The Holocene Ridgeland Formation 

And Associated Decker Soil

(New Names)

Near Great Salt Lake, Utah

GEOLOGICAL SURVEY BULLETIN 1457-C

The Holocene Ridgeland Formation 

And Associated Decker Soil 

(New Names) 

Near Great Salt Lake, Utah

By RICHARD VAN HORN

CONTRIBUTIONS TO STRATIGRAPHY

GEOLOGICAL SURVEY BULLETIN 1457-C

Two new units of Holocene age 

that are associated with ancient 

Lake Bonneville are named and described

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1979
UNITED STATES DEPARTMENT OF THE INTERIOR 

CECIL D. ANDRUS, Secretary

GEOLOGICAL SURVEY 

H. William Menard, Director

Library of Congress Cataloging in Publication Data

Van Horn, Richard, 1920

The Holocene Ridgeland Formation and associated Decker Soil (new names)

near Great Salt Lake, Utah. 

(Contributions to stratigraphy) 

(Geological Survey Bulletin 1457-C) 

Includes bibliographical references, p. 11

1. Geology, Stratigraphic Recent. 2. Soils Utah Great Salt Lake region. 

3. Geology Utah Great Salt Lake region.

I. Title. II. Series. III. Series: United States Geological Survey Bulletin 1457-C. 

QE75.B9 1457-C [QE699] 557.3'08s [551.7*93] 78-606058

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

Washington, D.C. 20402 

Stock No. 024-001-03168-0
CONTENTS

	Page

Abstract ................................................................... Cl

Introduction ............................................................... 1

Definition and description ................................................... 3

Ridgeland Formation ................................................... 3

Decker Soil ............................................................ 3

Type section ............................................................... 4

Geologic history ............................................................ 8

Age ....................................................................... 9

Climatic and environmental implications ...................................... 10

References cited ............................................................ 11

ILLUSTRATIONS

FIGURE 1. Map of Great Salt Lake and vicinity, showing localities mentioned in the

text .......................................................... C2

2. Photographs showing location and units of measured type section of the

Ridgeland Formation and of the Decker Soil..................... 6

III
METRIC-ENGLISH EQUIVAL

[SI, International System of Units, a modernized metric s

SI unit U.S. customary equivalent

Length

millimeter (mm) 

meter (m)

kilometer (km)

= 0.039 37 

= 3.281 

= 1.094 

= 0.621 4 

= 0.540 0

inch (in) 

feet (ft) 

yards (yd) 

mile (mi) 

mile, nautical (nmi)

Area

centimeter2 (cm2 ) 

meter2 (m2 )

hectometer3 (hm2 ) 

kilometer2 (km2 )

 0.1550

=: 10.76 

- 1.196

= 0.000 247 1 

= 2.471 

= 0.003 861

= 0.386 1

inch2 (in2 ) 

feet2 (ft2 ) 

yards2 (yd2 ) 

acre 

acres 

section (640 acres or 

1 mi2 ) 

mile2 (mi")

Volume

centimeter3 (cm3 ) 

decimeter3 (dm3 )

meter3 (m3 )

hectometer3 (hm3 ) 

kilometer3 (km3 )

= 0.061 02

At AO

= 2.113 

= 1.057 

- 0.264 2

= 0.035 31 

= 35.31

.oUo

= 264.2 

= 6.290

= 0.000 810 7 

= 810.7 

= 0.239 9

inch3 (in3 ) 

inches3 (in3 ) 

pints (pt) 

quarts (qt) 

gallon (pal) 

foot3 (ft3 ) 

feet3 (ft3 ) 

yards3 (yd3 ) 

gallons (gal) 

barrels (bbl) (petroleum, 1 bbl = 42 gal) 

acre-foot (acre-ft) 

acre-feet (acre-It) 

mile3 (mi3 )

Volume per unit time (includes flow)

decimeter3 per second 

(dm3 /s)

= 0.035 31 

= 2.119

foot3 per second (ft3 /s)

feet3 per minute (ft3 / 

min)

