPECTING 457 

Secondary indicator Control: sulfur, phosphorus

FIGURE 119. Deserttrumpet.

Altitude: 4,000-6,000 feet

Occurrence: Dry sandy alluvial soil.

Districts noted: Yellow Cat and Green River, Utah.
458 CONTRIBUTIONS TO THE GEOLOGY OF URANIUM

INCHES 

-4

-0

FIGURE 120. Eriogonum ovalifolium Nutt.

Family: Buckwheat, Polygonaceae.

Flowers: Pale-yellow to pink; in headlike cluster on 4- to 6-inch stalk. Calyx

yellowish with pinkish veins. Blooms from April to June. 

Leaves: Densely white-woolly; oval leaves at base of plant about one-half inch

in size.

Fruit: Dry, small. 

Plant: Hairy perennial with basal cushion of leaves and 10-inch flower

stalks. Woody base.
INDICATOR PLANTS AND METHODS OF BOTANICAL PROSPECTING 459 

Secondary indicator Control: sulfur, phosphorus

FIGUKE 121. Silver plant or cushion eriogonum.

Altitude: 

Occurrence:

5,000-7,000 feet.

Commonly on sandstone outcrops rooted in cracks and joints.

Phosphate absorber. 

Districts noted: Thompson, Utah; Ship Rock, in Arizona.

421588 57-
460 CONTRIBUTIONS TO THE GEOLOGY OF URANIUM

' ^'"'"v ^-Sulfur yellow

FIGURE 122. Eriogonum umbellatum Torr.

Family: Buckwheat, Polygonaceae.

Flowers : Twenty to thirty sulfur-yellow flowers in heads held in simple umbrellalike cluster with leafy bracts at base. Individual flowers tubular 

with reflexed lobes and 9 stamens. Flower stalks stout, woolly, 

and 4 to 12 inches long. Blooms through summer.

Leaves: Thick, oval-to-spatulate, % to 1 inch long, tapering to a stem. Green 

above, white-woolly underneath.

Seeds : Sharply three-angled, dry seeds.

Plant: Perennial with thick taproot. Branched woody base tufted with leaves 

at the nodes from which erect leafless flower stalks extend.
INDICATOR PLANTS AND METHODS OF BOTANICAL PROSPECTING 461 

Secondary indicator Control: sulfur, phosphorus

FIGTJKE 123. Sulfur eriogonum.

Altitude: 5,000-9,000 feet. 

Occurrence: Dry slopes. Phosphate absorber.

Districts noted: Jefferson County, Colo.; White Canyon, Utah; Phosphoria formation, Wyoming.
462 CONTRIBUTIONS TO THE GEOLOGY OF URANIUM

INCHES 

1-12

FIGURE 124. Elymus salina Jones.

Family: Grass, Gramineae.

Flowers: Dense spikes. Spikelets coming off in pairs from jointed axis. No

awns. Blooms through summer. 

Leaves: Broad blades, rolled inward. 

Plant: Perennial grass with harsh foliage. Grows in thick clumps several

feet high.
INDICATOR PLANTS AND METHODS OF BOTANICAL PROSPECTING 463 

Primary indicator Control: Probably phosphorus

Altitude: 

Occurrence

FIGURE 125. Salina wildrye.

3,000-7,000 feet.

A grass that formerly covered large areas of the West, now 

present only in relict areas. Common on mine dumps and 

along canyon rims, in the vicinity of uranium ore. Also 

known to occur around base-metal sulfide deposits; this is 

probably due to increased availability of phosphorus.

Districts noted: Ship Rock, in Arizona; Slick Rock, Paradox Valley, and 

Gypsum Valley, Colo.; Thompson, Green River, and Circle 

Cliffs, Utah.
464

FIGURE 126. Stipa comata Trin. & Rupr.

Family: Grass, Gramineae.

Flowers: Loose head 5 to 10 inches long with tightly twisted threadlike awns 

4 to 5 inches long resembling tails attached to the seeds. Tight 

twist in lower third only. Blooms in June and July.

Leaves: Harsh, flat, inrolled.

Plant: Deep-rooted perennial 1 to 2 feet high.
INDICATOR PLANTS AND METHODS OF BOTANICAL PROSPECTING 465 

Secondary indicator Control: probably phosphorus

FIGURE 127. Needleandthread.

Altitude: 

Occurrence:

4,500-8,000 feet.

Restriction to mineralized ground in many areas probably owing to increased availability of phosphorus.

Districts noted: Thompson, Utah; Gypsum Valley, Colo.; Grants, N. Mex. 

Closely related species in Ship Rock, in Arizona.
INCHES

FiGUKEl28. Oryzopsis liymenoldes (Roem. & Schult.) Rick.

Family: Grass Gramineae.

Flowers: Small dry flowers in open panicle with branches at right angles in

zigzag pairs. Individual spikelets one-flowered. Blooms in June

and July.

Leaves: Inrolled, narrow. 

Seeds: Small, ricelike; edible. 

