Smithsonian Institution Logo The Geology of Chaco Canyon, New Mexico
In Relation To The Life And Remains Of The Prehistoric Peoples Of Pueblo Bonito
Smithsonian Miscelleanous Collections
Volume 122, Number 7



The following sections, measured at various places along the main arroyo, record the character and thickness of the several strata from the top of the bank to its base, and give a record of human relics found therein. Each station is indicated on the accompanying map, figure 1, by its corresponding number.

Section 1

South bank of main arroyo, 200 yards east of expedition camp. No potsherds were recovered in this section but opposite, in the north bank, plain ware of coarse texture was found at a depth of about 12 feet.


FeetInches FeetInches
Laminated dark clay and sand, more clayey above40 40
Silt with streaks of clay30 70
Sand20 90
Laminated dark silt06 96
Silt and sand with thin streak of clay 18 in. above base34 1210
Dark clay, with shells08 136
Sand30 166
Covered below.


At the place on the map marked "Pit House" there was discovered in 1922 a structure partly destroyed by erosion of the arroyo bank. What remained was excavated and studied by Neil M. Judd, who has described it at length (Judd, 1924). It consisted of a single circular room with the middle of its slightly concave floor 12 feet 2 inches below the present surface. The original excavation was 6 feet deep (pl. 6, lower). The builders of this subterranean house lived when the flood plain was 6 feet lower than it now is, and doubtless they or their contemporaries are responsible for the human relics at deeper levels shown in the sections to follow.

Section 2

In a small tributary entering the main arroyo from northwest of Pit House.


FeetInches FeetInches
Soil and clay, more sandy above110110
Hard compact sandy clay with fragments of charcoal and 2 potsherds14
Clay with scattered bits of charcoal and with fire place at base marked by crescentic streak of charcoal and burned ground below0561
Sandy adobe3091

Near section 2 and in the same small arroyo, there is a ruined house now almost destroyed by erosion. Its foundations reach to a depth of 8 feet below the surface, yet the walls appear to be quite similar to masonry of the neighboring great pueblos and the potsherds are of both early and late types.

Two alternatives must be considered, either the pit house and this small pueblolike dwelling are contemporaneous, which is unlikely, or, granting that the pit house is older, the pueblo-type dwelling and section 2 are located in a later deposit.

Section 3

Section 3, on the south bank about 300 yards east of the pit house, represents a normal succession of beds. A potsherd at 4 feet below the surface is of undetermined type. Sherds found between depths of 17 feet and 20 feet 6 inches, are of Pit House or older age. This is the greatest depth at which potsherds were found.


FeetInches FeetInches
Soil and clay, upper 8 in. the most clayey 2626
Silt 1036
Alternate layers of clay and silt; potsherds 6 in. from top of this layer and 4 ft. from surface 1650
Clay 1060
Sand 2686
Alternate layers of clay and silt 16100
Silt and sand laminated and crossbedded and grading into lower layer 70170
Clayey sand; much scattered charcoal, sandstone fragments, some of which are reddened by fire, potsherds and worked cores of quartzite and agate 20190
Sand, with a few sandstone fragments and potsherds at bottom. Marks base of culture layer. 16206
Sandy adobe darker than that above with plant impressions 352311
Covered to bed of arroyo 71310

Section 4

In the north bank of the main arroyo and near the "store" at southeast corner of Pueblo del Arroyo (pl. 7, lower). The section was measured in the middle of a channel deposit which lies beneath a horizontal clay layer. The deposit itself is 13 feet 5 inches thick at the deepest point exposed, and its base is 15 feet below the level of the adjacent plain. Nearby, in 1877, Jackson found potsherds, bones, and a human skull at a depth of 14 feet, as discussed on page 32.


FeetInches FeetInches
Sand, with lenses of fine gravel and clay which dip toward center of old channel. Crescentic lense of laminated clay; depth of lowest part 12 ft., thickness 6 in. Sandstone blocks imbedded in this clay like steppingstones. Gravel layer at base. Many fragments of bones, broken rocks, a few shells and many potsherds especially near base135 151
Clay and laminated silt, scattered charcoal to depth of 21 ft. 6 in70 221

Section 5

South bank of main arroyo opposite Ruin No. 8 and a short distance east of section 16 (see pp. 29-30). Of special note is a Pueblo III fireplace (pl. 3, right) built when the surface was 5 feet lower than it is now, a second hearth at 12 feet 8 inches, and charcoal at 16 feet 3 inches.