SI un

Volume 

decimeter3 per sec

(dmVs)

meter3 per second 

gram (g) 

kilogram (kg) 

megagram (Mg)

Ma

kilogram per met

(kg/m3 )

kilopascal (kPa)

temp kelvin (K) 

temp deg Celsius 
CONTRIBUTIONS TO STRATIGRAPHY

By RICHARD VAN HORN

ABSTRACT

The lacustrine Ridgeland Formation (new name) was deposited during a low stage of 

Lake Bonneville in northwest Utah and was graded to the Gilbert shoreline. The Gilbert 

shoreline is about 15 m higher than the level of Great Salt Lake in 1977. The Decker Soil 

(new name) formed on the Ridgeland Formation and older formations and soils exposed 

at that time. The Ridgeland probably was deposited during the Holocene in early Neoglacial time. The lake cycle that produced this formation and soil indicates climatic changes 

that may be pertinent to understanding the modern changes in Great Salt Lake.

INTRODUCTION

The Ridgeland Formation and Decker Soil, of Holocene age, are 

herein named. The Ridgeland Formation named for the Ridgeland 

Canal is of lacustrine origin and is in the upper part of the Lake Bonneville Group (Gilbert, 1875, p. 89; Hunt and others, 1953, p. 17) and at 

present is only known to exist in the vicinity of Great Salt Lake, Utah. 

(See fig. 1.) The Decker Soil is named for Decker Creek that begins near 

the type locality and flows into Decker Lake located approximately 2 km 

southeast of the former Utah Central Airport. It is typically formed on 

the Ridgeland Formation but is much more widespread than the Ridgeland because it also formed on all exposed older soils and formations. 

The reason for naming these thin units is to ease communication in 

describing the late history of Lake Bonneville and the early history of its 

successor, the Great Salt Lake.

Lake Bonneville was a large lake of late Pleistocene and Holocene age 

that occupied much of northwestern Utah. It has a very complicated 

history that includes several cycles that resulted in three prominent and

Cl
C2 CONTRIBUTIONS TO STRATIGRAPHY

113° 112°

41'

FIGURE 1. Great Salt Lake (dark stipple) and vicinity, showing localities mentioned in the 

text. Heavy line is Bonneville (highest) shoreline of Lake Bonneville (light stipple). 

Star shows location of measured type section (S333) of the Ridgeland Formation and 

of the Decker Soil.
RIDGELAND FORMATION AND DECKER SOIL, UTAH C3

well-marked shorelines the Bonneville, Provo, and Stansbury 

shorelines. The Bonneville shoreline marks the highest level attained by 

the lake, and in the Salt Lake City area it is about 1,579 m (5,180 ft) above 

sea level. When the lake stood at this level it was about 310m deep. A 

much less prominently developed shoreline that is about 1,292 m (4,240 

ft) above sea level in the Salt Lake City area is called the Gilbert shoreline 

(Eardley and others, 1957, p. 1161).

DEFINITION AND DESCRIPTION

The Ridgeland Formation is a lake deposit that formed in late 

Holocene time after the development of the Midvale Soil. The Ridgeland was deposited during a cycle of Lake Bonneville that started when 

the lake was at an unknown altitude lower than 1,292 m (4,240 ft), 

continued as the lake rose to the altitude where the Gilbert shoreline was 

formed, and then fell to some unknown level. The deposits are principally silt and fine-grained sand, but may contain clay, oolites, brine 

shrimp fecal pellets, ostracods, gastropods, brachiopods, and 

Foraminifera. The known deposits of the Ridgeland formed as bay bars, 

offshore bars, and lake-bottom deposits.

The Decker Soil is an immature soil that has developed since Lake 

Bonneville stood at the Gilbert shoreline. The Decker Soil formed on the 

Ridgeland Formation as the water of Lake Bonneville slowly evaporated 

and retreated from the Gilbert shoreline.

