16 BUREAU OP AMERICAN ETHNOLOGY [bull. 54 



The volcanic mesas still hug the river on the west, while to the east 

 of the flood plain the areas of naked marl are small and the area of 

 gravel and silt-covered hills and mesas is of greater extent. 



The most striking section of the entire region herein described is 

 that bordering the Rio Grande on the west between the Chama river 

 and Cochiti. No other section in the Southwest has played a more 

 conspicuous part in human history. It became the principal focus 

 of ancient culture in the Rio Grande drainage, and its pecuhar 

 geologic structure powerfully influenced the aboriginal culture of the 

 entire Southwest, particularly in the domain of house hfe. It is the 

 eastern half of the elevated plateau upon which are superimposed 

 the Jemez mountains; to this has been given the name Pajarito 

 plateau. Its original uphft accompanied the formation of the 

 Jemez range, but important changes have since taken place. The 

 most important of those was the laying down of a vast sheet of 

 volcanic tufa of a maximum thickness of perhaps 1,500 feet, which 

 at one time completely covered the plateau but which has since been 

 rent, sculptured, and dissected by water and wind into the weirdly 

 beautiful condition that it now presents. In the northern part 

 hardly more than ten per cent of the original cap is left in place, the 

 remaining fragments standing out boldly from the foot of the moun- 

 tains as circular or elongated geologic islands. These sometimes 

 take the form of narrow tongues, several miles in length and from a 

 few feet to half a mile in width. Between are lightly timbered 

 valleys and dry arroyos. In this northern part, which is called the 

 Puye district, from its principal focus of ancient habitation, the 

 tufa cap has been entirely removed for a distance of several miles 

 back from the Rio Grande, being superseded by a level grassy plain. 

 Farther south the tufa cap approaches the river, and southward 

 from the point at which the Denver and Rio Grande railway crosses 

 the Rio Grande near San Ildefonso the massive yeUow bluffs appear 

 hundreds of feet above the river as the upper stratum, overlying the 

 recent basaltic extrusions. Thence southward from fifty to seventy 

 five per cent of the tufa sheet remains in place, and instead of pre- 

 senting the appearance of a large number of geologic islands, resting 

 upon a common level, as farther north, there is more the appearance 

 of a level plateau rent by thousands of canyons which sink below the 

 general level to a depth of from 50 to 700 or 800 feet. Above White 

 Rock canyon the eastern rim of the plateau is broken into detached 

 masses, which stand out as huge isolated bastions, while farther south 

 a continuous rim is presented toward the river, broken only by the 

 entrance of the side canyons. In the region contiguous to the Rio 

 Grande, lying between the Guages and the Pajarito, are many fine 

 examples of basaltic gorges. This section was the focus of the 

 recent volcanic activity, which here produced some of the most 



