Alluvial Fills Near 

Gallup, New Mexico

GEOLOGICAL SURVEY WATER-SUPPLY PAPER 1110-A

Alluvial Fills Near 

Gallup, New Mexico

By LUNA B. LEOPOLD and C. T. SNYDER

CONTRIBUTIONS TO HYDROLOGY, 1948-51

GEOLOGICAL SURVEY WATER-SUPPLY PAPER 1110-A

A study of erosion and deposition in late 

Pleistocene and Recent time

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1951
UNITED STATES DEPARTMENT OF THE INTERIOR 

Oscar L. Chapman, Secretary

GEOLOGICAL SURVEY 

W. E. Wrather, Director

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

Washington 25, D. C. - Price 15 cents
CONTENTS

Page

Abstract __________________________________________________________ 1

Introduction. _________ ____________________________________________ 1

General description of the Gallup area_ ______________________________ 1

Location and drainage_________________________________________ 1

Geologic history.__-_-____.-_____---_-___________-.____-___-___. 3

Stratigraphy of the alluvium._______________________________________ 3

Gamerco formation ________________ ____________________________ 6

Nakaibito formation____________________________________________ 9

General features at type locality___ ________________ _________ 9

Differentiation within the formation _________________________ 11

Post-Nakaibito erosion and channeling, _ ____---____-._______--___ 12

Conclusions: Correlation and interpretation.__________________________ 15

References cited-________--__----__________________---____-__--.-___ 17

Index._____________________________________________________ _____ 19

ILLUSTRATIONS

Page

FIGURE 1. Map showing location of Gallup area, N. Mex______________ 2

2. Puerco River channel east of Gallup, showing progress of

erosion.______________________________________________ 5

3. Caliche-veined Gamerco formation overlain by Nakaibito

formation in Puerco River channel____________ ___________ 6

4 Gamerco formation overlain by Nakaibito formation in arroyo

tributary to Puerco River _ ____________________________ 7

5. Contact betwaen Mesaverde formation and Gamerco formation in Mexican Springs Wash, north of Gallup ___________ 8

6. Sketch map and cross section on Mexican Springs Wash______ 10

7. Stratigraphic relations of alluvial fills in area near Gallup____ 12

8. Filled channel, cut in Nakaibito formation, on Puerco River. _ 13

in

CONTRIBUTIONS TO HYDROLOGY, 1948-51

ALLUVIAL FILLS NEAR GALLUP, NEW MEXICO

By LUNA B. LEOPOLD and C. T. SNYDER

ABSTRACT

Valleys near Gallup, N. Mex., similar to many in the Southwest, were filled 

In Recent time with alluvium. This material is now being eroded by systems of 

gullies, and the walls of these gullies provide exposures by which the history of 

the deposition of the alluvium can be traced.

Alluvial fills near Gallup have been eroded at least twice previously within 

Recent time. The middle fill of the three that are recognizable contains potsherds of Pueblo II age, indicating that deposition was occurring as late as 

A. D. 1200.

The chronology of alluviation and degradation for valleys in the Gallup area 

appears to agree with that for other valleys in the Southwest which have been 

studied.

INTRODUCTION

Geologic studies in the Southwest during the past two decades have 

furnished detailed knowledge of the late Pleistocene and Recent history of widely separated areas. Through the work of geologists and 

archeologists, a working hypothesis concerning the sequences of 

erosion and sedimentation and their probable relation to climate and 

to early man is available. This report discusses a locality where such 

relations have been worked out.

Part of the Water Resources Division's program for the investigation of sediment problems in the United States, the report was prepared in the Technical Coordination Branch under the general 

supervision of R. W. Davenport, Chief. The manuscript was read 

by the late Professor Kirk Bryan, of Harvard University, whose 

comments are gratefully acknowledged.

GENERAL DESCRIPTION OF THE GALLUP AREA 

LOCATION AND DRAINAGE

The area to be discussed includes the reach of the Puerco River (Rio 

Puerco del Oeste) at Gallup, in northwestern New Mexico, and certain

1
CONTRIBUTIONS TO HYDROLOGY,, 1948-51

ephemeral streams tributary to the Chaco River that drain the south 

end of the Chuska Mountains (fig. 1). These ephemeral streams are 

within the Mexican Springs Experiment Station, formerly under the 

jurisdiction of the U. S. Soil Conservation Service and now under 

the Bureau of Indian Affairs. The station is 18 miles north of Gallup 

on U. S. Highway 666.