RIDGELAND FORMATION

The Ridgeland Formation is light-gray to dark-brown silt or clay that 

is 15-190 cm thick. At the type section the deposit is silt that probably was 

deposited by east-trending lake currents in a relatively narrow zone near 

the shore. East and south of the type section are several southeasttrending deposits of silt and sandy silt as much as 700 m long and 50 m 

wide. These appear to be offshore bars. Farther north, on the delta of 

the Jordan River, the Ridgeland Formation is principally clay and was 

deposited in relatively still water. On the north side of Great Salt Lake 

several offshore and bay bars of Ridgeland Formation are composed of 

sandy silt that locally is pebbly.

At several places the Ridgeland overlies the Midvale Soil. At these 

places the Midvale Soil is from 10 to 45 cm thick, which is thinner than 

most exposures of Midvale Soil exposed at the surface.

DECKER SOIL

The Decker Soil ranges from dark gray to light gray in color and from 

silt to clay in grain size. It is similar in composition to the underlying
C4 CONTRIBUTIONS TO STRATIGRAPHY

Ridgeland Formation. The soil is generally 5-20 cm thick, but locally it 

may be as much as 30 cm thick.

The Decker Soil is an immature soil and consists of an A horizon 

enriched in organic material that gives it a color darker than the underlying parent material. There does not appear to be any significant 

downward dislocation of clay or calcium carbonate from the A horizon 

into the underlying parent material.

The recognized extent of the Decker Soil has the same distribution as 

the Ridgeland Formation. The Decker Soil has been recognized below 

the Gilbert shoreline in the Salt Lake City area and also in the desert 

north of the Great Salt Lake. It is thinner in the desert area than in the 

Salt Lake City area. The thickest development seen is in deposits on the 

Jordan River delta 5 km northwest of Salt Lake City.

The Decker Soil has been recognized only where formed on the 

Ridgeland Formation, but presumably it also formed on other deposits 

and soils that were exposed at the land surface after Lake Bonneville 

started retreating below the Gilbert shoreline for the last time. The only 

place a deposit is known to overlie the Decker Soil is 20 km northwest of 

Corinne adjacent to Utah Highway 83. Here, a natural levee of Salt 

Creek overlies the Decker.

TYPE SECTION

The type section of the Ridgeland Formation and of the Decker Soil is 

exposed in the west bank of the Ridgeland Canal in the SWiSE? sec. 20, 

T. 1 S., R. 1 W., Salt Lake Meridian in the Salt Lake City South, Utah 

7.5-minute quadrangle of the U.S. Geological Survey. (See figs. 1 and 2 

and measured section S333.) The section lies between the Ridgeland 

Canal and Vespa Drive at Salt Lake City coordinate 3440 West, 2575 

South. The outcrop is best approached from the east by way of the south 

runway of the former Utah Central Airport. Figure 2/4 shows the outcrop as viewed from this approach.

SECTION S333. Type Ridgeland Formation and Decker Soil and underlying units 

[Measured in the west bank of the Ridgeland Canal in the SWJSEJ sec. 20, T. 1 S., R. 1 W. ML, CL, and SM are letter 

symbols of Unified Soil Classification (U.S. Bur. Reclamation, 1960, p. 379-400]

Thickness in 

centimeters

9. Artificial fill and spoil from canal. Medium-gray silt-size fragments of clay.

Unconformable contact with underlying unit 8 ........................ 0-90

8. Soil A horizon of the Decker Soil formed on Ridgeland Formation. Dark-gray, 

massive, calcareous, tastes slightly salty, silt (ML). Locally contains long 

cylindrical, partly cemented worm(?) casts. Grades into underlying unit 7 __18

Total, Decker Soil .............................................. __18
RIDGELAND FORMATION AND DECKER SOIL, UTAH C5

SECTION S333. Type Ridgeland Formation and Decker Soil and underlying units Continued

Thickness in

7. Ridgeland Formation. Medium-gray, massive, calcareous, tastes slightly salty, c 

silt (ML). Contains small gastropods, ostracods, brine shrimp(?) pellets, 

nonmarine mollusks, and, according to P.B. Smith of the U.S. Geol. Survey 

(written commun. Aug. 2, 1971), Foraminifera. Undulating, sharp, unconformable contact with underlying unit 6 ........................... _51

