Smithsonian Miscellaneous Collections: The Geology of Chaco Canyon, New Mexico (Detailed Sections in the Recent Alluvium)

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

DETAILED SECTIONS IN THE RECENT ALLUVIUM

SECTIONS IN THE MAIN VALLEY FILL

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.

	Thickness		Depth
	Feet	Inches	Feet	Inches
Laminated dark clay and sand, more clayey above	4	0	4	0
Silt with streaks of clay	3	0	7	0
Sand	2	0	9	0
Laminated dark silt	0	6	9	6
Silt and sand with thin streak of clay 18 in. above base	3	4	12	10
Dark clay, with shells	0	8	13	6
Sand	3	0	16	6
Covered below.

PIT HOUSE

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.

	Thickness		Depth
	Feet	Inches	Feet	Inches
Soil and clay, more sandy above	1	10	1	10
Sand	0	2	2	0
Clay	0	2	2	2
Sand	0	7	2	9
Clay	1	7	4	4
Hard compact sandy clay with fragments of charcoal and 2 potsherds	1	4
Clay with scattered bits of charcoal and with fire place at base marked by crescentic streak of charcoal and burned ground below	0	5	6	1
Sandy adobe	3	0	9	1

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.

	Thickness		Depth
	Feet	Inches	Feet	Inches
Soil and clay, upper 8 in. the most clayey	2	6	2	6
Silt	1	0	3	6
Alternate layers of clay and silt; potsherds 6 in. from top of this layer and 4 ft. from surface	1	6	5	0
Clay	1	0	6	0
Sand	2	6	8	6
Alternate layers of clay and silt	1	6	10	0
Silt and sand laminated and crossbedded and grading into lower layer	7	0	17	0
Clayey sand; much scattered charcoal, sandstone fragments, some of which are reddened by fire, potsherds and worked cores of quartzite and agate	2	0	19	0
Sand, with a few sandstone fragments and potsherds at bottom. Marks base of culture layer.	1	6	20	6
Sandy adobe darker than that above with plant impressions	3	5	23	11
Covered to bed of arroyo	7	1	31	0

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.

	Thickness		Depth
	Feet	Inches	Feet	Inches
Clay	1	8	1	8
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 base	13	5	15	1
Clay and laminated silt, scattered charcoal to depth of 21 ft. 6 in	7	0	22	1

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.

	Thickness		Depth
	Feet	Inches	Feet	Inches
Dark clay, a fairly continuous layer that thickens and thins	0	8	0	8
Fine-grained sand, finely laminated and crossbedded, with impressions of roots	0	8	1	4
Clay	0	2	1	6
Sand, laminated and containing streaks of charcoal and chunks of clay	1	6	3	0
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 type	2	9	5	9
Compact rusty sandy clay with fragments of stone, potsherds, and charcoal. Potsherds are 6 ft. 3 in. from surface and of indeterminate type	0	6	6	3
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.	13	0	19	3
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.

	Thickness		Depth
	Feet	Inches	Feet	Inches
Dark clay. Potsherds at 4 ft. 6 in. and 5 ft	5	0	5	0
Crossbedded sand, with lenses of clay a few feet off the line of the section	3	6	8	6
Clay	1	6	10	0
Crossbedded sand and silt	2	6	12	6
Clay	2	0	14	6
Clayey silt to bottom of arroyo	4	0	18	6

Section 7

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

	Thickness		Depth
	Feet	Inches	Feet	Inches
Clay	3	0	3	0
Sand	3	0	6	0
Clay, with open hearth at base. Hearth is 8 ft. long and burnt (red) ground is nearly 1 ft. thick with much charcoal above	2	0	8	0
Sand and silt	1	2	9	2
Adobe	1	5	10	7
Sand and silt to bottom of arroyo	3	7	14	2

Section 8

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

	Thickness		Depth
	Feet	Inches	Feet	Inches
Dark clay	2	0	2	0
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 ft	25	4	27	4
Covered below.

Section 9

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

	Thickness		Depth
	Feet	Inches	Feet	Inches
Compact rusty sandy clay with fragments of stone and charcoal; potsherds at 6 ft. 3 in.	6	3	6	3
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 bank	13	0	19	3

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.]

