Source: Hack, J.T. 1942. The Changing Physical Environment of the Hopi Indians of Arizona. Papers of the Peabody Museum 35(1). Harvard University, Cambridge.
The following is the abstract from the above report, a classic of southwestern land cover and land use history which has withstood the test of time. A paperback reprint edition of the complete paper is published by Periodicals Service Co; ISBN: 0527012882.
The Hopi country [map] lies on the southern escarpment of Black Mesa, a dissected highland about 60 miles in diameter underlain by resistant Upper Cretaceous sandstone. This mesa is drained by the southwestward-flowing, ephemeral streams of the Tusayan Washes, which separate the fingering prongs of the escarpment and thence flow into the barren plains leading to the Little Colorado River. These streams bring sand and silt from Black Mesa to the lower plains where the prevailing southwest winds separate them and carry the sand back northward to bank it against the escarpments of that part of Black Mesa which is the Hopi country. Because of the relatively large quantities of dune sand resulting from this process, the Hopi country has a lower runoff after rain and more permanent springs than areas of similar climate nearby.
The population of the Hopi country numbers about 3000, mostly Hopi Indians, the western remnant of the larger Pueblo group who once occupied most of the southwest. These people are farmers who live in permanent houses built of stone and clustered in villages, located on the high southern spurs of Black Mesa near the springs. The villages are central to the fields on nearby mesa tops and in the broad valleys of the Tusayan Washes.
The Hopi country is too dry for growing crops by rainfall alone, so that special methods of farming are used. The Hopi raise corn and beans, the staple foods, by four different methods. Flood-water farming, in which fields are planted where the floods of streams spread in thin sheets of water, is the most important type. There are two major types of flood-water fields, those located at the "atchins" or arroyo mouths of small streams, and those located on the flood plains of large streams. Sand dune fields, in which the relatively high-moisture content of sandy soils is utilized, are also an important type of field. This type is not affected by epicycles of erosion and dissection of flood plains, as are the flood-water fields. The necessity for the protection of plants from moving sand requires the use of windbreaks, however, and makes this system of farming laborious. Some fields are watered by seepage. A small proportion in which rare and relatively valuable crops are grown are irrigated from springs. Flood-water fields are found in large areas around the Hopi country, but not in as great numbers. Higher regions than the Hopi country are too cold for growing corn. Lower regions are too dry except where fields are located along large water courses which have their sources in wetter regions.
The effect of a period of arroyo cutting in the Hopi country is to shift the position of flood-water fields from the main streams to the akchins or arroyo mouths of small streams and to increase the use of sand dune fields.
The large areas of sand dunes can be used as a means of deciphering climatic change in the recent past. The dune forms of this region are divided into three major types: 1) transverse dunes (including barchans), which are always free of vegetation and are aligned at right angles to the prevailing wind, 2) parabolic dunes, formed in the presence of specialized vegetation, consisting of irregular bow-shaped ridges with their tails or tips pointing into the wind, and 3) longitudinal dunes, long narrow ridges of sand extending across country for miles, and formed in the presence of specialized vegetation. These longitudinal dunes depend on a relatively small quantity of moving sand, derived from a restricted source, which in most places is a groove of deflation in an ancient sand cover. For this reason they can form only where the vegetative cover is relatively unaggressive. Ancient stabilized longitudinal dunes are found in other vegetative zones where nowadays over 15 inches of precipitation fall. Inasmuch as active dunes of this type occur only where there is less than 10 inches of precipitation, it is obvious that at the time of formation of most of the longitudinal dunes the climate was considerably drier than it now is. Stratigraphic evidence indicates a dry period between 2000 and 5000 B.C. during which time most of the fixed dunes now mantling the region formed.
The valleys of the Hopi country and adjacent areas are filled with deep alluvium, now dissected by deep channels or arroyos cut since 1880. The alluvium is exposed in their walls and is obviously divisible into three formations: the Jeddito formation, containing Elephant bones, and presumably deposited before 5000 B.C.; the intermediate Tsegi formation, containing evidence of human occupation; and the Naha formation, deposited since 1300 A.D. The deposition of these formations alternated with periods of erosion like the present, which were relatively dry. In the Jeddito-Tsegi period of erosion, the great system of dunes now mostly stabilized was formed.
Evidence of ancient farming occurs on the north side of the Jeddito Valley. Many areas of networks of stone lines used to support brush windbreaks are the remains of ancient sand dune fields. One of these is know to be as old as the thirteenth century A.D. Estimates of land available for flood-water farming in the past show it was relatively great in the first millennium A.D., was reduced at the end of the thirteenth century and increased somewhat from 1300 to 1600 or 1700 A.D. Population changes in the Jeddito Valley region may be related to widespread climatic changes and changes in areas available for farming. In any case, the history of the Pueblo peoples has been greatly affected by the changing physical environment.
The Hopi country is superior as a location for agricultural settlement to other nearby areas. The abundant dune sand provides a better ground-water supply, and inhibits arroyo cutting. The wide valleys provide large areas over which flood waters can spread.
J.T. Hack, 1942.