A U.S. GEOLOGICAL SURVEY 

DATA STANDARD

Codes for the Identification of 

Aquifer Names and Geologic 

Units in the United States and 

the Caribbean Outlying Areas

U.S. GEOLOGICAL SURVEY CIRCULAR 878-C
This report describes one of a series of data standards adopted and implemented by the U.S. Geological Survey for the standardization of data elements 

and representations used in automated Earth-science systems. Earth sciences 

are those scientific disciplines especially required to carry out the mission 

of the Geological Survey and are concerned with the material and morphology 

of the Earth and the physical forces relating to the Earth. These disciplines include geology, topography, geography, and hydrology.

The Geological Survey has assumed the leadership in developing and maintaining Earth-science data element and representation standards for use in 

the Federal establishment under the terms of a Memorandum of Understanding 

signed in February 1980 by the National Bureau of Standards, Department of 

Commerce, and the Geological Survey, Department of Interior. As such, in 

addition to developing and maintaining standards, the Geological Survey reviews and processes all requests referred by the National Bureau of Standards 

for exceptions, deferments, and revision of standards applicable to Federal 

Earth-science information systems; assists the National Bureau of Standards 

in assessing the need, impact, benefits, and problems related to the implementation of standards being considered for development, or developed, for 

use in the Earth sciences; and works with other agencies in developing new 

data standards in the Earth sciences.

The standard described in this report has been specifically approved for 

use within the U.S. Geological Survey. If the standard has been approved 

for use throughout the Federal establishment, it is also published by the 

National Bureau of Standards as a Federal Information Processing Standard.

Name of Standard: Codes for the Identification of Aquifer Names and

Geologic Units in the United States and the Caribbean Outlying Areas. 

Date of Approval: March 1985 

Maintenance Organization: U.S. Geological Survey

Water Resources Division

Office of the Assistant Chief Hydrologist

for Scientific Information Management 

440 National Center 

Reston, VA 22092

Implementation: All Geological Survey data standards are effective immediately upon the date of approval. Their use is mandatory for all new 

and developing systems within the Geological Survey that utilize data 

elements and representations described by the standards. All existing 

data systems will be modified in accordance with the standards at such 

time that future redesign and modifications to the systems take place.

Additional information about Geological Survey data standards and copies 

of published standards may be obtained from: 

Chairman, USGS Data Standards Committee 

U.S. Geological Survey 

National Mapping Division 

519 National Center 

Reston, VA 22092 

Telephone: (703) 648-4637 

FTS 959-4637
A U.S. GEOLOGICAL SURVEY 

DATA STANDARD

Codes for the Identification of 

Aquifer Names and Geologic 

Units in the United States and 

the Caribbean Outlying Areas

U.S. GEOLOGICAL SURVEY CIRCULAR 878-C

1988
DEPARTMENT OF THE INTERIOR 

DONALD PAUL MODEL, Secretary

U.S. GEOLOGICAL SURVEY 

Dallas L. Peck, Director

Printed 1985 

Revised 1988

Library of Congress Cataloging in Publication Data

Geological Survey (U.S.) 

Codes for the identification of aquifer names and geologic units in the United States and the Caribbean

outlying areas.

(Geological Survey circular ; 878-C) 

At head of title: A U.S. Geological Survey data standard.

Supt. of Docs, no.: I 19.4/2:878-C

1. Aquifers United States Abbreviations. 2. Aquifers Caribbean Area Abbreviations. 3. Geology, Stratigraphic Abbreviations. 4. Geology United States Abbreviations. 5. Geology Caribbean Area Abbreviations. I. Title. II. Series.