Plant: Extensive perennial grass 1 to 2 feet high, with deep fibrous roots.
INDICATOR PLANTS AND METHODS OF BOTANICAL PROSPECTING 467 

Secondary indicator Control: selenium

FIGURE 129. Indian ricegrass.

Altitude: As high as 10,000 feet.

Occurrence: Drought-resistant and alkali-tolerant grass common in any 

western soil which contains a small amount of selenium. 

Capable of absorbing large amounts of selenium and uranium 

although the selenium requirements are very low. Useful 

only in districts where selenium content of the ore is low; 

there the plant may be restricted to ore.

Districts noted: Gypsum Valley, Rifle, Slick Rock, Bull Canyon, and Paradox 

Valley, Colo.; White Canyon, Marysvale, Thompson, San 

Rafael, Henry Mountains, Green River, Moab, Monticello, 

Uinta Basin, and Circle Cliffs, Utah; La Ventana and Grants, 

N. Mex.; Wamsutter and Poison Basin, Wyo.; Ship Rock, 

in Arizona.
4H8 ' CONTRIBUTIONS TO THE GEOLOGY OF URANIUM

INCHES 

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Bracts

FIGURE 130. Aster venustus Jones.

Family: Sunflower, Compositae.

Flowers: Composite flowers in 1-inch heads with long white ray flowers resembling daisies. Heads solitary on 8-20-inch flower stalks. Bracts 

nearly equal in length. White "petals" turn lavender on aging. 

Blooms in May and June.

Leaves: Spatula-shaped, with callous point, hairy and alternate. One to two 

inches long.

Seeds: Small silky seeds remain in dried heads through summer months.

Plant: Woody perennial base and naked flower stalks ; long taproot. Plant 6 

to 18 inches high.
INDICATOR PLANTS AND METHODS OF BOTANICAL PROSPECTING 469 

Secondary indicator Control: selenium

FIGURE 131. Woody aster.

Altitude: 

Occurrence

3,000-5,000 feet.

Restricted to low altitudes. Common on clay soils of Mancos 

shale and alluvium of uranium districts in Utah. Although 

species absorbs large amounts of selenium when available, restriction to clay soils limits its usefulness to alluvium and 

drainage prospecting. 

Districts noted : Thompson, Moab, Henry Mountains, and Green River, Utah.
470 CONTRIBUTIONS TO THE GEOLOGY OF URANIUM

FIGURE 132. Townsendia incana Nutt.

Family: Sunflower, Compositae.

Flowers: Daisy-like composite with yellow disk flowers and one-half-inch white

to pink ray flowers. Blooms in April and May. 

Leaves: Spatula-shaped, blunt hairy leaves 1 inch long arising from basal woody

crown.

Seeds: Small flattened dry seeds. 

Plant: Hairy perennial with woody crown and flower stems less than 4 inches

high. Taproot.
INDICATOR PLANTS AND METHODS OF BOTANICAL PROSPECTING 471 

Secondary indicator Control: selenium

FIGURE 133. Hoary townsendia.

Altitude: 5,000-6,500 feet.

Occurrence: On selenium-bearing sands. Conspicuous only when in bloom.

Districts noted: Thompsons, Green River, Monticello and White Canyon, Utah.
INCHES 

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Linear leaves

FIGUEE 134. Aplopappus armeriodes A. Gray.

Family: Sunflower, Compositae.

Flowers: Heads clustered at top of stem with yellow tubular disk and one-halfinch long ray flowers. Blooms in June and July.

Leaves: Smooth, 3-nerved, linear leaves, 1 to 3 inches long.

Plant : Perennial herb with leafless flower stems 2 to 6 inches long arising from 

bunched leaves at woody base.
INDICATOR PLANTS AND METHODS OF BOTANICAL PROSPECTING 473 

Secondary indicator Control: selenium (?)

FIGURE 135. Goldenweed.

Altitude: 4,000-6,000 feet.

Occurrence: Dry sandstone mesas.

Districts noted: Thompson, San Rafael, Henry Mountains, Green River, and

White Canyon, Utah; Bull Canyon, Colo.; Ship Rock, Defiance

uplift, Ariz.
474 CONTRIBUTIONS TO THE GEOLOGY OF URANIUM

INCHES 

r3

Bract

FIGURE 136. Grindelia squarrosa (Pursh) Dunal, and closely related species.

Family: Sunflower, Compositae.

Flowers: Yellow radiate heads in flat-topped clusters. Green bracts of heads

strongly graduated in 4 to 8 rows with recurved tips and

mucilaginous. Blooms in fall.

Leaves: Undivided, alternate leaves clasping the stem; resinous and stiff. 

Seeds: Dry, small, and short. 

Plant: Biennial or perennial, 8 to 40 inches high; mucilaginous plant with

long taproot. Balsamlike odor from exuded gum.
INDICATOR PLANTS AND METHODS OF BOTANICAL PROSPECTING 475 

Secondary indicator Control: unknown

FIGURE 137. Curlycup gumweed.

Altitude: 

Occurrence:

As high as 9,000 feet.