Mexican Springs ' ES3'

Gallup

A -R I Z 0 N A / / N E \N

Chaco Canyon 

National Monument

\

Hoi brook...

'Ki

EXPLANATION

Areas discussed 

in this report

\

50 Miles

FIGURE 1. Map showing the location of the Gallup area, N. Mex.

The Puerco River rises in the Jurassic and Cretaceous sandstones 

and shales between the south face of the Dalton Plateau and the north 

edge of the Zuni Mountains; it flows westward through the town of 

Gallup toward the Little Colorado River. The streams in the Mexican 

Springs area head in the Eocene (?) Chuska sandstone and Tohatchi 

shale and flow eastward over extensive areas underlain by the Upper 

Cretaceous Mesaverde formation to join the Chaco River, a tributary 

of the San Juan.
ALLUVIAL FILLS NEAR GALLUP, NEW MEXICO 3

GEOLOGIC HISTORY

The late Tertiary and early Quaternary history of the area has 

been discussed by Reiche (1941). He mapped a series of eight graded 

erosion surfaces, generally gravel-capped, representing periods of 

temporary stability during the lowering of the local base level of 

Mexican Springs Wash and its predecessors. The erosion surfaces 

formed during these temporary halts are at successively lower altitudes and are considered by Reiche to be stages during the Canyon 

erosion cycle (Pleistocene) as defined at the Grand Canyon (Fenneman, 1931).

The Canyon erosion cycle was followed by the alluviation of the 

canyons. This process, which began while glaciers presumably still 

existed in the southern Rocky Mountains, was interrupted several times 

by erosion. The details of these alternating periods of erosion and 

deposition are the subject of the present discussion. Reiche, however, did not attempt to study these relatively recent episodes. He 

merely observes (1941, p. 56) : "The alluvium in the valley bottoms 

is a recent flood plain deposit with a thickness * * * in excess 

of thirty feet. It consists of silty clays and abundant if not predominant sandy members." He mentions, also, that "no single episode 

in the Quaternary history of the Mexican Springs district seems so 

characterized by wind action as the period between the No. 1 and 

No. 2 valley fills [Jeddito and Tsegi formations] described by Hack 

[1939; but see also 1942] for the Jeddito [Jadito] Valley, 90 miles 

to the west."

During the past century the present arroyos have cut into the alluvium and have exposed evidences of the previous periods of cutting 

and deposition on the gully walls, not only in the area described by 

Reiche, but also along the Puerco River near Gallup.

STRATIGRAPHY OF THE ALLUVIUM

The alluvium that fills the original valleys cut in the relatively 

soft shale and sandstone bedrock varies greatly in depth. At a 

point just above Gallup, the original valley of the Puerco River was 

cut to a level only 20 feet lower than the top of the alluvium, but 

borings at the new overpass on U. S. Highway 66, nine miles west of 

Gallup, have shown that bedrock lies 95 feet below the top of the 

alluvium at that locality.

This valley fill consists of bodies of alluvium separated by marked 

disconformities. The older alluvial fill is here called the Gamerco 

formation; it rests unconformably on bedrock and consists of sand 

and silt grading rapidly downward to gravel. On the eroded surface
4 CONTRIBUTIONS TO HYDROLOGY, 1948-51

of the Gamerco a distinct soil profile characterized by a zone of heavy 

caliche accumulation (B horizon) was observed. Just east of Gallup 

this surface lies about 15 feet below the top of the later alluvium.

After a period of strong erosion, a body of water-laid sand and silt 

containing lenses of fine gravel, here called the Nakaibito formation, 

was deposited on the eroded surface of the Gamerco. Potsherds of 

Pueblo I and Pueblo II types are found in this alluvium, which filled 

the Puerco River valley to the level of its present floor. A period of 

moderate to weak erosion followed, and in some localities long channels about 150 feet wide were cut. Ordinarily these channels were 

about 9 feet deep, but in places they reached a depth of 18 feet. They 

were probably discontinuous in many places but were nevertheless 

of appreciable size, and in them a third fill was deposited. In other 

localities examined, no erosion of consequence followed the deposition 

of the Nakaibito until, in modern times, the present arroyos were 

formed. Dune formation is now in progress, although most of the 

dunes are stabilized by vegetation.

