Dating a 20th-Century Fault, 

Elk Summit Talus Apron, 

Big Creek Area, Valley County, Idaho 

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Dating a 20th-Century Fault, 

Elk Summit Talus Apron, 

Big Creek Area, Valley County, Idaho 

By B.F. Leonard and Roger Rosentreter 

U.S. GEOLOGICAL SURVEY BULLETIN 2101 

U.S. GOVERNMENT PRINTING OFFICE, WASHINGTON: 1994 
U.S. DEPARTMENT OF THE INTERIOR 

BRUCE BABBITT, Secretary 

U.S. GEOLOGICAL SURVEY 

Gordon P. Eaton, Director 

For sale by U.S. Geological Survey, Map Distribution 

Box 25286, MS 306, Federal Center 

Denver, CO 80225 

Any use of trade, product, or firm names in this publication is for descriptive purposes only and 

does not imply endorsement by the U.S. Government 

Library of Congress Cataloging-in-Publication Data 

Leonard, B. F. (Benjamin Franklin), 1921-

Dating a 20th-century fault, Elk Summit talus apron, Big Creek area, Valley 

County, Idaho I by B.F. Leonard and Roger Rosentreter. 

p. cm.-(U.S. Geological Survey bulletin: 2101) 

Includes bibliographical references. 

Supt. ofDocs. no.: I 19.3:2101 

1. Fault (Geology)-Idaho-Valley County. 2. GeochronometryIdaho-Valley County. 3. Lichen-Idaho-Valley County. 

I. Rosentreter, Roger. II. Title. III. Series. 

QE75.B9 no. 2101 

[QE606.5.U6] 

557.3 s-dc20 94-21145 

[551.8'7'09796] CIP 
CONTENTS 

Abstract................................................................................................................................ 1 

Study Area .. ............ .......... .. .......... ... . . .. .... ... . .. ...... .. . . . . ........ ......... ........... ..... ... . . . . ........ .......... 1 

Lichenometry at Elk Summit . . . . . . . . . .. . . . . . . . . . .. . . . . . . . . . .. . . . . . . . . . . .. . . . .. . . . . .. . . . . . . . . . .. . . . . . . . . . . .. . . . . . . . . . .. . . . . . 3 

Lichenometry in Cemeteries . . . . .. . . . . .. . . . . . .. . . . . . . . . . . . . . . . . . . . .. . . . . .. . . . . . . . . . .. . . . . . . . . . .. . . . . . . . . . . .. . . . . . . . . . .. . . . .. 7 

Dating the Elk Summit Fault by Lichenometry . . . .. . . . . ... ........ ............ ........ ... ........... ... ........ .. 8 

Dating the Elk Summit Fault by Aerial Photography ........... ............ ... ........ ........... .. . .. ... . . . .. 10 

Seismic Effects . . . . . . . .. . . . . .. . ... . . . . . .. . ... . . . . . . .. . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . .. . .. . . . . . . .. . .. . . . . . . . . . . . . .. . . . .. . . .. . . . . . .. 11 

Conclusion ........................................................................................................................... 12 

References Cited.................................................................................................................. 12 

FIGURES 

1. Index map to area of Elk Summit, central Idaho......................................................................................................... 1 

2. Photograph showing trace of the Elk Summit fault in 1991 ... . . . . ......... .. ... ...... .. . ................. .. . . . ............... ..... .. ..... ........ 2 

3. H-mode very low frequency (VLF) profiles, Elk Summit talus apron........................................................................ 3 

4. Diagram showing Fraser-filtered very low frequency (VLF) inclinations, Elk Summit talus apron.......................... 4 

5. Diagram showing transects for lichenometry, Elk Summit talus apron...................................................................... 6 

TABLES 

1. Largest thalli of Rhizocarpon geographicum, Elk Summit talus apron...................................................................... 5 

2. Largest thalli of Lecidea atrobrunnea, Elk Summit talus apron................................................................................. 5 

3. Lichen species at Elk Summit and their relative abundance....................................................................................... 6 

4. Climatic data for montane communities near Elk Summit......................................................................................... 7 

5. Frequency of Rhizocarpon geographicum and Lecidea atrobrunnea on cemetery stones......................................... 8 

6. Rhizocarpon geographicum on cemetery stones......................................................................................................... 9 

7. Lee idea atrobrunnea on cemetery stones.................................................................................................................... 10 

8. Lichen species on the cemetery stones of the McCall and Finnish cemeteries and their relative abundance............. 10 

III 

Dating a 20th-Century Fault, Elk Summit Talus Apron, 

Big Creek Area, Valley County, Idaho 

By B .F. Leonard 1 and Roger Rosentreter2 

ABSTRACT 

A young fault cuts obliquely across the talus apron near 

Elk Summit in central Idaho. Twenty-five or thirty years ago, 

the fault was marked by a bare, brown, east-trending scarp 

that slashed across talus covered with lichens. The scarp, 

extending several hundred meters from a hinge point near Elk 

Summit, showed at its east end a maximum displacement of 

about 1 m, south block down, scarp dip perhaps 60°-70° S. 

The scarp has since degenerated to a narrow, discontinuous 

bench on which the talus blocks have few lichens. 

Comparative lichenometry of Rhizocarpon geographicum 

and Lecidea atrobrunnea from talus blocks at Elk Summit 

and headstones in local cemeteries indicates that the fault 

formed sometime between the 1960's and the first decade of 

the century. Aerial photographs indicate that, though the fault 

may have begun to develop before 1946, its surface expression did not become conspicuous until sometime between 

1954 and 1964. We believe that surface expression of the fault 

is earthquake related. No major earthquake epicenters have 

been reported from the Elk Summit area, but effects of the 

August 1959 earthquake at Hebgen Lake, Montana, were felt 

at an intensity VI (modified Mercalli scale) within 9-30 km 

of Elk Summit, 320 km distant from Hebgen Lake. 

Accordingly, the most likely date of the fault near ElkS ummit 

is 1959. 

STUDY AREA 

A young fault cuts the talus apron near Elk Summit 

(fig. 1), a road pass at 2,643 m elevation in the Wolf Fang 

Peak 7.5-minute quadrangle, Valley County, Idaho. When 

Leonard, the senior author, first recognized the fault 25 or 30 

1 U.S. Geological Survey, MS 905, Box 25046, Federal Center, Denver, Colorado 80225. 

2Bureau of Land Management, 3380 Americana Terrace, Boise, Idaho 

83706. 

years ago, it was marked by a conspicuous, bare, brown, 

east-trending scarp that slashed across talus covered with 

lichens. The scarp, extending several hundred meters from a 

hinge point about 100 m east of Elk Summit, showed at its 

east end a maximum displacement of about 1 m, south block 

down, scarp dip perhaps 60°-70° S. Leonard thought at the 

time that the growth rate of the large colonies of dark lichens 

might be useful for dating the fault, but, knowing little about 

lichens and feeling pressed for time to finish some geologic 

mapping, he failed to collect them or to photograph the fault 

scarp. When next he visited the area, in 1991, he found that 

the scarp had degenerated to a narrow, discontinuous bench, 

1-2 m wide, locally showing small bits of brownish rubble 

as well as sparsely lichen bearing talus slabs of 1-3 dm size, 

a few larger blocks from relatively stable talus upslope from 

the bench, and a little talus derived from recent rockfalls. 