Common in drainage and seeps from mines of high selenium content or rooted in ore deposits of low content. Plot studies indicate very high absorption of uranium and a marked increase 

in absorption in carnotite environment with development of 

anomalous growth habits. Intolerant of highly seleniferous 

soils. Calcium absorber. 

Districts noted: Thompson, Utah ; and others.

421588 57-
476 CONTRIBUTIONS TO THE GEOLOGY OF URANIUM

Base leaf

FIGURE 138. Senecio longilobus Benth.

 V

Family: Sunflower, Compositae.

Flowers: Yellow composite with %-inch disk and long yellow ray flowers. Heads

in flat-topped clusters. Blooms through summer months. 

Leaves: Pinnate leaves with linear, threadlike, hairy leaflets. 

Seeds: Small dry seeds. 

Plant: Ill-scented perennial 1 to 2 feet high covered with white-woolly hairs

and having a long taproot. The plant is very poisonous to cattle.

Poison, alkaloid.
INDICATOR PLANTS AND METHODS OF BOTANICAL PROSPECTING 477 

Secondary indicator Control: calcium

FIGURE 139. Threadleaf groundsel.

Altitude: 

Occurrence

4,000-7,500 feet.

Along roadsides and in dry, alkaline country. Various species 

of Senecio are known to act as indicators around many types of 

heavy-metal deposits. The control may be phosphorus or calcium. Useful secondary indicator.

Districts noted: Thompson, Utah, Ship Rock, Defiance uplift, Ariz.; Slick Rock 

and Gypsum Valley, Colo.
478 CONTRIBUTIONS TO THE GEOLOGY OF URANIUM

Gland 

Involucre

INCH

FIGTJKE 140. Euphorbia fendleri Torr. & Gr., and related prostrate species.

Family: Spurge, Euphorbiaceae.

Flowers: Minute flowers in peculiar "petaled" involucre from which stalked 

glands extend. Flowers occur in axils of leaves. Bloom from April 

to October.

Leaves: Oval, opposite, entire, pale-green leaves % inch long.

Fruit: Quadrangular seeds in lobed smooth capsule.

Plant: Prostrate, pale-green annual with forking stems radially branched at 

the base. Milky acrid sap which is poisonous and may cause dermatitis upon contact.
INDICATOR PLANTS AND METHODS OF BOTANICAL PROSPECTING 479 

Secondary indicator Control: calcium or sulfur

FIGURE 141. Sandmat or Fendler euphorbia.

Altitude: 4,000-7,000 feet.

Occurrence: Common on gypsum-bearing soils. Of importance only where 

soluble salts from ore deposits have migrated into the surface 

soils. Experimental plot studies show stems of this plant 

tend to be erect on high-sulfate soils and completely prostrate on low-sulf ate soils.

Districts noted: Thompson, San Rafael, and Henry Mountains, Uinta Basin, 

Utah; Grants, N. Mex.; Ship Rock, in Arizona.
480 CONTRIBUTIONS TO THE GEOLOGY OF URANIUM

INCHES 

r3

FIGURE 142. Mentzelia multiflora (Nutt.) A. Gray.

similar in appearance.

Several other species are

Family: Loasa, Loasaceae.

Flowers: Light-yellow, star-shaped flowers with 10 petals and many stamens.

Stamens in outer row are petallike. Opens in afternoon. Blooms

from May to August.

Leaves: Light green, sticky, alternate, and toothed. 

Fruit: Three- to five-valved capsule. 

Plant: Stems freely branching; plant 1 to 3 feet high. Barbed stinging hairs.

Perennial. Stout taproot.
INDICATOR PLANTS AND METHODS OF BOTANICAL PROSPECTING 481 

Secondary indicator Control: calcium

FIGURE 143. Desert blazingstar.

Altitude: 

Occurrence

As high as 7,000 feet.

A common weed of roadsides and disturbed ground. This 

genus is found around many uranium deposits and on the 

pure gypsum sands of White Sands, N. Mex. It absorbs 

large amounts of calcium. As the growth is favored by 

the presence of carnotite ore, several species may be used 

under certain circumstances as an ore indicator.

Districts noted: Lost Creek, Wyo.; La Ventana and Penasco Hot Springs, 

Grants, N. Mex.; Gypsum Valley, Colo.; Ship Rock, in 

Arizona ; and San Raf ael, Utah.
482 CONTRIBUTIONS TO THE GEOLOGY OF UEANIUM

INCHES 

4

FIGTJRE 144. Solidaffo petradoria Blake.

Family: Sunflower, Compositae.

Flowers: Five to eight small yellow flowers in heads in dense flat-topped clusters.

Blooms in July and August. 

Leaves: Linear-oblong, three-nerved, rigid alternate leaves, 2 to 4 inches long

and resinous.

Seeds: Dry, flat, five-nerved.

Plant: Low, tufted, perrenial herbs with short branched woody base. Smooth, 

4 to 6 inches long, erect flower stems from cushion of basal leaves. 