	Thickness		Depth
	Feet	Inches	Feet	Inches
Apparently uniform indurated sand mixed with adobe and a little silt	6	0	6	0
Laminated clay interbedded with slightly indurated sand. Fine interbeddings well defined and nearly parallel. Lower 0.7 ft. has broader laminae	2	7	8	7
Indurated sand laminated without adobe	1	6	10	1
Fine white sand slightly indurated and finely laminated	1	0	11	1
Nonlaminated clayey sand, indurated	0	5	11	6
White sand slightly and inconspicuously laminated	0	9	12	3
Well-indurated inconspicuously laminated sand with large content of fine silt or clay	2	8	14	11
Gray sand slightly laminated and indurated	2	8	17	7
Clay containing sand and showing tendency to granulate and fissure on shrinkage (adobe)	2	8	20	3
Fine nonlaminated sand slightly indurated	1	2	21	5
Clay containing some sand and showing tendency to granulate and fissure on shrinkage	2	7	24	0
Pulverant loamy sand containing minute black fragments (moist)	3	0	27	0

Section 15

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

	Thickness		Depth
	Feet	Inches	Feet	Inches
Alternate bands of sandy clay with internal cracks and compact sand	4	0	4	0
Compact sand	1	7	5	7
Sandy clay with internal cracks and streaks of compact sand	1	2	6	9
Minutely crossbedded compact sand with a few lenses of clay 3 to 4 ft. long near base	3	4	10	1
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 channel	3	0	13	1
Crossbedded sand, crossbedding on larger scale, streaks of pieces of black shale and coal	2	3	15	4
Compact crossbedded sand	2	7	17	11
Covered	5	0	22	11

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.

	Thickness		Depth
	Feet	Inches	Feet	Inches
Yellow pulverant sand derived from Rincon del Camino	0	6	0	6
Sandy clay with internal cracks	1	0	1	6
Yellow pulverant sand derived from Rincon del Camino	1	4	2	10
Sandy clay with internal cracks contains sand lense to south of section	2	8	5	6
Gray, minutely laminated sand; laminae slope to south, are interbedded there with clay layers	4	10	10	4
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 lenses	5	8	16	0
Sandy clay, upper part has internal cracks; base of buried channel	2	4	18	4
Compact laminated sand with lenses of clay having internal cracks to bed of arroyo	6	2	24	6

SECTIONS IN THE BURIED, OR POST-BONITO, CHANNEL

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 found	Thickness		Depth			Found at
	Feet	Inches	Feet	Inches	Potsherds	Feet		Inches
Dark sandy clay (adobe)	2	0	2	0
Laminated fine sand and silt	2	2	4	2
Dark sandy clay (adobe)	0	9	4	11
Sand with thin layers of laminated silt and clay	1	11	6	10
Laminated layers of silt and dark clay	4	1	10	11
Dark sticky clay	0	11	11	10 A few	A few	10 12	to	2
Laminated fine sand	2	5	14	3
Laminated clay	0	7	14	10
Laminated and minutely crossbedded coarse sand. This bed grades to south into gravelly clay that extends to depth of 16 ft. 10 in	1	5	16	3	Many	16 16	to	1 8
Dark clay	0	5	16	8
Fine sand	0	2	16	10
Gravelly clay containing large and small stones, grades into sand to south	1	5	18	3	Numerous	17 18	to	3 3
Fine sand	0	3	18	6	18

Log of test pit number 4

Sixty feet east from arroyo bank at section 4

Materials found	Thickness		Depth			Found at
	Feet	Inches	Feet	Inches	Potsherds	Feet		Inches
Gray-brown sandy clay (adobe)	1	10	1	10
Laminated sandy adobe, a lense	0	2	2	0
Hard brown sand with pieces of charcoal	2	2	4	2
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. apart	3	3	7	5	One only One only	7 7	0 2
Hard brown sand, containing at north end of pit an irregular lense of sandy and gravelly adobe containing charcoal and bones	2	5	9	10	Many	9	6
Dark sandy clay (adobe) with small lense of gravel	4	7	14	5	Many in gravel	10 10	to	6 8
					Many	11 11	to	6 8
Sand (a lense) that extends to 15 ft. at north end of pit	0	3	14	8
Adobe to bottom of pit	0	9	15	5	Many	15		0

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