The inner edge of the bench was defined by an almost 

continuous train of meter-size and smaller talus blocks 

liberally covered with dark lichens. The train of dark blocks, 

unimpressive at close quarters, is clearly visible at a distance 

(fig. 2). 

To Lewiston 

Chamberlain 

Basin • 

0 Warren 

eElk Summit 

OBigCreek 

(Edwardsburg) 

OYellow Pine 

• Meadow Creek 

Lookout 

50 KILOMETERS 

Figure 1. Index map to area of Elk Summit, central Idaho. Secondary roads not shown. Open circles represent settlements; filled 

circles indicate other geographic features. 
2 DATING A 20th-CENTURY FAULT, BIG CREEK AREA, IDAHO 

Figure 2. Trace of the Elk Summit fault in 1991. View from the ridge 0.8 km south of the talus 

apron. Elk Summit shows as a white patch of widened road near the left edge of the photograph. 

The distant view of the train of dark blocks suggests 

that the train is separated into two segments, the shorter 

eastern one offset less than 20 m upslope from the longer 

western one. The offset, hardly noticeable to an observer on 

the talus apron, shows plainly on some pairs of 1:20,000-

scale aerial photographs viewed stereoscopically (Richard 

B. Taylor, U.S. Geological Survey, oral commun., October 

1992). The offset might be attributed to actual left -lateral 

offset along a northeast-striking line (a fault trace?) that 

Taylor saw distinctly on the photographs, or it might be 

attributed to independent development of the eastern segment of the dark train. In the present study, we treat the dark 

train and the narrow bench that accompanies it as features 

that for practical purposes mark a single fault. 

The now unexposed fault can be detected by measurement of the local electromagnetic field. Four H-mode very 

low frequency (VLF) traverses along our lichen transects 

(described later) were run by means of a standard resistivity 

device, the Geonics EM-16, tuned to the Lualualei, Hawaii, 

radio transmitter, frequency 23.4 kHz. The measured inclinations (fig. 3) show no crossovers indicative of a strong 

conductor, but the contoured Fraser-filtered inclinations 

(fig. 4) show trends of low positive values that indicate a 

weak conductor beneath the fault bench or 5-15 m south of 

it. Higher electrical conductivity may result from increased 

pore water in the fault zone. The low positive values coincide 

with or are parallel to the fault bench; they are not parallel to 

the topographic contours sketched in figure 5. Better 

distance control for the VLF traverses gives an east strike for 

the fault trace, instead of the east-southeast strike sketched in 

figure 5, in which the relative positions of topographic 

contours and fault bench were approximated from elevations 

obtained using a pocket altimeter. The thickness of talus on 

the apron cannot be reliably estimated from the H-mode 

data, and the interpretation of conductors(?) north of the fault 

bench is uncertain, owing to the wide spacing of the VLF 

traverses. For the pros and cons of applying the simple 

numerical technique of date filtering introduced by Fraser 

(1969), see McNeill and Labson (1991, p. 614). 

Curiosity about a fault that looked as if it had cut a talus 

apron "only yesterday" led us to try dating the Elk Summit 

fault by lichenometry. The fault is minuscule in comparison 

with other faults that are present within a few kilometers of 

the summit. Many of these faults strike north, parallel to or 

within the Eocene Profile-Smith Creek dike swarm 

(Leonard and others, 1968, p. C4-C5; Leonard and Marvin, 

1982, fig. 1, table 1), a cross section of which is exposed on 

the ridge north of the talus apron. Talus from the dikes and 

the intervening screens of variably granulated, mylonitized, 

and granoblastic granite of the Idaho batholith forms the 

apron, whose largest dimensions are about 1,000 by 250 m. 

The blocks of the apron are mostly decimeters to 1-2 m in 

diameter, equant to slabby, without brownish, iron-stained, 

centimeter- to decimeter-size fragments of the sort found on 

parts of the fault bench and just downslope from it. The 

western half of the apron is devoid of trees and shrubs. We 

confined our lichen study to this area. 
LICHENOMETRY AT ELK SUMMIT 3 

N s 

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EXPLANATION 

0 --Inclination, in percent 

~- - Quadrature, in percent 

5 6 7 

STATION 

8 9 10 11 12 13 14 

10 METERS 

Figure 3. H-mode very low frequency (VLF) profiles, Elk Summit talus apron. Locations of transects are shown in figures 4 and 5. Inclination is that of the polarization ellipse of the electromagnetic field. Quadrature is a measure of the phase lag between the primary and 

secondary magnetic fields. 

LICHENOMETRY AT ELK SUMMIT 

Lichenometry-the measurement of the size of a 

lichen thallus in order to estimate the growth rate or age of 

the lichen-has been widely used to date Quaternary 

geomorphic features in North America and Europe. When 

lichenometry is applied to the dating of geomorphic features, it is customary to establish a suitable reference base 

by measuring the size of lichens on nearby, historically 

dated features such as cemetery monuments and buildings. 

The lichen commonly measured is Rhizocarpon geographicum sensu lato, a slow-growing, long-lasting areolate yellow lichen that has not always been discriminated from the 

rest of the Rhizocarpon subgenus. The Rhizocarpon used in 

our study has the characteristics given for Rhizocarpon 

geographicum (L.) DC. (Poelt, 1988; Benedict, 1988). 

We also used the dark-brown to black, areolate lichen 

Lecidea atrobrunnea, which is larger and more abundant 
4 

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DATING A 20th-CENTURY FAULT, BIG CREEK AREA, IDAHO 

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Figure 4 (left column). Fraser-filtered very low frequency (VLF) 

inclinations (in percent), Elk Summit talus apron. 

than Rhizocarpon geographicum at Elk Summit. Lecidea 

atrobrunnea has occasionally been used for the dating of 

geomorphic features. Carrara and Andrews (1973) gave data 

on thallus size, percentage of cover, and growth rate of this 

lichen, among others, in the San Juan Mountains, Colorado. 

Neither Rhizocarpon geographicum nor Lecidea atrobrunnea is ideally suited for dating geomorphic features less 

than a century old. Faster growing lichens such as Xanthoria 

elegans, used in the Canadian Rockies by Osborn and Taylor 

(1975), and Pseudephebe minuscula, used at Spitsbergen by 

Werner ( 1990), are more appropriate. At Elk Summit, X. 

elegans is rare, and P. minuscula has not been found. 

Rhizocarpon geographicum and Lecidea atrobrunnea 

are present separately or together, with or without other 

lichens in small amount, on talus blocks of the Elk Summit 

apron. No one of the rock types-rhyolite, latite, quartz 

latite, and granite-seems to be favored as a host for the 

lichens. However, the percentage of cover given by the two 

major species varies widely from one talus block to another. 

Estimated roughly for the area transected, the percentage of 

cover is about 1-15 percent for R. geographicum and about 

3-40 percent (commonly 15-20 percent) for L. atrobrunnea 

upslope from the fault bench, but less than 1 percent for both 

species on the fault bench. Percentage of lichen cover has 

been used by some workers to estimate the age of geomorphic features, but our semiquantitative data are not suitable 

for that purpose. Talus blocks from two obviously quite 

recent rockfalls are barren of lichens; our lichen transects did 

not cross these rockfalls. 