Extensive root system.
INDICATOR PLANTS AND METHODS OF BOTANICAL PROSPECTING 483

Tolerant

FIGURE 145. Rock goldenrod.

Altitude: 5,500-7,500 feet. 

Occurrence: Rock ledges and dry sandy soils.

Districts noted: Thompson and White Canyon, Utah; Paradox Valley and Bull 

Canyon, Colo; Defiance uplift, Ariz.
484 CONTRIBUTIONS TO THE GEOLOGY OF URANIUM

Pappus

INCHES 

r5

Recurved spines

FIGURE 146. Tetradymia splnosa Hook. & Arn.

Family: Sunflower, Compositae.

Flowers: Fleshy smooth heads of four yellow flowers % to % inch long arising 

from axils of the leaves. Bracts at base of heads woolly. Blooms 

from May to July.

Leaves: Primary leaves converted to woolly recurved spines % to % inch long. 

Secondary leaves linear, ^ to % inch long, fleshy and in clusters.

Plant: Divaricately branched xerophytic shrub 2 to 4 feet high with white 

woolly branches and characteristic recurved woolly spines which 

are soft and pliant when first produced. High potassium content 

in leaves and buds. Organic compound in plant poisonous to sheep.
INDICATOR PLANTS AND METHODS OF BOTANICAL PROSPECTING 485

Tolerant

FIGURE 147. Cottonthorn horsebrush.

Altitude: 4,000-7,000 feet.

Occurrence: Dry sandy plains and sandstone mesas.

Districts noted: Thompson, San Raf ael Swell, Unita Basin, Utah, Gypsum 

Valley, Colo.
486 CONTRIBUTIONS TO THE GEOLOGY OF URANIUM

INCHES 

4

FIGURE 148. Cowania stansburiana Torr.

Family: Rose, Rosaceae.

Flowers: Creamy yellow solitary flowers with 5 oval petals, 5 sepals, and many

stamens. Fragrant; resembles the wild rose. Flowers through

spring and summer whenever water is plentiful. 

Leaves: Alternate gland-dotted, evergreen leaves with 3 to 5 lobes and curledunder margins. White fuzz underneath. 

Seeds: Dry, attached to several long plumes which appear from each flower

before the petals have dropped. 

Plant: Twisted shrub, 3 to 12 feet high with shaggy gray bark and reddish

twigs. Plant has a bitter taste and very acid cell sap.
INDICATOR PLANTS AND METHODS OF BOTANICAL PROSPECTING 487

Tolerant

FIGURE 149. Stansbury cliffrose.

Altitude: 3,500-8,000 feet.

Occurrence: Phreatophyte, occurring with juniper and pinyon on rock mesas 

and along sandy washes. Called "vanadium-bush" and used 

as indicator by early prospectors although probably indicating water commonly trapped in ore rolls. Able to grow in 

highly mineralized ground and to absorb large amounts of 

uranium. Type locality: Stansbury Island, Great Salt Lake.

Districts noted: Ship Rock, Chilchinbeto, Chuska, and Defiance uplift, in 

Arizona; Thompson, San Rafael, White Canyon, Henry Mountains, and Circle Cliffs, La Ventana, and Grants, N. Mex.
488 CONTRIBUTIONS TO THE GEOLOGY OF URANIUM

Seed pod

FIGURE 150. Purshia tridentata (Pursh) DC.

Family: Rose, Rosaceae.

Flowers : Solitary at the ends of branches. Tube-shaped, hairy, five-lobed calyx,

five yellow petals. Many stamens in single series. Blooms from

April to July. 

Leaves: Alternate but crowded into fascicles. Three-cleft, 0.2 to 1 inch long,

wedge-shaped with rolled margins. White fuzz beneath. 

Seeds: Spindle-shaped, y2 inch long, exserted from calyx tube with persistent

break. 

Plant: Intricately branched shrubs 1% to 9 feet high with brown to gray

bark. Drought resistant. Foliage has bitter taste.
INDICATOR PLANTS AND METHODS OF BOTANICAL PROSPECTING 489

FIGURE 151. Antelope bitterbrush.

Altitude: 4,000-9,000 feet.

Occurrence: Arid plains and foothills. Common on volcanic flows.

Districts noted: Monticello, Utah ; Slick Rock, Colo.; Henry Mountains, Utah.
490 CONTRIBUTIONS TO THE GEOLOGY OF URANIUM

INCHES 

4

L- 0

Family: 

Flowers:

Leaves: 

Fruit: 

Plant:

Leaflet

FIGTJEE 152. Hedysarum boreale Nutt.

Pea, Leguminosae.

Showy rose-purple irregular flowers in loose racemes which grow from 

the axils of leaves. Stamens 9 and 1. Blooms in June and July.

Odd-pinnate with many oblong leaflets. Finely punctate, smooth on 

upper surface and sparingly hairy beneath.

Compressed, several-jointed pod divided into 2 to 4 separable rounded 

segments.

Perennial herb with 1 to 3 foot erect, leafy stems with scattered hairs. 