Bryan (1925) showed that the year 1885 marked the general beginning of arroyo cutting in the Southwest, but he indicated that in 

northern Arizona and southern Colorado the date is apparently earlier, 

perhaps soon after I860. This agrees in general with the notes of 

Beale (1858), who in 1857 observed that the Rio "Puaco" (Puerco), 

2 days' journey by wagon west of Navajo Church near Gallup, was 

a "deep gulley." However, where the Puerco joins the Little Colorado, 

Beale found large cottonwoods in the river bottom which would indicate no appreciable erosion at that place even though he had just 

cut down the banks of two arroyos "to admit passage of our wagons."

The modern arroyo, like many in the Southwest, probably began 

as a series of short discontinuous gullies. Figure 2 shows that the 

Puerco River above Gallup was about 6 feet deep in 1901 and suggests 

that a greater part of the erosion forming the present arroyo occurred 

in the period 1901-46 than in the 40 years prior to 1901.
ALLUVIAL FILLS NEAR GALLUP, NEW MEXICO

FIGURE 2. The Puerco River channel 2 miles east of Gallup, N. Mex., showing the 

progress of erosion in 45 years. The upper photograph was taken by N. H. Darton 

(USGS file no. 874) in 1901; the lower by L. B. Leopold in August 1946. The gully 

in 1901 was about 6 feet deep ; in 1946 it was 20 feet deep, and its walls were nearly 

vertical. Note that the road cut (A) in the 1901 view was filled with soil material 

when the railroad grade was moved; the old road now appears as light-colored fill (A) 

exposed in the gully wall just left of the center of the lower picture. The large rocks 

near which the man is standing in the lower photograph appear in the lower left of 

the upper photograph, showing the increase in the width of the gully.

947836 51-
6 CONTRIBUTIONS TO HYDROLOGY, 1948-51 

GAMERCO FORMATION

The Gamerco formation (fig. 3) receives its name from a suburb of 

Gallup. At the type locality near the outskirts of the town, 300 yards 

east of the El Rancho Hotel, the Gamerco crops out in the gully 

wall of the Puerco River. It appears near the bed of the present 

stream as an eroded remnant of fossil soil, the complete profile of

FIGURE 3. Caliche-veined Gamerco formation (A) overlain by sand and silt of the 

Nakaibito formation (B) in the Puerco River channel half a mile east of Gallup, N. Mex. 

The filled channel eroded in tlie Nakaibito appears at the top (C). Note the caliche 

veins protruding from the softer, stream-smoothed silt of the Gamerco formation.

which can be seen in only a few places. The formation occurs, also, 

in the arroyo tributary to the Puerco River where that tributary is 

bridged, iy2 miles east of Gallup, by the railroad and by Highway 66 

(fig. 4). It is exposed in the walls of Mexican Springs Wash 18 miles 

north of Gallup and 4,000 feet west of Highway 666, which crosses 

ihe wash on a bridge, and it crops out in Deer Springs Wash, Black 

Creek Wash, and Chuska Wash, all in the general vicinity of Mexican 

Springs.
ALLUVIAL FILLS NEAR GALLTJP, NEW MEXICO

i

FIGURE 4. Gamerco formation overlain by the Nakaibito formation at the railroad bridge 

over an arroyo tributary to the Puerco River 1% miles east of Gallup. The hammer 

has been placed near the contact. The relative hardness of the Gamerco, resulting from 

weathering and calcification, is shown by the smooth surface which stream abrasion 

produces.

The stratigrapllic sequence of the Gamerco formation at its type 

locality is as follows:

Stratigraphic sequence of Gamerco formation at type locality near El RancJio

Hotel, Gallup, N. Hex.

Nakaibito formation: Feet 

Clay, brown-buff, and sand___________ _ _ _ 12 

S'and, moderately coarse, yellow, with lenses of pebbles 3 

Disconformity. 

Gamerco formation:

Sand, reddish to reddish-brown, silty, fine, compact, containing hard, calcareous concretions % to 1 inch in diameter and caliche-filled tubes % to % inch in diameter 

(grades into next bed)_ 2
8 CONTRIBUTIONS TO HYDROLOGY, 1948-51

Ptratiffrap/lie sequence of Oamcrco formation at type locality near El Runcho 

Hotel, Gallup, N. Hex. Continued

Gaiuerco formation Continued Feet 

Sand, brown, compact, silty, fine, with white mottling of 

caliche. S'mall veins of caliche extend downward nearly 

to base of section : top 12 inches is particularly hard and 

forms cliffs ; whole compact layer is fluted and abraded by 

flow of present stream. Nodules and veins of caliche 

stand out in relief from water-worn surfaces (fig. 3)__ 4 

Gravel, fine, partly cemented with caliche, containing subrounded pebbles of different types of rocks characterizing 

area; many pebbles covered with strong layer of caliche 

(fig. 5)_-_____________ ___ ____ 1-2 

Disconformity.