Total, Ridgeland Formation ..................................... 51

6. Midvale Soil. Very dark gray, very calcareous, does not taste salty, slightly 

sandy silt (ML). Contains a few animal burrows. Gradational contact with 

underlying unit 5 ................................................... _33

Total, Midvale Soil ............................................. _33

5. Draper Formation. Very light gray, very calcareous, tastes salty, silty clay (CL). 

Upper part has platey structure. This unit may be a Cca soil horizon (zone of 

calcium carbonate accumulation). Grades into underlying unit 4 ........ 59

4. Draper Formation. Medium-gray, calcareous, no salty taste, clay (CL). Contains some small round openings like root holes. Grades into underlying unit 

3 ....................... ...\ ....................................... 33

3. Draper Formation. Light-brown with medium-gray mottles, calcareous, no 

salty taste, clay (CL). Contains a few 0.1-cm-thick and 13-cm-long lenses of 

very fine grained sand. Has sharp even contact with underlying unit 2 .. 59

2. Draper Formation. Light-gray, calcareous, uniform grain size, silty, very fine 

grained sand (ML-SM). Contains gastropods, ostracods, and sparse mica. 

Has sharp even contact with underlying unit 1 ........................ 3

1. Draper Formation. Medium-gray, calcareous, no salty taste, silty clay (CL).

Contains a few 0.1-cm-thick very fine grained sand lenses. Base not exposed 60

Total, Draper Formation ........................................ 214

Samples from units 8, 7, 6, and 1 were examined by R.M. Forester of 

the U.S. Geological Survey (written commun. June 14, 1977) who recognized the following organisms, mostly ostracodes.

Unit 8 contained (abundance not given):

Candona rawsani Tressler, 1957.

Cyprinotus glaucus? Furtos, 1933.

Eucypris serrata (Muller, 1900).

Candona caudata Kaufmann, 1900.

Cyclvcypris ampla Furtos, 1933.

Limnocythere illinoisenais Sharpe, 1897.

Foraminifera(P). 

Unit 7 contained:

Ilyocypris biplicata (Koch, 1838)............ Abundant.

Ilyocypris gibba (Ramdohr, 1808) .......... Rare.

Limnocythere illinoisensis Sharpe, 1897 ...... Rare.

Cytherissa lacustris? (Sars, 1863) ........... Rare.

Cyprinotus glaucus? Furtos, 1933 .......... Rare.

rawsoni Tressler, 1957 ........... Common.
CONTRIBUTIONS TO STRATIGRAPHY

FIGURE 2. Location of measured type section (S333) of the Ridgeland Formation and of 

the Decker Soil in a cut perpendicular to the bank of the Ridgeland Canal..4, The cut is 

visible between the truck body and the concrete mixer. View is to the west from the 

former Utah Central Airport. B, From the top down are artificial fill (unit 9), Decker Soil 

(unit 8), Ridgeland Formation (unit 7), Midvale Soil (unit 6), and Draper Formation 

(unit 5). The shovel is 150 cm long. View is to the north.
RIDGELAND FORMATION AND DECKER SOIL, UTAH C7

Unit 7. Continued.

Candona adunca Lister, 1975 ............. Rare.

Potamocypris? sp ......................... Rare.

Cypridopsis vidua (Muller, 1776) ........... Rare.

Eucypris serrata (Muller, 1900) ............ Rare.

Physocypris pustulosa Sharpe, 1897 ......... Rare.

Cyclocypris ampla Furtos, 1933 ............ Rare.

Cyprideis sp. (Juv) ....................... Rare.

Chara sp. (charophyte) ................... Rare.

Foraminifera(?).

Unit 6 contained:

Candona rau'soni Tressler, 1957 ........... Abundant.

Ilyocypris hiplicata (Koch, 1838) ............ Rare.

Unit 1 contained:

Limnocythere illinoisensis Sharpe, 1897 ...... Abundant.

Candona caudatn Kaufmann, 1900 ........ Common.

Candona adunca Lister, 1975 ............. Rare.