Resembles the Astragalus genus closely in general appearance except for seeds and hairy roughness.
INDICATOR PLANTS AND METHODS OF BOTANICAL PROSPECTING 491

Tolerant

FIGURE 153. Northern sweetvetch. .«

Altitude: 4,000-7,000 feet.

Occurrence: Phreatophyte, tolerant of mineralized ground. 

Districts noted: Thompson, White Canyon, Circle Cliffs and San Rafael, Utah ; 

Paradox Valley, Colo.; Defiance uplift and Chuska, Ariz.

421588 57 7
492 CONTRIBUTIONS TO THE GEOLOGY OF URANIUM

INCHES 

r2

Family: 

Flowers:

Leaves: 

Fruit: 

Plant:

Seed podFIGUEE 154. Castilleja Integra Gray.

Figwort, Scrophulariaceae.

Spikes of flowers consisting of three-cleft, brilliant scarlet bracts

surrounding yellowish fused calyx and narrow yellow petals. Four

stamens. Blooms throughout summer. 

Alternate, sessile, linear leaves, 2 to 4 inches long. 

Two-celled capsule containing many seeds. 

Erect perennial herb with simple leafy stem and spike of red or yellow

bracted flowers. Roots fibrous, partly parasitic on other plants.
INDICATOR PLANTS AND METHODS OF BOTANICAL PROSPECTING 493

Tolerant

FIGURE 155. Indian paintbrush or paintedcup.

Altitude: 

Occurrence

3,000-7,500 feet.

In sandy soils. Capable of absorbing considerable selenium

although not believed to be an indicator plant.

Districts noted : Thompson and White Canyon, Utah; Grants, N. Mex.; Chilchinbeto and Chuska, Ariz.
494 CONTRIBUTIONS TO THE GEOLOGY OF URANIUM

FIGURE 156. Plantago purshi Roem. & Schult.

Family: Plantain, Plantaginaceae.

Flowers: Tiny dry flowers in dense cylindrical spike resembling wheat. Spike

y2 to 1% inches long on 2-inch woolly stem. Individual flower parts

in fours. Blooms throughout summer. 

Leaves: Woolly, linear, 3-ribbed leaves 1 to 2 inches long on a short stem from

the base of the plant. 

Fruit: Oblong, 2-seeded pod which divides in middle so that top half falls

off like a lid.

Root: Long taproot; most deeply placed roots of any annual. 

Plant: Tiny, drought-resistant, winter annual consisting of several leaves

and single flower spike which arise from the base. Seeds become

mucilaginous when wet.
INDICATOR PLANTS AND METHODS OF BOTANICAL PROSPECTING 495

Tolerant

FIGURE 157. Woolly indianwheat.

Altitude: 1,000-7,000 feet.

Occurrence: Full sunlight and dry sandy soil. Commonly associated with

sulfur-indicator plants. 

Districts noted: Thompson, Utah ; Grants, N. Mex.
496 CONTRIBUTIONS TO THE GEOLOGY OF URANIUM

Female fruiting 

bract

i-o

FIGURE 158. Atriplese confertifolia (Torr.) S. Wats.

Family: Goosefoot, Chenopodiaceae.

Flowers: Small dense clusters. Blooms in late summer.

Leaves: Thickened, ovate, scurfy leaves; resembling a shad scale. Leaves

have short stem. 

Fruit: Fruit in large conspicuous yellowish-green to pinkish bracts at ends

of the branches. Bracts never with wings. 

Plant: Grayish-green xerophyte shrub 1-4 feet high; woody and branched.

Branches ending in spines. Seeds not produced on same plants

with pollen.
INDICATOR PLANTS AND METHODS OF BOTANICAL PROSPECTING 497

FIGURE 159. Shadscale saltbush.

Altitude: 4,200-6,000 feet.

Occurrence: Drought-resistant and alkali-tolerant plant commonly the dominant species of uranium districts. Plant has ash content of 

about 25 percent consisting mostly of sodium. Absorbs uranium and selenium readily although not restricted in distribution to mineralized ground. Type locality: Great Salt Lake.

Districts noted: Wamsutter, Poison Basin, and Lost Creek, Wyo.; La Ventana, 

N. Mex.; Slick Rock, Colo.; Thompson, San Rafael, White 

Canyon, Moab, and Uinta Basin, Utah.
498 CONTRIBUTIONS TO THE GEOLOGY OF URANIUM

FIGURE 160. Atriplex canescens (Pursh) Nutt.

Family: Goosefoot, Chenopodiaceae.

Flowers: Staminate flowers small glomerules in dense spikes. Pistillate flowers

enclosed in bracts with no calyx or petals. Blooms in June and

August.

Leaves: Linear, thick, grayish, scurfy. 2 inches long. No leaf stem. 

Fruits: Fruits one seeded with four prominent wings. Fruiting bracts

stalked, thick, fleshy and ovoid. 

Plant: Woody perennial 2-8 feet with male and female flowers on separate

plants. Branches circular in cross sections, white scurfy. Bark

peels from old stems in thin layers. Roots reach 20 feet in length.
INDICATOR PLANTS AND METHODS OF BOTANICAL PROSPECTING 499

Tolerant

FIGUEE 161. Fourwing saltbush.