FeetInches FeetInches
Dark clay, a fairly continuous layer that thickens and thins 0808
Fine-grained sand, finely laminated and crossbedded, with impressions of roots 0814
Sand, laminated and containing streaks of charcoal and chunks of clay16 30
Dark clay and laminated sand. Clay is in irregular thin layers which slope from south to north and fade out in irregular broken chunks of clay imbedded in sand. A firebox formed of nearly vertical sandstone slabs at depth of 5 ft. is of P. III type2959
Compact rusty sandy clay with fragments of stone, potsherds, and charcoal. Potsherds are 6 ft. 3 in. from surface and of indeterminate type0663
Crossbedded sand to crescentic hearth 12 ft. 8 in. below top of section; scattered charcoal at 14 ft. 8 in. and, 50 ft. south of section, at 16 ft. 3 in.130193
Covered below.

Sections 6 and 7

Sections 6 and 7 are near each other and in the north branch of the main arroyo opposite Una Vida (fig. 1). The bedding is very irregular in this vicinity, and none of the layers listed is persistent. Section 6 has potsherds considered to be of Pueblo III type between 4 feet 6 inches, and 5 feet below the surface. Section 7 shows a very large hearth 8 feet from the surface.

Section 6

In north bank of north channel, near Una Vida.


FeetInches FeetInches
Dark clay. Potsherds at 4 ft. 6 in. and 5 ft50 50
Crossbedded sand, with lenses of clay a few feet off the line of the section 3686
Crossbedded sand and silt26126
Clayey silt to bottom of arroyo4 0186

Section 7

In south bank of north channel, 100 yards upstream from section 6.


FeetInches FeetInches
Clay, with open hearth at base. Hearth is 8 ft. long and burnt (red) ground is nearly 1 ft. thick with much charcoal above2080
Sand and silt1292
Sand and silt to bottom of arroyo37 142

Section 8

South bank of main arroyo 2 miles east of Wejegi and outside the area of our map.


FeetInches FeetInches
Dark clay2 020
Laminated and crossbedded sand with a few lenses of gravel. At depth of 10 ft. 4 in. there is a streak of charcoal resting on burnt (red) earth; at 13 ft. 2 in., a second streak of charcoal, directly below the first but no red earth; scattered charcoal occurs to depth of 21 ft25 4274
Covered below.

Section 9

In arroyo of Rincon del Camino, about 300 feet south of the road and in the fan of the rincon.


FeetInches FeetInches
Compact rusty sandy clay with fragments of stone and charcoal; potsherds at 6 ft. 3 in.6 363
Crossbedded sand with impressions of plant stems and scattered charcoal to depth of 14 ft. 8 in. At depth of 12 ft. 8 in. there is a hearth crescentic in section and consisting of baked and reddened floor 2 ft. 1 in. across and rising 3 in. at the ends with layer of charcoal from 1/2 to 1-1/2 in. thick. South 50 ft. from this section, scattered charcoal occurs to a depth of 16 ft. 3 in. from top of bank13 0193

Section not numbered

North bank of main arroyo west of 1924 dump. [South of the Wetherill corrals and 100 yards, more or less, west of the expedition camp.—N. M. J.]


FeetInches FeetInches
Apparently uniform indurated sand mixed with adobe and a little silt6 060
Laminated clay interbedded with slightly indurated sand. Fine interbeddings well defined and nearly parallel. Lower 0.7 ft. has broader laminae2 787
Indurated sand laminated without adobe1 6101
Fine white sand slightly indurated and finely laminated1 0111
Nonlaminated clayey sand, indurated0 5116
White sand slightly and inconspicuously laminated0 9123
Well-indurated inconspicuously laminated sand with large content of fine silt or clay2 81411
Gray sand slightly laminated and indurated2 8177
Clay containing sand and showing tendency to granulate and fissure on shrinkage (adobe)2 8203
Fine nonlaminated sand slightly indurated1 2215
Clay containing some sand and showing tendency to granulate and fissure on shrinkage2 7240
Pulverant loamy sand containing minute black fragments (moist)3 0270

Section 15

In middle of buried channel, on south bank of main arroyo and 200 yards upstream from mouth of Rincon del Camino.


