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 ordinary rainfall throughout most of the southwestern United States and northern Mexico is insufficient to grow crops. Such lands, however, as are overflowed by the muddy water of ephemeral streams or by rainwash from hillsides will support a hazardous agriculture. Floodwater farming was first adequately described by Gregory (1916, pp. 103-105) and a rather complete account with maps of fields has recently been published by the present writer (Bryan, 1929). The additional data given herewith apply particularly to conditions that once obtained in Chaco Canyon.

Gregory (1916, pp. 104-105) outlines, as follows, the methods and results of floodwater farming in the Navaho Country, an area that includes Chaco Canyon:

From experience and tradition the Indians have learned to know the areas liable to be flooded during occasional showers as well as those annually inundated by the successive rains of July and August. Along the flood plains of the larger washes the practice is to plant corn at intermediate levels in widely spaced holes 12 to 16 inches deep. The grain germinates in the sand and rises a foot or more above the surface before the July rains begin. With the coming of the flood the field is wholly or partially submerged. After the water has receded parts of the field are found to have been stripped bare of vegetation and other parts to have been deeply buried by silt; the portion of seeded ground remaining constitutes the irrigated field from which a crop is harvested. The Hopis, and to a less extent the Navajos, sometimes endeavor to direct the floods and to prevent excessive erosion within the fields by constructing earthen diversion dams a few inches to a foot or more in height—dams which require renewal each season. . . . Much work is done by the Indians while the flood is in progress, and an everyday sight during showers is the irrigator at work with hoe or stick, or even with his hands, constructing ridges of earth or laying down sagebrush in such a manner as to insure a thorough soaking of his planted field. By these methods of flood irrigation the Navajo and Hopi together cultivate about 20,000 acres of land widely distributed over the reservation in fields about 3 acres in average size, rarely exceeding 200 acres.

Similar methods of cultivation are in wide use throughout the plateau of Mexico and in New Mexico and Arizona (Hoover, 1930, pp. 437-438; Hack, 1942, p. 26). The Mexican calls such a field sombrado (planting) or temporal (temporary field). The Nahuatl word milpa is also used. In favored localities and usually at high elevations these terms are applied to fields dependent on rainfall alone but generally flood irrigation from the rainwash of higher slopes or from ephemeral streams is essential to a crop.

Since they were first visited by whites in 1698 and doubtless long before, the Papago Indians of southern Arizona have supported themselves largely by floodwater farming pursued on the broad plains of their undissected desert valleys. Corn, squash, and tepari beans are their main crops (Lumholtz, 1912; Bryan, 1925b; Hoover, 1929).

Floodwater farming for the production of stock feed is widely practiced in northern Nevada. Quinn River valley (Bryan, 1923b) may be taken as typical. The valley—

is bordered on the east by the Santa Rosa and Buckskin mountains and on the west by the Quinn River Mountains. It heads in Oregon about 10 miles north of the Nevada line and extends southward about 45 miles to the Slumbering Hills, which separate it from the broad valley of Humboldt River. The valley is 10 to 12 miles wide and is drained by Quinn River, which runs southward through it for about 40 miles, turns west, and, passing south of the Quinn River Mountains, is lost in the Black Rock Desert. The river is formed about 4 miles south of the Oregon line by the union of East Fork of Quinn River and McDermitt, Washburn, and other creeks. Its drainage basin includes about 1,164 square miles.

The valley floor consists of plains formed of beds of sand, gravel, and clay deposited by the existing streams. A small part of the valley bounded by a line of bluffs that extends from the Oregon line east of McDermitt southeastward to the National mine differs from the larger part in that the streams flow in flat-bottomed valleys that lie 50 to 100 feet below the level of sloping plains formed by the same streams at an earlier time, when they flowed at a higher level. In general, however, each stream, on leaving the mountains, wanders through circuitous and branching channels over the alluvial slopes to the axial flat, where it joins in grassy meadows the small meandering channel of Quinn River.

The region is arid, none of the streams containing water throughout the year. The principal streams carry considerable water or are in flood in the spring, when the snow on the mountains is melting. The spring floods are not violent, and the water, which may be almost clear, is easily diverted into semi-permanent ditches to irrigate the cultivated fields. In the axial flat there are large fields that are irrigated from Quinn River or from its tributaries. Near the mouths of the canyons of the principal mountain streams there are smaller fields, many of which are irrigated by the water of streams that seldom reach the lower, larger fields. About 14,000 acres is irrigated. Native grasses, which are used both for pasture and for hay, form the principal irrigated crops, but there are also fields of alfalfa and small grain.