Altitude: 

Occurrence

4,000-8,000 feet.

Dry sandy plains and hills. Alkaline soil. High ash content 

largely sodium. Replaced by A. confertifolia in extremely saline areas.

Districts noted: Yellow Cat and Green River, Utah; Ship Rock, Grants, and 

Nambe, N. Mex.; Uravan, Colo.
500

INCHES 

rlO

Staminate

Pistillate

FIGURE 162. Sarcobatus vermiculatus (Hook.) Torr.

Family: Goosefoot, Chenopodiaceae.

Flowers: Pollen and seeds not produced on same plant. Seed-producing flowers 

axillary and with cup-shaped enlarged calyx. Pollen-producing 

flowers small, in terminal spikes. Blooms from June to September.

Leaves: Alternate, linear, and fleshy leaves, %-!% inches long. Sessile.

Seed : Nutlet attached to expanded, membranous calyx.

Plant: Erect shrub 4-8 feet high, much branched and thorny with gray bark 

and fleshy linear leaves.
INDICATOR PLANTS AND METHODS OF BOTANICAL PROSPECTING 501

Tolerant

FIGURE 163. Black greasewood.

Altitude: 1,000-7,000 feet.

Occurrence: A phreatophyte or ground-water plant tolerant of alkaline and 

saline soils. An indicator of "black alkali," or sodium carbonate. Poisonous to sheep in spring, owing to salate of sodium 

and potassium in sap. Absorption of uranium very high.

Districts noted: Thompson and Henry Mountains, Utah; Lost Creek, and Poison 

Basin, Wyo.
502 CONTRIBUTIONS TO THE GEOLOGY OF URANIUM

(enlarged)

FIGURE 164. Ephedra sp.

Family: Jointfir, Gnetaceae.

Flowers: Small male and female yellow flowers in short catkins with persistent 

bracts. Stamens united, 2-lobed flower tube. Blooms in spring.

Leaves: Scalelike in pairs or threes at stem joints.

Seeds: Hard nutlets.

Plant: Shrubs 6-25 inches high with rigid jointed striated branches resembling Equisetum and reduced leaves. Twigs opposite or clustered 

at stem joints.
INDICATOR PLANTS AND METHODS OF BOTANICAL PROSPECTING 503

Tolerant

FIGURE 165. Jointfir, or mormon tea.

Altitude: 4,500-9,000 feet.

Occurrence: Dry desert areas.

Districts noted: Yellow Cat and Henry Mountains, Utah; Ship Rock, N. Mex.
504 CONTRIBUTIONS TO THE GEOLOGY OF URANIUM

FIGURE 166. Opuntia engelmanni Salm-Dyck and other species.

Family: Cactus, Cactaceae.

Flowers: Many waxy colored petals, numerous sensitive stamens, and short 

green calyx supported on cup-shaped tube. Diurnal flowers normally several inches across arise from same growing centers as 

spines. Blooms in May and June.

Leaves: Small, awl-shaped deciduous, as much as % inch long.

Roots: Extensive fibrous roots.

Fruit: Fleshy edible berry as much as 2 inches long with many bony seeds.

Plant: Succulent shrubs as much as 5 feet high with fleshy, jointed, flattened 

stems. Areoles, or growing centers, bear minute leaves, spines, and 

bristles. Water content 80 percent in stems. Acid cell sap.
INDICATOR PLANTS AND METHODS OF BOTANICAL PROSPECTING 505

Tolerant

FIGURE 167. Engelmann pricklypear.

Altitude: 1,000-8,000 feet. 

Occurrence: Sandy plains and sandstone mesas.

Districts noted : Thompson, Henry Mountains, and Green River, Utah; Defiance 

uplift, and Ship Rock, in Arizona.
506 CONTRIBUTIONS TO THE GEOLOGY OF URANIUM

FIGURE 168. Mirabilis multiflora A. Gray.

Family: Four o'clock, Nyctaginaceae.

Flowers: Clusters of 6 rose-colored, funnel-shaped flowers 2 inches across enclosed in a large funnel-shaped bract. Three-five unequal stamens. 

Flowers open toward sunset. Blooms in July and August.

Leaves: Thick, opposite, entire leaves, oval or heart-shaped and 2-3 inches 

long.

Seeds: Oval black seeds, 10-furrowed toward base.

Roots: Large and fleshy.

Plant: Perennial herbs with thick root stalk and stout stems, spreading or 

ascending, 2-3 feet long.
INDICATOR PLANTS AND METHODS OF BOTANICAL PROSPECTING 507

Tolerant

FIGURE 169. Colorado four-o'clock.

Altitude: 2,500-7,500 feet. 

Occurrence: Hillsides and rocky mesas.

Districts noted: Thompson and White Canyon, Utah; Ship Rock and Grants, 

N. Mex.; Uravan, Colo.

421588 57 8
508 CONTRIBUTIONS TO THE GEOLOGY OF URANIUM

INCHES 

r 4

L 0

i-Winged fruits

FIGURE 170. Fraxinus anomala Torr.