Bedrock: Shale and sandstone of Gibson coal member of Mesaverde formation (Upper Cretaceous), comprising floor of present stream channel at this point.

FIGURE 5. Contact between the Mesaverde formation (Upper Cretaceous) below and the 

Gamerco formation above in Mexican Springs Wash, 4,000 feet upstream from Highway 

666 and 18 miles north of Gallup, N. ilex. This is a good exposure of the Gamerco 

in that it shows the caliche-coated basal gravel overlain by the compact, cliff-forming 7> 

horizon of the fossil soil. The compactness results from the high content of caliche 

cementing the grains. The A horizon of the fossil soil is missing. The slopes above 

the vertical wall are composed of material of the Nakaibito formation, whose surface 

is hummocky with small stabilized dunes.
ALLUVIAL FILLS NEAR GALLUP, NEW MEXICO 9

The calichified horizon containing concretions is considered to be 

the B horizon of a fossil soil. The material of this layer, when observed under a lens, is seen to be perforated with large numbers of 

minute, irregular holes and tubes, mostly lined with calcite, aragonite, 

or amorphous caliche. These minute tubes appear to have been 

formed by the decomposition of enclosed rootlets. No bones nor 

artifacts have yet been found in this formation.

Practically every exposure of the Gamerco formation occurs where 

bedrock, the Mesaverde formation, crops out in the gully channel. 

It appears that the few remnants of the Gamerco are preserved only 

where the bedrock locally prevented further deepening of the channel 

or inhibited complete erosion by lateral corrasion.

NAKAIBITO FOEMATION 

GENERAL, FEATURES AT TYPE LOCALITY

Most of the alluvium in the valleys near Gallup varies greatly in 

detail from one wash to another, depending primarily on the rocks 

from which the sand, silt, and clay were derived. Mexican Springs 

Wash near Nakaibito, 18 miles north of Gallup, is chosen as the type 

locality of the Nakaibito formation because the formation contained 

potsherds there. "Nakaibito"" is the Navajo word for Mexican 

Springs and is the local name for the immediate vicinity of the experiment station headquarters buildings.

The exposure at the type locality is shown on the map and the diagrammatic cross section of figure f>. The older Gamerco formation 

also is exposed, and the eroded surface on which the Nakaibito was 

laid down is easily seen. The Nakaibito here consists of 22 feet of 

interbedded tan-brown sand and silt, including several thick layers 

of imcemented yet massive sand. The fill is irregularly cross-bedded 

and contains occasional lenses of unconsolidated, subrounded fine 

gravel, particularly near the base. Bits of coal from the nearby Gibson 

coal member of the Mesaverde formation are abundant.

Near Gallup, the fill that overlies the Gamerco formation and prewumably is equivalent to the Nakaibito consists of 20 feet of sandy silt 

in layers 1 to 3 feet thick. It is cross-bedded in places and contains 

occasional lenses of fine gravel. Darker bands representing partial 

soil development occur, particularly near the top of the fill.

Two potsherds were buried 14 feet from the present top of the 

exposure at the type locality, as shown in the cross section of figure 6. 

They lay in place within a horizontal distance of 50 feet and a vertical 

distance of only 1 foot. One sherd, of late Pueblo I utility ware, included part of a handle. The second sherd was Chaco black-on-white 

ware of Pueblo II age. Both were identified and dated by Dr. Dorothy 

L. Luhrs, of the Hancock Foundation, whose assistance is gratefully 

acknowledged.
10 CONTRIBUTIONS TO HYDROLOGY, 1948-51

From plone-toble mop by Luna B. Leopold, 

October 10, 1949

EXPLANATION

Dunes and wind-worked 

colluvium

Gamerco formation 

sand and gravel

Mesoverde formation 

bedrock

FIGURE 6. Sketch map and cross section on Mexican Springs Wash, 18 mi'es north of 

Gallup, N. Mex., and 4,000 feet upstream from the bridge on Highway 666.

On the bedrock hill adjacent to the type locality of the Nakaibito 

formation, potsherds were common, lying on the surface of the recent 

wind-worked colluvium. Identified by Dr. Luhrs, they included fragments of Exuberant-corrugated ware of Pueblo I age, Kiatuthlanna 

of Pueblo II age, and Chaco black-on-white of Pueblo II age. These 

sherds probably indicate that the locality was a camp site, occupied 

occasionally over a period of time.