GB1199.2.G46 1985 551.49 85-600132

Free on application to the Books and Open-File Reports Section, 

U.S. Geological Survey, Federal Center, Box 25425, Denver, CO 80225
CONTENTS

Page

Abstract......................................................... C1

Acknowledgments.................................................. C1

1. Purpose and Scope................................................ C2

2. Specifications for the codes..................................... C2

2.1 Purpose and source of the codes............................. C2

2.2 Description of the codes.................................... C2

2.3 Development of the codes.................................... C2

2.3-1 Development of the first part of the code................. C2

2.3.2 Development of the second part of the code................ C2

2.3.3 Development of the third part of the code................. C6

2.4 Examples of the codes....................................... C6

2.5 Qualifications of the codes................................. C6

3. Availability of the codes........................................ C8

TABLES

Table 1. Numeric codes for geologic time-stratigraphic

identification............................................. C3

2. Order of letter elimination.................................. C5

ILLUSTRATION 

Figure 1. Example of aquifer names and geologic unit codes............ C7

III

Abstract

This standard provides codes to be used for the identification of aquifer 

names and geologic units in the United States, the Caribbean and other 

outlying areas. Outlying areas include Puerto Rico, the Virgin Islands, 

American Samoa, the Midway Islands, Trust Territories of the Pacific Islands, 

and miscellaneous Pacific Islands. Each code identifies an aquifer or rockstratigraphic unit and its age designation. The codes provide a standardized 

base for use by organizations in the storage, retrieval, and exchange of 

ground-water data; the indexing and inventory of ground-water data and 

information; the cataloging of ground-water data aquisition activities; and a 

variety of other applications.

Acknowledgments

Acknowledgment is given to the following personnel of the U.S. Geological 

Survey who served on a technical working group which had the responsibility 

for the technical review and validation of this standard:

Claire B. Davidson, Water Resources Division 

Robert L. Laney, Water Resources Division 

Gwendolyn W. Luttrell, Geologic Division 

David V. Maddy, Water Resources Division 

Charles 0. Morgan, Water Resources Division 

Owen 0. Williams, Water Resources Division

Cl
1. Purpose and Scope

This standard provides codes used for the identification of aquifer names and 

geologic units in the United States, the Caribbean and other outlying areas. 

Outlying areas include Puerto Rico, the Virgin Islands, American Samoa, the 

Midway Islands, Trust Territories of the Pacific Islands, and miscellaneous 

Pacific Islands. Each code identifies an aquifer or rock-stratigraphic unit 

and its age designation. The codes provide a standardized base for use by 

organizations in the storage, retrieval and exchange of ground-water data; the 

indexing and inventory of ground-water data and information; the cataloging of 

ground-water data acquisition activities; and a variety of other applications.

The codes apply to all areas of the United States and the Caribbean outlying 

areas including Puerto Rico and the Virgin Islands. Codes have also been 

developed for use in American Samoa, the Midway Islands, Trust Territories of 

the Pacific Islands, and miscellaneous Pacific Islands.

2. Specifications for the Codes

2.1 Purpose and Source of the Codes. The codes were developed for use 

in the U.S. Geological Survey's National Water Data and Storage System 

(WATSTORE) that was established in 1971. The coding procedures are based on 

the rock-stratigraphic coding system proposed by the American Association of 

Petroleum Geologists and published in its October 1967 bulletin. The code 

identifies the aquifer or rock-stratigraphic unit and its age designation.

2.2 Description of the Codes. The codes are alphanumeric, a maximum 

eight characters in length, and consist of three parts. The first part 

contains three numeric characters that identify the erathem, system, and 

series (time-stratigraphic units) of the rock unit. The second part contains 

up to four alphabetic characters for the name of the rock-stratigraphic 

unit. A mnemonic code is developed by the selection of letters from the 

name. Rules for this procedure are given below. The third part of the code 

is a single character in position eight and denotes a qualifying term for 

parts of the rock unit such as upper, middle, lower, or basal part. The third 

part may not always exist.

2.3 Development of the Codes. The following sections describe the rules 

to be used in the development of the codes.

2.3.1 Development of the First Part of the Code. Table 1 lists the 

numeric codes that may be used for the first part. If a rock unit extends 

across more than one time-stratigraphic unit, the numeric code for the 

youngest unit is selected.

2.3*2 Development of the Second Part of the Code. The rules used for 

the second part of the code are:

(1) The second part of the code is developed by eliminating letters 

from the orginal name until no more than four letters remain. 

Prior to eliminating letters, the following should be dropped 

from the rock-stratigraphic name.