Family: Olive, Oleaceae.

Flowers: Four-toothed, bell-shaped flowers. Blooms in April and May. 

Leaves: Simple, smooth, rounded leaves 1-2 inches long occurring in threes. 

Fruits: Dry, winged, oblong one-seeded fruits % to 1 inch long. 

Plant: Small tree 5 to 15 feet high, with 4-angled twigs and thick simple 

leaves. Extensive root system.
INDICATOR PLANTS AND METHODS OF BOTANICAL PROSPECTING 509

Tolerant

FIGURE 171. Singleleaf ash.

Altitude: 2,000-7,000 feet.

Occurrence: Dry sandstone mesas and sandy washes in full sun. 

Districts noted : Ship Rock, N. Mex.; Thompson, San Raf ael, and Green River, 

Utah.
510 CONTRIBUTIONS TO THE GEOLOGY OF URANIUM

FIGURE 172. Hymenopappus filifolius Hook.

Family: Sunflower, Compositae.

Flowers: Several heads of tubular yellow flowers with tubes longer than lobes.

No ray flowers. Blooms in July and August. Bracts at base of head

with yellowish tips.

Leaves: Woolly basal leaves twice-divided into threadlike segments. 

Seeds: Small dry seeds with long silky hairs. 

Plant: Woolly perennial plants with leaves crowded at branching woody base

and 10 to 20-inch stalks.
INDICATOR PLANTS AND METHODS OF BOTANICAL PROSPECTING 511

FIGURE 173. Fineleaf hymenopappus.

Altitude: 3,500-8,000 feet.

Occurrence: Semiarid hills and mesas, commonly on sandstone.

Districts noted : Thompson, Utah ; Pojoaque, N. Mex.
512 CONTRIBUTIONS TO THE GEOLOGY OF URANIUM

Ray flower 

(enlarged)

FIGURE 174. Actinea acaulis (Pursh) Spreng.

Family: Sunflower, Compositae.

Flowers: Single composite head of yellow flowers on 8-inch leafless scape or 

flower stalk. Single series of ray flowers, 3-toothed, with orange 

veins. Bracts at base of flower in 2 or 3 rows, not united and 

densely hairy. Blooms from June to September.

Leaves: Basal rosette of linear leaves, % to 2 inches with entire margins, silky. 

Glands prominent.

Seeds: Dry, angled, hairy seeds crowned with 6 papery scales.

Plant: Perennials with woody base and strong taproot. Single leafless flower 

stalk with leaf rosette. Bitter, aromatic taste.
INDICATOR PLANTS AND METHODS OF BOTANICAL PROSPECTING 513

Tolerant

FIGURE 175. Stemless actinea.

Altitude: 3,500-12,000 feet. 

Occurrence: Dry rocky slopes. 

Districts noted: Thompson and San Raf ael, Utah ; Grants, N. Mex.
514 CONTRIBUTIONS TO THE GEOLOGY OF URANIUM

GLOSSARY

Awn_________ A slender bristlelike appendage on grasses.

Axil_________. The angle formed by a leaf or branch with the stem.

Bract_________ A modified leaf subtending a flower or flower cluster.

Calyx_________ The outer series of parts in a flower immediately surrounding the petals.

Corolla_______. The inner series of parts in a flower. Composed of petallike parts which may be brightly colored.

Deciduous______ Falling away at the end of the growing period; not persistent. Commonly said of plants with such leaves.

Disk-flowers____ Tubular flowers of a composite head as distinct from the 

peripheral ray flowers.

Diurnal_______ Daily; new flowers opening each day.

Irregular______ A flower in which one or more of the petals are unlike the 

rest.

Keel_________. The two anterior petals of a legume flower joined in such a 

way as to resemble the keel of a boat.

Pinnate_______. Compound (leaf) with leaflets arranged on each side of a 

common stem. Featherlike.

Punctate _ . Dotted with depressions or with translucent glands.

Raceme _ . A simple cluster of stalked flowers upon a common elongated 

stem.

Ray-flowers_____. Straplike marginal flowers of a composite.

Sepal_________. Division of the calyx corresponding to petals in the corolla.

Sessile _ Attached directly at the base; without a stalk.