Because of the adjacent camp site, it may be logically assumed that 

sherds of various ages were washed by floods from some similar camp 

site farther upstream during the deposition of the Nakaibito forma-
ALLUVIAL FILLS NEAR GALLTJP, NEW MEXICO 11

tion. The sherds in place in the fill indicate that alluviation was in 

progress at the type locality during or after Pueblo II time, or A. D. 

900-1100.

DIFFERENTIATION WITHIN THE FORMATION

Though in most places there are no indications of discontinuities 

within the Nakaibito formation, two localities offer evidence of a 

possible pause during deposition. Exposed in the walls of Deer 

Springs Wash, 1 mile above the diversion dam and 2 miles southeast 

of the Mexican Springs Experiment Station headquarters, is an eroded 

mass of older material, buried by the main portion of the Nakaibito 

formation. No lithologic evidence of any age difference between this 

buried, eroded mass of alluvium and the main body of the fill was 

observable other than the markedly disconformable contact. The 

buried mass consists of layers of yellowish-buff sand and silt, whereas 

the overlying material consists of thin layers of yellowish-buff clay 

and sand. The contact, which slopes 19° to 27° in the exposed section, 

is marked by a thin layer of clay containing gray clay masses which 

break open to show radial cracks stained with limonite.

The stratigraphic relations are shown diagrammatically in section 

D of figure 7. As is indicated, an outcrop of heavily calichified fossil 

soil of the Gamerco formation occurs nearby, and the buried sand 

outlier of the older phase of the Nakaibito contains no caliche. The 

sand outlier therefore is probably much younger than the Gamerco 

formation.

A second indication of a possible pause during the deposition of the 

Nakaibito occurs in the wall of Mexican Springs Wash about a quarter 

of a mile above the mouth of Chuska Wash. It is shown in the following section:

Stratigraphic section in Mexican Springs Wash, one-quarter mile above mouth

of Chuska Wash

Feet

Loam, dark-brown, sandy (present soil), with slight development of caliche at B horizon____________________ 2

Sand, tan-brown to buff_______________________ 6

Disconformity, flat but sharply defined.

Silt, medium brown to pinkish, sandy, with caliche mottling; 

compact. Small veins of caliche reach to top of layer and 

fade out below depth of 16 inches. Clay has filled root 

cylinders, surfaces of which are white with thin layer of 

caliche. No concretions______________________ 2

Sand, tan to light-brown, without caliche_____________ 6

The caliche in this section was not nearly so well developed as that 

in the Gamerco formation, and the absence of concretions, which have
12 CONTRIBUTIONS TO HYDROLOGY, 1948-51 

BLACK CREEK PUERCO RIVER

PUERCO RIVER DEER SPRINGS WASH

Horizontal scale

50 Feet

Vertical scale 

EXPLANATION

Modern colluvium

Channel deposits

Nakaibito formation

sand and silt 

Upper part is younger phase

Upper part cemented by caliche

Mesaverde formation 

bedrock

FIGURE 7. Stratigraphic relations of alluvial fills in the area near Gallup, N. Mex.

been found in every outcrop of the Gamerco, definitely shows that 

the alluvium just described is younger than the Gamerco. The moderately well developed soil at the present ground surface of this 

section indicates greater stability of the upper surface here than 

over the wide areas of the Nakaibito occurring at lower altitudes, 

where soil development at the present surface is mostly absent.

The foregoing evidence indicates that the Nakaibito formation has 

two phases, the older of which is separated by erosion from the 

younger. This division, as will be shown, also is characteristic of 

Hack's (1942) Tsegi formation in the Hopi area and Albritton and 

JBryan's (1939) Calamity formation in trans-Pecos Texas.

POST-NAKAIBITO EEOSION AND CHANNELING

Channels of moderate size were cut and wholly or partly filled 

after the deposition of the Nakaibito formation was essentially complete. In the 2-mile reach upstream from Gallup, a filled channel
ALLUVIAL FILLS NEAR GALLTJP, NEW MEXICO 13

cut in the Nakaibito is well exposed and easy to trace. Just east of 

Gallup it consists of a cut 9 to 13 feet deep and 150 feet wide, filled 

with thin bands of red sandy clay and reddish-brown sandy silt. 

