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Dear Sir: I am sending herewith the manuscript and illustrations of a series of three papers under the general title of "The Physiography of the Rio Grande Valley in Relation to Pueblo Culture," by Edgar L.

LETTER OF SUBMITTAL

THE RIO GRANDE VALLEY, NEW MEXICO

The geographers and geologists have not yet produced any thorough studies of the Rio Grande Valley. The Rio Grande Valley embraces the Pueblo region which belongs to the Atlantic side of the continental divide.

HEWETT] RIO GRANDE VALLEY, NEW MEXICO 17 striking scenery from the geologic point of view to be found in the

18 BUREAU OF AMERICAN ETHNOLOGY [bull.54 water to the confluence for a considerable part of the year. The well-vegetated portion of the rectangle is, (1) the Santa Femoimtaiiis area, including the entire eastern side of the basmen; (2) the Placer and Sandia momitains area, a small section in the south-central part; and (3) the Jemez Plateau, the region lying west of the Rio Grantle and north of the latitude of Santa Fe.

HEWETT] RIO GRANDE VALLEY, NEW MEXICO 19

Specimens of charred corn embedded in so-called "lava" have come into the hands of the writers from four places in the Rio Grande drainage and one in the San Juan. It could be suggested, however, that the evidence now available indicates that the original culture that arose in the Rio Grande Valley was not wholly or mainly dependent on UTigation, but that it became so.

GEOLOGY AND TOPOGRAPHY OF THE

RIO GRANDE REGION IN

JUNIUS HENDERSON

GEOLOGY AND TOPOGRAPHY OF THE RIO GRANDE

REGION IN NEW MEXICO^

26 BUREAU OF AMERICAN ETHNOLOGY [bum.M fall to lower elevations and finally merge into the general level of the region. The western part of the basin is part of the Jemez Plateau, which includes the Jemez Mountains and is bounded on the west by. Roughly parallel canyons extending from east to southeast divide the plateau into a series of mesas, which slope rather gently from the mountains to the rim of the Rio Grande Gorge.

Standing on any high point west of Santa Fe, we can obtain a clear idea of the larger features of the topography—a broad basin lying between two mountains, the country descending somewhat regularly from the foot of the mountains on each side to the river. While traveling through the region, to those unfamiliar with them, these larger features of the landscape can often appear swallowed up or obscured by the size and abruptness of the topographical forms in the observer's immediate vicinity, so that the final impression is of a confusing web of deep, narrow. In traveling down the valley from Santa Fe to Taos on the east side of the Rio Grande, Carboniferous formations are found along the flanks of the mountains with low westward dips exposed to the wear of the overlying "marls."

It seems likely that the contours of this valley were established as a synclinal fold well before the Nlid-Tertiary period of deposition, but the height of the mountains is then only a matter of conjecture.

HENDERSON] GEOLOOY AND TOPOGRAPHY 27

Speaking of the parts of the pool not examined by the author, some scientific experts have expressed the same opinion. This is especially true of the numerous fragments of pumice, some of which are several centimeters in diameter. This, and the lack of a range of material, provides very strong, though perhaps not conclusive, evidence against the idea of settling in water.

A . careful examination of the weathered crystals shows in most cases that the facets are clear, bright and sharp, but one side is. usually broken off. The quartz crystals cannot explain the origin of the tuff. I believed that they were formed in the magma by its partial crystallization before it was ejected, and that they would probably exist in their present condition whether the tuff was ejected in the form of ash or of mud. In the area around El Rito de los Frijoles, the upper half of the tuff slab is heavier, harder and 'usually darker in color than the lower half'.

An excellent place to study the relationship of the sedimentaries, the tuff and the basalt is in the vicinity of Buckman, at the crossing of the KioGrandeon, the present road from Santa Feto El Rito delos Frijoles.

HENDERSON] GEOLOGY AND TOPOGRAPHY 31 by the ancient inhabitants for ceremonial purposes. It varies con-

This wider part of the canyon, less than two miles long, was occupied in prehistoric times by a considerable number of inhabitants and some. Even lower, where the stream has cut into the basalt and sandstone, the canyon narrows again. Oddly, instead of following the contact or cutting the tuff where the canyon reaches the hard basalt, it cuts through the basalt to a great depth to reach the Rio Grande.

In this environment the latter flows itself, rather than following or cutting off the contact of basalt and tuff. Access from the south to the open part of the gorge is possible almost everywhere, although the slope is steep. LOWER CANYON EL RITO DE LOS FRIJOLES, WHERE IT IS CUT INTO THE BASALT AT THE UPPER FALLS, WITH THE SANDSTONE BELOW THE FALLS.

HENDERSON] GEOLOGY AND TOPOGRAPHY 33 means very slowly from the point of view of human history>\ At th(^.