FeetInches FeetInches
Alternate bands of sandy clay with internal cracks and compact sand4040
Compact sand1757
Sandy clay with internal cracks and streaks of compact sand1269
Minutely crossbedded compact sand with a few lenses of clay 3 to 4 ft. long near base34101
Crossbedded compact sand with lense of gravel 1 ft. thick and 4 ft. long at base, containing burnt sandstone blocks up to 6 in. across, clay pellets, blocks of clay, and potsherds of late type, base of buried channel30131
Crossbedded sand, crossbedding on larger scale, streaks of pieces of black shale and coal23154
Compact crossbedded sand271711
Covered5 02211

Section 17

At the mouth of Rincon del Camino a narrow point projects into the main arroyo from the north. On the east face of this point a well defined buried channel is exposed. Section 17 was measured in the middle of this exposure.


FeetInches FeetInches
Yellow pulverant sand derived from Rincon del Camino0 606
Sandy clay with internal cracks1 016
Yellow pulverant sand derived from Rincon del Camino1 4210
Sandy clay with internal cracks contains sand lense to south of section2 856
Gray, minutely laminated sand; laminae slope to south, are interbedded there with clay layers4 10104
Yellow crossbedded compact sand with gravel lenses. To the south a clay lense. Upper gravel at 13 ft. 7 in., lower at base, contains clay balls, pellets, and potsherds of late type in both lenses5 8160
Sandy clay, upper part has internal cracks; base of buried channel2 4184
Compact laminated sand with lenses of clay having internal cracks to bed of arroyo6 2246


In 1922 Mr. Judd had dug a number of pits in the vicinity of Pueblo Bonito in order to obtain soil samples for analysis. None of these pits exceeded 10 feet in depth because that appeared to be well below the level of fields once cultivated by the villagers and subsequently overlain by post-Bonito alluvial deposits. Pit number 3, located in the plain between the expedition camp and the ruin, had been fenced and left open for possible further tests. When this pit was deepened at my suggestion in 1925 we were all surprised to find late Bonito potsherds at depths of 10 to 18 feet. This meant we were right in the middle of the buried channel. Some fragments showed the influence of contact with the Mesa Verde culture, thus further identifying the channel fill as contemporaneous with the last years of Pueblo Bonito or even later and, of course, much later in age than the main valley fill.

Log of test pit number 3

Between Pueblo Bonito and expedition camp

Materials foundThickness

Found at

FeetInches FeetInches PotsherdsFeet
Dark sandy clay (adobe)2020
Laminated fine sand and silt2242
Dark sandy clay (adobe)09411
Sand with thin layers of laminated silt and clay111610
Laminated layers of silt and dark clay411011
Dark sticky clay0111110 A few A few10
Laminated fine sand25143
Laminated clay071410
Laminated and minutely crossbedded coarse sand. This bed grades to south into gravelly clay that extends to depth of 16 ft. 10 in15163 Many16
Dark clay05168
Fine sand021610
Gravelly clay containing large and small stones, grades into sand to south15183 Numerous17
Fine sand0318618

Log of test pit number 4

Sixty feet east from arroyo bank at section 4

Materials foundThickness

Found at

FeetInches FeetInches PotsherdsFeet
Gray-brown sandy clay (adobe)110110
Laminated sandy adobe, a lense0220
Hard brown sand with pieces of charcoal2242
Brown sand in part finely laminated with lenticular streaks of dark laminated clay 1/2 to 1 in. thick and spaced 2 to 10 in. apart3 375 One only
One only
Hard brown sand, containing at north end of pit an irregular lense of sandy and gravelly adobe containing charcoal and bones2 5910 Many96
Dark sandy clay (adobe) with small lense of gravel4 7145 Many in gravel10

Sand (a lense) that extends to 15 ft. at north end of pit0 3148
Adobe to bottom of pit0 9155 Many15

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Last Updated: --2008