The banks are somewhat rounded, and the cross section has the form 

of a flat U (fig. 8). At one exposure a remnant of a bank 4 feet high 

is still preserved because the channel at that point was not completely filled. (See sec. B of fig. 7.) A short distance upstream,

FIGURE 8. Wide U-shaped channel, cut in the Nakaibito formation and later filled with 

red clay and sand, on Puerco River 1 mile upstream, from Gallup, N. Mex.

however, the red material filled the channel to the top and actually 

was deposited as a layer nearly a foot thick over a broad zone adjacent 

to the filled channel.

Three miles east of Gallup, at the hogback formed by steeply 

dipping beds of the Cretaceous Dakota sandstone, the filled channel 

in the Nakaibito formation was as deep as the present arroyo (20 

feet), and its floor actually reached bedrock, which also constitutes 

the floor of the present arroyo there. The filled channel is more
14 CONTRIBUTIONS TO HYDROLOGY, 1948-51

%

than 120 feet wide at this point, and its sides slope 60°. The lowest 10 

feet is filled with thick layers of coarse reddish sand and a few thin 

layers of red silt. The upper 10 feet consists of thinly iiiterbedded 

red clay and lenses of reddish sand. (See sec. C of fig. 7.) The 

difference in color between the filled channel and the adjacent older 

alluvium is striking.

Upstream from the hogback, a large part of the alluvium is red 

and the buried channel was not traced in detail. Downstream from 

Gallup, the Puerco River channel becomes very shallow and its banks 

are no more than 4 feet in height. No evidence of fill channeling 

was observed. The fact that the main body of the fill loses its redness 

downstream indicates that tan alluvium from the lower tributaries 

masked the red material contributed by headwater tributaries. The 

old channel extended upstream in a continuous gully far enough to 

tap the predominantly red material with which it was filled. The 

disappearance of the red color downstream was not due to gradual 

shallowing of the buried channel, at least in the reach where exposures 

are found, although possibly this channel was discontinuous and 

shallowed downstream below the reach where its outcrops could be 

mapped.

At the type locality of the Nakaibito on Mexican Springs Wash, a 

filled channel, the bottom of which is only 3 feet above the present 

arroyo floor, is exposed. The top of the filled channel occurs 

at the level of an old meander scar, as can be seen in figure 6. Numerous small tributaries in the vicinity were graded to the level of 

this well-preserved scar, 13 feet above the present channel. The 

buried channel seems to have been cut after the meander scar was developed and subsequently to have been filled to that same level. The 

contemporaneity of the filled channel and the meander must be considered tentative, however, because present-day wind action and rain 

wash have disturbed the surface material of the meander, somewhat 

obscuring the relations with the exposed filled channel.

Recent dunes have formed on the old meander, active blow-outs have 

reworked the surface layers, and the wind has drifted sand from the 

meander against the adjacent slopes. The dunes are mostly stabilized 

by rabbitbrush, saltbush, grass, and weeds.

Along Black Creek, near the south boundary of the Mexican Springs 

Experiment Station, channeling of the Nakaibito formation similar 

to that in Mexican Springs Wash is observed. A diagrammatic cross 

section of one of these buried channels is shown in section A of figure 

7. Their depth is nearly as great as that of the present arroyo (17 

feet). On Black Creek Wash the channels later were partly filled, 

and the present-day gully has left that surface as a well-marked terrace 12 feet above the present stream bed. The older fill is more high-
ALLUVIAL FILLS NEAR GALLUP, NEW MEXICO 15

ly consolidated than the younger and is lithologically distinct; the 

terrace was observed near the bridge where Black Creek crosses U. S. 

Highway 666 and intermittently upstream for at least a mile. This 

depositional terrace is similar to that seen on Mexican Springs Wash 

at the type locality of the Nakaibito formation and at nearly the same 

height above the stream bed.

CONCLUSIONS: CORRELATION AND INTERPRETATION

Though no bones nor artifacts were found in the Gamerco formation, the well-developed caliche layer, the nodules and caliche-filled 

tubes, and the stratigraphic position of the formation appear to make 

it comparable to the "intermediate alluvium" of Bryan and McCann 

(1943) at Grants, which is only 60 miles away. The authors have inspected some of the exposures at Grants described by Bryan and McCann as contemporaneous with the Neville formation of the transPecos region (Albritton and Bryan, 1939) and have found that the 

caliche-cemented gravels of the Neville seem to resemble those at 

the base of the Gamerco.