Four 70-meter-long transects spaced 100m apart were 

laid out across the fault trace in 1992 (fig. 5). A 6-meter-wide 

strip along each transect was scanned for large thalli of 

Rhizocarpon geographicum and Lecidea atrobrunnea, 8-15 

of these were measured, and the 5 largest thalli of each species were accepted as indicators of maximum growth. The 

dimension measured is the diameter of the largest circle 

inscribable within a discrete thallus, one occurring in isolation or within a coalescing colony. The procedure for measurement is that recommended by Locke and others (1980). 

The lichen thalli that we measured showed no evidence of 

abrasion; the talus blocks were virtually in place before 

lichens grew on them. None of the blocks carrying measured 

lichens was a "bird rock," a perch on which chemical 

contamination from leached bird droppings might have 

promoted lichen growth. 

The results for Rhizocarpon geographicum are given in 

table 1. At one standard deviation s, mean thallus size of R. 

geographicum does not differ significantly on upslope segments of the four transects (table 1). One thallus, diameter 54 

mm on transect 4, might be taken as exceptionally large; if it 

is disregarded, thallus size on the upslope transect is 28-41 
LICHENOMETRY AT ELK SUMMIT 5 

Table 1. Largest thalli of Rhizocarpon geographicum, Elk Summit talus apron, Big Creek area, Valley County, Idaho. 

Thi!llys diruneter (millimeter:!) 

n Range Mid-range Median x±s 

Transect 1 

Upslope segment 5 33-41 37 38 38.0±3.1 

Fault bench 5 7-8 8 8 7.8±0.4 

Downslope segment 5 32-45 38 35 37.2±6.0 

Transect 2 

Upslope segment 5 36-45 40 38 39.4±3.4 

Fault bench 5 6-10 8 7 7.4±1.7 

Downslope segment 5 26-39 32 32 31.8±4.9 

Transect 3 

Upslope segment 5 32-48 40 40 39.0±6.3 

Fault bench 5 7-10 8 10 9.0±1.4 

Downslope segment 5 24-38 31 31 29.8±5.6 

Transect4 

Upslope segment 5 32-54 43 34 38.6±9.4 

Fault bench 5 7-9 8 8 7.8±0.8 

Downslope segment 5 32-41 36 38 37.4±3.9 

Combined data 

Upslope segment 20 32-54 43 38 38.8±5.6 

Fault bench 20 6-10 8 8 8.0±1.3 

Downslope segment 20 24-45 34 32,33 34.1±3.8 

Table 2. Largest thalli of Lecidea atrobrunnea, Elk Summit talus apron, Big Creek area, Valley County, Idaho. 

Thidlus diameter (millimeters) 

n Range Mid-range Median x±s 

Transect 1 

Upslope segment 5 59-82 70 62 65.4±9.5 

Fault bench 3 5-33 19 7 15.0±15.6 

Downslope segment 5 20-30 25 25 25.0±3.5 

Transect 2 

Upslope segment 5 66-89 78 72 75.8±8.9 

Fault bench 5 13-25 19 18 18.6±4.6 

Downslope segment 5 60-73 67 62 66.0±6.4 

Transect 3 

Upslope segment 5 68-92 80 72 76.8±9.6 

Fault bench 5 12-26 19 12 14.8±5.2 

Downslope segment 5 46-78 62 62 60.4±12.3 

Transect4 

Upslope segment 5 90-110 100 93 98.2±10.0 

Fault bench 5 12-28 20 15 17.0±6.3 

Downslope segment 5 95-110 102 100 102.0±7.6 

Combined data 

Upslope segment 20 59-110 84 72,80 79.0±15.0 

Fault bench 18 5-33 19 15 16.5±7.2 

Downslope segment 20 20-110 65 62 63.4±29.0 
6 DATING A 20th-CENTURY FAULT, BIG CREEK AREA, IDAHO 

CJ) 2,750 

a:: 

LU 

~ 2,700 

:2: 

z 

;; 2,650 

0 

~ 2,600 LU 

-I 

LU 

2,550 

s 

- 700--- ---2 

N 

PROFILE 

Contour interval 50 m (approx.) 

Figure 5. Transects for lichenometry, Elk Summit talus apron. 

The profile for transect 1 is representative. 

mm, x ±s=33.4±4.8 mm. We doubt that the exception should 

be made. The combined data for thallus size on upslope 

segments of the four transects are accepted as reliable at 

x ±s=38.8±5.6 mm. 

The maximum thallus size of Rhizocarpon geographicum on the fault bench is 8.0±1.3 mm, its coefficient of variation is the same as that for specimens measured upslope, 

and at three standard deviations there is no overlap in mean 

size. The lichen is not only sparser on the fault bench, it is 

much smaller-about one-fifth the size of thalli measured 

upslope. 

Data for Lecidea atrobrunnea are given in table 2. This 

lichen is not only more abundant than Rhizocarpon 

geographicum, its thallus is about twice as large and, in 

proportion, shows greater variation. For L. atrobrunnea, the 

coefficient of variation is about 20-45 percent; for R. 

geographicum, it is about 10-15 percent. A few thalli of L. 

atrobrunnea approach or exceed 150 mm in diameter. These 

exceptionally large thalli have been excluded from 

consideration in table 2. 

The combined data (table 2) for thallus size of L. 

atrobrunnea on the fault bench show a range from 5 to 33 

mm. Within this range, 60 percent of the thalli are 12-18 mm 

in diameter. We later refer to this range as the common 

range. It has, for n=11 thalli, a midrange of 15, a median of 

14, and x±s=14.0±2.0 mm. The common range assumes 

some importance when we compare the data from Elk 

Summit with those obtained from cemetery stones of the 

region. 

Owing to steepness of slope, the upslope, fault bench, 

and downslope segments of the transects may not yield 

equally reliable measurements of lichen size. Talus blocks 

upslope from the fault bench present no problem because the 

blocks constitute a single population. However, some slight, 

local contamination of the on-bench assemblage by talus 

blocks displaced from above, and of the below-bench 

assemblage by blocks displaced from the bench, is 

inevitable. Block size, position, and degree of weathering are 

aids in classifying lichen-bearing blocks as essentially in 

place or transported, but the application of these criteria is 

judgmental. 

Paul Carrara (written commun., 1993) presented the 

hypothesis that two populations of lichens, differing in age, 

are present on the fault bench. He advanced this hypothesis 

as support for the two episodes of faulting discussed in the 

Conclusion of our report. However, the low coefficient of 

variation (12 percent) of the maximum thallus size of 

Rhizocarpon geographicum speaks against the hypothesis. 

For Lecidea atrobrunnea, the case is not so clear; the 

corresponding coefficient of variation is large ( 44 percent). 

By measuring at least 100 large thalli of this lichen one might 

find evidence of more than one size-age population, but we 

doubt that so many representatives are available for 

measurement. Thus, the Carrara hypothesis remains to be 

tested. 

Other lichen species from the Elk Summit talus apron 

are given in table 3. The nomenclature follows that of Egan 

Table 3. Lichen species at Elk Summit, Big Creek area, Valley 

County, Idaho, and their relative abundance. 

Lichen species Abundance 

Acarospora chlorophana Rare. 

Acarospora sp. (dark) Common. 

Aspicilia cinerea Common. 

Aspicilia gibbosa Common. 

Aspicilia sp. Abundant. 

Candelariella vitellina Rare. 

Lecanora sp. Rare. 

Lecidea atrobrunnea Abundant. 

Lecidea tessellata Common. 

Rhizocarpon geographicum Common. 

Rhizoplaca melanophthalma Rare. 