C2
Table 1. Numeric Codes For Geologic Time-Stratigraphlc Identification

Code 

Unknown Age....................000

Cenozoic....................... 100

Quaternary................... 110

Holocene................... 111

Pleistocene................ 112

Tertiary....................... 120

Pliocene.....................121

Miocene...................... 122

Oligocene.................... 123

Eocene....................... 124

Paleocene.................... 125

Mesozoic.......................200

Cretaceous...................210

Upper......................211

Gulfian..................212

Lower......................217

Comanchean...............218

Coahuilan................219

Jurassic.....................220

Upper......................221

Middle.....................22*1

Lower...................... 227

Triassic.....................230

Upper......................231

Middle.....................234

Lower......................237

Paleozoic...................... 300

Permian...................... 310

Upper......................311

Ochoan...................312

Guadalupian..............313

Lower......................317

Leonardian...............318

Wolfcampian..............319

Pennsylvanian................320

Upper......................321

Virgilian................322

Missourian...............323

Middle.....................324

Desmoinesian............. 325

Atokan...................326

Lower......................327

Morrowan.................328

Code

Mississippian....................330

Upper..........................331

Chesterian................... 332

Meramecian...................333

Lower.......................... 337

Osagean...................... 338

Kinderhookian................339

Devonian......................... 340

Upper..........................341

Middle.........................344

Lower.......................... 347

Silurian.........................350

Upper..........................351

Cayugan...................... 352

Middle.........................354

Niagaran.....................355

Lower.......................... 357

Alexandrian.................. 358

Ordovician....................... 360

Upper.......................... 361

Cincinnatian.................362

Middle.........................364

Champlainian.................365

Lower..........................367

Canadian.....................368

Cambrian.........................370

Upper..........................371

St. Croixan..................372

Middle.........................374

Lower..........................377

Precambrian (informal time term).400

Proterozoic (formal time term)...401 

Late...........................410

Middle......................... 420

Early..........................430

Archean (formal time term).......404

Late...........................440

Middle.........................450

Early..........................460

Pre-Archean (informal time term).407

C3
A. The rank off the unit; such as group, formation, member. 

B. Any lithologic descriptors; such as, sandstone, shale, or

limestone.

C. Insignificant words; such as, the, on, a, an. 

D. Qualifying terms such as upper, middle, or lower. These

terms are used in the development of the third part of the

code (see below).

(2) Rock names such as McGregor, St. Lawrence, Van Alien are to be 

considered as two words. Abbreviations, such as "St. 11 , are to be retained and 

not written out.

(3) Replace all non-alphabetic characters with blanks, except in the 

infrequent case of aquifers or other rock units named by their depth of 

occurrence at some geographic locality, such as the "500-foot sand of the 

Memphis area."

A. If no depth of occurrence is indicated, a mnemonic code of 

up to four alphabetic characters is generated from the 

name to form the second part of the data code.

B. If depth of occurrence is included with the name, the first 

two characters of the second part are numeric and represent 

the depth, while a two-character mnemonic is generated from 

the alphabetic portion of the name to form the last two 

characters of the second part. To obtain the numeric representation, form the depth value into a four-digit numeric by 

adding leading zeros if necessary, and then select the two 

leftmost digits. For example:

500-foot of the Memphis area 05MP 

2000-foot sand of the Baton Rouge area 20BR

(4) Deletion of letters and double letter elimination proceed in the 

sequence of steps given in table 2. For double letter 

elimination (step 9 of table 2), one letter of each double 

letter is deleted. For elimination of each individual letter 

(other steps of table 2), deletion proceeds from right to left; 

each occurrence is deleted except for the first letter of a 

word.

(5) Deletion is continued until the mnemonic is reduced to at least 

four characters, or two characters if the depth of occurrence is 

included.

(6) In the rare instances where the mnemonic reduces to a first letter 

and two sets of double letters (as FTTRR) eliminate the first 

letter on the right without regard for the letter sequence shown 

in table 2.

(7) If the original word is smaller than four characters and the depth 

of occurrence is not indicated, the word is entered in the data 

field left justified. Do not add any characters to fill up the 

data field. Leave unused spaces blank.