HENDERSON] GEOLOGY AND TOPOGRAPHY 33 means very slowly from the standpoint of human histor>\ At th(^

34 BUREAU OF AMERICAN ETHNOLOGY [bull54 . material breaks through the harder crust so that the interior* . the diameters of most of the cavities are greater than the tliameters of the entrances. The large ceremonial cave at the upper end of the valley has primarily been excavated by the wind in the softer material between two of the previously mentioned hard zones. Whatever may be said of the past, all these forces of erosion are evidently working rather slowly at the present time.

The ]:)laster- iiiig over the entrances to some of the caves remains mtact, although the walls of the buildings that once stood in front of them have crumbled badly. It is very probable that occasional floods, affecting the banks of the streams where humus would otherwise accumulate, prevented the formation of such soil, and away from the banks of the streams the aridity of the region would serve as a prevention . The source of the selenite and clay is not definitively known, but they were probably not obtained in the immediate vicinity.

HENDERSON GEOLOGY AND TOPOGRAPHY 35 The use of tufa in the construction of the walls of buildings is a.

HENDERSON GEOLOGY AND TOPOGRAPHY 35 The use of tufa in the construction of the walls of buildings is a

Fragments of the harder upper tuff, sliding down steep slopes, came to rest and formed protective caps for the soft tuff below. Storms hitting the parts of the slopes not protected in this way carried away the material around the protected areas, leaving the latter sticking out and partially isolated from the slopes. Some of these cones have also been developed by the dissection of the cliff directly beneath a hard cap, with a fragment of the rock on the summit left in place by the weathering process.

The south wall of the portion of the gorge where the ruins occur is notable for the absence of terraces, cliffs, and cones, as just described, rather than. The repetition of the steep cliff in all the canyons of the region, always on the north side, is an important feature of the environment of the ancient inhabitants. A study of recent meteorological maps from the ITnited States Weather Bureau indicates that prevailing winds are from the southwest.

Such storms, striking the north wall of the canyon at a high angle, would affect it more radically than the south wall, washing most of the debris from the slopes and thus constantly exposing fresh surfaces to subaerial erosion and in the same time. prevention of soil accumulation.

HENDERSON] GEOLOGY AND TOPOGRAPHY 37 canyon meantime would be more protected from such winds, while

With the same hard zone underlain by soft material on the south side of each gorge, high cliffs must certainly form on that side, unless some force not acting on the north side is engaged in breaking down all incipient rocks. This force is frost, one of the most effective causes of dissolution in all areas where water finds its way into the crevices of rocks and freezes. Since snow occurs and the water freezes in the area under discussion, it is easy to explain the absence of the cliff on the south side - the side that faces.

When the weathering of the soft material leaves one of the hard zones standing out on the south side as an incipient cliff or terrace, water from winter storms finds its way into the cracks and. It is not difficult to understand why this does not also occur on the northern one. As differential erosion in a formation like this would produce rocks in the absence of a force tending to tear them down, the presence of a force which would tear the rock down on one side and not act on the other .

TUFA SHOWING HARD BANDS AND THE BEGINNING OF THE FORMATION OF "TELTRACKS" DUE TO THE PROTECTION OF THE SOFT LOVER PART OF THE HARD BANDS.

HENDERSON] GEOLOGY AND TOPOGRAPHY 39

CLIMATE AND EVIDENCE OF CLIMATIC CHANGES

It seems likely that the rainfall at Rito de los Frijoles is about 14 inches, provided it finds support in the fact that the dominant vegetation (pinon pine and cedar) on the lower part of the mesas is the same. A short distance back from the edge of the Rio Grande canyon on the mesas and in the canyons are stone pines. its presence indicates slightly greater rainfall. The waters of the Pangong salt lake, on the side of the Himalayas, appear to have receded within the period.

Certain traditions of the former existence and drying up of particular springs and streams, on the other hand. With fertile, valleys, good water and better opportunities at the bottom of the ravines for protection and seclusion from enemies, it works much more. Therefore, a logical conclusion is that probably most of the dwellings in the canyons and on the mesas were simultaneously occupied by some.

However, the relationship between the two major plant formations in the region seems to provide some evidence of gradual climate change.

Fig. 1.— Mean precipitation, bj- montlis, at Santa Fe, Espanola, New York, and St. Louis.

ROBB^T^'^] CLIMATE AND EVIDENCE OP CLIMATIC CHANGES 57

Although it seems very likely that the disappearance of the inhabitants from the region was due to progressive desiccation, it is. It has been thought by some geologists that the great canyons in the southwest must have been cut by much larger volumes of water than now flow through them. In many cases, the inability of floods to reach previous levels is due to deepening of channels.

A natural consequence of such slow desiccation would be the gradual reduction of population and concentration of remains in favorable places. Its effect on the native vegetation would be mainly in the direction of slightly altering the boundaries of the plant formations. The more complete examination of the definitive traditions of the peoples with regard to past climatic and agricultural conditions.

Also a careful study of old Spanish records and literature of the region ^with this question in mind.

BIBLIOGRAPHY

Notes on the Eocene and Pliocene lacustrine formations of New Mexico, including descriptions of some new species of vertebrate fossils.

75 Huntington, Ellsworth. A geologic and physiographic reconnaissance in ccuiral