Stamen_ _ . One of the pollen-bearing organs of a flower.
PLANT INDEX

Actinea acaulis............ ___...__._.__. 512, 513

Attium acuminatum.......-._____........ 434,435

Antelope bitterbrush.--___......___ 488,489

Aplopappus armeriodes.......... ____-__._ 472,473

Astereenustus........_____-______ 468,469

Astragalus aculeatus....... .__....-___ 432,433

bisulcatus..................... _____ 422,423

confertifloras. ............ ._______ 420,421

dodgianus___.......__.....____ 428,429

lonchocarpus................... .____ 426,427

missouriensis........._._........... 424,423

pattersoni........................ ... 409,414,415

preussi................................. 416,417

lenellus...-.--.......................... 430,431

thompsonae............................. 418,419

Atriplex canescens. -...................... 598,499

confertifolia............................. 496,497

B

Black greasewood-__..______._... 500,501 

Blue poisonvetch,-......................_ 420,421

C

Calochortug nuttalli... _.____,________._.___.. 436,437

Castillejainte.gr a............................ 492,493

Colorado four-o'clock_______-______ 506,507

Cottonthorn horsebrush_______.___. 484,485

Cowania stansburiana....................... 486,487

Cryptanth-. - - - - __ 448,449

Cryptanthaflava............................ 448,449

Curlycup gumweed_--._____________. 474,475

Cushion eriogonum....._.....______ 458,459

D 

Desert blazingstar.______________ 480,481

princesplume.---_-.-.________________ 440,441

Deserttrumpet...___....._________ 456,457

eriogonum.__ ...__.____.___... .. 454,455 

Dodgemilkvetch-_-..-___-________..___.___ 428,429

Elymussalina... .... . .......... .. ...... ... 462,463

Englemann pricklypear. .---_---._ _ ...... 504,505

Ephedrasp ..... .. _ _ _ _ _ ... _ _ ___ .. 502,503

Eriogonum fusiforme ... _ _ ..___.______ _ 456,457

inflatum... ____ _ _ ... __ --.-. __ _ .. 454,455

ovalifolium.. ... ....... ... . .............. 458,459

umbellatum ................................. 460,461

Euphorbia fendleri. ......................... 478,479

F

Fendler euphorbia _______________ 478,479 

Fineleaf hymenopappus... ______ _ _ __ 510,511

Four-o'clock, Colorado.------... _ ..... _ _ 507

Fourwing saltbush.... ____ ___ __ _ _ 498,499

Fraxinus anomala ... .. __ ___ . _ __ _ 508, 509

G 

Goldenweed------.-.. -------_----.--. 472,473

Grassy deathcamas.--- ____________ 438,439 

Greasewood. _______ _____ _ ... __ __ 500, 501

Grindelia squarrosa... ....................... 474, 475

421588 57 9

H Page

Hairy-pod pepper weed..._____ 444,445 

Hedysarum boreale.................. ._.... 490,491

Hoary townsendia.--.-.--------.------ 470,471

Hymenopappus filifolius.................... 510,511

I

Indian paintbrush_______________ 492,493 

Indian ricegrass. _______________ 466,467

J 

Jointfir..................................... 502,503

Lepidium lasiocarpum...................... 444,445

montanum_________________ 442,443 

Long-seeded milkvetch__________.. 426,427 

Looseflower milkvetch____________ 430,431

M

Mariposa...- - --_-_ --- -- . 436,437 

Mentzeiia muttiflora........................ 480,481

Mirabitis multiflora......................... 506,507

Missouri milkvetch______________ 424,425 

Mormon tea________ __________ 502,503 

Mountain pepperweed____________ 442,443

N 

Needleandthread._______._.-..-. 464,465

Northern sweetvetch.____________ 490,491

O 

Oenothera albicaulis......................... 452,453

caespitosa............................... 450,451

Opuntia engelmanni........................ 504,505

Oryzopsis hymenoides....................... 466,467

Paintedcup.._...................... ... 492,493

Patterson poisonvetch.._._____ _ 414,415

Plantago purshi............................. 494,495

Preuss poisonvetch________._-_____._ 416,417

Purshiatridentata. ....................... 488,489

R 

Rock goldenrod. _______________ 482,483

S

Sandmat. - . .--- - .- 478,479

Salina wildrye_____....__________ 462,463

Sarcobatusvermiculatus..................... 500,501

Segolily . ... . . 436,437

Senecio longilobus........................... 476,477

Shadscalesaltbush-.._..._................. 496,497

Silverplant 458,459

Singleleaf ash............................... 508,509

Sisymbrium altissimum..................... 446,447

Solidagopetradoria........................... 482,483

Spring milkvetch---.--.-.-..-----.---.-.. 432,433

Stanleyapinnata............................ 440,441

Stansbury cliflfrose..______....____ 486.487

Stemlessactinea --..--.-.-.-.-...-.---.. 512,513

515
516 INDEX

Page 

Stipa comata___----------__-____-_. 464,465

Sulfur eriogonum_______________ 460,461

Tapertiponion. - ._ 434,435

Tetradymiaspinosa. ......_______ 484,485

Threadleaf groundsel___________.__- 476,477

Thompson loco.____ .__________._ 418,419

Townsendia incana. -------___-______. 470,471

Tufted evening-primrose--____.-._.- 450,451

Page

Tumblemustard___-----___.-__.--- 446,447 

Two-grooved poison vetch _.-___--.- __ __.. 422,423

W 

Whitestemmed evening-primrose.------_- 452,453

Wild onion, tapertip... ........ 434,435

Woody aster..-__--------._. _ 468,469

Woolly indianwheat -.--_--.---------.--- 494,495

Z

Zigadenus gramineus.._.___--._.-.. 438,439

o