C4
Table 2. Order of Letter Elimination

1. A 10. T 19. G

2. E 11. N 20. P

3. I 12. S 21. K

4. 0 13. R 22. B

5. U 14. L 23. V

6. W 15. D 24. X

7. H 16. C 25. J

8. Y 17. M 26. Q

9. Double Letters 18. F 27. Z 

(delete one)

C5
(8) If duplicate codes appear, some alteration of the code will be made 

by the U.S. Geological Survey. This must be done to insure 

system-wide uniqueness. The rule to be followed with formal 

names will be to retain the correct mnemonic code with the name 

which has priority in time. The second name will be coded 

retaining the first vowel. If more than two names reduce to the 

same mnemonic, it may be necessary to make some arbitrary code 

adjustment for the third and any subsequent names. These same 

rules will be used, where possible with informal names.

2.3*3 Development of the Third Part of the Code. Position eight of the 

code may be used for modifiers and qualifying terms of the rock-stratigraphic 

unit. If the word to be coded in position eight is upper, middle, or lower, 

use the letters U, M, or L, respectively, for the code. If any other word is 

to be coded in position eight and the first letter is U. M, or L, use the last 

letter that remains after following the elimination procedure of table 2, 

other than U, M, or L.

2.4 Examples of the Codes. Figure 1 contains a sample list from the 

assigned codes for aquifer names or rock stratigraphic units within one State.

2.5 Qualifications of the Codes. Requests for changes or additions to 

this standard may be made by U.S. Geological Survey employees and must be 

forwarded to the Assistant Chief Hydrologist for Scientific Information 

Management, Water Resources Division, U.S. Geological Survey, 440 National 

Center, Reston, Virginia 22092, who will verify the acceptability of requests 

with the Water Resources Division's representative on the Geologic Names 

Committee. A copy of each request should also be forwarded to the Chairman, 

Data Standards Committee, U.S. Geological Survey, 115 National Center, Reston, 

Virginia 22092. When requesting new codes, the following information must be 

provided:

1. States(s) in which the name of the unit is to be used.

2. Name of the unit for which a code is being requested. If the unit is 

a member of a formation, include the formation name also.

3. Geologic age of the unit; if more than one age is represented, 

provide a Isit of all ages involved.

When requesting changes to existing codes, the following information must be 

provided:

1. The listing of the code and aquifer name exactly as it appears in the 

standard's list of codes and names.

2. The corrections) to be made.

3. The reason for the change and verification that the requested change 

is acceptable to any other States that may be affected.

C6
INDIANA 

CENOZOIC 

CENOZOIC ERATHEM................................................. 100CNZC

QUATERNARY

DUNE DEPOSIT..................................................... 11ODUNE

QUATERNARY SYSTEM................................................ 110QRNR

TERRACE DEPOSITS................................................. 110TRRC

VALLEY TRAIN DEPOSITS............................................ 110VLTR

HOLOCENE

ALLUVIUM......................................................... 111ALVM

COLLUVIUM........................................................ 111CLVM

HOLOCENE SERIES.................................................. 111HLCN

PLEISTOCENE

ICE CONTACT DEPOSITS............................................. 112ICCC

LAKE DEPOSITS.................................................... 112LAKE

LAFAYETTE GRAVEL................................................. 112LFTT

LOESS............................................................ 112LOSS

OUTWASH.......................................................... 1120TWS

PLEISTOCENE SERIES............................................... 112PLSC

TILL............................................................. 112TILL

TERTIARY

OHIO RIVER FORMATION............................................. 1200RVR

TERTIARY SYSTEM.................................................. 120TRTR

PALEOZOIC

PALEOZOIC ERATHEM................................................ 300PLZC

PENNSYLVANIAN

PENNSYLVANIAN SYSTEM............................................. 320PSLV

UPPER PENNSYLVANIAN

BOND FORMATION................................................... 321BOND

MCLEANSBORO GROUP................................................ 321MCLB

MATTOON FORMATION................................................ 321MTTN

UPPER PENNSYLVANIAN SERIES....................................... 321PSLVU

PATOKA FORMATION................................................. 321PTOK

SHELBURN FORMATION............................................... 321SLBR

Figure 1. Example of aquifer names and geologic unit codes

C7
3. Availability of the Codes

The list of codes for the identification of aquifer names and geologic units 

is dynamic in that codes are frequently added or changed as new information 

becomes available. A current list of codes assigned to the standard may be 

obtained by written request to the National Water Data Exchange, U.S. 

Geological Survey, M21 National Center, Reston, Virginia 22092.

C3