Tremolecia atrata Rare. 

Umbilicaria hyperborea Rare. 

Umbilicaria krascheninnikovii Rare. 

Xanthoparmelia sp. Rare. 

Xanthoria elegans Rare. 
LICHENOMETRY IN CEMETERIES 7 

(1987). Vouchers of these lichens are in the Snake River 

Plains Herbarium at Boise State University, Boise, Idaho. 

LICHENOMETRY IN CEMETERIES 

Before we interpret the data for thallus size on the Elk 

Summit talus apron, we present for comparison data on 

Rhizocarpon geographicum and Lecidea atrobrunnea from 

headstones in cemeteries of the region. Unfortunately, there 

are no dated, lichen-bearing features near Elk Summit. The 

three graves found at Big Creek (fig. 1) have concrete or 

metal markers. The cemeteries at Warren and Yellow Pine 

have few graves, and few of these have stone markers. 

Cemeteries in the McCall area, 60 km southwest of Elk Summit, have some selection of stones useful to the lichenometrist. Even so, these cemeteries are not favorably situated, in 

elevation, climate, or stone type, to provide the extensive 

data base that we hoped to get for Rhizocarpon geographicum and Lecidea atrobrunnea. 

Cemetery elevations and locations are given in the 

notes accompanying table 6 (later). The cemetery at Warren, 

elevation 1,850 m, is the highest; it is nearly 800 m lower 

than Elk Summit, elevation 2,643 m. The other cemeteries 

are 1,100-1,400 m lower than Elk Summit. The scarcity of 

Rhizocarpon geographicum in cemeteries of the McCall 

area, the small size of its thalli, and the absence of this lichen 

from stones in the cemetery at Meadows suggest that the 

lower limit of elevation for R. geographicum is between 

1,200 and 1,500 m under the climatic conditions prevailing 

here, at lat 45° N., during the last 100 years. 

Climate at the cemeteries is broadly similar, in spite of 

differences in elevation (table 4). The montane climate at 

Warren and Big Creek is similar to the subalpine climate of 

Elk Summit, the high pass between those settlements, but the 

differences may be considerable. At Elk Summit, the 

mid-winter temperature may not be much lower than at Big 

Creek, but snow accumulates earlier in the fall (late August 

to late September) and lasts about a month longer in the 

spring (late June to late July). Summer days are about 5°C 

cooler, and many of them are windy. Artificial watering of 

the McCall, Finnish, and Meadows Valley cemeteries keeps 

them damper than the Elk Summit talus apron and, with 

some shade, promotes the growth of foliose lichens. Rhizocarpon geographicum and Lecidea atrobrunnea on the cemetery stones are restricted to the cooler, less sunny north and 

east sides, as are most of the foliose lichens. One crustose 

lichen, Aspicilia calcarea, grows profusely on the tops and 

west sides of the stones. 

Much stone used in the cemeteries after 1920 is chemically comparable to talus rock at Elk Summit: various red 

and gray granites, red granite gneiss, dark-gray hornblende 

quartz diorite and hornblende-biotite quartz diorite, and 

minor syenite and anorthosite in the cemeteries; rhyolite, 

latite, quartz latite, and deformed granite at Elk Summit. 

Texturally, however, there are differences: the cemetery 

stones are mostly medium to coarse grained; the talus rock is 

mostly fine grained, even where phenocryst bearing. The 

unfinished surfaces of cemetery stones less than 50-60 years 

old are virtually unweathered; the surfaces of talus blocks 

range from smooth to slightly rough, all blocks except those 

from very recent rockfalls show at least some weathering 

(usually as bleaching, or as limonitic staining), and thin 

weathering rinds have developed on some. Rhizocarpon geographicum and Lecidea atrobrunnea do not grow on the 

sanded or polished surfaces of cemetery stones; some other 

lichen species do. 

The record for cemetery stones suitable for our 

lichenometry is a short one, about 70 years. Nearly all the 

stones bearing death dates earlier than the mid-1920's are 

gray or white marble, commonly lichen bearing but devoid 

of Rhizocarpon geographicum and Lecidea atrobrunnea. 

Considered as a whole, the cemeteries have no more than 10 

or 15 percent of these old marble stones. 

Another problem in the use of cemetery stones for 

lichenometry is also cultural. Most of the local graves are 

Table 4. Climatic data for montane communities near Elk Summit, Big Creek area, Valley County, Idaho. 

[Data supplied by Idaho State Climatologist, written commun., September 1992] 

Elevation Annual Mean January Mean July Years of Length of 

Community (meters) precipitation temp. temp. record record 

Warren 1,800 67.4±15.8 -6.9±1.2 13.6±0.5 1962-1991 30 

Big Creek 1,753 72.9±14.9 -6.8±1.6 14.7±0.4 1952-1967 16 

Yellow Pine 1,451 66.1±17.1 -6.5±1.3 15.4±0.5 1971-1987 20 

1989-1991 

McCall 1,527 68.4±12.4 -6.6±1.7 16.9±0.5 1930-1955 61 

1957-1991 

New Meadows1 1,213 61.3±11.9 -7.3±2.0 17.3±0.7 1962 1991 30 

1

New Meadows is 3 km west of Meadows. 
8 DATING A 20th-CENTURY FAULT, BIG CREEK AREA, IDAHO 

Table 5. Frequency of Rhizocarpon geographicum and Lecidea 

atrobrunnea on cemetery stones. 

[See table 6 for elevation and location of cemeteries] 

Number of stones Total number 

bearing measurable of stones Percent bearing 

thalli examined the lichen 

Rhizocarpon geographicum 

Warren 4 8 50 

Yellow Pine 1 5 20 

McCall 12 380 3 

Finnish 8 -250 3 

Spink 3 62 5 

Meadows 0 462 0 

Lecidea atrobrunnea 

Warren 0 8 0 

Yellow Pine 0 5 0 

McCall 20 380 5 

Finnish 27 -250 11 

Spink 4 62 6 

Meadows 0 462 0 

marked with headstones but no footstones for the individual 

graves in a plot; many headstones commemorate two members of a family and thus may bear two widely different death 

dates; and, judged from stone type and lettering, some stones 

were set years after the death date marked on them. Actual 

setting dates were sought but not found. 

Rhizocarpon geographicum is sparse and small on 

stones in the cemeteries. Lecidea atrobrunnea is roughly 

twice as abundant and twice as large. Most prevalent is an 

areolate lichen that looks somewhat like L. atrobrunnea in 

form; it is Aspicilia calcarea, which is gray and prefers a calcareous substrate. We have not recognized A. calcarea at Elk 

Summit; there, all substrates are noncalcareous. 

The frequency of Rhizocarpon geographicum and 

Lecidea atrobrunnea on cemetery stones, expressed as percent of stones bearing measurable thalli, is shown in table 5. 

(The frequency so expressed is not equivalent to percent of 

lichen cover, which-too low to be reliably measured-may 

be of the order of 1x1o-2-1x1o-5 percent.) The marked 

decrease in the frequency of R. geographicum from Warren 

to the McCall area suggests that Warren and Yell ow Pine, 

closer to Elk Summit, are more favorable for the growth of 

this lichen. Nevertheless, the growth rates calculated for the 

Warren samples differ but little from the rates calculated for 

samples from the McCall and Finnish cemeteries. 