Candona sp. (Juv) ....................... Rare

Forester stated:

The above assemblages of ostracodes occur throught much of the Quaternary. The exact 

ranges of the majority of these species have not been determined with any real confidence 

due to a general lack of study. The approximate 2,000-year date associated with the 

Ridgeland Formation (represented by these samples) is supported but not confirmed by 

these ostracode species.

The depositional environment suggested by these assemblages is one ranging from a 

fresh water to slightly saline lake. The vast majority of the ostracodes noted above are fresh 

water species, but all can tolerate slight salinities many are known from salinities up to 5 

parts per thousand. Cyprideis sp. which occurs in unit 7 is both an estuarine and hypersaline 

species. These specimens are noded, however, which is typical for very low salinity 

conditions. The presence of several species of Candona in the various samples suggests that 

the temperature was as low as 0 to 5 degrees Celsius during part of the year. The 

occurrence of Cyclocypris and Physocypris and to a lesser extent Cypridopsis suggests a very 

shallow depositional environment probably no more than 2 to 3 meters of water. The 

Chara sp. would support a pH of 7 or more and fairly hard water. The occurrence of 

so-called foraminifera is not confirmed beyond a reasonable doubt. There are a number of 

agglutinated tubes present in both samples U7 and U8, which could be thecamoebians or 

basically fresh water foraminifera. These tubes could also be casings surrounding certain 

types of insect larvae. If they are foraminifera they do not support a high salinity for this 

environment.

J. P. Bradbury of the U.S. Geological Survey (written commun., Sept. 

19, 1977) recognized the following organisms.

Samples S-333 U-l, U-6, and U-8 were barren of diatoms.

Sample S-333 U-7 was assigned USGS paleobotany locality number D5755. This sample 

contains a sparse diatom flora. Most specimens are fragmented. The following species 

were identified.
C8 CONTRIBUTIONS TO STRATIGRAPHY

Amphora ovalis v. lybica Gomphonema sp.

Amphora ovalis v. pediculus Gyrosigma sp.

Biddulphia laevis Hantzschia amphioxys

Cocconeis pediculus Navicula cincta?

Cymbella triangulum? Navicula mutica

Diploneis smithii Navicula mutica v. cohnii

Epithemia argus Nitzschia amphibia

E. adnata Pinnularia borealis

Fragilaria construens Synedra ulna 

Fragilaria construens v. venter

Plant phytoliths, chrysophycean cysts and sponge spicules are also present.

The most common diatom fragments are those of Biddulphia laevis. This diatom commonly lives attached to the substrate in slightly saline rivers, lakes, and estuaries, although 

it can tolerate salinities approaching that of sea water. It is present in the Cache La Poudre 

and St. Vrain Rivers in Colorado and in several rivers in the Great Plains States of 

Wyoming, Kansas, Missouri, Nebraska, and Oklahoma. The specific conductance of the 

Colorado and Missouri localities is generally between 700 and 1800 micro mhos per cm. (a 

salinity aboutis of seawater). In addition I have seen the species in large lakes such as Lake 

Valencia, Venezuela which has conductivity values between 1700 and 1800. Frequently the 

water in which this species lives has a high organic content and is turbid. Many of the other 

species found in this sample are tolerant or prefer water with some dissolved solids, and it is 

possible that they lived in association with Biddulphia laevis.

However, the common presence of specimens of Hantzschia amphioxys, Pinnularia borealis 

and of Navicula mutica and its variety cohnii suggests that the sample is a mixed diatom 

assemblage. These are common soil diatoms, which can live in moist subaerial habitats, 

although they are not unknown from alkaline lakes and rivers. In general these specimens 

are unfragmented, and it is probable that they lived in subaerial habitats not too far 

removed from the site of deposition. I suspect that the Biddulphia laevis fragments may be 

reworked from higher deposits surrounding Great Salt Lake when the lake was brackish, 

but neither highly saline as it is today nor fresh as it must have been when it produced the 

Bonneville and Provo shorelines.