Only two potsherds were found in place in the Nakaibito formation. 

One was of Pueblo I and the other of Pueblo II age. This paucity 

of datable material makes any correlation tentative, but the fact that 

the sherds occur in the lower half of the upper part of the Nakaibito 

near Mexican Springs would indicate that alluviation was continuing as late as A. D. 1200. Inasmuch as the Nakaibito rests on the 

eroded surface of a fill apparently comparable to Bryan and McCann's "intermediate alluvium" and the Neville formation, the 

Nakaibito seems to fit into the deposition 2 position of the Bryan-McCann chronology, making it comparable with the Tsegi of Hack 

(1942), the Calamity formation of the trans-Pecos region, and the 

Sand Canyon formation of Judson (1948).

The sparse yet unavoidable indications of a period of stability or 

erosion during the deposition of the Nakaibito formation are evidence, 

comparable to that found elsewhere, that deposition 2 consisted of a 

lower and an upper portion (Hack, 1942; Bryan and McCann, 1943). 

It would appear, then, that the older fill occurring as an outlier in the 

Nakaibito of Deer Springs Arroyo and the calichified lower part of 

the fill in upper Mexican Springs Wash correspond to the earlier portion of deposition 2. It therefore seems probable that the main body 

of the Nakaibito formation which makes up most of the alluvium exposed in the washes of the Gallup area is comparable in age to the upper portion of deposition 2. The present data add to the increasing 

volume of evidence indicating that the erosional break during deposition 2 was of considerable significance (Judson, 1948).
16 CONTRIBUTIONS TO HYDROLOGY, 1948-51

The period of channel erosion in the Nakaibito formation seems to 

correspond to the erosion period following the Tsegi formation of 

the Hopi country and that following the Calamity formation of the 

trans-Pecos region. Bryan and McCann (1943) tentatively assume 

that this period of erosion was more or less contemporaneous throughout the localities in the Southwest that have been studied. On the 

basis of the tentative chronology for the Southwest, deposition 3 is believed to have begun about A. D. 1300; it was probably still continuing 

when present-day arroyo cutting began in the last quarter of the 

nineteenth century.

Deposition 3 is represented in the Hopi country by the Naha formation described by Hack (1942), in the trans-Pecos region by the 

Kokernot formation of Albritton and Bryan (1939), and at the western edge of the High Plains by the Wheatland formation of Judson 

(1948). The Naha formation represented a considerable volume of 

material but did not fill to the top the channel that was cut after 

deposition 2 (the Tsegi formation) was completed. In the transPecos region, deposition 3 not only filled completely the channels 

cut in the earlier alluvium but covered the whole width of the valley 

with a thin sheet of alluvial material.

The Wheatland formation of Judson (1948) was a deposit that 

did not completely fill the channels in which it was laid down. In 

the Grants area, Bryan and McCann (1943) found deposition 3 to 

be small in amount of material compared with their deposition 2. 

These relative volumes are approximately those found in the Gallup 

region. The channels cut in the Nakaibito formation varied from 

10 to 18 feet in depth near Gallup, and at that place the later fill was 

just sufficient in volume to fill the arroyo approximately to its former 

level.

In the Mexican Springs area, the erosion that followed deposition 

2 cut a channel 19 feet deep. This channel was then filled about halfway to the top (fig. 6). In Deer Springs Wash an indistinct terrace about 3 feet in height can be traced for a considerable distance. 

It is possible that this terrace marks the depth of cutting during the 

period between the end of the Nakaibito deposition and the initiation 

of the present-day arroyos. In Black Creek Wash, only a couple of 

miles away, the post-Nakaibito erosion cut a channel 17 feet deep, and 

deposition 3 refilled that channel to a level within 5 feet of the old 

valley floor.

These observations indicate that the relative sizes of channels cut 

in the erosion period after deposition 2 varied, not only between such 

\videly separated areas as the Hopi country and the trans-Pecos region, but even between closely adjacent localities in the Gallnp area.
ALLUVIAL FILLS NEAR GALLUP, NEW MEXICO 17

This is true, also, of the latest epicycle of erosion. At the present 

time wide differences exist in the size and depth of arroyos, not only 

between streams, but along the length of a single channel. Arroyos 

in the vicinity of Notam, Utah, reach 45 feet in depth and 30 feet in 

width. The channel of the Rio Puerco (del Oriente) varies from 

10 to 40 feet in depth and has an average width of 600 to 800 feet 

through considerable reaches. Yet there are innumerable valleys 

with a drainage area comparable to that of Mexican Springs Wash 

above U. S. Highway 666 which have a much smaller arroyo than 

it contains.