The scarcity of Rhizocarpon geographicum and 

Lecidea atrobrunnea on cemetery stones severely limits the 

collection of data on thallus size. Data for these lichens are 

given in tables 6 and 7. Some stones carry one of the two species but not the other; some stones carry both species. The 

absence of R. geographicum from stones bearing death dates 

later than 1959 or 1963 (?) suggests that this lichen may take 

about 30 years to become established and grow to detectable 

size in the cemeteries. Small thalli of L. atrobrunnea are 

difficult to identify and for that reason were not sought. 

Other lichens in the cemeteries are listed in table 8. 

DATING THE ELK SUMMIT FAULT 

BY LICHENOMETRY 

Our first trial is a direct and simple one, that of matching the size of the largest thalli of Rhizocarpon geographicum on the fault bench and in the cemeteries. On the fault 

bench, it is 6-10 mm, x ±s=8.0±1.3, n=20 (table 1, combined data). The closest size match, given by the 1932 stone 

at Warren, is 7-10 mm, x ±s=8.0±1.4, n=5 (table 6). This 

would give a single date for the fault, 1932. 

Matching for Lecidea atrobrunnea is not so simple 

because the size of the largest thalli on the fault bench has a 

wide range, 5-33 mm, x ±s=16.5±7.2, n=18 (table 2, combined data). The common range, however, is 12-18 mm, 

x ±s=14.0±2.0, n=11. We think it appropriate to seek a 

match based on the common range. At the cemeteries, a 

close match is 9-21 mm, median 14 (table 7, entry B), death 

dates on stones 1919-1951. We now have an estimate of the 

range of possible dates for the fault. 

Growth-rate curves for Rhizocarpon geographicum and 

Lecidea atrobrunnea from the cemeteries cannot be constructed, owing to the scattering of data points given by 

highly discrepant dual death dates incised on many stones. 

Therefore, for R. geographicum we use growth rates from 

the few stones that have singular death dates or a pair not 

widely different. Growth rates so based are 0.12 or 0.13 mm 

per year (table 6, entries A and B). If we accept the value 

0.13±0.04 because it has a wider range, and if we also take 

into account the standard deviation of the mean size of R. 

geographicum on the fault bench, the dates estimated for the 

fault range from 1913 to 1936, mean 1925±7. 

Growth rates for Lecidea atrobrunnea in the cemeteries 

have a wide range, even if we eliminate from consideration 

the rates based on thalli smaller or larger than those in the 

range common for Elk Summit. The mean growth rate for 

thalli above the common range is not significantly different, 

at one standard deviation, from the mean growth rate for 

thalli in the common range (table 7, entries Band C); either 

value is usable. We shall use 0.28±0.06 mm per year, the 

average obtained by weighting the B and C values according 

to the number of stones bearing the lichen. Taking into 

account the standard deviation in thallus size of L. atrobrunnea on the Elk Summit fault bench, as well as the standard 

deviation of the growth rate, we estimate the dates for the 

fault to be 1919 to 1957, mean 1940±12. 
DATING THE ELK SUMMIT FAULT BY LICHENOMETRY 

Table 6. Rhizocarpon geographicum on cemetery stones. 

Cemetery 

Warren 

Yellow Pine 

McCall 

Finnish 

Spink 

Meadows 

Death dates 

on headstones 

1920--1936 

1920 

1932 

1938 

1923-1959 

1934, 1946 

1943 

1919-1947 

1918-1942 

Number of Number of 

stones bearing measured largest Thallus diameter (millimeters} 

the lichen thalli per stone Range Midrange Median X±s 

4 2-5 1.5-13 7 5, 7 

1 5 3-13 8 5 6.2±3.9 

1 5 7-10 8 7 8.0±1.4 

5 5-8 6 5 5.8±1.6 

12 1-5 2-14 8 6, 7 

1 5 7-14 10 8 9.6±3.2 

1 3 4-6 5 5 5.0±1.0 

8 1-2 2-6 4 3 

3 2-6 4 

0 

Growth rate summary (in millimeters per year) 

n Range Midrange 

9 

Growth rate 

(millimeters 

per year) 

0.12 

0.13 

0.11 

0.17, 0.21 

0.10 

Median x±s 

A. Values from all individual stones (in calculating x, 5 0.10--0.21 0.16 0.13 0.13±0.04 

death dates averaged for stone having two dates) 

B. Values from individual stones having single death date 4 0.10--0.13 0.12 o:11, 0.12 o.12±0.01 

Description of cemeteries 

Warren Cemetery, Warren. Elevation 1,850 m, 150 m northeast of road (main street) and 45 m above it. Warren quadrangle. Moderate 

shade. Death dates on headstones 1900-1988; oldest death date on wooden markers 1870. 

Pioneer Cemetery, Yellow Pine. Elevation 1,437 m, east bank of Johnson Creek, 1.0 km south-southwest of Yellow Pine Post Office. 

Yellow Pine quadrangle. No shade. Death dates on grave markers not recorded in field notes; 5 headstones, 17 markers of concrete or 

metal. 

McCall Cemetery, McCall. Elevation 1 ,539 m, Mission Street, 1.0 km south of East Lake Street {main street). or 0.6 km north of 

airport. McCall quadrangle. Much shade. Death dates on headstones 1907-1992. 

Finnish Memorial Cemetery. Elevation 1,524 m, Farm to Market Road, 9.8 km north of Roseberry, a hamlet 30 km south-southeast of 

McCall. Lake Fork quadrangle. Little shade. Death dates on headstones 1904-1992. 

John Spink Memorial Cemetery. Elevation 1,500 m, Farm to Market Road, 7.4 km north of Roseberry. Lake Fork quadrangle. Little 

shade. Death dates on headstones 1900--1991. 

Meadows Valley Cemetery, Meadows. Elevation 1,210 m, just east of Cemetery Road, 2.2 km north of Highway 55, Meadows 

quadrangle. Death dates on headstones 1886-1991. 

So far, we have adhered as closely as possible to the 

currently recommended practice in lichenometry: base estimates of age on the mean diameter of the five largest thalli. 

Formerly, age estimates were based on the size of the single 

largest thallus. It is instructive to revert to the older practice 

to see what it gives for the age of the fault when we use 

Rhizocarpon geographicum. The largest thallus on talus of 

the fault bench has a diameter of 10 mm (table 1, combined 

data). The largest thallus in the cemeteries has a diameter of 

14 mm; it is on a stone bearing two death dates, and the calculated growth rates are 0.24 and 0.30 mm per year (table 6, 

McCall cemetery, dates 1934 and 1946). Obviously one of 

the growth rates is specious, but we do not know which. 

Therefore, the estimated date of the fault is either 1950 or 

1959. Both dates are credible, the latter more so when we 

recall that the fault scarp looked fresh in the mid-1960's. 

Lee idea atrobrunnea, treated in the same way, gives a 

much older date. The largest thallus on talus of the fault 

bench has a diameter of 33 mm (table 2, combined data). The 

largest thallus in the cemeteries has a diameter of 26 mm 

(table 7, entry C). This thallus is on the stone that also bears 

the largest Rhizocarpon thallus, the death date on the stone is 
10 

0 0 

DATING A 20th-CENTURY FAULT, BIG CREEK AREA, IDAHO 

00 

VI 

..... 

..... 

..... 

II") 

0'1 

d: 

..... 

0'1 

..... 

N 

N 

0 

N 

0 

N 

II") 

('f') 

0'1 

:b 

..... 