In general, diatom samples from the shoreline terraces are difficult to interpret because 

the sediment can contain diatoms reworked from higher lacustrine deposits. In addition, 

samples from sediments derived largely from soils or subjected to soil-forming processes 

frequently contain some potentially non-lacustrine diatoms that could complicate 

paleolimnological interpretation. In the case of S-333 U-7, there is no guarantee that any 

of the diatoms encountered lived at the time the terrace of the Ridgeland Formation was 

formed. Nevertheless, it is encouraging that they are preserved and if proper lacustrine 

sediments are found, diatoms will very likely provide a detailed paleolimnological history 

for Great Salt Lake.

GEOLOGIC HISTORY

Lake Bonneville has undergone numerous advances and retreats in 

response to climatic changes during the latter part of the Pleistocene. 

There were several major high lake levels with intervening periods of 

desiccation to near dryness from 1^00,000 to 30,000 years ago, when the 

Alpine Formation was deposited. During the succeeding 20,000 years, 

the lake refilled and the Bonneville Formation was deposited the lake 

advanced to its high level twice; then the lake retreated to some un-
RIDGELAND FORMATION AND DECKER SOIL, UTAH C9

known low level between these advances. After the second advance to 

the high level, the lake overflowed and rapidly eroded an outlet channel 

more than 100 m deep. The lake then desiccated and retreated to some 

unknown level. This was followed by filling almost to the level of the 

outlet channel and the Draper Formation was deposited. Three moderately deep lake cycles are recorded by the Draper Formation in the 

succeeding 5,000 years.

The presence of the Ridgeland Formation and the succeeding Decker 

Soil implies still more climatic changes. Lake Bonneville must have 

desiccated to some unknown but low level following deposition of the 

Draper Formation. The Midvale Soil developed on the Draper during 

and after the lake retreat to that low level. In response to a subsequent 

climatic change, the lake rose to the level at which the Gilbert shoreline 

then formed. During this rise, which climaxed at a standstill at the 

Gilbert shoreline, and the following period of desiccation when the lake 

again fell, the Ridgeland Formation was deposited. As the lake receded 

from the Gilbert shoreline, the Decker Soil began to form on the Ridgeland and on all other formations and soils exposed at the land surface. 

Where the Decker Soil developed on virgin parent material it formed a 

weak immature soil. Where it developed on an older soil, such as the 

Midvale, it increased the degree of development of the older soil. This 

sequence of events fits the climatic theory of Eardley, Gvosdetsky, and 

Marsell (1957, p. 1189).

AGE

The precise age of the Ridgeland Formation is not known. It is 

post-Midvale Soil (altithermal) and therefore is younger than 4,000 

years. The high levels of older stages of Lake Bonneville just south of 

Salt Lake City have coincided with the maximum glacial advances at 

Little Cottonwood Canyon (Morrison, 1965, p. 53). It is likely that the 

same is true for the younger stages of Lake Bonneville. If so, the 

Ridgeland correlates with one of the advances of the Neoglaciation 

which started about 4,000 years ago and continued to about 1850 A.D.

Several workers in the Rocky Mountains indicate that there were three 

glacial advances during the post 4,000 B.P. (before present) period 

which are now assigned to the Neoglacial. The lake rise represented by 

the Ridgeland may correlate with the earliest of these, which has been 

dated from as much as 4,500 B.P. to about 2,500 B.P. (Miller, 1973).

The rate of isostatic rebound of the land surface, after Lake Bonneville started drying up, gives a possible clue to the age of the Ridgeland 

Formation. The Ridgeland does not occur above the Gilbert shoreline. 

The Gilbert shoreline has been warped by isostatic rebound of the 

Bonneville basin which resulted from the loss of tremendous amounts of 

water from Lake Bonneville since the last time it occupied its high shore,
CIO CONTRIBUTIONS TO STRATIGRAPHY

the Bonneville shoreline (Gilbert, 1890). According to Crittenden (1967, 

fig. 4B), the Bonneville shoreline in the center of the lake began rising at 

a nearly constant rate 18,000 years ago. As he states, this is a simplification of a very complex sequence of events because of the different rates 

of retreat and because of several lake cycles that occurred during the 

past 18,000 years. The actual rebound is probably based on an exponential decay, which is not decipherable from the available information.