These present-day conditions in no way detract from the possibility that the latest fills observed in various valleys of the Southwest are essentially contemporaneous despite the differences in their 

relative size.

The discontinuous channels and the lack of heavy alluviation during the period A. D. 1400-1860 possibly indicate an instability of the 

fill. The climate was not quite humid enough to cause further alluviation, nor was it sufficiently arid to cause degradation. On such 

a stage, postsettlement grazing could play a quick-acting and decisive 

role.

REFERENCES CITED

ALBKITTON, C. C., and BRYAN, KIRK, 1939, Quaternary stratigraphy in the Davis 

Mountains, trans-Pecos Texas: Geol. Soc. America Bull., vol. 50, no. 9, 

pp. 1423-1474.

BEALE, E. F., 1858, Wagon road from Fort Defiance to the Colorado River: 35th 

Cong., 1st sess., H. Ex. Doc. 124, pp. 36-43.

BBYAN, KIRK, 1925, Date of channel trenching (arroyo cutting) in the arid 

Southwest: Science, new ser., vol. 62, no. 1607, pp. 338-344.

BRYAN, KIRK, and MCCANN, F. T., 1943, Sand dunes and alluvium near Grants, 

N. Mex.: Am. Antiquity, vol. 8, no. 3, pp. 281-295.

FENNEMAN, N. M., 1931, Physiography of western United States, New York, 

McGraw-Hill Book Co., Inc.

HACK, J. T., 1939, The late Quaternary history of several valleys of northern 

Arizona: Mus. [Northern Arizona] Notes, vol. 11, no. 11.

 , 1942, The changing physical environment of the Hopi Indians of Arizona : 

Peabody Mus. Archaeology and Ethnology Papers, vol. 35, no. 1, Cambridge, Harvard Univ.

JUDSON, S., 1948, Geologic antiquity of the San Jon site, eastern New Mexico 

(manuscript thesis, Harvard Univ.).

REICHE, PARRY, 1941, Erosion stages of the Arizona Plateau as reflected in a headwater drainage area : Plateau, vol. 13, no. 4, pp. 53-64.

INDEX

Page

Black Creek Wash_________ 6, 14-15, J6 

Bryaii, Kirk, assistance acknowledged- 1 

views on arroyo cutting_____ 4 

work near Grants (with McCann) _____._____ 15,16

Calamity formation_________ 12, 15, 16 

Caliche ____________ 4, 6. 7, 8, 9, 11, 15 

Canyon erosion cycle__ -_ 8 

Chuska Wash _______________ 6, 11 

Correlation with other arcas_ 15-17

Deer Springs Wash____ ____-_ 6, 11, 16 

Deposition, periods of__ _ _-_ 15-17 

Drainage _ ______ _ 1-2

Dunes __.__________________ 4, 8, 14

Gamerco formation_ 8-4, 6-9, 10, 11-12, 15 

measured section___________ 7-8

Geologic history-_____________ 3 

Gibson coal member of Mesaverde

formation ___________ 8, 9

Grants, work near____ ___ _ 15, 16

Hopi country_______________ 12, 16

Jadito [Jeddito] Canyon. 

Jeddito formation____.

Kokernot forma tion- 16

Page 

Location of area____________ 1-2

Lnhrs, Dorothy A., potsherds identified by__________ 9-JO

Mesaverde formation________ 2, 8, 9, 10

Mexican Springs Wash____ _ 3,

6. 8, 9, 10, 11, 14, 15, 17

Naha formation __ __ _ _ _ ____ 16 

Nakaibito formation ______ 4, 6, 7, 8, 9-16

measured section - 

Neville formation 

11

15

Post-Nakaibito history______ 12-15 

Potsherds _______________ 4, 9-11, 15 

Puerco River________ 2, 3, 4, 5, 6, 12-11

Reiche, Parry, discussion of geologic

history by__ ______ 3

Rio Puerco (del Oeste). See Puerco 

River.

Rio Puerco (del Oriente)_________

Sand Canyon formation_____ 

____ 17

____ 15 

Soil, fossil______________ 4, 6, 8, 9, 11

Stratigraphy _______________ 3-17

Trans-Pecos region______ 12, 15, 16 

Tsegi formation__________ 3, 12, 15, 16

Wheatland formation- 16

19

O