Paradise Valley lies east of the Santa Rosa Mountains and is enclosed on the north and northeast by unnamed volcanic plateaus and mountains and on the east by the mountain range that culminates in Hot Springs Peak. It is drained by Little Humboldt River, which is formed by the union of Indian, Martin, and other creeks with the east fork of Little Humboldt River. The topography of this valley is like that of Quinn River Valley, though the central flats are wider and the area irrigated is larger.

In both valleys communication with centers of population elsewhere is difficult. The distance from some of the ranches to Winnemucca, the nearest railroad station, is more than 60 miles. Only cattle on the hoof can be readily marketed, and the irrigated land is devoted to the raising of stock-feed. In April and May the cattle are turned loose in the plains and lower foothills, where they browse on the sage, weeds and grass, and as the snow melts they gradually climb higher into the hills, reaching the summits in midsummer. As the cattle leave the valleys the ranchers begin to irrigate their land, starting with the first floods and continuing to use the water as long as it lasts. In August great quantities of hay are made from the native grass and from alfalfa.

The cattle begin to come down from the hills late in August and early in September—according to the local saying, "as soon as they hear the mowing machines." Late in September and during October the ranchers bring the last of the cattle out of the hills to the owners' fields, where they are pastured on the still green native grass and on greasewood until it is necessary to feed them hay. In ordinary years the cattle are brought through the winter in excellent condition.

About 13 miles east of Pueblo Bonito and beyond Pueblo Pintado, small Navaho fields are cultivated in the floors of valleys more or less obstructed by sand dunes. The effect of sand dunes in spreading the floods of ephemeral streams and in providing localities suitable for floodwater farming is also of large importance in the Hopi country (Hack, 1942). In canyons tributary to Arroyo Salado, in the Rio Grande drainage and some 70 miles east of Pueblo Bonito, there is limited floodwater farming. The Cañada (de) las Milpas doubtless had, before the existing deep arroyo was formed, enough fields to justify its name. Here, as late as 1922 on hill slopes at Juan Chaves's ranch, there were two small fields irrigated by the runoff from high bluffs. In 1921 the writer saw in Rincon de Lopez 40 to 50 acres of corn and beans that had been irrigated by floodwater.

About 10 miles from Cañada las Milpas is Bernalillito, a locality so called because people from Bernalillo on the Rio Grande 35 miles distant formerly moved there each summer to plant and tend their fields. Bernalillito Wash heads on the eastern escarpment of the Mesa Prieta and flows in a broad flat valley eroded in shales and sandstones about 10 miles east to a narrow gap in a massive sandstone cliff. Below this cliff there is a canyon in places broad and in others narrow. About half a mile below the cliff is the single ranch house of Bernalillito. Nearby is one field of 15 acres suitable for planting corn and beans and to one side a smaller area where hay may be cut. The sandy alluvial fan of a tributary gulch causes the main flood to spread and the gentle overflow makes possible the cultivation of the field and the growth of grass on the meadow. The flood is also caused to spread more widely by a low dam of brush and stone (atarque) at the lower end of the field. Just below field and meadow is the headwater falls of an arroyo which has already dissected similar flats in the canyon below and now threatens to destroy the remaining fields. In 1920 this ranch came under the control of H. M. Bryan, who has planted with the results shown in the table on the following page.

Crops at Bernalillito, N. Mex., 1919 to 1925
(Data furnished by H. M. Bryan)

The years 1920 to 1923 were generally unfavorable in this part of New Mexico and similar planting in years of greater rainfall might have produced better results. However, the flood of September 1921, which broke down and washed out part of the corn, is an incident that might happen any year. When this flood arrived, a bean crop estimated at 1,000 pounds was ready for harvesting but only 200 pounds—the equivalent of the seed planted—were saved. Similarly, the loss from intruding cattle that broke through the outside fence to obtain water in 1920 and 1922 might have been avoided. Such hazards are, however, a part of this type of farming although the prehistoric floodwater farmers were saved at least the risk due to domestic animals. It is true also that this piece of ground was poorly farmed during these years. The owner at the time was a sheep man whose herds during the summer season were in the mountains more than 60 miles away. Consequently the farming was done during intervals of other, more important work, and by hired labor. Cockleburs and Russian thistle grow so rapidly that strict attention to cultivation is necessary. Because this attention could not be given, the owner converted the plowed land into meadow with the intention of cutting hay for winter use.