0'1 

-

Q) 

~ 8 

8 

Table 8. Lichen species on the cemetery stones of the McCall 

and Finnish cemeteries and their relative abundance. 

Lichen species 

Acarospora chlorophana 

Acarospora sp. (brown) 

Aspicilia calcarea 

Bacidia sp. 

Caloplaca holocarpa 

Candelariella rosulans 

Lecanora muralis 

Lecanora sp. 

Lecidea atrobrunnea 

Melanelia subelegantula 

Physcia caesia 

Physcia sp. 

Rhizocarpon geographicum 

Rhizoplaca chrysoleuca 

Rhizoplaca melanophthalma 

Staurothele clopimoides 

Toninia caeruleonigricans 

Umbilicaria hyperborea 

Umbilicaria krascheninnikovii 

Umbilicaria virginis 

Xanthoria elegans 

Xanthoria fallax 

Xanthoria polycarpa 

McCall 

Absent 

Rare 

Common 

Common 

Rare 

Common 

Common 

Rare 

Common 

Common 

Rare 

Rare 

Common 

Absent 

Rare 

Absent 

Absent 

Rare 

Common 

Absent 

Absent 

Rare 

Rare 

Finnish 

Rare. 

Rare. 

Common. 

Common. 

Rare. 

Common. 

Abundant. 

Rare. 

Common. 

Common. 

Rare. 

Rare. 

Common. 

Common. 

Common. 

Common. 

Rare. 

Common. 

Common. 

Common. 

Common. 

Abundant. 

Common. 

1935, and the calculated growth rate of L. atrobrunnea is 

0.46 mm per year. From this growth rate, the estimated date 

of the fault is 1920. 

In summary, the comparative lichenometry of Rhizocarpon geographicum and Lecidea atrobrunnea gives a 

range of dates, 1913 to 1959, for the fault that cuts the Elk 

Summit talus apron. The precision of estimate for the 

limiting dates is not high. Inasmuch as the range is 

1913-1919 for the earliest dates and 1950-1959 for the latest, it is reasonable to suppose that some few years might be 

subtracted from 1913 and added to 1959, placing the earliest 

date of faulting in the first decade of the century and the latest in the 1960's. Lichenometry and geologic observation are 

in agreement: the fault is young, formed sometime after settlements were established at Warren and Big Creek. 

Comparative lichenometry also indicates that talus upslope from the fault trace (excluding talus from recent rockfalls) is about 250-300 years old. This unexpectedly ancient 

age points to considerable stability of the upper surface of 

the main part of the talus apron. 

DATING THE ELK SUMMIT FAULT 

BY AERIAL PHOTOGRAPHY 

The range of dates given by lichenometry can be narrowed by examining a series of aerial photographs taken 

between 1946 and 197 4. The scale of the photographs ranges 
SEISMIC EFFECTS 11 

from 1:20,000 to 1:60,000. Contact film negatives were 

required for resolution of critical features on the 1946 and 

1954 photographs; positive prints were adequate for photographs taken subsequently. Photographs taken on September 

29, 1946, show the talus apron covered with snow. Nevertheless, a poorly defined, east-trending linear feature is visible 

on the west half of the talus apron, and a better defined linear 

feature is visible at the east edge of the apron. The features 

are collinear, though separated by a gap. A faint northeasttrending zone can be projected into the gap, but the zone 

does not appear to offset the east-trending features. Photographs taken July 31, 1954, also show snow on the talus 

apron. A barely visible break in slope defines the western 

linear feature, the eastern one is not evident, and the northeast-trending zone is obscure. Photographs taken on August 

24, 1964, clearly show straight, dark lines marking the 

segmented fault trace, though the talus apron has some snow 

cover. The offset of the segments, estimated perpendicular to 

their length, is about twice the 4-meter width of the nearby 

forest road, or about 10m. (Compare figure 2.) Photographs 

taken on August 20, 1969, still show straight, dark lines 

marking the segmented fault trace. Photographs taken on 

September 2, 1974, also show the dark lines, but the lines are 

slightly crinkly or wavy, distorted a little by local movement 

of talus. Richard B. Taylor (oral commun., October and 

December 1992) reported the foregoing observations after 

examining the whole series of photographs stereoscopically. 

The evidence from the series of aerial photographs 

indicates that the Elk Summit fault had some surface expression as early as 1946, little changed in 1954 but conspicuous 

by 1964. The major change in surface expression is thus 

narrowed to the interval1954-1964. 

SEISMIC EFFECTS 

Most young faults that have surface expression have 

resulted from earthquakes or are known to be associated with 

them. Is the Elk Summit fault earthquake related? The seismicity map of Idaho (Stover and others, 1991) shows no epicenters close to Elk Summit. Only one earthquake centered 

within 100 km of Elk Summit is reported to have had an 

intensity as high as VII on the modified Mercalli scale. That 

moderately strong earthquake, of magnitude 6.1 mb, 

occurred in 1944 in the Sheep Mountain area 60 km southeast of Elk Summit (Stover and others, 1991). We have no 

information on effects that might have been felt in the Big 

Creek-Yell ow Pine area. 

Major earthquakes commonly have effects that extend 

far from their epicenters. One such earthquake, felt at Big 

Creek and near Yellow Pine, was the August 18, 1959, earthquake at Hebgen Lake, Montana. The magnitude of the principal shock was 7.1 mb (Reagor and others, 1985). The 

effects of the earthquake were felt over an area of -6x105 

mi2 (Murphy and Brazee, 1964, p. 15), equivalent to 

-1.6x1 06 km2. The seismologists' August 18 date is referred 

to Coordinated Universal Time (06:37:15 UCT); the equivalent in Mountain Standard Time is 11:37 p.m., August 17. 

At Big Creek, Robin McRae was sleeping in a twostory frame house set on concrete blocks on Quaternary 

deposits of the valley floor. He awoke about 2:30a.m. when 

"an earthquake almost tore the cabin apart. He thought it was 

a bear trying to get into the house. [McRae] thought that it 

was the same earthquake that struck in Montana on the Madison river" (James Collord, written commun., August 14, 

1992). The discrepancy in time between the 11:37 p.m. 

shock and McRae's sensing of it at 2:30 the next morning 

may be significant, but we are inclined to discount the 

discrepancy. 

Also at Big Creek, the Wiles cabin close to the McRae 

house was shaken. "The quake of 1959 shook my cabin * * * 

rattled stovepipe, windows etc. It also cut the flow of a spring 

on Mountal [Monumental] Cr. to about 'h what it was" (Wilbur Wiles, written commun., September 22, 1992). The 

spring is at the mouth of an unnamed creek 0.3 km northeast 

of Diamond Creek, 22 km east of Elk Summit. The estimated 

intensity of the earthquake's effect at the spring is VIII 

(modified Mercalli scale), in contrast to VI at Big Creek. 

At Chamberlain Basin, 30 km northeast of Elk Summit, 

Earl Dodds was awakened during the night when his woodfloored frame tent was severely shaken twice within a short 

time span. He thought that a bear was the shaker, but his 

searches for the bear showed no evidence that one had been 

present (Earl F. Dodds, former U.S. Forest Service District 

Ranger, Big Creek district, oral commun., October 16, 

1992). 