The following simplified calculations indicate that the Gilbert 

shoreline, and presumably the Ridgeland Formation, was formed during the early part of the Neoglacial. The Gilbert shoreline in the Salt 

Lake City area is at 1,292 m (4,240 ft) above sea level. At Rozel Point, 100 

km northwest of Salt Lake City, the Gilbert is at 1,296 m (4,253 ft) or 

about 4 m higher. The difference is probably caused by isostatic uplift of 

the central part of the Bonneville basin since the Gilbert shoreline was 

formed. According to Crittenden (1963, fig. 3; 1967, fig. 2), the Bonneville shoreline has risen to 1,579 m (5,180 ft) altitude in the Salt Lake 

City area and to 1,603 m (5,260 ft) altitude in the vicinity of Rozel Point 

since the Bonneville shoreline was last occupied, about 18,000 years ago. 

This indicates that the Bonneville shoreline has rebounded 24 m higher 

in the vicinity of Rozel Point than it did near Salt Lake City. If the 24 m of 

differential elevation of the Bonneville shoreline can be assumed to have 

taken place at a constant rate over the entire 18,000 years, the rate of 

rebound between the two localities is 24-H 18,000 or 0.0013 m/yr. If this 

rate is applied to the differential elevation of the Gilbert shoreline at 

these two localities it would indicate that the Gilbert was formed about 

4-^0.0013 or 3,000 years ago. Similar calculations using the Provo 

shoreline £, ^ base indicate that the Gilbert shoreline was formed about 

1,700 years ago.

CLIMATIC AND ENVIRONMENTAL IMPLICATIONS

Each rise of Lake Bonneville to a different shoreline may be interpreted to mean a wetter, colder, or cloudier environment, which would 

provide more water to the lake either by increased precipitation, less 

evaporation, or a combination of both. Each falling of the lake could 

represent a return to the reverse of the above.

A better understanding of the late history of Lake Bonneville and the 

early history of Great Salt Lake is needed if we are to try to predict the 

rise and fall of Great Salt Lake, which may have serious economic 

consequences on the human population and land use in the vicinity of 

the lake.
RIDGELAND FORMATION AND DECKER SOIL, UTAH C11

REFERENCES CITED

Crittenden, M. D., Jr., 1963, New data on the isostatic deformation of Lake Bonneville:

U.S. Geol. Survey Prof. Paper 454-E, p. E1-E31. 

______1967, Viscosity and finite strength of the mantle as determined from water and

ice loads, in Internal. Upper Mantle Comm. Symposium on non-elastic processes in

the mantle, Newcastle-upon-Tyne 1966, Proc.: Royal Astron. Soc. Geophys. Jour., v.

14, nos. l^t, p. 261-279. 

Eardley, A. J., Gvosdetsky, Vasyl, and Marsell, R. E., 1957, Hydrology of Lake Bonneville

and sediments and soils of its basin: Geol. Soc. America Bull., v. 68, no. 9, p. 1 HI1201. 

Gilbert G. K., 1875, Report on the geology of portions of Nevada, Utah, California, and

Arizona: U.S. Geog. and Geol. Surveys West of the 100th Meridian Report (Wheeler),

v. 3, p. 17-187.

______1890, Lake Bonneville: U.S. Geol. Survey Mon. 1, 438 p. 

Hunt, C. B., Varnes, H. D., and Thomas, H. E., 1953, Geology of northern Utah Valley,

Utah: U.S. Geol. Survey Prof. Paper 257-A, 99 p. 

Miller, C. Dan, 1973, Chronology of Neoglacial deposits in the northern Sawatch Range,

Colorado: Arctic and Alpine Research, v. 5, no. 4, p. 385^100. 

Morrison, R. B., 1965, Lake Bonneville Quaternary stratigraphy of eastern Jordan

Valley, south of Salt Lake City, Utah: U.S. Geol. Survey Prof. Paper 477, 80 p. 

U.S. Bureau^of Reclamation, 1960, Earth manual: Washington, U.S. Govt. Printing Office,

751 p. [Revised 1963].

U. S. Government Printing Office: 1979 O-677-026/3!