PLATE 10. Upper: The Chaco in flood. Tents of a General Land Office surveying party at left; men on opposite bank and rider at right stand on approaches to the wagon crossing. Pump on Wetherill's well, destroyed a few weeks later, is seen above the fourth horse from the right. (Photograph by Neil M. Judd, 1921.) Lower: Middle south wall of Pueblo del Arroyo with a partially refilled section of Jackson's "old arroyo in the foreground. (Photograph by Neil M. Judd, 1920.)

PLATE 11. Left: A pit house with floor 13 feet 6 inches below the present surface, 9 miles east of Pueblo Bonito, had been long forgotten before the Pueblo III village was constructed on an upper level a few feet distant. (Photograph by Neil M. Judd, 1926.) Right: An Early Pueblo cooking pot covered with a sandstone slab lay 6 feet below the surface of a sand dune in Wirito's Rincon, about 1-1/2 miles, southeast of Pueblo Bonito. (Photograph by Neil M. Judd, 1927.)

The record of these six years indicates that, with an adequate reserve for lean years, this field would support a family requiring no more than was necessary for prehistoric Pueblo peoples. But this family would need to give the crop the constant attention which modern Hopi lavish on their own fields.

It is obvious that the condition of aggradation that once prevailed in the valleys and canyons of the Southwest was favorable to floodwater farming. At that time the floods spread widely and were confined to channels at only a few places. Small localized showers that fell on the walls of canyons, if sufficient to produce runoff, flooded the adjacent flat floor, whereas now the runoff flows into an arroyo below the general level of the plain.

Water that soaked into the ground could not so easily drain away and consequently underlay the valley floors at moderate depths. It was thus available to supply the roots of trees and bushes which doubtless once flourished in valleys where they are now absent. At favorable places, lakes and swamps existed in which grew the rushes (tule) frequently found in prehistoric ruins. Because of this higher water table a thinner layer of earth was dried out between floods; smaller floods were sufficient to wet the dry ground. These smaller floods also covered larger areas since less of their flow was absorbed by the dry ground. The result of such a regimen was a denser vegetation on the canyon floors.

Of this denser vegetation an important part was perennial grasses. Even today where floods spread widely over the floors of undissected tributaries to Chaco Canyon there is a fairly dense cover of perennial grass, usually alkali sacaton. Meadows of this type were so numerous in the Rio Puerco region, 80 miles to the southeast, that a principal occupation of the Mexican inhabitants in the late 1890's was the cutting of hay to be hauled 30 miles or more to market in Albuquerque.

The presence of these meadows was advantageous to white men, and their destruction by the formation of arroyos has been a distinct loss. The forage they were capable of producing naturally was of no value to prehistoric farmers without domestic animals to feed, and their agricultural potentialities remained untested because those same prehistoric farmers lacked tools adequate to the task of uprooting sod. At the present time grass is apt to grow thickest on the more clayey soils and, to the extent that they are effectual in spreading flood waters, grassy areas tend to postpone arroyo cutting. The inhabitants of Pueblo Bonito undoubtedly planted on the sandier soil bordering such grassed areas, on alluvial fans below the cliffs, and along the vague and meandering course of the main stream. Such soils were more or less disturbed by successive floods but, despite annual loss of part of the planted crop, they were doubtless recognized as the best agricultural land because of their superior tilth and relative freedom from deep-rooted perennial grasses.

In 1921 Mr. Judd dug a trench 20 feet in depth to study the stratigraphy of the west refuse mound at Pueblo Bonito. Four years later when he extended it out into the flat fronting the mound, the trench cut across several obviously artificial canals or ditches. They ran parallel to the front of the refuse mound and, therefore, essentially east and west. They were from 4 to 10 feet wide and were enclosed on the downhill (south) bank by walls of slushed mud (adobe) laid with care and in places supported by the dumping of house refuse. Filled with both fine and coarse materials, including Late Bonito potsherds, these ditches presumably had carried floodwaters from upcanyon, perhaps from the rincon of Chettro Kettle, to fields west of Pueblo Bonito. As each filled up or was washed out, a new one was constructed along the same route. Such more or less temporary ditches for the spreading of water are fairly common features of floodwater fields in New Mexico. If these before Pueblo Bonito were more elaborately constructed than is usual, it is doubtless because they lay close to the village where labor was readily available. The data Mr. Judd has gathered relative to comparable structures for control of floodwaters in Chaco Canyon will be presented by him in connection with the subsistence problem of the Bonitians.