At Meadow Creek Lookout, a one-story frame building 

set on the bedrock of Meadow Ridge 13.3 km southeast of 

Yellow Pine, the Forest Service observer was awakened 

when canned goods stored on the rafters rained down upon 

him. Quite distraught, he burst into Leonard's camp 2 km 

southeast of the lookout early next morning to report the 

accident. Leonard, his field assistant, and his packer had 

slept peacefully on the ground on their air mattresses; no one 

felt the shock, and it did not "spook" the horses and mules 

grazing nearby. Everyone agreed that the accident at the 

lookout was caused by an earthquake, but no one knew until 

a newspaper became available some days later that the 

epicenter of the earthquake was at Hebgen Lake, 320 km east 

of the lookout. 

At the Cox Ranch, 14.4 km south of Yellow Pine, 

Emma Cox (written commun., November 4, 1992) "felt [the 

earthquake while] standing in the kitchen and some of the 

cabinet doors came open. Later we noticed the cement on the 

fireplace chimney on the outside had a crack clear through 

that had not been there before." 

These examples of earthquake effects felt or later 

observed near Elk Summit indicate the wide-ranging effect 

of the Hebgen Lake earthquake. Was the effect great enough 
12 DATING A 20th-CENTURY FAULT, BIG CREEK AREA, IDAHO 

to develop a fault across the Elk Summit talus apron? No one 

can say, because an understanding of the intensity of earthquake effects that occur far distant from an earthquake focus 

is only now developing. 

Was there, at the time of the Hebgen Lake earthquake, a 

discrete earthquake centered much closer to Elk Summit-an 

earthquake not detected instrumentally because its signal was 

irresolvable from those given by the Hebgen Lake shocks? 

The question arises, but it is unanswerable. 

An initially puzzling feature of the size distribution of 

fragments on the talus apron is consistent with an earthquake 

origin for the fault, whatever its date. This feature is the 

brownish, iron-stained fines that are restricted to the fault 

bench and a narrow zone downslope from it. The fines, 

mostly of centimeter size, are very likely the analog of the 

sand and gravel erupted as sand boils or sand spouts along 

earthquake-induced faults in unconsolidated sediments. (For 

a description of the sand spouts caused by the Hebgen Lake 

earthquake, see Swenson, 1964, p. 162-163.) On the Elk 

Summit talus apron, fines that had been eluviated from the 

surface and deposited at shallow depth were forced upward 

when snowmelt stored in the talus was squeezed out along 

the fault during local compaction of the talus blocks. The 

finest material so erupted has been dispersed, as it has been 

from sand spouts in soft sediments, but centimeter-size 

fragments remain to give the material on the fault bench its 

anomalous, iron-stained, screelike character. 

CONCLUSION 

The lichenometry of Rhizocarpon geographicum and 

Lecidea atrobrunnea gives a wide range of 20th century 

dates, including 1959, for the Elk Summit fault. The evidence from aerial photographs narrows the range of dates for 

conspicuous surface expression of the fault to 1954-1964. A 

1959 date is consistent with the fresh appearance of the fault 

scarp in the mid-1960's, and with the obliteration of the 

scarp sometime between the 1960's and 1991. If the scarp 

degenerated to an inconspicuous bench in a period of 25 or 

30 years, it is unlikely that the scarp persisted for 25 or 30 

years before the 1960's. We believe that the Elk Summit 

fault dates from 1959, the year of the Hebgen Lake, Montana, earthquake. The effects of that far-distant earthquake 

were felt strongly or observed later within 9-30 km of Elk 

Summit. This fact suggests that the Elk Summit fault 

resulted from the Hebgen Lake earthquake or from some 

attendant shock, not detected instrumentally, that may have 

occurred closer to Elk Summit. The earthquake may have 

served only as a trigger for surface faulting related to a bedrock fault of far greater age. 

We readily admit that neither a 1959 date for the fault 

nor an earthquake origin for it can be proved by our study, 

provocative as the facts and inferences may be. We also 

admit that we are puzzled by the poorly defined linear 

feature visible on 1946 air photographs of the talus apron. 

The feature suggests that an episode of surface faulting may 

have occurred sometime between the first and fifth decades 

of this century. Judged from lichenometry, an earlier date is 

unlikely. It is tempting to relate this enigmatic episode of 

faulting to the 1944 Sheep Mountain earthquake, but to do so 

is conjectural. We set out to date the fault that had conspicuous surface expression during the 1960's; that date is most 

likely 1959. 

Acknowledgments.-We are grateful to many people 

for their help: to U.S. Geological Survey members Robert C. 

Bucknam and Henry Spall for information on seismic events 

in central Idaho, Ann Donovan and Steven Johnson for 

tracking down a series of aerial photographs of Elk Summit 

and its environs, Richard B. Taylor for stereoscopic examination of the photographs, and David L. Campbell for helpful comments on the VLF survey; to Scott Lemberes, Payette 

National Forest, for the loan of air photographs taken for the 

U.S. Forest Service; to Jerry Jacoby, U.S. Forest Service, 

Ogden, Utah, Wayne London, Agricultural Stabilization and 

Conservation Service, Salt Lake City, and EROS Data Center, Sioux Falls, South Dakota, for the preparation of contact 

film negatives of air photographs; to Sherri K. Pittam, 

formerly of National Museum of Natural History, for 

encouraging Leonard's interest in lichens, putting him in 

touch with lichenologist and co-author Rosentreter, and supplying references on Lecidea atrobrunnea; to Paul Carrara, 

U.S. Geological Survey, and J.T. Andrews, University of 

Colorado, for a discussion of their lichenometric work in the 

San Juan Mountains; to Big Creek residents James Collord, 

Robin McRae, Jack and Sally Walker, and Wilbur Wiles, 

and former resident Earl Dodds, for information on earthquakes felt in the Big Creek area; to Lafe and Emma Cox for 

information on 1959 earthquake effects felt at the Cox Ranch 

near Yell ow Pine; to Leroy Yoakum, caretaker of the McCall 

Cemetery, for information on headstones; to Loti Harp, 

McCall, for directions to the cemetery at Warren; and to 

Eleanor V. Leonard for assistance in the field. 

REFERENCES CITED 

Benedict, J.B., 1988, Techniques in lichenometry-Identifying the 

yellow Rhizocarpons: Arctic and Alpine Research, v. 20, 

p. 285~291. 

Carrara, P.E., and Andrews, J.T., 1973, Problems and applications 

of lichenometry to geomorphic studies, San Juan Mountains, 

Colorado: Arctic and Alpine Research, v. 5, p. 373-384. 

Egan, R.S., 1987, A fifth checklist of the lichen-forming, lichenicolous and allied fungi of the continental United States and 

Canada: The Bryologist, v. 90, no. 2, p. 77-173. 

Fraser, D.C., 1969, Contouring of VLF-EM data: Geophysics, v. 

34, p. 958-967. 

Leonard, B.F., and Marvin, R.F., 1982 [1984], Temporal evolution 

of the Thunder Mountain caldera and related features, Idaho, in 

Bonnichsen, Bill, and Breckenridge, R.M., eds., Cenozoic 
REFERENCES CITED 13 

geology of Idaho: Idaho Bureau of Mines and Geology Bulletin 

26, p. 23-41. 

Leonard, B.F., Mead, C.W., and Conklin, Nancy, 1968, Silver-rich 

disseminated sulfides from a tungsten-bearing quartz lode, Big 

Creek district, central Idaho: U.S. Geological Survey Professional Paper 594-C, 24 p. 

Lock[e], W.W., Andrews, J.T., and Webber, P.J., 1980, A manual 

for lichenometry: British Geomorphological Research Group 

Technical Bulletin 26, 4 7 p. 

McNeill, J.D., and Labson, V.F., 1991, Geological mapping using 

VLF radio fields, in Nabighian, M.N., ed., Electromagnetic 

methods in applied geophysics, v. 2, Applications, part B: 

Society of Exploration Geophysicists Investigations in Geophysics 3, p. 521-640. 

Murphy, L.M., and Brazee, R.J., 1964, Seismological investigations of the Hebgen Lake earthquake, in The Hebgen Lake, 

Montana, earthquake of August 17, 1959: U.S. Geological Survey Professional Paper 435, p. 13-17. 

Published in the Central Region, Denver, Colorado 

Manuscript approved for publication May 24, 1994 

Edited by Judith Stoeser 

Graphics and photocomposition by Marl L. Kauffmann 

Tables typeset by Judith Stoeser 

-trU.S. ~ PRINriR; OFFICE: 1994-673-046/86061 

Osborn, Gerald, and Taylor, John, 1975, Lichenometry on calcareous substrates in the Canadian Rockies: Quaternary Research, 

v. 5, p. 111-120. 

Poelt, J., 1988, Rhizocarpon Ram. em. Th. Fr. subgen. Rhizocarpon 

in Europe: Arctic and Alpine Research, v. 20, p. 292-298. 

Reagor, B.G., Stover, C.W., and Algermissen, S.T., 1985, Seismicity map of the State of Montana: U.S. Geological Survey Miscellaneous Field Studies Map MF-1819, scale 1:1,000,000. 

Stover, C.W., Reagor, B.G., and Algermissen, S.T., 1991, Seismicity map of the State of Idaho: U.S. Geological Survey Miscellaneous Field Studies Map MF-1857, scale 1:1,000,000. 

Swenson, F.A., 1964, Ground-water phenomena associated with 

the Hebgen Lake earthquake, in The Hebgen Lake, Montana, 

earthquake of August 17, 1959: U.S. Geological Survey Professional Paper 435, p. 159-165. 

Werner, Al, 1990, Lichen growth rates for the northwest coast of 

Spitsbergen, Svalbard: Arctic and Alpine Research, v. 22, 

p.129-140. 



SELECTED SERIES OF U.S. GEOLOGICAL SURVEY PUBLICATIONS 

Periodicals 

Earthquakes & Volcanoes (issued bimonthly). 

Preliminary Determination of Epicenters (issued monthly). 

Technical Books and Reports 

Professional Papers are mainly comprehensive scientific reports 

of wide and lasting interest and importance to professional scientists and 

engineers. Included are reports on the results of resource studies and of 

topographic, hydrologic, and geologic investigations. They also include 

collections of related papers addressing different aspects of a single scientific topic. 

Bulletins contain significant data and interpretations that are of 

lastin~ scientific interest but are generally more limited in scope or geographic coverage than Professional Papers. They include the results of 

resource studies and of geologic and topographic investigations; as well 

as collections of short papers related to a specific topic. 

Water-Supply Papers are comprehensive reports that present significant interpretive results of hydrologic investigations of wide interest 

to professional geologists, hydrologists, and engineers. The series covers 

investigations in all phases of hydrology, including hydrology, availability of water, quality of water, and use of water. 

Circulars present administrative information or important scientific information of wide popular interest in a format designed for distribution at no cost to the public. Information is usually of short-term 

interest. 

Water-Resources Investigations Reports are papers of an interpretive nature made available to the public outside the formal USGS 

publications series. Copies are reproduced on request unlike fonnal 

USGS publications, and they are also available for public inspection at 

depositories indicated in USGS catalogs. 

Open-File Reports include unpublished manuscript reports, maps, 

and other material that are made available for public consultation at depo~itories. They are a nonpermanent form of publication that may be cited m other publications as sources of information. 

Maps 

Geologic Quadrangle Maps are multicolor geologic maps on topographic bases in 7 1/2- or 15-minute quadrangle formats (scales mainly 1:24,000 or 1 :62,500) showing bedrock, surficiaL or engineering 

geology. Maps generally include brief texts; some maps include structure 

and columnar sections only. 

Geophysical Investigations Maps are on topographic or planimetric bases at various scales, they show results of surveys using geoph~sical techniques, such as gravity, magnetic, seismic, or radioactivity, 

~h~ch reflect subsurface structures that are of economic or geologic sigmficance. Many maps include correlations with the geology. 

Miscellaneous Investigations Series Maps are on planimetric or 

topographic bases of regular and irregular areas at various scales; they 

present a wide variety of format and subject matter. The series also includes 7 1/2-minute quadrangle photogeologic maps on planimetric 

bases which show geology as interpreted from aerial photographs. The 

series also includes maps of Mars and the Moon. 

Coal Investigations Maps are geologic maps on topographic or 

planimetric bases at various scales showing bedrock or surficial geology, 

stratigraphy, and structural relations in certain coal-resource areas. 

Oil and Gas Investigations Charts show stratigraphic information for certain oil and gas fields and other areas having petroleum potential. 

Miscellaneous Field Studies Maps are multicolor or black-andwhite maps on topographic or planimetric bases on quadrangle or irregular areas at various scales. Pre-1971 maps show bedrock geology in relation to specific mining or mineral-deposit problems; post-1971 maps 

are primarily black-and-white maps on various subjects such as environmental studies or wilderness mineral investigations. 

Hydrologic Investigations Atlases are multicolored or black-andwhite maps on topographic or planimetric bases presenting a wide range 

of geohydrologic data of both regular and irregular areas; the principal 

scale is 1:24,000, and regional studies are at 1:250,000 scale or smaller. 

Catalogs 

Permanent catalogs, as well as some others, giving comprehensive 

listings of U.S. Geological Survey publications are available under the 

conditions indicated below from USGS Map Distribution, Box 25286, 

Building 810, Denver Federal Center, Denver, CO 80225. (See latest 

Price and Availability List.) 

"Publications of the Geological Survey, 1879-1961" may be purchased by mail and over the counter in paperback book form and as a set 

microfiche. 

"Publications of the Geological Survey, 1962-1970" may be purchased by mail and over the counter in paperback book form and as a set 

of microfiche. 

"Publications of the U.S. Geological Survey, 1971-1981" may be 

purchased by mail and over the counter in paperback book form (two 

volumes, publications listing and index) and as a set of microfiche. 

Supplements for 1982, 1983, 1984, 1985, 1986, and for subsequent years since the last permanent catalog may be purchased by mail 

and over the counter in paperback book form. 

State catalogs, "List of U.S. Geological Survey Geologic and Water-Supply Reports and Maps For (State)," may be purchased by mail 

and over the counter in paperback booklet form only. 

"Price and Availability List of U.S. Geological Survey Publications," issued annually, is available free of charge in paperback booklet 

form only. 

Selected copies of a monthly catalog "New Publications of the 

U.S. Geological Survey" is available free of charge by mail or may be 

obtained over the counter in paperback booklet form only. Those wishing a free subscription to the monthly catalog "New Publications of the 

U.S. Geological Survey" should write to the U.S. Geological Survey, 

582 National Center, Reston, VA 22092. 

Note.-Prices of Government publications listed in older catalogs, 

announcements, and publications may be incorrect. Therefore, the prices 

charged may differ from the prices in catalogs, announcements, and publications.